Been running the amp as you recommend for a while now. Pretty happy with it! However, I was thinking, I now have a 1w 27k carbon film node resistor. All my other resistors on the doghouse board are metal oxide. I tend to get a little OCD, and want to put in a 2w metal oxide 27k as well, for reliability and for looks (I like uniformity). I have one on the way, but it's gonna take another week to get here. Was thinking, as the plate voltages on the tubes connected to that node are now reduced a bit (around 200v), would there be any benefit to decreasing that resistor value a bit to up the voltage? I have a 22k and 15k metal oxide laying around....martin manning wrote: ↑Sat Apr 18, 2020 9:21 pm I believe it is due to the different voltages causing DC current to flow along several paths, including through the 470k LNFB resistor, which is connected to the grid of the mixer stage. Those voltages will change with different tubes, too. Switching the supply node must be reducing the DC current at the mixer grid.
AB165 Bassman crackle in V1 and V3 stages??
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lespaulnmarshall
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Re: AB165 Bassman crackle in V1 and V3 stages??
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martin manning
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Re: AB165 Bassman crackle in V1 and V3 stages??
Sure why not give it a try. That 27k resistor used to have about 3 mA flowing through it, and now it's more like 4 mA. I think if you reduce the value by 3/4 it will get the voltages back to about the same as they were. 27 x 3/4 = 20.2, so I'd try the 22k.
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lespaulnmarshall
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Re: AB165 Bassman crackle in V1 and V3 stages??
Sweet, I'll be giving that a try tomorrow! I'm planning to add a mid pot to the normal channel so can do the resistor while I'm at it. Will report back as usual.martin manning wrote: ↑Thu Apr 23, 2020 8:24 pm Sure why not give it a try. That 27k resistor used to have about 3 mA flowing through it, and now it's more like 4 mA. I think if you reduce the value by 3/4 it will get the voltages back to about the same as they were. 27 x 3/4 = 20.2, so I'd try the 22k.
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lespaulnmarshall
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Re: AB165 Bassman crackle in V1 and V3 stages??
Did the mod, voltages went up but only a little. Getting 200 to 212v on the plates now, was getting 190 to 200v before. Not a huge difference but I might like the sound just a hair better!martin manning wrote: ↑Thu Apr 23, 2020 8:24 pm Sure why not give it a try. That 27k resistor used to have about 3 mA flowing through it, and now it's more like 4 mA. I think if you reduce the value by 3/4 it will get the voltages back to about the same as they were. 27 x 3/4 = 20.2, so I'd try the 22k.
Re: AB165 Bassman crackle in V1 and V3 stages??
A little late to the party, but I also swapped the node which has solved removed a persistent 60mV on the grid of V2 that I had not been able to remove. Overdrive tone has improved phenomenally! and it seems to have removed a few gremlins that had been plaguing V2 as well, much quieter now. Just thought I would add this incase anyone else is having issues with voltage on the grid of V2, as I'd spent all this time thinking I had a conductive board. 