Need help: Rob Robinette Bassman Micro Build
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Need help: Rob Robinette Bassman Micro Build
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
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
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Re: Need help: Rob Robinette Bassman Micro Build
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Re: Need help: Rob Robinette Bassman Micro Build
Livinloud777 wrote: ↑Mon Dec 04, 2023 10:11 pmV4: 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.
I build and repair tube amps. http://amps.monkeymatic.com
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Re: Need help: Rob Robinette Bassman Micro Build
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
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Re: Need help: Rob Robinette Bassman Micro Build
Something wrong there. Should be more like this:Livinloud777 wrote: ↑Mon Dec 04, 2023 10:11 pm Voltages are:
V2: 1-270, 2-0, 3-0, 4-3.15, 5-3.15, 6-284, 7-270, 8-51, 9-3.15
V2: 1-158, 2-0, 3-1.04, 4-3.15, 5-3.15, 6-284, 7-158, 8-159, 9-3.15
Re: Need help: Rob Robinette Bassman Micro Build
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.
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Re: Need help: Rob Robinette Bassman Micro Build
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.martin manning wrote: ↑Mon Dec 04, 2023 11:33 pmSomething wrong there. Should be more like this:Livinloud777 wrote: ↑Mon Dec 04, 2023 10:11 pm Voltages are:
V2: 1-270, 2-0, 3-0, 4-3.15, 5-3.15, 6-284, 7-270, 8-51, 9-3.15
V2: 1-158, 2-0, 3-1.04, 4-3.15, 5-3.15, 6-284, 7-158, 8-159, 9-3.15
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Re: Need help: Rob Robinette Bassman Micro Build
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 wrote: ↑Tue Dec 05, 2023 12:05 am 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.
Re: Need help: Rob Robinette Bassman Micro Build
It may be wired like Rob showed it, but it is the wrong jack. You need a Switchcraft 12A jack.Livinloud777 wrote: ↑Tue Dec 05, 2023 1:54 amI 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 wrote: ↑Tue Dec 05, 2023 12:05 am 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.
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Re: Need help: Rob Robinette Bassman Micro Build
Got it! Sorted and that part is working now. Still issues with v2.
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Re: Need help: Rob Robinette Bassman Micro Build
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.
Cathode resistor off of pin 8 tests fine when pulled from circuit.
Re: Need help: Rob Robinette Bassman Micro Build
Put some solder down the top of the circled turret. Any better?
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Re: Need help: Rob Robinette Bassman Micro Build
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!
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- Reeltarded
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Re: Need help: Rob Robinette Bassman Micro Build
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!
I most want one of these with a 12 and a Tweedle Dee with cascaded stages. Too many big amps block the path.
Congrats!
Signatures have a 255 character limit that I could abuse, but I am not Cecil B. DeMille.