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Well all the parts finally got here......

40.136.250.222

Posted on December 2, 2016 at 15:14:05
vinnie2
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The holiday must have messed up the mail 'cause everything was several days later than estimated by the sellers. Anyway, I got the two solid state switcher units units (these are only 3 amps and are for the 26 tubes). Also got the halogen light transformers, the ones that will give me 12 volts of AC.
Spent most of the afternoon installing one of the small switchers on the right channel and tracing down some grounding issues I had in that side as well. When I finished I had music coming out the other end and the same operating points as the bread board I did with the conventional transformers for filament voltages. Not sure about the sound yet, I tend to think I liked the other better, but I have not done any tweaking yet. The next thing I will do is install the halogen transformers on the two 813's of the left channel and then do a shoot out between it and the right channel. The winner stays and the loser gets replaced by the original version with the filament transformer for the 26. Which ever one of those wins gets built into the final amp. Should be interesting and will definitely keep me busy for a while. Ray P, I will start going through one of the halogen transformers tomorrow and try to follow the instructions you put in the post. Most likely I will be hollering for help before long .....

 

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RE: Well all the parts finally got here......, posted on December 2, 2016 at 16:46:29
deafbykhorns
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I've done a few of these halogen supply's in the past.
Just don't forget to add the capacitor to the supply
Anxious to see how you like it!

 

RE: Well all the parts finally got here......, posted on December 2, 2016 at 18:06:25
used-hifi
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I too am still waiting on a few parts I totally understand waiting for parts sux

 

RE: Well all the parts finally got here......, posted on December 2, 2016 at 18:29:27
vinnie2
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I don't know if I have a large enough cap, may have to order one. I am interested to see how it sounds compared to the switcher unit.

 

RE: Well all the parts finally got here......, posted on December 2, 2016 at 18:33:18
vinnie2
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Some of these "free shipping" offers are slow as can be. I may just pay the freight next time.......

 

RE: Well all the parts finally got here......, posted on December 2, 2016 at 18:42:52
used-hifi
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I agree but even when you pay for expedited shipping it still takes forever!


Anyways I am anxious to get my pset gm70 project started

Lawrence

 

RE: Well all the parts finally got here......, posted on December 2, 2016 at 18:49:04
RayP
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Holler away, but I suspect you won't have too many problems. By the way, I performed my inital tests using a power resistor before I tried connecting a tube.

I trust you have a multimeter that can measure true RMS.

ray

 

RE: Well all the parts finally got here......, posted on December 3, 2016 at 04:16:17
vinnie2
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It's a fluke 179 and it says "true rms" right on the front. How will I know if it is lying to me? I will use a resistor too, and then a crappy 12v tube before hooking it up to anything good.

 

a warning, posted on December 3, 2016 at 04:33:53
RayP
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I realized during the night that I had forgotten to warn you that the 560 uf caps develop a 25 to 30 volt charge that is not dissipated. I have placed a 1 meg resistor across the terminals which I presume will not harm operation of the AC unit but will be safer.

From what I understand, the most accurate way to measure the voltage is with a scope. I suspect your Fluke will be more accurate than either of my DMMs, but my two DMMs (EdTech EX205T and Harbor Freight $24 model) each measure close to each other. GK-71 tubes are cheap.

I am currently rebuilding my amp for the third time and hope to have it back in action later today or tomorrow.

ray

 

thermistor, posted on December 3, 2016 at 04:49:11
RayP
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I don't know if it is really needed, but I use a thermistor as a part of the turn on circuit. I usually do this for bigger amps.

ray

 

RE: a warning, posted on December 3, 2016 at 06:02:05
vinnie2
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Thanks for the warning, I will be sure to do that. I think my flukes are not really "true rms" even though they say so right on the front. I just hooked up one of the units to a variac, put a 12sn7 on the output for a load and put my fluke on it as well to see what I would get. The newer fluke, the 179 read about 300 mVac. The older fluke, the 79III read 1.5 vac. I am going to give my scope a try next and see if I get anywhere near the 12vac I was expecting. I am going to have to by the right sized cap as well, don't seem to have one lying around.
One last question (for now : ) at least). My unit has both diodes on one side of the caps. Does it make any difference which pair of diodes I hook up too? Thanks!

 

RE: thermistor, posted on December 3, 2016 at 06:03:42
vinnie2
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Do you have a drawing that shows how you hook it up? Also which thermistor? Is it there to prevent surge on start up? Thanks>

 

RE: thermistor, posted on December 3, 2016 at 06:32:00
RayP
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This photo probably shows it best.

smps photo P1090486_zps4eo4ol9j.jpg

At the top right you can see the dual switch arrangement which you can read about in the link below. You don't have to use this idea but the photo shows that I connect the thermistor from one of the switches to one of the 110 vac terminals of a 12.6 ac transformer. The 110 vac terminals are also connected via the thick black wire(s) to the red wires feeding the AC unit.

The 12.6 vac transformer is used to power the PCB circuit that provides DC to the 6SK17-v tubes. The input terminals are just convenient to use.

I hope that helps and I trust your wiring is much neater than mine.

ray

 

diodes, posted on December 3, 2016 at 06:44:59
RayP
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The positive connection with the orange wire.
positive photo P1090529_zpsyfh5lyi1.jpg

The negative connection with the blue wire.

negative photo P1090530_zpslx4sfwd0.jpg

On my units there are two diodes on each side that form a bridge. They are connected at the edge and you should be able to use either of them to solder your wire to.

ray

 

RE: diodes, posted on December 3, 2016 at 08:30:17
vinnie2
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Great photos! Thanks!

 

RE: thermistor, posted on December 3, 2016 at 08:34:09
vinnie2
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Wow, what a heap of hardware! Why do you need so many? I think I will try mine without the thermistor first and see what happens. Thanks!

 

RE: thermistor, posted on December 3, 2016 at 09:17:25
RayP
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Each smps module delivers 48 vdc and I stack them with the grounds not connected. 12 x 48 = 596. 4 x -48 = -192. See link below for where I got the idea from.

Most of my amps become too complicated since I like to combine ideas that other people come up with. Sometimes the ideas produce decent sound, sometimes not,but I learn by trying. From what I can see, you are doing much the same thing.

ray

 

RE: thermistor, posted on December 3, 2016 at 10:18:22
vinnie2
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Roger on that. It's the most fun too!

 

RE: a warning, posted on December 3, 2016 at 10:59:01
Palustris
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Vinnie, the Fluke manual for the 179 gives accuracy for ACV 45Hz to 500Hz is 1% and 500Hz to 1kHz is 2%. They don't give any figures beyond 1kHz for accuracy. It is standard practice to measure higher frequencies with a scope.

 

RE: a warning, posted on December 3, 2016 at 12:03:33
vinnie2
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That explains it, but see my new post above. I am still floundering. Thanks.

 

ok, what is happening here????, posted on December 3, 2016 at 12:10:48
vinnie2
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Hooked my scope up to the output of the halogen transformer. Volts/div is 10 vac, sec/div is 1ys> so the the scope is showing 35 vac right? Why is it not showing 12 vac or close to it? That is supposed to be the output of this unit.I am confused once again. Is there some place to set the frequency?
PS I have not installed the big ass cap yet, this is right out of the box just to see what I get.

 

RE: ok, what is happening here????, posted on December 3, 2016 at 12:34:21
Palustris
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You need to calibrate the 'scope to achieve any accuracy. If you have a 12V transformer and a variac, use the variac to set the output of the 12V transformer to exactly 12V using the Fluke meter to read the voltage. Since the frequency is 60Hz it will be in the sweet spot for the meter.

Set v/div dial on the 'scope for "2". In theory you should see 3 divisions above and 3 divisions below the center line (6 X 2 = 12); use the up and down "position" control to horizontally center the sweep. Use the center dial, usually marked "calibrate" to achieve 3 divisions above and 3 divisions below the center line.

----------------------------------------------------------------------
Edit:

Just to be clear: what is above is not correct. The meter reads RMS and the scope shows you peak to peak. The RMS voltage read on the scope needs to be multiplied by 2.828 to get the peak to peak voltage that will be displayed by the 'scope.

If you have a 12V transformer and a variac, use the variac to set the output of the 12V transformer to exactly 10.6V (this makes reading the correct voltage on the scope easy because it will be 10.6V x 2.828 = 30V p-p) using the Fluke meter to read the voltage. Since the frequency is 60Hz it will be in the sweet spot for the meter.

Set v/div dial on the 'scope for "5". In theory you should see 3 divisions above and 3 divisions below the center line (6 X 5 = 30); use the up and down "position" control to horizontally center the sweep. Use the center dial, usually marked "calibrate" to achieve 3 divisions above and 3 divisions below the center line.

 

RE: ok, what is happening here????, posted on December 3, 2016 at 12:35:11
cpotl
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Well, first of all what you are showing there is about 35V peak-to-peak, and hence 35/2 = 17.5V peak. (I am assuming when you said the scope is set to a Volt/div of 10Vac you just meant to say 10V.)

If that were a pure square wave, it would therefore also be 17.5V rms.

If it were instead a pure sinewave with 35V peak-to-peak, it would again be 17.5V peak, but this would then correspond to 17.5/(sqrt 2) V rms, i.e. about 12.3V rms.

Your waveform is neither pure square wave nor is it a sinewave. The rms value is going to be less than 17.5V rms. Maybe about 15V rms or so.

Is that on no load? If so, it would probably come down somewhat when properly loaded.

Chris

 

RE: ok, what is happening here????, posted on December 3, 2016 at 13:37:31
vinnie2
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Could it really be that much out of calibration that I would get 35 volts? I have a 5 volt transformer I can try it with just to see what happens. Thanks.

 

RE: ok, what is happening here????, posted on December 3, 2016 at 13:39:11
Palustris
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Chris is correct: the scope is showing peak to peak voltage not RMS - my post below is incorrect with respect to the voltages.

If you divide peak to peak in 2 you get the peak voltage and this is accurate for a square wave. If the wave is more of a sine you need to divide by two to get the peak and multiply by .707 to get the true RMS voltage. As Chris says, this is unloaded and you should put a proper load on it to determine the net voltage.

 

RE: ok, what is happening here????, posted on December 3, 2016 at 13:40:08
vinnie2
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Well that is better, but it still seems to be a lot for it to be off. I had a small load on it, the filaments of a 12sn7 tube. Forgot about the peak to peak bit. Thanks.

 

RE: ok, what is happening here????, posted on December 3, 2016 at 13:42:26
vinnie2
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What would a proper load be? I think the 12sn7 filament draws about 0.3 amps. Is that enough?

 

RE: ok, what is happening here????, posted on December 3, 2016 at 13:46:34
vinnie2
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Actually, I guess I could hook it to the filaments of a 813 as they draws 5 amps and they are what I want to use these on and I would be using one per 813.

 

RE: ok, what is happening here????, posted on December 3, 2016 at 13:55:17
Palustris
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Sorry, I rarely have to use the scope to read voltages and forgot that the scope shows peak to peak NOT VRMS.

So the 35VAC is correct: peak would be 17.5 and RMS would be 12.37VRMS.

 

RE: ok, what is happening here????, posted on December 3, 2016 at 13:58:37
Triode_Kingdom
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Vinnie, this is the issue I described earlier about some of the lighting transformers I purchased more recently. They should output 24V pk-pk, but they're running about 30-35V instead. The only way to reduce this is with resistors. Even at 24V (12V rms), I had to do that for my 10V filaments.

My suggestion is to first load it more heavily. Wire two or preferably three of your 813 filaments in series and connect them to the output. Then examine it again with your scope. With careful trimming of the Trigger Level control, you should be able to get a fairly clean display.

Report back regarding amplitude and waveshape. :)


 

RE: ok, what is happening here????, posted on December 3, 2016 at 14:21:51
vinnie2
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I must have missed that the first time around. Thanks for the heads up. I will have to check and see what the amp rating is on these little puppies, but I think they could handle two 813 filaments anyway. I will post pics when I get some results. Thanks.

 

RE: ok, what is happening here????, posted on December 3, 2016 at 14:26:45
vinnie2
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Now you lost me again. How do you get down to 12.37 rms? That is what it should be, isn't it? I don't understand how you got there though. I would appreciate an explanation of how you got that for my note book for current and future reference. Thanks!

 

RE: ok, what is happening here????, posted on December 3, 2016 at 14:29:15
vinnie2
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Palustris has an interesting post a ways on down the thread. If i understood it correctly he says it is actually showing 12.37 volts rms. I have asked him to elaborate.

 

RE: ok, what is happening here????, posted on December 3, 2016 at 14:46:45
cpotl
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One needs to be a bit careful because of the shape of the waveform. If it were a precise square wave, then 12V rms would require 24V peak-to-peak. If your rather shaky looking scope trace is accurate, then the sides that should be vertical in a true square wave actually have quite a slow rise and fall time. This means the rms voltage is somewhat less than simply half the peak-to-peak voltage.

That is why I was saying that your 35V peak-to-peak is maybe corresponding to something of order 15V rms, rather than the 17.5V rms that it would have been for a pure square wave.

(It would have been about 12.3V rms if it were a pure sinewave with 35V peak-to-peak. But the waveform you showed in that photo of the scope trace looks as if it would have a bigger area under the square of the curve than for a sinewave, but certainly less than for a pure square wave.)

It might help if you could get a steadier scope trace by fiddling with the sync level, as TK suggested. One could then more easily estimate the rms voltage.

If I understand correctly, your "square wave" is from a switching power supply operating at about 140KHz or so; is that right? (I'm guessing your statement of the horizontal axis being 1ys> per division was meant to be saying 1 microsecond per division?)

A typical cheap "true rms" meter might very well give a more or less meaningless reading at such a frequency. (I saw some discussion of this issue higher up the thread.)

Chris

 

RE: ok, what is happening here????, posted on December 3, 2016 at 15:03:34
vinnie2
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This trace is from a halogen light transformer. I am not sure what the frequency is. I will have to look and see it it says the on the transformer. The y was as close as I could get to the symbol, which looked like a backward y. I am going to hook it up to an 813 or two in the morning and then try fiddling with the scope and see if I can get a better trace.

 

One puppy per tube, posted on December 3, 2016 at 16:15:00
RayP
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I suspect you find find it simpler to have each 813 have its own supply.

ray

 

Careful Vinnie, that's not what I said!, posted on December 3, 2016 at 17:12:19
Triode_Kingdom
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"I think they could handle two 813 filaments anyway."

It will handle a million of them if you wire them in SERIES. That's what I said to do - two or three in SERIES.

 

RE: One puppy per tube, posted on December 3, 2016 at 17:15:27
vinnie2
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Me too.

 

RE: Careful Vinnie, that's not what I said!, posted on December 3, 2016 at 17:16:15
vinnie2
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Think I will just go with one since that is the way I intended to use them anyway.

 

RE: Careful Vinnie, that's not what I said!, posted on December 3, 2016 at 17:19:15
Triode_Kingdom
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You must have misunderstood my post. This was only for the purpose of temporarily loading the transformer so you can test it again. You can't simply hook one tube to the transformer; the voltage is too high. So, you can do what I suggested or you can buy a HUGE power resistor.

 

square wave rms is not calculated like sine, posted on December 3, 2016 at 17:24:10
elblanco
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right?

 

Frequency and Wave Shape, posted on December 3, 2016 at 17:24:55
Triode_Kingdom
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"If I understand correctly, your "square wave" is from a switching power supply operating at about 140KHz or so"

I'm pretty sure Vinnie has mis-stated the sweep time. All the lighting transformers I've purchased operate closer to 20 kHz out of the box. That's why the transformer must be modified. As for the waveshape, I did notice that on the later transformers. My earlier units were much more square. This issue definitely changes the method needed for ensuring that the tubes have the correct power applied.

Hate to say it, but I'm not sure I would use this method again. Pulling the square wave from a standard DC switcher and filtering it to a sine wave now seems to make more sense.


 

RE: ok, what is happening here????, posted on December 3, 2016 at 17:45:34
cpotl
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"The y was as close as I could get to the symbol, which looked like a backward y."

The backward y sounds like it is probably a Greek mu, which is why I thought you probably meant 1 microsecond per division.

But the frequency is not really important, as far as the rms voltage is concerned, except that the higher the frequency is, the less likely a cheap "true rms" voltmeter will give an accurate figure.

I just tried an estimate based on the shape of the approximately trapezoidal waveform in that scope trace, and it looked to me as if the rms voltage is coming out to be about 15.4V.

Chris

 

RE: Frequency and Wave Shape, posted on December 3, 2016 at 17:55:54
vinnie2
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I may have misstated the name, but the number was correct, it was 1. Like I said the symbol looks like a backwards y.
We are talking about the halogen AC transformer right, not the switching transformer?

 

RE: ok, what is happening here????, posted on December 3, 2016 at 17:57:11
vinnie2
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Well that is closer at least.

 

RE: Careful Vinnie, that's not what I said!, posted on December 3, 2016 at 18:00:44
vinnie2
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I was planning on using my variac and just taking it up until I get to 10 volts for now. By seeing at what percetage of full power I get to 10 volts at if will give a fair idea of what volts will be at full power. Good enough for now, and will give me some idea of how many volts I am going to have to drop.

 

RE: Frequency and Wave Shape, posted on December 3, 2016 at 18:09:07
Triode_Kingdom
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I don't know what that could be. I've never seen a scope with any markings for time other than S, mS, uS and nS. I also can't think of any "1" setting for these categories that corresponds with 7 divisions, unless the frequency is *much* higher or lower than I've seen in these units. 7uS is roughly 140kHz. 7mS is 140Hz. Yes, we're discussing the lighting transformers with (supposedly) 12VAC output.


 

RE: Careful Vinnie, that's not what I said!, posted on December 3, 2016 at 18:12:34
Triode_Kingdom
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Well then, you're in uncharted territory. I doubt the reduction in output voltage is a linear relationship to the input. These oscillators work by means of a saturable core transformer. They don't behave at all like coupled inductors. I hope you have some junk 813s you can sacrifice for this experiment.

 

Where I'm Headed..., posted on December 3, 2016 at 18:16:52
Triode_Kingdom
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The performance of the last two lighting transformers I purchased was very disappointing. Like yours, the voltage was higher than anticipated, and the wave shape not very square. My next ultrasonic heating project will be based on tapping off the square wave from a standard, adjustable DC switcher. Then I'll filter it to approximate a sine wave. That will hopefully resolve both these issues.






 

RE: Frequency and Wave Shape, posted on December 3, 2016 at 18:17:44
vinnie2
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I just went and check my scope. On the sec/div dial there are 3 sections, S, mS and the backwards y with a tip on the short end which probably equates to your uS, and the setting I was using was 1 uS in that case.

 

RE: Frequency and Wave Shape, posted on December 3, 2016 at 18:20:09
Triode_Kingdom
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If you really have a 140 kHz lighting transformer, it would be very helpful to know the model number. A pic of the inside when you have time would also be of use. Thanks!



 

RE: Where I'm Headed..., posted on December 3, 2016 at 18:20:28
vinnie2
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Well, if it works out I hope you will share it with us as this whole filaments voltage thing is making me crazy! It more trouble than all the rest of the wortk combined. Curse you 10 volt filaments, curse you!

 

RE: Frequency and Wave Shape, posted on December 3, 2016 at 18:22:07
vinnie2
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I will take one in the morning and post it. It's bed time for this old fart.

 

RE: Careful Vinnie, that's not what I said!, posted on December 3, 2016 at 18:25:13
vinnie2
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Well there goes that plan. Now, where did I put that big freakin' resistor?
But how did the 12sn7 filament I had hooked to it survive?

 

RE: Won't work like that with the variac., posted on December 3, 2016 at 18:30:27
megasat16
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I think Triode Kingdom hits the nail. Reducing the input voltage will most likely reduce the DC pluse frequency instead of the output voltage for these type of chopper transformers.

I don't think it will sound the best also at the reduced DC pulse. Why not use a regular 12V SMPS power supplies and reduce the output down to near 10V? I have experienced with them and found they work quite well for the 10V filaments in the Big Transmitter tubes.
.
.
.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.

 

RE: Careful Vinnie, that's not what I said!, posted on December 3, 2016 at 18:35:03
megasat16
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Well, most filaments don't usually burnt out right away even at the higher voltages. Even if the filament doesn't burnt out, you just accelerated the aging of the heater / cathode and the emissions. The heater / cathode may never burnt out even at higher voltages but actually shorten the tube life.

12SN7 heater work fine with 12V so it may be just fine.


.
.
.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.

 

RE: ok, what is happening here????, posted on December 3, 2016 at 20:10:08
deafbykhorns
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Mine looks a lot better than that one.
I removed a couple turns and got it down to 10volts
I use some old used up 6550's in series to load the supply before using the real tube


 

RE: Won't work like that with the variac., posted on December 3, 2016 at 21:06:31
Triode_Kingdom
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"Why not use a regular 12V SMPS power supplies and reduce the output down to near 10V?"

The goal is to heat with AC at an ultrasonic frequency. Quite a few enthusiasts, myself included, have found that AC sounds better than DC heating.



 

Making it Work, posted on December 3, 2016 at 21:11:55
Triode_Kingdom
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Well, the transformers you bought can be used. As we discussed, you'll need to A) add a capacitor (at least 47uF) to smooth the 160VDC power at the output of the rectifiers, B) replace the fusible resistor at the input with a 2-5 ohm, 3W standard resistor, C) unwind all but one turn on the oscillator transformer (increases the frequency, may not apply to yours), and D) use a small value resistor in each side of the output to drop voltage to the proper value for your 5A filament. We know this can work, so don't give up. :)


 

RE: Won't work like that with the variac., posted on December 4, 2016 at 02:58:13
vinnie2
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I wasn't suggesting a permanent reduction, just a temp one. Doesn't sound like it will work anyway. I am already using smps units on one channel, wanted to try AC on the other to see what difference there might be in the sound.

 

RE: Careful Vinnie, that's not what I said!, posted on December 4, 2016 at 03:00:13
vinnie2
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If what everyone is saying is correct, it actually had 15 vac on it for a while.

 

update , posted on December 4, 2016 at 05:08:33
vinnie2
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nt

Well now I am really confused. I tried to measure the voltage on a 5v filament transformer with my scope and it read 16 volts. I then adjusted it with the calibrate button in the center of the volts/div dial to read 5.2 volts (low as it would go, full counter clock wise), but then when I measured the halo trans it read 12.5 volts p to p. I was not able to get any better trace than what I got yesterday. I had volts/div at 10 and sec/div at 2 us.
I really want to give this a try, but I can't seem to even get started with it at the right voltage.
Not much info on the cover (see pic) of the ebay add. Also included photo of inside.

 

RE: Making it Work, posted on December 4, 2016 at 06:32:34
deafbykhorns
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Why not just unwrap one of the windings on toroidal, one or two shouldn't hurt anything.
I was able to drop it down to 4.5 volts before the transformer gave out(saturated?)

 

RE: pull some windings off the smaller choke and, posted on December 4, 2016 at 10:36:15
deafbykhorns
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You should raise the output freq

 

Output Transformer, posted on December 4, 2016 at 10:59:51
Triode_Kingdom
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The units I initially used measured close to 24V pk-pk. At that voltage, nothing too exotic was required in terms of dropping resistors to reduce it to 10V. At 33-34V, that's no longer true. You would need total resistance of about 1.2 ohms and 30W dissipation capability. Do your units have toroidal output transformers, or are they conventional like the ones I purchased? The former would be easy to modify.



 

RE: update , posted on December 4, 2016 at 11:11:01
cpotl
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"Well now I am really confused. I tried to measure the voltage on a 5v filament transformer with my scope and it read 16 volts."

You mean a good old-fashioned mains transformer with a 5V filament winding?

When you say "it read 16V" do you mean the sinewave was 16V peak-to-peak? That would be about right. 16V peak-to-peak for a sinewave translates to 16/(2*Sqrt2) V rms, which is about 5.7V rms. If you were measuring the output of the transformer with no load, then 5.7V rms might very well be right for a nominally 5V rms transformer.

Chris

 

RE: update , posted on December 4, 2016 at 11:49:28
Triode_Kingdom
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I agree with cpotl. Like anything else, filament transformers have winding resistance. They're rated for output voltage at full load. Your measurement is essentially correct.

About the lighting transformer, yours has a toroidal output transformer. Based on the photo, the output winding has 9 turns, which means approximately 3.89V pk-pk/turn (35V pk-pk total). So, if you remove three turns (11.67V), the output should decrease to 23.33V pk-pk, or (for a perfect square wave) 11.67V RMS. Because your output wave isn't as square as we would like, I would deduct perhaps 10-15% from that, which leaves 9.92-10.5V RMS. Under load, it will probably decrease somewhat, but in any event, this should be safe for the 813.

When you remove the turns, try to spread out the remaining turns so they're fairly evenly spaced around the core. That will aid primary-secondary power transfer.

Can you provide a link to the units you purchased? That oscillator transformer is also different than the ones I've been buying. I suspect it's a lower permeability, which would account for the higher switching frequency. Also on this point, if you wouldn't mind, could you confirm the measurement regarding frequency that you made earlier? Don't need a photo, just confirmation. Thanks!

 

RE: update , posted on December 4, 2016 at 12:41:28
vinnie2
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Those are some pretty good guesses there TK. Whilst you and cpotl were responding to my last email, I was out in the shop slinging solder. I had decided to just go ahead and take a couple of turns off the winding just to get something rolling. I left the 12sn7 hooked up to it so it would have a load and I got about 30 volts p to p, which gave me roughly 10.6 volts, but probably less since my square wave must have been rubbing up against a sine wave and some of rubbed off. A long ways from perfect. Any way, I figured with the 813 on there it would drop a bit more as well. So decided to try my luck with an 813. I got 27.5 volts for about 9.8 rms so decided to go for it and do a visual check at the moment I turned it on. The second 813 in the right channel is still on a switcher unit, and it is right on 10 volts dc. I figured if the ac one glowed too much brighter than that one at turn on I would shut it down instantly and hope for the best. As it turned out it glowed darned close to the same brightness, just a tad less, so I think my voltage estimates are pretty close. I will have to do this all again when the caps have been installed as they will boost the voltage, but it is a fairly simple process.
I went ahead and played some music for a while as the hum was not as bad as thought it might be. Probably because it's a hybrid right now with half dc and half ac on the filaments. It didn't sound too bad at all. I think if I can get the noise whipped we might be on to something here. Tomorrow I will move this halogen to the left channel and also add the second halogen to that channel so that I can compare the sound of the ac halogen channel to the dc switcher channel. I have the 560 uf caps ordered, but they will probably be a few days getting here. I hope they will knock out most of the hum.
Almost forgot.... I looked up that symbol and it is the Greek letter mu and it is used for micro as coptl suggested. All of my measurements were done with the sec/div on either 1 or 2 microseconds.
I have attached a pic showing the halo in the front and the switcher in the back. It takes up a lot less real estate. I will look up the link you wanted and post it soon.
Found it right away. Here it is...

 

RE: Output Transformer, posted on December 4, 2016 at 14:51:13
vinnie2
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I actually never checked, but I will. I really want to see if I can hear the AC "difference" in the sound of the amp though. That will be the deciding factor for me, all other things being equal.

 

RE: update , posted on December 4, 2016 at 15:48:03
Triode_Kingdom
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Great, sounds like good progress! Is the 560u cap for the purpose of smoothing the DC in the lighting transformer? If so, you can get by with much less. Probably as lttle as 47u/250V will render the hum inaudible. I'm just sayin' if you have something like that lying around, you might not have to wait. Congrats on getting this together, I'm anxious to know whether you hear an improvement using AC with the 813!


 

One more thing..., posted on December 4, 2016 at 15:52:35
Triode_Kingdom
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No need to post the link to the switcher. I searched eBay, and there's only one listing for a 120W lighting transformer. I'm guessing only the high wattage units have toroid outputs. The smaller ones can use conventional transformers without regard for their reduced efficiency, plus they're cheaper.

I would still appreciate it if you could confirm the frequency when you have time.

 

infrared thermometer, posted on December 4, 2016 at 16:07:00
RayP
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I tried using an infrared thermometer in my early tests but did not have too much success since I was only testing a resistor on a sheet of aluminum. I could not get much consistency.

tempature photo P1020262_zpscilrxhzo.jpg

However it might be interesting to use such a thermometer to check the temperature of DC heating compared to AC heating or high frequency AC heating if you could devise some accurate repeatable set up. Hand held is not good enough I suspect.

ray

 

RE: infrared thermometer, posted on December 4, 2016 at 18:19:54
Triode_Kingdom
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Why not attach a thermistor to the resistors and read the resistance hot? You'd need to calibrate it using the DC supply, say at 9.5, 10 and 10.5 VDC. The reading with AC could then be compared and adjusted to obtain the same RMS power.


 

RE: update , posted on December 4, 2016 at 18:23:22
vinnie2
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560 is what Ray P used used in his, so I thought it was needed. However, I sure will try it with less in the meantime, like tomorrow, as I have some 47uf/450v units in my parts bins. Thanks for the tip. Let's see what happens.
Wait a minute, it just dawned on me you said reduce the ripple in the DC.... where is the dc in the halogen unit, I thought it was all ac?

 

RE: One more thing..., posted on December 4, 2016 at 18:25:44
vinnie2
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I thought I had. How do I confirm the frequency?

 

RE: The lower wattage have toroidal , posted on December 4, 2016 at 18:35:14
deafbykhorns
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I have the 60 and 80w units

 

RE: One more thing..., posted on December 4, 2016 at 18:39:29
Triode_Kingdom
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Sorry, I was just asking you to check it one more time for me.


 

RE: infrared thermometer, posted on December 4, 2016 at 18:41:57
RayP
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Good idea.

ray

 

RE: update , posted on December 4, 2016 at 19:49:22
Triode_Kingdom
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The halogen switchers are configured like the schematic below. If you don't add the capacitor in dotted lines for filtering, the output will be a square wave modulated from zero to peak voltage at a 120 Hz rate. IOW, probably just as bad from the standpoint of audible hum as a standard transformer.

Look at the output of the supply again with your scope. Reduce the sweep speed so you can see low frequencies, and the 120Hz modulation envelope will be clear.






 

RE: update , posted on December 5, 2016 at 03:35:36
cpotl
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"Reduce the sweep speed so you can see low frequencies, and the 120Hz modulation envelope will be clear."

I hadn't realised that these switchers were operating on unfiltered rectified AC. That could perhaps explain why the scope trace that vinnie got was so shaky.

But more significantly, it could also mean that the true rms output voltage may be substantially less than might at first appear. If that 35V peak-to-peak is only what is achieved at the peak of the mains voltage cycle, and it is then dropping down to essentially zero during the part of the mains cycle where the switching transistors are receiving only a small voltage from the rectified mains, then the true rms output voltage from the transformer, with the averaging now being done over the entire cycle of the mains frequency, will be much less than simply the rms calculated under the previous assumption of a continuous somewhat distorted 35V peak-to-peak square wave.

Maybe this could indeed bring the true rms voltage down close to the advertised 12V. I can imagine the relation between the instantaneous rectified mains voltage and the output square wave voltage on the transformer could be a rather non-linear one, and so estimating how to do the further rms averaging over the 120Hz cycle might be tricky.

It would be very interesting indeed to see a scope trace of the modulated output voltage with the timebase synced to the mains frequency. This could allow a fairly useful estimate of the true rms output voltage to be made.

Chris

 

RE: update , posted on December 5, 2016 at 04:03:11
vinnie2
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Tell me how to set it up and I will take and post a picture.

 

RE: One more thing..., posted on December 5, 2016 at 04:05:05
vinnie2
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I am still unclear on how I am supposed to check it. All I did was check the sweep speed. What is it exactly that I need to do to check the frequency?

 

RE: update , posted on December 5, 2016 at 04:24:35
cpotl
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"Tell me how to set it up and I will take and post a picture."

Try turning the vertical sweep rate down to something like 2mS per division (2 milliseconds), or so. With luck, you might be able to adjust the sync so that it locks onto the mains frequency that will be modulating the high frequency square-wave oscillations.

You should hopefully be able to get a trace that shows as a sort of solid block but with an amplitude that is modulated in sync with the mains. (Imagine first a rectangular filled-in strip running across the screen, and then imagine that the top and bottom edges of the strip are themselves wobbling up and down in some sort of vaguely sinusoidal fashion.)

If you can't make it sync on the mains frequency that is modulating the amplitude of the high-frequency output, then assuming you have a dual-trace scope there is another way you could achieve it. First hook up that 5V mains transformer you were talking about yesterday to the one of the scope inputs, and get the sinewave nicely displaying and synced. Then, connect the output of the halogen switcher to the second scope input. You will still be getting the syncing from the 5V transformer, but the second display, which is the one you really want to see, should be nice and steady too. (Of course, the 5V transformer should be connected to the mains supply for this procedure to work.)

Chris

 

RE: update , posted on December 5, 2016 at 06:12:48
TomWh
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Is there any reason a fluke RMS meter would be far off. Vinnie has one of these and now with the combined issues on the scope would RMS meter be less quess work?

In regards to the sine square wave combination would that be better or worst than a pure sine or square wave for filament supplies?

This is on my to do list now. Would be nice to get rid of 10,000 to 20,000 electro caps on current filament supplies.

Thanks Tom

 

RE: update , posted on December 5, 2016 at 06:54:35
vinnie2
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Someone posted that the the fluke gets flaky on voltage past a frequency of 1k. Apparently that is all it is designed for.

 

RE: update , posted on December 5, 2016 at 06:57:16
vinnie2
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I will see if I can do this.

 

latest progress report....., posted on December 5, 2016 at 07:09:46
vinnie2
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Well, we have good news and bad news..... I got the right channel all converted to AC using the halogen transformers on the 813's and a standard filament trans on the 26. I installed a 100uf cap across one pair of diodes on each halo because that is what I had. See pic. The good news is the hum is quite low with the caps in place. The bad news is even though it doesn't sound too bad, it has a distinct edge to it, a bit on the harsh side. Not sure why that would be. If anyone has any ideas I would sure like to hear them.
The next step is to do the left channel with dc and see if comparing the two channels with a mono source confirms what I think I am hearing now. I hope it can be figured out because as you can see from the pic the total package with the halo trans has a pretty small foot print. I know on past amps I have built I always thought they sounded better with ac on the filaments, but then I wasn't using honker transmitter tubes then either.
Question for Ray P: First thanks for the procedure you outlined in that post, it worked great and was not too difficult at all. I am also wondering how you came up with the 560uf for the value of the cap you used and if it was intended only for reducing mains ripple or if it had some other purpose as well. Thanks again!

 

RE: update , posted on December 5, 2016 at 07:34:35
TomWh
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Good catch Vinnie!!! Looked up my 87 specs and it is not happy from 5k to 20k. Keep us posted this is what DIY is all about.

Thanks Tom

 

RE: latest progress report....., posted on December 5, 2016 at 07:45:05
TomWh
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Hey Vinnie

If you have a 50 uf to 100uf plastic or oil cap my try it instead of electrolytic cap. Those things can sometimes make things sound nasty???

Tom

 

RE: latest progress report....., posted on December 5, 2016 at 08:32:52
cpotl
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There is one further issue one might want/need to worry about, if one modifies the operation of the halogen switcher by putting a smoothing capacitor on the DC side of the bridge rectifier that is connected to the mains supply. To the extent that the smoothing capacitor actually smooths the rectified AC to make it DC, this will mean that the time average of the voltage seen by the switching transistors will be considerably greater. That is to say, instead of them seeing a pure rectified sinewave, they will be seeing a steadier continuous voltage that is close to the peak voltage of the pure rectified sinewave.

The upshot from this would be that, rather than producing a strongly modulated square-wave output that reaches, say, 35V peak-to-peak at the maximum of the mains voltage, the unit will now instead be producing more nearly a steady and unmodulated 35V peak-to-peak square wave. This will mean the true rms voltage of the output will be substantially increased, relative to what it would have been with the unfiltered rectified mains feeding the transistors.

Now it seems to me that 100uF would still be giving quite a significant amount of ripple on the rectified supply to the transistors. But probably there will be a fairly significant increase in the rms voltage on the output side. And a larger smoothing capacitor on the rectifier would give a much steadier DC voltage and hence a further increase in the rms output voltage from the unit.

I'm looking forward to seeing the scope trace of the modulated output from the switcher (preferably first without the capacitor modification, and then with it).

Chris

 

cap value, posted on December 5, 2016 at 08:47:30
RayP
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The 560 uf was a recommendation from Alex, see link below. You have to scroll down a ways to get to the section on AC heating.

'270 to 330uF/400V cap (for European 230-240V AC mains) '

For 115 - 120 AC mains, he recommended twice the uf value and 200 volts. I happened to pick 560 uf.

ray

 

RE: One more thing..., posted on December 5, 2016 at 09:16:50
Triode_Kingdom
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Vinnie, I'm not asking you to do anything different. Just to do it again and confirm that you get the same result. No matter what the level of experience, people make mistakes. It's always good to confirm things like this, especially if initial results don't seem to fit the norm.


 

RMS Output, posted on December 5, 2016 at 09:24:12
Triode_Kingdom
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"The upshot from this would be that, rather than producing a strongly modulated square-wave output that reaches, say, 35V peak-to-peak at the maximum of the mains voltage, the unit will now instead be producing more nearly a steady and unmodulated 35V peak-to-peak square wave. This will mean the true rms voltage of the output will be substantially increased, relative to what it would have been with the unfiltered rectified mains feeding the transistors."

That's an interesting point. The earlier units I purchased didn't output such a high-value square wave. I'm wondering now if the manufacturer has increased it in order to accommodate the 120Hz envelope and produce a more correct RMS value. I never worried about it because I was filtering the DC. The amplitude of the square wave itself was representative of RMS output. Thanks for bringing this up!



 

RE: it does get flaky, try playing with range, posted on December 5, 2016 at 10:28:22
deafbykhorns
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I found on my Fluke 87 that if I use a certain range, its pretty close.
Automatic range will bounce back all sorts of voltages depending on which range scale the reading falls on. I can back check this and tell you which scale. You'll see it right away if you try it, results will be around 12v on one scale and jump 20 volts on another.
Whats weird, is the the freq (Hz) on the 87 will give the correct frequency.

 

RE: cap value, posted on December 5, 2016 at 11:14:28
vinnie2
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Thanks for the link. I have ordered some 560 units and will give one a try when they get here. I will be curious to see what difference I can hear.

 

RE: it does get flaky, try playing with range, posted on December 5, 2016 at 11:18:32
vinnie2
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thanks for the suggestion. I will have to give that a try.

 

RE: One more thing..., posted on December 5, 2016 at 11:20:12
vinnie2
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TK, WHAT is it you want me to do again? I do not know how to check the frequency is what I have been trying to tell you....... If I have already done it I don't know what it was I did. Please spell it out for me what you want me to do.

 

LOL, posted on December 5, 2016 at 18:13:53
Triode_Kingdom
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Ahh, miscommunication, sorry!! I was just asking you to put the trace on your scope again and note the sweep speed (1uS, 2uS, 10mS, or whatever it happens to be) and note the number of divisions for a full wavelength. That would be the distance between two consecutive rising edges, or between two consecutive falling edges.

 

a breakthrough at last......, posted on December 5, 2016 at 18:18:38
vinnie2
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I finally got around to checking out deafbykhorns post that talked about using different voltage ranges on the fluke with higher frequencies, and also on actually measuring the frequency itself. I had never done this before with my 179, never had a reason too. Just tried it a few minutes ago and it worked like a charm! The results are a frequency of 32.5 khz, and a voltage of 9.65 vac. That is after I modified the transformer of the halo trans of course. That matches very closely to the 9.55 volts I got using my scope and dividing the 27 volts I got with it by 2.828. I guess I had better become more familiar with all the things my flukes will do. It is true rms after all, if you use it correctly.
Thanks "deaf", I feel much more confident about my voltage on the 813's now. And TK, I can finally tell that the frequency of the output ac for the little halo transformer, 32.5 khz.

 

RE: The lower wattage have toroidal , posted on December 5, 2016 at 18:19:45
Triode_Kingdom
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The 60W lighting transformers I've purchased do not have toroidal output transformers.







 

RE: a breakthrough at last......, posted on December 5, 2016 at 18:31:00
Triode_Kingdom
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Thanks, 32.5 kHz makes more sense, although I'm still curious why the scope display showed about 140 kHz. That's worth revisiting, because you now have two instruments telling you different things. The scope won't lie, and that's the reason you need to repeat the previous measurement (I also posted on this below). Anyway, if 32.5 kHz is correct, it's too close to the audio band. That might be the reason it sounded harsh. So, you might still need to modify the little oscillator transformer to raise the frequency. I can walk you through that with photos if it will help (I'll need to do it to an unmodified unit and photograph the sequence). We should look at the scope display again before I do that.

 

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