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I have just fitted a schottky bridge, tested the fwd voltage and am coming out now at 19v in the sockets (tubes out, socket to socket pin 8 to 8)
which is too high for my 6SN7 heaters (parallel 6SN7's)
How do I get this down to 13v (6.5 a side)?
Edits: 06/01/15 06/01/15 06/01/15 06/01/15Follow Ups:
Ok would someone please ok these choices for me>
KBU6J - Replace can it be suitably replaced with C3D06060F?
http://www.vishay.com/docs/88657/kbu6.pdf
http://www.mouser.com/ds/2/90/C3D06060F-276420.pdf
Grr, just noticed fwd voltage is different...
Having trouble on Mouser selecting a KBU4K replacement 4A seems to be the problem..
http://www.mouser.com/Search/Refine.aspx?N=18337915
" That's their way of saying that pin 7 connects to the supply and pin 8 of that tube is connected to pin 7 of the other and grounded and pin 8 of that second tube is connected to the other leg of the supply. "Aha ok now I see, I never did manage to understand that! (hence they are in series in my "parallel 300b" amps) Still, I had to read and re-read the above several times for it to sink in.
So in theory I could measure from pin 7 on the one 6SN7 to pin 8 on the other and get my (same as from the bridge)dc voltage reading. I'm just not used to thinking like this at all it's quite a struggle, these circuits kick my ass I feel like I'm in pre-school learning the alphabet.
I did figure out to measure after the resistor and noted how much the 1ohm was pulling down. I think it was from 13.1v to 12.6v if my memory serves correctly, I got 6.3v to ground each tube, which is less than 5% under the optimum 6SN7 heater voltages, in other-words "spot on."This series connection probably might explain why the (power on) led on the front panel is connected to different 6SN7 pins in each mono amplifier, I need to think about this? That had me very confused.
Should I think about installing a switch to disconnect the led from the circuit, will it degrade the sound by much?
"13.1V is essentially correct, although it's a little high. This isn't a regulated supply, so some variability is to be expected."
Would the led which is presently disconnected in this amp pull the voltage down to where it might seem more err, normal?
On another note, Is it worth thinking about another project for sometime in the future to regulate this supply maybe with a little couple of discrete burson modules,(rather than a LM7XX regulator aren't they supposed to be very noisy.)Come to think of it, I installed some hexfreds in my filament supply back along and am only getting in 4.8v at the 300B filaments is there a way to "simply" correct this, I remember reading that they will perform better at their optimal 5v, is it really worth it?
Thanks so much guys! I can sit back relax and enjoy the music once again now...
Edits: 06/02/15 06/02/15 06/02/15 06/02/15
typically have a much larger voltage drop across them than do Schottky diodes. I would wager that if you replace the hexfreds with Schottkys, you would "find" the missing filament voltage where it should be, running the 300B filaments.
talk about Schottky diodes . we would list some series of these which work best in filament so inmate can try them out. there is so many of these Schottky diodes and soon get confuse.
LT
What filaments? You'd want a very different Schottky diode to heat a 45 than, say, a 2A3.
"What filaments? You'd want a very different Schottky diode to heat a 45 than, say, a 2A3"
Oh goodness, I've heard that schottky's were susceptible to blowing at turn on/in-rush. I just thought as long as the amperage was high and the voltage not to high about 600v then I'd be good to go.
Have gone and used Cree C3D04060 For my 6SN7 bridge here?
I'd like some suggestions for my 300B filaments...
The C3D04060 has a pretty high voltage drop, which is a tradeoff to get the higher operating voltage. This is not a particularly good selection for a low voltage heater supply.
300B's don't need a ton of current, 1N5820 ought to do fine.
Diode selection is a balance between forward voltage drop, device dissipation (load current * forward voltage at that current), and supply voltage vs. load voltage.
If you use the C3D04060 to heat your 300B's, you'll see a little over 1V of drop across each diode at 1.25A, so we'll say 1.375W of dissipation. The datasheet doesn't specify the thermal resistance to ambient, but it may be somewhere around 60-70C/W, so you may see a 90 degree temperature rise in the diode, which will reduce its lifetime and burn the board that it's attached to (unless you heatsink it).
If you go to a diode that drops less than 0.5V, you end up with much less heat dissipated, as well as more available voltage.
Turn-on will rarely damage these parts, as they are almost always cool at turn-on, and the stress of initially heating a filament isn't going to raise the device temperature quickly enough to matter.
If you are modifying an amplifier that is a commercial design, I would suggest that you are doing a lot more harm than good.
Gathered enough from your recommendation IN type diode, have gone with Vishay Schottky VT5202. Thanks for your help
http://www.mouser.com/Search/ProductDetail.aspx?R=VT5202-M3%2f4Wvirtualkey61350000virtualkey78-VT5202-M3%2f4W
What will you do if the Schottky bridge makes too much voltage?
"What will you do if the Schottky bridge makes too much voltage?"
Increase the single 1R resistor after the diode bridge.
Conversely, if there was too low a voltage would it be possible to drop the value of the the two before the bridge say to 0.1R? What is the purpose of these two and how low could one safely go?
If you are modifying an amplifier that is a commercial design, I would suggest that you are doing a lot more harm than good.
It all started with replacing the ordinary lytics for black gates and film caps, and progressed from Std's to here. I now have the caps around the 300B's BG NH in Super-E config and VK's with the 5687's.
Tants on the main board and 6SN7 board takmans grid. Still have the same iron, but these are pretty much what Audio Note would have done if I had shipped it (tants) as for super-e config and VK's I've prolly pushed it a little further than I could have paid for. And it has been a ton of fun.
The diode bridges were just standard KBU types, I am surprised to see that they don't seem to put schottky's in the level five gear.
If the amp is designed for KBU's, use KBU's.
"If the amp is designed for KBU's, use KBU's."Seems, that I'm starting to do a full circle back to where I started.
I did contact Peter Qvortrup of Audio Note initially with my thoughts as to changing from KBU's to Schottky's and I got a favorable response without any particulars just saying to keep the voltage requirements reasonable (not too high)
I have these neat little boards lined up from china and this is where I would really appreciate some help, I guess schottky's with a similar spec to the KBU4K for the 6SN7's, And KBU6J for the 300b's.
I don't know why AN would specify these, but to my thinking wise to not stray too far from these requirements, but hey I'm clueless here?Schottky's that I can solder directly into this board?
The C3D4060 I have learned I didn't make a particularly good choice, they do however fit right into this board and heatsink...
Edits: 06/07/15 06/07/15
well.
just like a few that good for filament and heater DC and that should be good .
I wouldn't use DC on the 45 or the 2A3 . so may be list a good dioes that is good for DC heater ,
LT
Well, I guess you'd go on Mouser or Digikey and select for low voltage high current types that exceed the needed parameters by a healthy margin. That's what I did, when I changed over to Schottkys from Hexfreds for my preamplifier filament supply, which is also voltage-regulated. Sort of like the OP, I couldn't figure out why I had too little V for proper regulation, until I made the swap.
"Come to think of it, I installed some hexfreds in my filament supply back along and am only getting in 4.8v at the 300B filaments is there a way to "simply" correct this, I remember reading that they will perform better at their optimal 5v, is it really worth it?"
Yeah, don't use Hexfreds, use Schottkys diodes.
"Would the led which is presently disconnected in this amp pull the voltage down to where it might seem more err, normal?"
I don't think the LED would draw enough current to make much of a difference.
Do you see the 1 ohm resistor in series with the heater supply? The one between the + output of the bridge and the 4700uf cap?
You could increase it's value to lower the voltage going to the tubes.
"Is it worth thinking about another project for sometime in the future to regulate this supply maybe with a little discrete burson module?"
Other than regulating against fluctuations in your line voltage, the heaters of the tubes don't need to be regulated because their current draw is constant.
Regulation is only needed when the load current changes with the music.
As for the fluctuation of your line voltage, tubes work just fine with the heater voltage +/- 5% of the rating (12.6 in your case) so I wouldn't worry about it.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
With no load, the voltage will read high after the resistor. the voltage directly off the bridge will always be higher than after the resister if there is a load. with no load, it will be the same. you need a load to get any drop across the resistor.
If you are looking for 13V
then you must have them
in series not parallel.
Top diagram is series
Bottom is parallel
DanL
.
Have Fun and Enjoy the Music
"Still Working the Problem"
Which shows no wiring of IDHT filaments.
Again they would be in series if ~13V
is the required filament voltage.
Not parallel as OP stated.
DanL
Lower right of the line stage box (middle box, top of image).
7 (F3)
7/8 (gnd)
8 (F3)
That's their way of saying that pin 7 connects to the supply and pin 8 of that tube is connected to pin 7 of the other and grounded and pin 8 of that second tube is connected to the other leg of the supply.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
"Which shows no wiring of IDHT filaments."
It shows the series-connected 6SN7s connected to power supply terminals F3.
--------------------------
Buy Chinese. Bury freedom.
Maybe I should have posted this in tubes Dan.
All I really need to know is if 13.1v DC read across the bridge + & - is ok for my heaters (tubes are in sockets no and I can now only read off the bridge)?Am I reading this correctly?
Is this voltage ok (tubes in place?)
Edits: 06/01/15 06/01/15
13.1V is essentially correct, although it's a little high. This isn't a regulated supply, so some variability is to be expected.
--------------------------
Buy Chinese. Bury freedom.
I must be missing something; it's not clear why you would be applying 13V to two parallel 6SN7s. Can I suggest that you simulate this in PSUD? It's free to download, and much better for you to have the means to make adjustments and tweaks yourself. As for the method you're using, I've never been comfortable powering filaments with a raw DC supply. I wouldn't do this without a regulator of some sort.
--------------------------
Buy Chinese. Bury freedom.
The problem is I have no idea how to simulate this.
These are my Audio Note P4 monos, they only use one half of the 6SN7.
I'm measuring the + & - on the bridge in dc, with tubes in sockets I can't measure as I have no access except on the bridge itself.
Was measuring before between pin 8 and pin 8 with my meter dc between the two. (tubes removed)
Am I measuring correctly?
Edits: 06/01/15
Did you measure the voltage between the same two nodes before removing the previous rectifiers and replacing with Schottky's? Schottky's have a very low voltage drop compared to almost any other class of rectifier. When you're working with filament voltages that are already low compared to B+, etc, then changing from some other rectifier to Schottky's can have a significant effect, just like the one you are measuring, where it seems your voltage is high-ish (because less voltage is being dropped across the Schottky bridge than was dropped across the previous rectifiers). So, that's one issue, but your final V of 13.1 is not so bad, as long as it is being seen across the two tubes in series, as others have mentioned repeatedly. 13.1VDC is too high for parallel connection of 6SN7 filaments, obviously. Hope that helps.
Actually - With the 6SN7's in circuit, I'm reading 13.1v dc off the diode bridge which I guess is just about spot on huh?(This is on the bridge not at the socket)
Edits: 06/01/15 06/01/15 06/01/15
Ok, 6.3 to ground from the +
and 6.3 to ground from the -
at the bridge whilst tubes are in the socket.
Is it ok to be measuring at the bridge whilst tubes are inserted (can't access sockets?)I know you all here are badass with electronics, whilst I'm badass in the kitchen and pretty clueless with all of this, please don't be too hard on me, thanks
Edits: 06/01/15 06/01/15
Without the tubes inserted (unloaded),
the voltage measurements would be useless.
From the posted schematic it seems fine.
DanL
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