5F1 Champ DIY: No sound (Tube/Transformer)

[Enzo]

Welcome to the forum.

Better yet, start a new thread for your amp. Not only might you have a different problem as MWJB points out, you also will get better response than by tacking yours onto the end of an old multipage thread.

[mazzas]

Okay. I just didn't want to post the same problem twice or miss out on the work that was already done in the same arena, if it was applicable.

[mazzas]

At any rate, here are the readings that MWJB requested:

6V6:
#3: 390 vdc
#4: 340 vdc
#8: 20.83 vdc

12ax7:
#1: 204 vdc
#6: 198 vdc
#3: 1.36 vdc
#8: 1.278 vdc

Pictures will follow...

[MWJB]

Voltages look good. We'll see what the pics reveal.

[mazzas]

Here are pictures. I tried to get the off board wiring in both of these. If they do not show enough useful information, I'll be happy to retake them.


See the images here: http://twitpic.com/2hxp4 and here: http://twitpic.com/2hxlr

[MWJB]

Your layout is just about as bad as it can be. You should have the PT, rectifier, then the power tube at one end of the amp, the input jacks & preamp tube at the other.

You have signal paths criss-crossing back and forth accross the amp. It's a recipe for disaster.

Your high input jack is wired wrong, there should be a jumper from the grounded tab to the middle (switch) tab, but you hve a jumper from the hot terminal to the switch instead. This shouldn't stop the amp from working, just make it noisy with no instrument plugged in.

But inevitibly I don't think that the way that chassis is laid out is going to work well at all.

[mazzas]

Id settle for noisy over nothing at all.

[MWJB]

I couldn't see any wiring at the speaker jacks/output transformer. Because I can't see the full chassis, I can't tell where both ends of a particular wire terminate, therefore it's very hard to spot errors.

Honestly, I really wouldn't perservere with that chassis, buy a 5F1 chassis and swap the parts over to that.

If you keep that chassis then that board will have to go.

Turn the amp on, volume up, now probe the 6V6 plate with your voltmeter (pin 3) do you hear any noise? Then do the same at 12AX7 pin 6, then pin 1. Be aware that if there is signal at the 12AX7 pins 1 & 6 there will be LOUD pops, careful not to panic & short anything.

[mazzas]

Thanks for the advice. This is part of a Champ "600" conversion that somehow turned into a "total gut and rehab." Assuming that I can get it to work at all, I fully intend to "re-wrap" it in a nice tweed cabinet with something other than a 6" speaker. At which point I'll have to pick up a new chassis, anyway.

In the meantime, I'll see if I can get some response by probing the indicated pins. I'll let you know what happened. Thanks.

[mazzas]

At half volume I hear nothing on the 6V6 pin 3 (which registers 400 vdc).
At half volume I hear nothing on the 12ax7 pin 1 (which registers 207 vdc).
At half volume I hear nothing on the 12ax7 pin 6 (which registers 201.7 vdc).

The high jack may be wired wrong, but I actually have the ground and middle jumpered. The High goes to the middle of the low jack, and all grounds are tied together (just like this: http://www.dockeryamps.com/web/Docs/...amp-layout.pdf).

The input jack wiring is all that I took from the above referenced diagram. The rest of the wiring (to the best of my knowledge) matches this: http://www.kbapps.com/audio/schemati...5f1layout.html

[MWJB]

If you hear nothing at 6v6 pin 3 then the problem sounds like it is between the 6V6 and the speaker. Check connections to output trensformer and from output transformer to speaker.

"The high jack may be wired wrong, but I actually have the ground and middle jumpered." Not in the photo you don't. Three tabs - left is the tip, you have a jumper from this tab to the middle tab (AKA switch). There is no jumper from ground (RH tab) to middle tab (switch). The ground tab is easy to spot, it is physically connected to the centre ring of the jack.

[mazzas]

The wiring to the output transformer seems pretty straight forward. The transformer is this one from Triode Electronics: http://store.triodestore.com/tfchxfwi48oh.html. I do not currently have the 8-ohm tap connected.

Black: ground
Yellow: 4-ohm tap
Green: 8-ohm tap (not currently connected)
Red: B+
Blue: 6V6, pin 3.

All connections seem good (no cold joints). I have another Champ OT. Maybe it's worth swapping them out?

[MWJB]

Well, there's still the speaker jack between the OT and the speaker, are you sure that this is wired correctly. It'll only take a few minutes to swap OT's, so if yuo find the speaker jack is OK then try it.

Bear in mind that it is more likely that the amp makes no sound because something is wired wrong, rather than a brand new component doesn't work.

[mazzas]

Okay... now we're getting somewhere...

Squeals very loudly... fairly high pitched. OT leads reversed? Not according to the wiring layout (I think).

Moving wires around with a drumstick produces no change in the squeal.
Replacing all tubes, likewise, has no affect.

[tubeswell]

Remember that even transformer wiring companies get the colours on the leads mixed up now and again. If its a squealing SE amp, its quite possibly because you are getting positive feedback from the NFB circuit (instead of negative feedback) due to the OT primaries being the wrong way around. As MWJB says, it only takes about 1 minute to swap them and see