gyraf pultec voltage problem. first diy, only 175v.

Hi, thanks everyone for the input on the forum. I've had alot of fun
building the gyraf pultec and have used basiclly, chuckd's list.

I was mostly successfull, except for when it came to the power and the transformers.

1st, I had to order the 62082 instead, but that was suggested as a possible alternitive, digikey doesn't have any of the 62062's.
http://www.groupdiy.com/index.php?topic=1600

But I can only get 175 volts out of the second transformer, if I strap it
into 220 mode I get 350volts (didn't hook that up), but that's it, or 140volts, but nothing like 210 or 220. I'm at a loss I tried just about every comination i could think of on the sheet of paper.

And I'm not sure I dig that 6.3v transformer, because it's too loud.

but did I toast something or do I need to do something to the first transformer to adjust it?

It's been quite fun, But it's been a week now and I can't figure out what I've done wrong, after blowing up the board once, I'm back to square one. Looking forward to more diy, and a couple more kicks from discharged caps too..

So no 220 get a new transformer?

I'd say you're probably fine. Strap it for 220V, and bear in mind that 220VRMS is 311V peak, and that unloaded it'll be a bit higher than that

be very careful when you are measuring and testing...!!!

the caps are still loaded with 350 V, even if you have disconnected the mains voltage !!

Great, nothing toasted.

I seem to have signal now with no gain though, all the front controls

work and modify like expeected, but the gain structure / load impedence
doesn't seem right, whether I come in on the balanced or unbalanced connector the gain is the same.

Is there a easy way to test whether the tube gain stage is working correctly?

The power up and power down scheme definately now amplify's the signal, charges and discharges with power on/off.

Ah, anyway, a whole new frontier of exploration for sure, thanks!

The first 220uf cap started to melt/smoke after awhile.

Is it better to try and get the correct voltage or just get a bigger
rated cap?

I have a complete new set of parts on order to do a stereo
part and to do debug, but anyone have any ideas?

The shipping is delayed until tuesday now, unforunately, I expected it all here today. But I'm noty sure exactly how to tackle it, is it possible it has to do with the 4.1 amps in the first transformer?

So, two new transformers, and the same configuration.

175 volts. total.

tested the secpnd transformer sepately..
7.8 volts from the pc mount triad transformer when fed in what should be
the 6.3v configuraiton (right out of the box) in parralell.

and the 62082 is the 4.1 amp version of the other transformer.

Is there something one whould normally have to do to these to

make them read differently or are these ok outputs?

350 volts made things smoke, which was the traid (second transformer) in non-paralell mode.

chuck anybody?

I don't know those particular transformers that you use - are they both 220:12V like the ones in the schematic?

Jakob E.

Let me start by saying I have not built this (yet) but I will try to help if I can.

I looked up the data sheet for the transfermer you have so I could understand what you have on hand. They are dual primary/dual secondary 12V transformers. Hooked up in parallel, with no load, you can expect about 7.5V or so. You get 7.8 so that is fine. Once you have this in circuit, loaded with voltage regulator and heaters it will be correct. With this hicher voltage feeding your second transformer's secondary, you can expect to get 350V or more from the primary in parallel. This will come down when loaded in the circuit.

I suggest you do the low voltage circuit first. Get your heater circuit working first. Then move to the B+ side. Your circuit will be easier to get in line this way I think.

No, one is 115:12v and the others is 115v:6.3v (237-1046-ND)
The other transformer can be configured to do 115v 12v as well as 6.3v.
But chuck's picture seems to indicate 6.3v as does it in parralell so, if I did the math right here's what I did:

the first transformer 62082, primary to secondary is 12 volts at 4.1 amps.

115/6.3 = 18.25

so, I connected the 12 volts to the secondary on the transformer.

18.25 * 12 = 219

and connected those to the board per the diagram (and also what I can deriave from chucks picture.)

See the problem with chucks picture is that transformer looks the same back and foreth, and you can't see the other side of it, so you can't actually see really well if it is truely wired in parralell.

Humbly, I'm quite the newbie, but I tried to follow all the directions and all the posts, and hooking up primary to primary seemed to give 18.25/12 = 1.45 (It's been about a week). When I connected the 6.3v transformer up in parralell mode, but tapped center (220v) I get 350v, but this quickly burnt out my cap on the circuit board. It was overly loud and didn't quite smell right either, like the chemical in the transformer was melting.

I haven't read the other posts, just trying to figure out what you are trying in this post. So, are you using the 12v transformer for your first one, the heater circuit? Then using the second one with secondaries in parallel(6V), connected to the secondary of your 12v transformer? Then the primary of this transformer connected in series to derive your B+ voltage? Do I have your configuration right?

If I have it figured out, you should get about 330V unloaded from your secondaries for B+ in the finished circuit, and 15V or so from the 12 V secondaries unloaded. My advice is still to get the low voltage circuit up and running first, then do the HT circuit next. If you use 12V secondary to feed the voltage regulator circuit as the Gyraf schematic shows, it should work fine. Hooking your second transformer with secondaries in parallel to the properly loaded 12V winding of the first transformer, and the primary output of this transformer in series, you should get around twice the line voltage when loaded or about 330V unloaded. This will go higher if the first transformer feeding this has no load as well. I think that may be why your first capacitor fried.

Hope this helps.

Power transformers tend to be somewhat unpredictable when used back-to-back like we do here.

Is it possible to wire the second (step-up) transformer as 12:230V? That is 6.3+6.3:115+115V hookup in stead of 6.3:115V? This should give you higher voltage..

Both the capacitors in the HT powersupply should be 350V types - they should not be bothered by getting 350V? Unless, off course, you mean 350V AC?

The last resort would be to try with a 5V:115V second transformer - that should bring you closer to the needed voltage. This circuit will work well from 200V to 250V DC (measured under load, tubes heated and running)

Jakob E.

>Is it possible to wire the second (step-up) transformer as 12:230V? That >is 6.3+6.3:115+115V hookup in stead of 6.3:115V? This should give you >higher voltage..

I think is how I got 350V AC, and it would eventually fry the capacitor and the second transformer would smell kind of funny.

Right now, starting over, I have it in the what I think is the "suggested" configuration, and even though it only reads 175V, with a 6.5 amp fuse (I am assuming because the first transformer is bigger) I got 2 hours usage out of it without failure. I'm not 100% sure the gain is right, but it's really close. I did not have both lundahl's on the new board. This is the completely new power board with a completely new set of parts never plugged into anything but the 175v configuation and it appears to work.
So my next step is to see if I can replicate that with the original board and see if I have what was the same issue, knowing that the filter section is fine, etc.
(Which was basiclly no gain.)

The two old transformers still measure 175v. I just found it odd nobody
this problem.

The voltages can depend a lot on the exact type of transformers.

Hmm, that's really weird, I was readying the posts, and didn't seem to see them in order correctly, that's for you help you guys.

FYI, and for those that look later , assuming it's fixed..

I stuck with second transformer in parralell, not the secondary side in series for 350v. It seemed to work fine that way, except that the transformer eventually gets too hot.

I finally got it working, in fact in stereo! yes two of them at once.
it even worked for about 4 hours, I by that time I had it calibrated had listen and compared and was just about to turn it off and let it rest when boom. That was it for one of the 6.3v transformers, besides the sound and the smell (they always did that.) I have been looking, but chuck mentioned this too, they are just to hot and I wouldn't suggest them in the us. Cause a fan is two noisy and it would be by far the loudest thing
in the control room in a stereo config.

But you're right loaded everything working the voltages went up, and varied on each side, but didn't go up until on the board it seemed..

Anyway, many, many lessons learned. So I'll hunt for a better transformer, then I'll start something easier and less dangerous like the ssl.
Just needed an eq first.

Any reccomendations from Farnell, Rs, Bejoken, Elfa etc?
12:220 (1.5A), i would prefer non circuitboard types.
Probably a really silly question, but i´m just crap at finding the correct components. I really find this the hardest when it comes to D.I.Y
Thanks / Toby