pdf64 wrote: ↑Wed Jun 22, 2022 10:40 am
Link for schematic?
The layout image seems rather blurry, and different to the photos?
Regarding the second issue, have you scoped it for oscillation?
sluckey wrote: ↑Wed Jun 22, 2022 11:42 am
It seems that the crackle is coming from V1 circuitry. The power supply schematic does not match the layout? The layout seems more likely.
There were some changes made with regards to the power supply after more info came to hand in the ‘benson - monarch’ thread… the layout is the most up to date and what others have used for their builds.
Sorry, I never looked at the schematic to see what V3s function was.
In terms of your reverb hum issue, the cable from the outout side of the pan ( return) needs to be sheilded, and the output side of the pan needs to be as far away from the power transformer as possible.
Hopefully at least 6" in both a horizontal and vertical plane.
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It's my understanding that crackle-pop is due to a bad plate load resistor. Tube pulling strongly suggests it is V1. See if you can figure out which section is the problem. (It could be both.) Run a jumper from the 68K input resistor to the grid of the second triode. This will bypass the first triode. If it solves the problem, change the 56K plate load resistor. I'd suggest using metal film type. If the noise continues, then it is probably the second triode, so change the 100K plate load resistor. Maybe I missed it, but I'm surprised no one suggested this. Maybe I'm all wrong?
Hey – thanks to everyone for helping me troubleshoot this..!
@stevem
With regards to the reverb hum… its occurred to me that I haven’t specifically used shielded cable for any of the signal connections.. I just used 22awg hook-up wire throughout… it would be useful to know exactly which wire’s need to be shielded?? (this is clear evidence that im learning as I go!! ) ….. with regards to distance.. I don’t think its quite 6inch but it might be.. (at work.. can check later).
@phil_s
Interesting with regards to narrowing it down to V1… when you say ‘run a jumper from the 68k input resistor to the grid of the second triode”.. im not sure where the grid of the second triode is… also, would you used use a cable with alligator clips?? These seem like really solid suggestions.. interested to hear what others think.. there were a couple of builds in the benosn-monarch thread that certainty used carbon film resistors, instead of CC, for the load resistors .. (example attached)
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The grid connections on a 12AX7 are pins 2 and 7. Make a short cable, two clips and a bit of 22awg wire. Connect pins 2 and 7. The alternative is to clip onto the 68K and the wiper of the volume pot. It's the same either way.
The 68K goes directly to one of those grid pins. (I don't know which way you wired it, but it doesn't matter.) The jumper wire will connect the 68K directly to the second grid pin. That will cut out everything between the 68K and the second triode input.
Some will disagree with me. There is no "tone" on the plate load resistors. It doesn't matter what kind you use. Metal film are a good choice when you have noise. You might also use 1W rated resistors.
Phil_S wrote: ↑Thu Jun 23, 2022 12:51 am
The grid connections on a 12AX7 are pins 2 and 7. Make a short cable, two clips and a bit of 22awg wire. Connect pins 2 and 7. The alternative is to clip onto the 68K and the wiper of the volume pot. It's the same either way.
The 68K goes directly to one of those grid pins. (I don't know which way you wired it, but it doesn't matter.) The jumper wire will connect the 68K directly to the second grid pin. That will cut out everything between the 68K and the second triode input.
Some will disagree with me. There is no "tone" on the plate load resistors. It doesn't matter what kind you use. Metal film are a good choice when you have noise. You might also use 1W rated resistors.
Thanks Phil… will give this a go this evening a report back the results. I’ll start with connecting the grid pins and see what happens before jumping in with the soldering iron and replacing those load resistors… although I suspect that might be the next step.
Update: so I’ve just jumpered pins 2 and 7 and the crackle is still present. So now the idea is that I swap out the 100k load resistor..? I bought some 100k carbon film resistors earlier so good to go. Is it a good idea to change othe CC resistors to carbon film? Like the input resistor..? Or should I just do one at a time?
Also, re shielded cable, it was hard to find something locally that was the right size.. seemed too big or too small. Then I was wondering whether I could use the cable from good quality rca cables I’ve had without purpose for some time..?
This is really important. Change only one part at a time. Otherwise, you'll never know what was wrong. When you change more than one thing you might fix one thing and break another. Or you you might make two things worse!
If you need shielded cable, use what you have or what you can find.
Phil_S wrote: ↑Thu Jun 23, 2022 12:58 pm
This is really important. Change only one part at a time. Otherwise, you'll never know what was wrong. When you change more than one thing you might fix one thing and break another. Or you you might make two things worse!
If you need shielded cable, use what you have or what you can find.
UPDATE: the crackle and pop has disappeared!! Amazing… I changed the 100k load resistor and that was it! All that’s left is a ‘shhhhhhhhhh’ white noise that I think I can tolerate although would love to be able to reduce it if possible… any ideas?? thank you so much for your help
Stevem wrote: ↑Thu Jun 23, 2022 3:32 pm
In regards to the reverb hook up, just get a decent set of Hi Fi RCA cables and cut the ends off to wire it in .
Note, you do not need to get the up scale ones with Gold plated connectors.
UPDATE: just replaced both wires with shielded wire and now the reverb cuts out at the last 5% of the sweep.. which is something I can live with!! However, when I do turn it all the way up (before it cuts out) it does introduce hum… however it’s ok before that point. Thank you for helping me along with this!
Edit.. no hum.. I just repositioned the reverb tank and the hum vanished!
Stevem wrote: ↑Thu Jun 23, 2022 3:32 pm
In regards to the reverb hook up, just get a decent set of Hi Fi RCA cables and cut the ends off to wire it in .
Note, you do not need to get the up scale ones with Gold plated connectors.
UPDATE: just replaced both wires with shielded wire and now the reverb cuts out at the last 5% of the sweep.. which is something I can live with!! However, when I do turn it all the way up (before it cuts out) it does introduce hum… however it’s ok before that point. Thank you for helping me along with this!
Edit.. no hum.. I just repositioned the reverb tank and the hum vanished! … and it doesn’t cut out at all!
unknowntome wrote: ↑Thu Jun 23, 2022 11:17 pm
UPDATE: the crackle and pop has disappeared!! Amazing… I changed the 100k load resistor and that was it! All that’s left is a ‘shhhhhhhhhh’ white noise that I think I can tolerate although would love to be able to reduce it if possible… any ideas?? thank you so much for your help
Pull tubes one at a time like you did for the crackle pop. See if you can identify the source of the white noise. There may be another plate load resistor to replace. Or it may require using 1W plate load resistors. Or maybe something else. White noise can be more difficult to find and cure. You may want to just live with it.
) ….. with regards to distance.. I don’t think its quite 6inch but it might be.. (at work.. can check later).
