Need help: Rob Robinette Bassman Micro Build

[Livinloud777]

Hi all,
Trying to learn the troubleshooting process with a new build that powers up on a dim bulb but has no sound. Have researched stuff but am stumped. Any pointers are welcome.

I have checked the audio path and have signal from input to through the bright volume to pin 2 of v2. If I send signal to fx return I have signal from the return to coupling caps. I measured voltages but don’t quite know how to interpret them. Voltages are:

B+1- 320
B+2- 318
B+3- 284

V1: 1-147, 2-0, 3-2.4, 4-3.15, 5-3.15, 6-147, 7-0, 8-2.4, 9-3.15

V2: 1-270, 2-0, 3-0, 4-3.15, 5-3.15, 6-284, 7-270, 8-51, 9-3.15

V3: 1-202, 2-18.4, 3-28.7, 4-3.15, 5-3.15, 6-197, 7-19.2, 8–28.7, 9-3.15

V4: 1-319, 2-0, 3-3.15, 4-3.15, 5-3.15, 6-0, 7-0, 8-3.15, 9-3.15

V5- 1-139, 2-251, 3-319, 4-3.15, 5-3.15, 6-251, 7-139, 8-0, 9-0

[Livinloud777]

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[xtian]

V4: 1-319, 2-0, 3-3.15, 4-3.15, 5-3.15, 6-0, 7-0, 8-3.15, 9-3.15

V4 is your 12AU7 push-pull power amp, right? The grids (pins 2,7) look ok with zero DC. The plates (pins 1,6) should both be B+1 (about 300v). The cathodes (pins 3,8) should be the same value, low DC, which yours are, but your 3.15 value looks suspiciously like your heater voltage (pins 4,5,9).

Check your wiring. If pin 6 really is at 0 volts, that's a clue. I can't see the tube socket in your photos clearly enough to tell.

[Livinloud777]

V4 is the 12AU7. Pin 6 is at 0. Pin 3,4,5,& 9 are heater voltages with 3 & 9 being wired for the artificial center tap.

[martin manning]

Voltages are:
V2: 1-270, 2-0, 3-0, 4-3.15, 5-3.15, 6-284, 7-270, 8-51, 9-3.15

Something wrong there. Should be more like this:
V2: 1-158, 2-0, 3-1.04, 4-3.15, 5-3.15, 6-284, 7-158, 8-159, 9-3.15

[Ten Over]

It looks as though the OT is connected to ring instead of to tip. If you wired that jack as per Rob's layout, then you have tip and sleeve hooked together and grounded for one OT lead and the other lead connected to ring. The OT secondary would be shorted when a plug is fully inserted.

[Livinloud777]

Voltages are:
V2: 1-270, 2-0, 3-0, 4-3.15, 5-3.15, 6-284, 7-270, 8-51, 9-3.15

Something wrong there. Should be more like this:
V2: 1-158, 2-0, 3-1.04, 4-3.15, 5-3.15, 6-284, 7-158, 8-159, 9-3.15

I am definitely at 0 for pin 3. What does that mean I should be considering? My brain is mush from tracing this and I can’t think straight. Been staring and poking at this all day.

[Livinloud777]

It looks as though the OT is connected to ring instead of to tip. If you wired that jack as per Rob's layout, then you have tip and sleeve hooked together and grounded for one OT lead and the other lead connected to ring. The OT secondary would be shorted when a plug is fully inserted.

I think I follow what you are saying but I am confused. Are you saying that it is the way it should be or that I have it wrong? Unless I am missing something I believe I wired it the way rob indicated in the layout.

[Ten Over]

It looks as though the OT is connected to ring instead of to tip. If you wired that jack as per Rob's layout, then you have tip and sleeve hooked together and grounded for one OT lead and the other lead connected to ring. The OT secondary would be shorted when a plug is fully inserted.

I think I follow what you are saying but I am confused. Are you saying that it is the way it should be or that I have it wrong? Unless I am missing something I believe I wired it the way rob indicated in the layout.

It may be wired like Rob showed it, but it is the wrong jack. You need a Switchcraft 12A jack.

[Livinloud777]

Got it! Sorted and that part is working now. Still issues with v2.

[Livinloud777]

V2: 1-231, 2-0, 3-0, 6-271, 7-231, 8-231

Cathode resistor off of pin 8 tests fine when pulled from circuit.

[sluckey]

Put some solder down the top of the circled turret. Any better?

[Livinloud777]

Got it! Bad solder on pin 4&5 so the heater wasn’t kicking on for that side. We now have a working amp! Thank you all for your help! Learned a few things thanks to you all!

[Livinloud777]

Put some solder down the top of the circled turret. Any better?

Thx for the suggestion! That was one of the things I tried. Good eye!

[Reeltarded]

It is a crazy good lil amp, it'n it?!!

I most want one of these with a 12 and a Tweedle Dee with cascaded stages. Too many big amps block the path.

Congrats!