Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Diverted on February 12, 2018, 12:32:15 pm
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I'll never figure this stuff out. I've built many a simple amp, sure it was correct and fired it up only to have to do the usual debugging that would sometimes take weeks.
Then there's yesterday, when I applied power to my Fender Princeton reverb 1164 for the first time. Amazingly, the amp plays close to 100 percent straight out of the gate. Voltages all within 3 percent of spec, plenty of volume, luscious tremolo and killer reverb (used three spring tank with dwell control pot). Biased at about 65 percent so it's good for just under 16 watts. Plenty loud for me.
One question: I installed a mid/raw pot in place of the 68K resistor tied from the bass pot to ground in the schematic. It seems to work fine; my question is with the bass control. It seems to change the low end very little, if at all. I don't have experience with this tone stack; what kind of bass response should I be getting with this? It seems very minimal to me. Have checked all wiring, etc., and all looks good to me.
Other mods done to this set:
Backup diodes on the HV secondary
Adjustable fixed bias pot
Screen and grid resistors on the output tubes.
Dwell control
Mid/raw control
Thanks!
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> mid/raw pot in place of the 68K resistor tied from the bass pot to ground
68K sounds wrong. It was 6.8K in the big amps, 15K in the Champ.
The mid resistor/pot pulls everything down. The Bass pot adds-back some bass. If the mid R is not cutting much, then the Bass pot can't add-back much.
Un-do your pot and put in a 5K-15k fixed resistor. Now does the Bass pot do something?
Put back your pot but first measure-out the ~~6.8K position. When you want full Bass/Treb action, the Mid pot has to be there or lower. For "raw" (louder and and little B/T action) you turn the Mid higher.
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Look at Doug's 2 channel AB763 documentation for the proper way to add a mid pot in the Fender tonestack
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> mid/raw pot in place of the 68K resistor tied from the bass pot to ground
68K sounds wrong. It was 6.8K in the big amps, 15K in the Champ.
The mid resistor/pot pulls everything down. The Bass pot adds-back some bass. If the mid R is not cutting much, then the Bass pot can't add-back much.
Un-do your pot and put in a 5K-15k fixed resistor. Now does the Bass pot do something?
Put back your pot but first measure-out the ~~6.8K position. When you want full Bass/Treb action, the Mid pot has to be there or lower. For "raw" (louder and and little B/T action) you turn the Mid higher.
I'm sorry, that was a typo. It's a 6.8K. Anyway I'm going to try your suggestions when I get home from work. Quickly falling in love with this amp.
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Look at Doug's 2 channel AB763 documentation for the proper way to add a mid pot in the Fender tonestack
Thank you, I will check it out and compare schematics. Wish I wasn't at work :sad2: