Fig . 2
Fig . 3
multiple smaller values . I would start with a 47 pF and work up to a 100 pF , a 220 pF , or even a 470 pF to see what suits you best . Of course , if you play with the preamp volume on 10 , this is all moot , since the capacitor is electrically out of the circuit at that point . A nice feature here might be to have this cap switchable using a push-pull pot for the preamp control .
This way you could tailor the amp depending on your guitar choice .
If the amp is still too bright , the next place I would go would be the high-pass cap ( C102 ) across the 470k resistor that feeds the signal to the preamp control ( Fig . 2 ). This is typically a 470 pF cap and can simply be lifted from one side of this resistor . If you then like the amp , you can either completely remove the cap or install a push-pull pot for the master volume control and make this capacitor switchable as well . It ’ s always good to have choices .
Less gain , more pain ? The above two modifications deal with components that are typically not board mounted . In these early amps , they are usually connected directly to the input jack or preamp volume pot , making for easy access and modification .
There is one more component that you may want to consider experimenting with . It is the cathode bypass cap ( C2 ) in the first gain stage ( Fig . 3 ). The value of this cap is typically 0.68 µ F and is connected across the 2.7k cathode resistor of V1 . This helps the tube amplify more of the higher frequencies , but removing this , however , removes some gain and tends to leave the amp a bit lifeless .
My suggestion would be to parallel this with a larger cap . This won ’ t decrease the high-frequency amplification , but rather raise the full-frequency amplification . It will give you the relative effect of less treble , while increasing the gain a bit overall . I would start with maybe a 4.7 µ F 25V DC cap and see how you like it . You can use a pair of alligator leads here . Just be sure that the positive (+) side of the capacitor is toward the tube . You can go up in value from there to , say , a 10 µ F , 25 µ F , 50 µ F , even a 100 µ F to see if any of these are to your liking . If so , simply solder it across the 0.68 µ F cap , being aware of the polarity .
Well , there you have it . One or more of those modifications should get your amp to where you have a useable combination again . Glad I could help with the Taming of the Shrill .
JEFF BOBER is one of the godfathers of the low-wattage amp revolution . He co-founded and was originally the principal designer for Budda Amplification , though he launched EAST Amplification ( eastamplification . com ) in 2010 . You can catch his podcasts at ampsandaxescast . com or email him at pgampman @ gmail . com .
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