SUNN Model T 2nd Gen Power up ?

[Gtr_tech]

Run a jumper wire from the gnd point at pins 1 and 8 over to pin 6 where the other cap that doesn't show a gnd connection. That should get rid of the hum. When you removed the old caps I bet you snipped a gnd wire and didn't realise it.

[gtrplayr1976]

Looking at the original gut shot there is nothing on pin 6 but the cap +. With the tube in I'm thinking it would show grounded.

[Gtr_tech]

Nope. There's no connection to pin 6 on most common pin compatible octal tubes used in guitar amps. Thats why some mfgrs use it as a tie point. Jumper the other cap to gnd and I'll be you'll be in business.

[gtrplayr1976]

OK..I'll give it a shot...tomorrow when my eyes aren't burnin' Thanks

[gtrplayr1976]

Nope. There's no connection to pin 6 on most common pin compatible octal tubes used in guitar amps. Thats why some mfgrs use it as a tie point. Jumper the other cap to gnd and I'll be you'll be in business.

Ya know....I think when I changed the caps I should have connected the two positive ends via pins 6 and 8 . I think I remember the lead from pin 6 extending to pin 8. Does that make sense ?

[Gtr_tech]

Thats what you need to do. If you don't, there will be no gnd connection to the second cap....taking it out of the circuit.

[gtrplayr1976]

I intend to do that when I get off work this evening. I just found a gut shot of another Model T showing just that ....so hopefully that solves the hum issue.

[gtrplayr1976]

ok...got the cap straight , powered it up , definitely better , but still some hum, and when I turn the volumes up there's a horrible buzz/hum . I noticed one of the preamp tubes is brighter than the other two also. Got the preamp tube straight....still way too much noise.

[Gtr_tech]

Whats the ripple (AC voltage reading) on pin 5 of the output tubes now? If there's still more than a few MV then the diode is leaky. Hum from another part of the preamp can be sorted out *only* after the bias supply is clean.

[gtrplayr1976]

I'll check that again. I got in late ,so I didn't get to do much. Finding those diodes may be hard. I can't find anything with that # . I really appreciate this help. My friend thanks you ,and this forum also.

[Jazz P Bass]

1N4004 diode.
About as common a diode as they get.
Got a Radio Shack nearby?
99 cents each.

[gtrplayr1976]

1N4004 diode.
About as common a diode as they get.
Got a Radio Shack nearby?
99 cents each.

Thanks Jazz. I have some 1N4007s , but I understand in order to replace the CR2, and CR3 I have to have 3 in series for each of those. These are the 22-0416 diodes.

[Jazz P Bass]

CR1 is the bias negative voltage diode. -55Vdc
CR2 & CR3 are the positive voltage diodes. +500Vdc.

[gtrplayr1976]

Then the 4007 would work if I connect them in series. Do you know why I am seeing a -22 plate voltage with the amp in standby mode ? I've never seen this before.

Thanks Jazz

[Jazz P Bass]

The 1N4004 is rated at 400volts. 1 amp.
The 1N4007 is rated at 1000volts. 1 amp.
The higher ratings are a good thing if that is what you have.
One 1N4007 is all you need.