GZ34 Voltage

[titanicslim]

I just installed a GDS transformer in a 36w that I built a few months ago and I'm not getting sufficient voltage to run it.

I've got exactly 290VAC at each of the transformer's HV taps but the b+ at the GZ34's #8 pin is only 325VDC. Thus are all my plates getting about... well, many less volts than they should.

Am I missing something?:hmm:

Dave

[57chevy]

Is your STBY switch in the operate position? What exactly is your plate voltage on the output tubes?

[krx]

That's not too far off the data sheet specs:

http://www.drtube.com/datasheets/gz34s-jj2003.pdf

First chart on the left. 300V input, 200-250mA draw. I'd say you're getting about what you should.

325V should sound good still, just a little dirtier overall than 350V. If you want a higher voltage, use silicon rectifiers. If that makes it too high, put in a sag resistor. I'd try something like 50 Ohms @ 10W.

[titanicslim]

Hey, Guys

Thanks for responding! Since I'm coming down with a migraine I think I'd better let it sit and self-repair a day or two. Then I'll start from the beginning.

It's a TMB-EF86, using Nik's layout from Ceriatone:
http://www.ceriatone.com/images/layoutP ... iatone.jpg
He has evidently changed most of his layouts to incorporate some kind of [surge protection?] diodes on the recto socket. I assume the HV leads are just using vacant pins instead of an extra terminal strip. Any reason I can't leave these off, at least until I get it working?

Also, I included the "half-power" switch and the NFB switch that he shows at the output. That may be a faux pas as well.

Anyway, I'm getting 328v on v.1 and v.2 plates, and 318v on v.3 and v.4
with 12.6v on the #3 pins.

I appreciate all the assistance
Dave

[Phil_S]

Just to get another point of view on expectations...I'm not so sure it's as right as somone else says. Rectified voltage in a perfect world is one leg * sqrt (2), in this case 290*1.4 = ~406. The GZ34 will give a 30V drop, bringning the number to ~376. Allow 5% for the various loading factors, that brings it to ~357.

If you do this the "other way", the rule of thumb on a GZ34 is 1.3x, in this case 1.3 * 290 = 377, ~same result as above.

I would have expected more, but sometimes a transformer under load just doesn't get to the calculated number and that's that. If your build is otherwise good, there isn't much you can do about it. Anyway, I don't think it is very desirable to run EL84's at such high voltage. So, in the end, I think you are better off.

I'd move on and leave this behind as a point of curiosity.

[krx]

Just to get another point of view on expectations...I'm not so sure it's as right as somone else says. Rectified voltage in a perfect world is one leg * sqrt (2), in this case 290*1.4 = ~406. The GZ34 will give a 30V drop, bringning the number to ~376. Allow 5% for the various loading factors, that brings it to ~357.

Did you read the data sheet? It basically says that he should be getting the voltages he is. When you push the GZ34 (or any rectifier) close to its maximum current, it becomes a lot less efficient.

[Phil_S]

Oh...<embarassed>...I never thought to look. I just pulled up the Philips data sheet. It says at 300v per plate, cap input, at 250mA, voltage out = 330. So, much for rules of thumb. Sorry, I wasn't intending to post mis-information.