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Re: Volume/Tone pot interaction affecting voltage & creating noise
Posted: Mon 01/30/23 12:59 pm
by yello
Looks like my two el84 power tubes are at 14+ watts each and 120%+ plate dissipation.
Stock cathode resistor was 130, but I used 150 ohm.
Looking at my voltage chart, to compare this amp to its twin (same amp circuit but different power transformer as built in different countries, Canada versus Japan) that Bill Krinard modded, the voltages produced by each PT are different. I used the same B+ cap/resistor scheme, so not surprised I'm getting different results.
What is the best approach to address my higher voltages? Zener? Higher B+ node A resistor? Higher Cathode resistor? Some combo of those?
Re: Volume/Tone pot interaction affecting voltage & creating noise
Posted: Mon 01/30/23 2:38 pm
by JMPGuitars
yello wrote: ↑Mon 01/30/23 12:59 pm
Some combo of those?
Correct. Shoot between 180 to 220 for the cathode, and figure out what you want your B+ to be, then drop it there. Take some new voltages, do some more math, and play some guitar.
Re: Volume/Tone pot interaction affecting voltage & creating noise
Posted: Mon 01/30/23 2:46 pm
by yello
JMPGuitars wrote: ↑Mon 01/30/23 2:38 pm
yello wrote: ↑Mon 01/30/23 12:59 pm
Some combo of those?
Correct. Shoot between 180 to 220 for the cathode, and figure out what you want your B+ to be, then drop it there. Take some new voltages, do some more math, and play some guitar.
The math is my new frontier, learning better how to calculate the needed value of parts, especially on the B+.
Re: Volume/Tone pot interaction affecting voltage & creating noise
Posted: Mon 01/30/23 2:50 pm
by JMPGuitars
yello wrote: ↑Mon 01/30/23 2:46 pm
JMPGuitars wrote: ↑Mon 01/30/23 2:38 pm
yello wrote: ↑Mon 01/30/23 12:59 pm
Some combo of those?
Correct. Shoot between 180 to 220 for the cathode, and figure out what you want your B+ to be, then drop it there. Take some new voltages, do some more math, and play some guitar.
The math is my new frontier, learning better how to calculate the needed value of parts, especially on the B+.
You can cheat for your dissipation here:
https://robrobinette.com/Tube_Bias_Calculator.htm
For B+, well, that's usually determined by how the circuit behaves at different values.
Re: Volume/Tone pot interaction affecting voltage & creating noise
Posted: Mon 01/30/23 2:56 pm
by yello
JMPGuitars wrote: ↑Mon 01/30/23 2:50 pm
yello wrote: ↑Mon 01/30/23 2:46 pm
JMPGuitars wrote: ↑Mon 01/30/23 2:38 pm
Correct. Shoot between 180 to 220 for the cathode, and figure out what you want your B+ to be, then drop it there. Take some new voltages, do some more math, and play some guitar.
The math is my new frontier, learning better how to calculate the needed value of parts, especially on the B+.
You can cheat for your dissipation here:
https://robrobinette.com/Tube_Bias_Calculator.htm
For B+, well, that's usually determined by how the circuit behaves at different values.
That's the exact tool I use for dissipation.
Re: Volume/Tone pot interaction affecting voltage & creating noise
Posted: Sat 02/11/23 8:45 pm
by yello
This one is wrapped up and sounding nice. Got the bias set at a good level, and my friend and I both like how it sounds, so he is getting it back to enjoy.
Thanks for the great guidance - I learn more with every one, and each amp I work on I feel more skilled and confident, and can get things done more efficiently. Certainly makes it more fun!
On to the next one...