2nd Gen Build Started (that didn’t take long…)

[dbharris]

Your build looks great! Interested to hear your report on how it sounds.

Here’s a random new guy question:

Given the space and alignment issues I’m experiencing with this build, is it a bad idea to put the V1 and 2 terminal strips up on washers - allowing the plate leads to pass underneath - thus providing more separation and shortening them by 33-66%?

Anybody ever done this and regretted it or know of why it might not work?

Thanks in advance!

I've found that you can also bend the chassis lug 180 degrees before you install the terminal strip and it will provide enough lift to slip a wire under.

-Dan

[Raoul Duke]

Couple of new guy questions (again):

1. Expecting to fire this up later today - should I start with the limiter even though I’ve already tested the power amp?

2. Don’t have my foot switch ready yet, so does the amp switch from clean to OD when it’s on “manual”?

3. Follow-up on the tube question: any opinions?

Thanks in advance! Going to try to disappear for a little while and get that last connection done. The house is quiet right now - but that could change any second, lol.

[martin manning]

1. Expecting to fire this up later today - should I start with the limiter even though I’ve already tested the power amp?

I would, just in case something got screwed up.

2. Don’t have my foot switch ready yet, so does the amp switch from clean to OD when it’s on pedal?

When you move the switch to manual you should get OD. I guess you didn't check the relay operation earlier?

3. Follow-up on the tube question: any opinions?

You could put them in and power up with your limiter, and watch for any behavior that differs from your other set. If you can get them biased at full line voltage maybe they're ok, but a sound check would maybe say otherwise. It just depends on if and how much damage might have been done.

If you scrap them, I'd much rather get bias probe kit(s) from Hoffman than mess with salvaging the bases.

The house is quiet right now - but that could change any second, lol.

The test-as-you-go approach has served you well, and I can recall only one mistake that was caught this time around.

[Raoul Duke]

Martin, how would I check the relay operation? My gut says I need the foot switch for that - but I’m not sure?

Yes, “test as you go” is definitely the way for me until I get a lot smarter at this, lol.

Thanks!

[martin manning]

Just setting the switch to manual should energize the relay. Come to think of it you did do that, and noted the voltage change on the coil.

[Raoul Duke]

Ok, thought that confirmed something - but wasn’t certain.

Did the limiter then full power test. Bulb flashes all good.
- volume, treble, bass, and mid controls don’t work - switches don’t seem to work
- can’t get any OD
- poked around a little and found V1 terminal strip and plate leads are microphonic(?)
- FET is super weak, barely audible through speaker
- “thud” when switching operate to standby

Voltages
B+1: 457
B+2: 455
B+3: 429
B+4: 302
B+5: 294

V1A: 183
V1B: 196
V2A: 206
V2B: 205
V3A: 291
V3B: 282
V3 cathode: 119

Tubes biased at -43 mV (~63%)
Relay 11.8
Heaters all at 6.4

And I thought I was doing pretty well, lol…

[martin manning]

Those voltages look good for the DC op point. Check cathode voltages on V1 and V2 (pins 3 and 8) just to confirm they are conducting current, and check the voltages at the top and bottom of the FET drain resistor.
As for no sound, seems like there is a break or unintentional grounding in the signal path somewhere.

[Raoul Duke]

Will do.

As for the break or grounding - where’s the best place to start and check? Am I looking for continuity from cap to cap on the main board from left to right or something similar?

One other thing is when I turn the master up, I get a dull hum that increases in volume as the MV is turned up. Sounds like when you have your finger on the 1/4” plug if you unplug the guitar with everything on.

[Raoul Duke]

Update:

Just checked pins 3 & 8:
V1: 1.4, 1.4
V2: 1.6, 1.4

FET Drain:
1.5 top
9.2 bottom

[martin manning]

V1 & V2 cathodes look reasonable, FET is biased a bit hot. You said the FET input gets some sound, but nothing from the normal input? Maybe start by checking the input jack wiring over carefully. You could try putting signal into the input and tracing through the signal path to see where it stops using your DMM, measuring AC volts or frequency.

[Raoul Duke]

FET is very low, Normal gets sound, but only Level seems to work on the front controls.

It’s a nice clean for sure, hopefully there’s more in there somewhere, lol.

[martin manning]

So you do get guitar sound from the speaker, but the tone controls don't work?

[Raoul Duke]

Yes

[martin manning]

I'm back to broken signal path, accidental grounding, or possibly a wiring error. Can you get sound in both clean and OD?

[Raoul Duke]

No, OD and Man/Ped switch do nothing.

I was thinking of lifting the main board and taking a peak underneath. If I undo everything on the pot side I can peel it backwards without disrupting tube sockets I think?