mojo760 power transformer

[scole]

i am building a blackface princeton rev. im using mojo's 760 power transformer. i hooked up the fillaments to the tube sockets and then to the lamp and grounded them with 100 ohm resistors. something is not wright. am i suposed to ground one side as the original fender?

[Bruce / Mission Amps]

i am building a blackface princeton rev. im using mojo's 760 power transformer. i hooked up the fillaments to the tube sockets and then to the lamp and grounded them with 100 ohm resistors. something is not wright. am i suposed to ground one side as the original fender?

!??!
You are not stating what is wrong so I have no idea how to respond...
What's not right?
If there are only two green wires you did it OK.... if there are three green with one having a yellow stripe, then you don't bother with the 100 ohm resistors.

No, don't ground one side.

[scole]

hi bruce, this is the champ project we had the 4 page post on a couple months ago. i used an allen upgrade pt wich was to much voltage. i just put the mofo in and had noise. i lifted the 100 ohm rsistors, that did nothing. then i moved the vol pot (cge) and found that the pot had developed a bad spot at 0 to about 1. i plugged in a guitar and the amp works fine as soon as i turn the vol up a little the situation goes away. somehow the pot got domething in it i guess. the amp has some hum but not to bad. the allen was dead quiet though. im thinking of replacing the mojo now and the cge pots. i think i might try a hammond. the allen had a ct for the heaters wich is nice but i cant find a normal pt with the 6.3v ct. im going to put the monster allen in my blackface princeton rev project.

[Bruce / Mission Amps]

CGE pots... oh oh.

hi bruce, this is the champ project we had the 4 page post on a couple months ago. i used an allen upgrade pt wich was to much voltage. i just put the mofo in and had noise. i lifted the 100 ohm rsistors, that did nothing. then i moved the vol pot (cge) and found that the pot had developed a bad spot at 0 to about 1. i plugged in a guitar and the amp works fine as soon as i turn the vol up a little the situation goes away. somehow the pot got domething in it i guess. the amp has some hum but not to bad. the allen was dead quiet though. im thinking of replacing the mojo now and the cge pots. i think i might try a hammond. the allen had a ct for the heaters wich is nice but i cant find a normal pt with the 6.3v ct. im going to put the monster allen in my blackface princeton rev project.

I'm finding a lot of the new CGE pots with dead spots at the first part of rotation... make me sick as they cost much more then the custom Alpha pots (with brass 3/8" bushings) I was using in the 5E3... which is VERY sensitive to very low volume position.
I wish I had more info on the MOJO 760... not sure why it would hum more unless the gauss lines from it are effecting the OT.
Can you rotate the OT 90 degrees?
Take the common end of your 100 ohm resistors off ground and connect them to the cathode of your power tube fro better hum control.

[scole]

i forgot about that trick bruce, i will try regrounding the 100's when i get my moflo cts 1m pots wich are on backorder. by the way, the amp is sounding much better now, more free and very fendery. ive got 367v on the plate. 24v across the kathode resistor. im still high about 18 watts dissipation. thats with an nos rca 5y3.

[Bruce / Mission Amps]

i forgot about that trick bruce, i will try regrounding the 100's when i get my moflo cts 1m pots wich are on backorder. by the way, the amp is sounding much better now, more free and very fendery. ive got 367v on the plate. 24v across the kathode resistor. im still high about 18 watts dissipation. thats with an nos rca 5y3.

OK... by the way, I think I got a little confused... are you trying to build a cathode biased Princeton Reverb?
18 watts for two 6V6s isn't bad at all but 18 watts for each tube or one tube in the Champ is viscous.

[scole]

sorry about that, im trying to finish the champ, meanwhile im starting a princeto rev. back to the champ, my bias meter tells me i have 48ma. i measured 367 volts on pin 3, 24v across the cathode resistor. looks like 16.5 watts.

[Bruce / Mission Amps]

sorry about that, im trying to finish the champ, meanwhile im starting a princeto rev. back to the champ, my bias meter tells me i have 48ma. i measured 367 volts on pin 3, 24v across the cathode resistor. looks like 16.5 watts.

OK... is the 367 plate volts measured from lug 3 to ground or lug 3 to lug 8?
If lug 3 to ground then don't forget to subtract the 24v from the plate voltage.

OK I just did the math and it looks like it is 3 to 8.
16.5w/.048a = 344v


I'd consider dropping the plate voltage more... have you thought of using some 5 watt zener diodes in the Hi-V center tap?

[scole]

the 367 volts was measured to ground. the reason i changed to the mojo tranny was to get the amp under control. im not sure why i still have 367 volts. so you think 16.5 is still to high? then i guess the only other thing to do is the zeners. do you have a mouser part number? or does rat shack have them?

[Bruce / Mission Amps]

the 367 volts was measured to ground. the reason i changed to the mojo tranny was to get the amp under control. im not sure why i still have 367 volts. so you think 16.5 is still to high? then i guess the only other thing to do is the zeners. do you have a mouser part number? or does rat shack have them?

... Not super too high but high enough that I would still try to tame it down.
Send me your snail mail address again and I'll mail you a few 5 watters to try.

Added:
Are you using a NOS 5Y3GT here or a Russian one?

[scole]

its an nos rca 5y3.