Volume/Tone pot interaction affecting voltage & creating noise

Forum to discuss amp circuits besides the 18 Watters and their ilk.

Moderators: JMPGuitars, Daviedawg, Graydon, CurtissRobin, colossal, zaphod_phil

User avatar
yello
Occasional poster
Occasional poster
Posts: 223
Joined: Thu 09/03/09 2:00 am
Location: Unknown

Re: Volume/Tone pot interaction affecting voltage & creating noise

Post 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?
0 x

User avatar
JMPGuitars
Super Duper Admin
Super Duper Admin
Posts: 4103
Joined: Tue 09/18/12 8:00 pm
Location: South Central, MA
Contact:

Re: Volume/Tone pot interaction affecting voltage & creating noise

Post 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.
1 x
'I installed a skylight in my apartment yesterday... The people who live above me are furious.' - Steven Wright

Modern Ground Schemes
Soldering Technique
B+ Voltage Reduction
Amplifier Tools & Parts Info


Web Design: DolceVittoria.com
Guitars / Amps / Effects: JMPGuitars.com
(anti)Social: Facebook · Instagram
Items for Sale

User avatar
yello
Occasional poster
Occasional poster
Posts: 223
Joined: Thu 09/03/09 2:00 am
Location: Unknown

Re: Volume/Tone pot interaction affecting voltage & creating noise

Post 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+.
0 x

User avatar
JMPGuitars
Super Duper Admin
Super Duper Admin
Posts: 4103
Joined: Tue 09/18/12 8:00 pm
Location: South Central, MA
Contact:

Re: Volume/Tone pot interaction affecting voltage & creating noise

Post 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.
1 x
'I installed a skylight in my apartment yesterday... The people who live above me are furious.' - Steven Wright

Modern Ground Schemes
Soldering Technique
B+ Voltage Reduction
Amplifier Tools & Parts Info


Web Design: DolceVittoria.com
Guitars / Amps / Effects: JMPGuitars.com
(anti)Social: Facebook · Instagram
Items for Sale

User avatar
yello
Occasional poster
Occasional poster
Posts: 223
Joined: Thu 09/03/09 2:00 am
Location: Unknown

Re: Volume/Tone pot interaction affecting voltage & creating noise

Post 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.
1 x

User avatar
yello
Occasional poster
Occasional poster
Posts: 223
Joined: Thu 09/03/09 2:00 am
Location: Unknown

Re: Volume/Tone pot interaction affecting voltage & creating noise

Post 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...
1 x

Post Reply