18 Watt TMB Build issues

[Spunky99]

The squeal is coming from the OT to the EL84 tubes. I have swapped the leads, twisted them and moved them all about but still get the squeal.

Is there a missing ground, a ground loopback or anything else I can do to get rid of this?

[Littlewyan]

Ok so you say the amp only squeals when you turn the master volume up. Does it still squeal if both pre amp volumes are turned down?

[sluckey]

Do I see an impedance selector switch mounted next to V1? If so, you need to move that down close to the PT end of the chassis. Get those OT wires away from the highly sensitive preamp circuits. Pull them out from under the board and keep them away from V1 and V3 circuitry. They'll be fine down near the power tube end of the board. If you can't re-route the OT wires inside the chassis, consider routing them on the outside of the chassis.

EDIT... Keep the speaker jack away from V1 and V3 also.

[Structo]

Yep that is a no no.

Also, I notice quite a few solder joints don't look real good.

They should be smooth and shiny, not dull or crusty looking.

Are you using leaded solder?

At your EZ81 rectifier, do you have the high voltage (HT) wire on pin 3 to the standby switch and from there to the filter cap?

[Spunky99]

I rerouted the OT speaker out to the outside of the chassis and removed the speaker jack from the chassis to make sure none of the wires were anywhere near the rest of the amp and hung it outside the chassis. No change.

I Moved the OT input wires, twisted them and reversed them, no change.

I resoldered all the tube connections using the same Kester #44, .050 60/40 solder. No change.

I removed the covers from V1 - V3 and tapped them with a chopstick.
V1 was extremly microphonic and it was like tapping a pickup on a guitar plugged in. I replaced it with 4 other brand new tubes...NO change.

So far nothing changes the condition at all.

[Spunky99]

Littlewyan,

"Ok so you say the amp only squeals when you turn the master volume up. Does it still squeal if both pre amp volumes are turned down?"

YES....I turned both channel volumes to zero and the squeal is there when the MV is at about 3/4 full.

[Littlewyan]

Its going to be a lead dress issue. Good part is you've ruled out anything before the volume controls. Try and shorten some of your wires and keep your power amp wires away from your pre amp wires.

[Spunky99]

What concerns me is that if I turn up the volume but leave the MV low enough that it doesn't squeal, if I tap on V1 it sounds like a guitar pickup. V2 and V3 don't do this and it is not normal.

[rock_mumbles]

I had some squealing on an 18 watt Superlite that ended up being the output of the master volume.

Play with the lead out of the master volume to the phase inverter ... is this lead a shielded lead?

--==--

As far as the noise on V1 and not on the other tubes ... V1 is the most sensitive tube as it's the input for both channels ... V2 is the phase inverter, V3 is the second preamp stage and cathode follower for the TMB channel.

[Littlewyan]

Yeah V1 is very sensitive so it will make a noise if you hit it. Be careful tapping valves as you can actually cause a microphonics issue if you keep on hitting them.

Go with Rock_mumbles advice and check your master volume control wires.

[Spunky99]

I use a chopstick and gently tap on the tube. If you turn up the volume high, you only have to barely tap it to hear it. I keep my fingers out of amps after getting hit by the cap can on a 2203 with 6550 tubes. I was thrown against a wall and all the tubes broke when the amp fell off the bench and onto the ground.
I haven't been bitten since...

[Spunky99]

I redressed all the pots. I followed the grounding exactly as shown in the layout attached. No change at all.
I thought maybe because I had the extra grounds I somehow had a ground loop or something. I shortened grounds and verified all the connections.

I guess it is a matter of what haven't I touched now. The list gets shorter.

I can run the amp at 10 on the normal channel and it works perfectly. It is just the TMB that has the squeal.

[Spunky99]

I'll have to let this project go on hold for a week now.
Prepping for surgeries on my wrist and elbow tomorrow.

Thanks you all for the help.

[Reeltarded]

Seepdy recovery on that operation!

Hate to keep you tap dancing but try tapping on the V1 cathode bypass caps when you get a chance.

Good luck on the bionics. Try not to break doors off.

[Spunky99]

Thanks Reeltarded, I needed some humor about now.

I'm getting a carpal tunnel release and an ulnar nerve relocation oon the right hand. The surgery has been rescheduled 3 times since last October so I am really jazzed to finally go forward. I have absolutely no feeling at all in my hands so the 2nd degree burns on my fingers from the soldering iron doesn't hurt. I probably wouldn't have gotten burned if I had any feeling or control tho. That is the problem, I have no control of the muscles as well as no feeling so if they were bionic, I would do some serious damage. When you can't feel the pick with the right or the strings with the left it is hard to play guitar. (not impossible tho) After the right side heals, they will do the same to the left. Then maybe my frustration level will be a little lower.
Trying to build an amp or anything else is really an exercise in patience and concentration. It took me almost an hour of fumbling around with the nuts and bolts to mount the amp in the cabinet last night. I was laughing at myself as this has been my life for a while now. Eating dinner is always an adventure too. Chop sticks..LOL...try eating with them left handed....that is what it is like for me.

I hope I get another dim light bulb to come on and figure out what is wrong and get this amp finished. I have 2 more 18 watt builds and a 50 watt (model 1986) bass head to do.