The Amp Garage

From memory and looking at a sd80 schematic I have- it looks like the same exact preamp.

just read this article says rust is good on the transformers?
http://www.mercurymagnetics.com/pages/n ... mernik.pdf

I read in one of the weber books that its not good - something about eddy currents from the rust causing excessive heat. Who to believe?

I talked to Skip at skipz circuits and he recommended this kit
http://www.skipzcircuits.com/Accessories.html only $19 I have used Skip's stuff before great guy great stuff IMHO thanks for all the info and help.

would I be able to switch the voltage (450 -390) if I used the zener? The chassis would be the heat-sink for the zener? This dosent effect the heater voltage right? thanks

The caps allow AC (the signal) to bypass the cathode resistors, which prevents any negative feedback from occuring. They will charge up over some small time, though, and cause the bias point to shift downward. This is what creates the sound and feel of a cathode biased power amp. thanks for all the...

I have an old marshall JMP (1980) it has the different transformer which runs around 450 plate volts. I like to know if there's an easy safe way to lower the plate volts to around 390? like my older jmp (1977)sounded and felt better

what does the bypass capacitors do in the studio 15? is it there to add bass?
does a lot of voltage pass through there (the resistor/cap )? The resistor is pretty big but the cap is only rated at 25 volts? just curious thanks.


added pictures to show it - not my amp

Blackburn wrote:Check out the Vox AC50...

http://www.voxac50.org.uk/images/misc/c ... ark_03.jpg

hey thanks great stuff

great! thanks for the help- I have it open so Ill replace them. didn't know you could have a mixed fixed/cathode bias- have to hit the search engine about that one. all the best

Have a Marshall studio 15 that I changed all the filter caps on. I noticed on pin 8 on the 6v6's there's a 22uf parallel with 270 ohm resistor to ground. My first question is what does the cap do? the amp was made in 1986 - so far I changed all the filter caps and the bias caps (the two 10uf caps) a...

This master does sound good at low volumes IMHO. A lot better then the rich mod i had on my old plexi. The one on the plexi sounded terrible, harsh unless you turned it up and then it was to loud. Martin- are you sure the master pot is flying leads? Mine looked like it was mounted to the circuit boa...

So the thing attenuates the lower part of the signal in a sim with a sine wave input (as suggested above), but if I hook two of them up to a LTP there is just a small amount of attenuation on both the top and the bottom of the output waveforms, presumably because the two triodes talk to each other ...

I have changed out all those caps with mustards, I wouldn't do it again not worth the work and time very little tonal difference- maybe a little less highs with the mustards

I have the sd18 which I love. You could try changing the 220k plate resistors to 100k it will open up the sound make a little brighter . There's also a cap on v2? Trying to remember- that shunts higs to ground I think it's.002? Again not sure of value, half the value of that cap. For more highs. Jef...

Thanks Martin is your studio15 stock?