pics of builds for reference. OR be the first to spot mistak
Posted: Sun Sep 14, 2008 1:05 pm
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pics of builds for reference. OR be the first to spot mistak
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Re: pics of builds for reference. OR be the first to spot mistak
Posted: Sun Sep 14, 2008 1:16 pm
You forgot to solder one of the 68k input resistors...at least it looks like that. Other than that; nice build! Have you fired it up yet?
Re: pics of builds for reference. OR be the first to spot mistak
Posted: Sun Sep 14, 2008 1:47 pm
gonna fire up now 
Re: pics of builds for reference. OR be the first to spot mistak
Posted: Sun Sep 14, 2008 3:21 pm
the amp is up and running! no noteworty problems so far really.
this thing kills with a mal young gretsch. and a strat w/hsrv specials sounds good too. it sound a little fizzy. not really noisy considered how dirty the wall power is here. the high wall voltage at the moment results in a b+ at 514V.
had to change the 150k bias resistor to a 220k in order to get the right range. changed it back. two tubes were HOT while two was slightly cold. have to get a new quartet it seems. now they are 14ma apart. just a tad more than what is good right?
this thing kills with a mal young gretsch. and a strat w/hsrv specials sounds good too. it sound a little fizzy. not really noisy considered how dirty the wall power is here. the high wall voltage at the moment results in a b+ at 514V.
had to change the 150k bias resistor to a 220k in order to get the right range. changed it back. two tubes were HOT while two was slightly cold. have to get a new quartet it seems. now they are 14ma apart. just a tad more than what is good right?
Re: pics of builds for reference. OR be the first to spot mistak
Posted: Thu Sep 18, 2008 8:05 am
ok, one problem: there is a bit of oscillation when the pots are in a certain constellation. a 100pf across the 100k plate resistor removes it and moving the v1b plate wire (pin 5) clearly affects the oscillation. I'll try to get rid of it without restoring to the 100pf
Re: pics of builds for reference. OR be the first to spot mistak
Posted: Sun Sep 21, 2008 5:15 pm
the oscillation went away when I changed preamp tubes from jj and groove tube to tungsram and tele ribbed plate. 
I experimented a bit with different values. ended up with 220uf v1 cathode bypass cap,
500pf bright cap and .027uf pi coupling caps. reducing the v1 cathode cap is good for tight riffs but you loose that EC (and hendrix) sound, esp. the lead sound. reducing the coupling caps reduces bass without taking away as much gain. Also, I use .018uf after v1, not because I don't have .022ufs but because I'd like to tame the bass just a tad. having said that, this amp has a much tighter and more powerful bottom that the jtm45. the bass control and the presence control are much more useful than on my jtm45. The amp has about 30 hours on it now BTW.
I experimented a bit with different values. ended up with 220uf v1 cathode bypass cap,
500pf bright cap and .027uf pi coupling caps. reducing the v1 cathode cap is good for tight riffs but you loose that EC (and hendrix) sound, esp. the lead sound. reducing the coupling caps reduces bass without taking away as much gain. Also, I use .018uf after v1, not because I don't have .022ufs but because I'd like to tame the bass just a tad. having said that, this amp has a much tighter and more powerful bottom that the jtm45. the bass control and the presence control are much more useful than on my jtm45. The amp has about 30 hours on it now BTW.