Another SSS Build

[Aaron]

Well now I have a slight issue. While waiting for parts to arrive, I'd thought I would change the OT to a 4/8/16 multi instead of the single 4 ohm output. And now the amp isn't working right. It's distorted and the volume goes up and down. If you strum hard it fades out and then slowly comes back and then drops etc. I'm getting the same voltages as before the swap, I tried different valves throughout, I've done the chopstick to check for anything loose, nothing.
Any ideas?? Maybe faulty transformer?

Thanks,
Aaron

[jelle]

Could be. Did you try if the switch is ok, mabe by bypassing it like you prob did with the 4 ohms transformer?

jelle

[Aaron]

Hi Jelle,
I forgot to mention that I did bypass the switch to check, same issue. I put a multimeter across the primary and got very little resistance, it beeped on the continuous check.
These aren't the easiest to swap back over, I was hoping to save myself a couple of hours

Aaron

[jelle]

Meh. You should see about 40-50 ohms from center tab to each plate. Sorry to hear that.

[Aaron]

Damn. It only measured 3 ohms.

[jelle]

Yeah, that's bad....

[Aaron]

Oh well, back to the single tap for the time being.

Thanks Jelle.

[Aaron]

Output transformer update...my replacement arrived today. This time I thought to check the primary's before installing, from C.T to each side I'm still only getting 17ohms and continuity.
The transformer in question is a Hammond 1760W. I've attached the spec sheet.
Am I really that unlucky?

Aaron

[martin manning]

The spec sheet says it should be 11.4 ohms on each side.

[Aaron]

Hi Martin,

Thought I'd double check first cause my Blackface Twin transformer measures 40/39ohms

Aaron

[Aaron]

Okay, wired in new transformer. Same problem. Checked the primary's again and they are still the same, 17ohms. Secondary taps 3.5ohms.

So check biasing again, all good except........now on the driver I have -40v on the cathodes and -20v on the grids. 20v difference, how can this be. And when I probe the grids, the 6L6's red plate instantly.

I am stuck. Any thing I am missing??

Thanks,
Aaron

P.S:- just to add insult to injury, I check the first transformer again and measures fine. Exact same as the replacement!! So tonight I used a different multimeter.

[martin manning]

I can see where touching the grid with your meter might upset the bias of the driver and cause the power tube bias voltage to shoot up, so don't do that.

This all started when you changed the OT? You've probably retraced your steps already, but maybe have another look. Can you link the schematic you used?

[Zippy]

So check biasing again, all good except........now on the driver I have -40v on the cathodes and -20v on the grids. 20v difference, how can this be. And when I probe the grids, the 6L6's red plate instantly.

So tonight I used a different multimeter.

Does the same thing happen if you chop stick the same test points?

I'm wondering if you have a bad connection or a bad socket.

[crbowman]

Wired up my first FET circuit!!!! All I had was a MPF102, so have used that to test it until my NTE452's arrive.

I think I'll change the capacitors throughout as well. In my Pentode build I used yellow tubulars and the amp sounded a bit dark, so for this amp I used 715/6 orange drops and this amp is a bit too bright for my taste. I've ordered some 6PS orange drops, so maybe a mixture of both?

I've been reading threads on different capacitors and their effect on the tone. Anyone used a combination of different capacitors? Eg, 716's for PI and 6PS's for tonestack or vice versa.

Aaron

I have an old Deluxe Reverb that had 716's throughout and was a tad bright. I subbed in 6PS's for coupling caps (left the 716's in the tone stacks) and it seemed to tame it although the difference was fairly subtle.
More than anything, it just seemed to sweeten it a bit. FWIW, I like the idea of mixing caps. You get less of the prevalent character of any one type or make of cap.
BTW, good luck with the new transformer!

[Aaron]

Finally finished! Faulty output transformer and P.I valve (probably my fault from putting in and pulling out valves so much while trouble shooting).
I also changed orangedrops from 716's to 6PS's in the pre, reverb and mix stages, but kept the 716's in the P.I and driver. Sounds much nicer now. Before it had this hard, top edge sound to it. Sounds more rounder now (if that makes sense).
Thank you for the input and ideas in the trouble shooting.

Finally get to start a Tweedle D build.

Aaron