|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
70.185.110.199
I'm in the process of gathering parts for the PP 6CB5A amp which I've mentioned on here before. I picked up this transformer, mainly because it has high current 6.3v windings - the four 6CB5As alone will draw 10A!
I'm thinking of using a voltage doubler on the 176v secondary to provide the B+. The transformer doesn't have a center tap. I've used similar transformers with hybrid rectification in the past without problem but can a doubler work with this transformer? Also, I'd like to bring up the B+ slower than SS diodes would. Has anyone here used a pair of 6AX4GTB damper diodes (or similar) in such a doubler circuit? I have a bunch of them and have heard good things about them in normal rectifier circuits.
. . . Charlie
Follow Ups:
I've got 2 active amps with damper voltage doublers. A hi-fi amp (1 x 6BY5) and a guitar amp (2 x 6W4). Thousands of hours on the hi-fi, hundreds on the guitar amp. Had another hi-fi, now retired, with 2 x 6AX4 doubler. Thousands of hours. Never had any issues, never replaced a damper.
Recommend a relatively small (40 uf or less) pair of inital caps with a great big one after the L or R. That will keep the dampers happy and your ears happy, too.
I've been using 6DL3s in a classic voltage doubler on my PSE845 monos for many years without a single failure anywhere. My B+ is up around 1KV and average current about 170mA. I'd have over a thousand hours on them by now. Your requirements differ and so do your rectifiers but this should serve as a real world guide.
BTW and FWIW, the only failure ever on one amp happened to be with a critical Jenson coupling cap which have a reputation for going leaky (and I'd been meaning to change). It resulted in the dampers having to handle several hundred mA average for, I'm guessing up to a couple of hours, (long story) but they still didn't fail so my confidence in these particular tubes is understandably high!
Naz
Charlie,
You really should use SS diodes in a doubler, as huge stack caps. work well. However, you can use dampers after the stack, strictly for delaying B+ rise. TANSTAAFL applies and you can safely draw only 175 mA. from the 700 mA. winding, when working into a doubler.
Eli D.
I did a quick PSUD simulation and found 725 mA in the transformer with 140 mA DC from the doubler.
-BUT-
The 0.7A rating may be conservative - measure the winding resistance.
And you're not using the other secondaries to capacity. So that 176V secondary MIGHT be good for 1A or more.
I measured the primary (117v) and got 1.4 ohms. The 176v secondary was 5.9 ohm and the 97v was 4.4 ohm. Not sure how that relates to the amount of current available . . . ??? I definitely won't be using the full current rating of all the windings.
I was planning on using only one of the filament windings to power all the filaments. Not sure exactly what front end I'll use. Douglas (PakProtector) sent me some info on his PP 6CB5A project which will use 6BQ5s in LTP. I'm also considering 6SN7s and 6GK5s.
I'm not sure if I'll use the 97v winding or not. If I run the 6CB5As in pentode, I could use the 97v winding as a screen supply, which would draw very little current. Or I might use the 97v to power the front end tubes.
Any suggestions are welcome! My knowledge of design is minimal, at best.
I DO want to build something fairly simple - cap coupled, no interstage transformers, no CCS for now. As usual, I'll be trying to use scrounged parts. Output transformers will likely be pulled from a Pilot 654 receiver (PP 7591). They are 5.6k primary and pretty hefty. I also have a Scott 299A around that could also be a OT donor, I suppose. If this power transformer is unsuitable, I could also pull the PT from the Pilot or use one from a Sansui 1000A, which used a doubler circuit. I'd like to be able to make this one work though.
. . . Charlie
Hi Charlie,
Notice "Augmented Cooling" on the PT. Consider that some.
What are the DCRs of the primary and HV secondaries?
Jeff Medwin
Jeff - As stated above:
"I measured the primary (117v) and got 1.4 ohms. The 176v secondary was 5.9 ohm and the 97v was 4.4 ohm. Not sure how that relates to the amount of current available . . . ??? I definitely won't be using the full current rating of all the windings."
So, what does "augmented cooling" mean? I've never seen that term before.
. . . Charlie
Post a Followup:
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: