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Planning to put together a power supply for a 26 pre.
I'll be using a RGN 1064 mesh anode rectifier. It requires 4 volts on it's heater, but I can only find transformers at 5 volt.
Calculations on a dropping resistor on the 5v secondary are pretty easy as the filament draw is a tick over 1 amp (1.1A). 1 volt drop @ 1 amp = 1 ohm @ 1 watt.My concern, since the rectifier is directly heated, is the potential sonic degradation that might be incurred using this method, if in fact it does degreade the sound. There will be a voltage regulator of some sort downstream after the LCLC filter ( still undecided and playing around / looking at S.S. or tube based regs), so if the dropping resistor effects the over all sonics it might just be extremely minimal if at all ?... But I have no experience in this area.
I would be using a separate transformer for the heater so it would be possible to do something on it's primary to not have to worry, but I have little if no knowledge on how this would be done....
Soooooo...... this post.
Thanks fella'a
JD
Edits: 05/25/12 05/25/12 05/25/12 05/25/12 05/25/12Follow Ups:
just found this interesting way to drop AC voltage using diodes:
http://home.cogeco.ca/~rpaisley4/xACdropper.html
JD
Jeff,Might not a diode in series be far worse than the resistors you originally sought to avoid !!
Jeff Medwin
Edits: 05/26/12
its just an article I found...couldn't be worse that a bridge rectifier or those diodes used for cathode biasing.
JD
I ordered mind from Heyboer, originally for my U18 or u19 rectifier. secondary is 4v 4 amp, open frame. I think I paid $ 30 for each plus shipping.
wal
actually that's a fantastic i.d.er.
Last night I placed an order from Edcor for some chokes for the project.
I just got off the phone with them this afternoon and they can do a L.V. tranny @ 4V & 2A for a slight fee over their regular one. Since this will be an end of Summer project, the 5 week wait or so for the chokes will have the transformers added on to the order and all arrive at the same time.
JD
Hi Jeff,Consider this also : have then do a multiple tap primary, like 116-120-124 so you can "NAIL it" to both your line's AC level AND as to how the trannie acts under load.
EDCOR told me they will not add TCSS lead outs to the secondary, because they use automated machines and their machines won't handle teflon coating.
I use TCSS (times two) on ALL my SE rectifier winding lead outs Jeff. Its like chicken soup, it may not help ... but it won't hurt !!
Jeff Medwin
Edits: 05/25/12 05/25/12
Jeff
Use a current limiter on the primary.
Depending on the transformers efficiency
you would need a CL-50, CL-60 or CL-70.
At $2ea get all three and see which one
will give you the desired output voltage.
It will also give you a nice slow warm-up.
You could also try a 1.5 ohm resistor.
That is just an estimate as you will
need to adjust for the aforementioned
efficiency of the transformer varience.
DanL
They usually accept a range of input voltages and knock it down to the desired voltage. To get 5 volts DC, you can start at 6.3 volts RMS AC.[I have just been working with my supply, but I went with too little voltage to the regulator: 6.3 RMS AC to 5.5 volts DC. It was suppose to be 6.3 volts DC! Oh well, it runs cooler and still sounds the same to my ears -- my goal was to run the regulators cooler by dropping less voltage, but they have a mininum of 3 vols DC differential in order to operate within specs. I think it is an LM317 regulator on heatsinks.]
Edits: 05/25/12
the regulator would "after" the B+ filter to reduce 195v down to 120 to 150 volts for the 26. I am only concerned with this post regarding the 5v to 4v for the RGN1064 heater.
JD
Without thinking about it too hard, it seems to me if your not using the center tap of the 5 volt winding as your B+ take off point, just one side of the filament, the drop resistance is not in the B+ path.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
not quite sure what you're saying... put the resistor in series on one leg of the secondary and forget / not use the c.t. at all?
That is what I was initially thinking, use the full secondary of the transformer and put the resistor in series with one leg before the rectifiers heater.
JD
Yes, that's what I meant.
If you were to use the CT, then the resistor would be in the B+ path.
But if you don't use the CT then the resistor is not a concern.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Just to make sure of the understanding. I am using a separate filament transformer for the rectifiers heater, not using the the main B+ HV power transformer at all.
JD
I totally understand.
The question is, will a voltage drop resistor in the filament line for the rectifier tube harm the sonics of the amplifier?
I say it can't if it's not in the B+ path.
The "normal" way to use a DH rectifier tube is to use a filament winding with a CT and use to the CT as the B+ take off point like the example above.
In the example above, a resistor in either leg of the filament winding would be in the B+ path and could cause sonic harm (actually I doubt that it would).
If you don't have or don't use the CT of the filament winding for the B+ take off point then the voltage drop resistor will not be in the B+ path (between the B+ and the audio circuit) so it can't harm the sonics of the amplifier.
I hope this is clear this time.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
bingo....
here's a quick chicken scratch sketch of my proposition:
http://www.flickr.com/photos/78107938@N05/7268681404/in/photostream/lightbox/
JD
IMO that will work just fine.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Why not use an open frame transformer and unwind the secondary until
you have 4 volts under load?
Since I'm doing dual mono and decon / recon struction on a transformer is a bit beyond my skillset, while that does sound like a good "idea", practical reality is that will probably not be an option.
JD
Inserting one ohm into the filament lead or B+ line at this point will have no impact on sound quality. Save your time and worry for real problems.
--------------------------
Buy Chinese. Bury freedom.
Thanks!... that was the main point of the question... i.e. potential impact on the sonics. so a good non-inductive ww resistor should have extreme minimal or no impact on this invention. :)
JD
This won't require a non-inductive resistor. Any type with sufficient power rating will work. Remember, this is the part of the circuit where some designers place several Henries of chokes. A few microhenries in the resistor will be insignificant.
--------------------------
Buy Chinese. Bury freedom.
gotcha
JD
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