DanElectro Twin Twelve repairs

[Teleman55]

I have restored a Series D,Model 98 Dano and have some questions.It came in squealing like a pig so I went through it,most of the caps and many resistors later it sounds great.The screen resistors were 130 ohm 1/2 watt carbon,I had 150 0hm carbon film ,and stood them high and off to the side,the closest 5wt I have are 250 ohm would they be OK? The tremolo isn't working,I have replaced all the caps but I don't have a tube to replace the 6SN7 with maybe a bad tube? There was a 2.2k 1/2wt resistor (I think it was pretty cooked,I could only see a red band the other 2 were red or brown-it measured 3k) from the choke to pin 4 of the 6L6s.I replaced it with a 2.2k 10wt and voltages are at 350v.The Output tube cathodes are tied to a 39 ohm 5wt carbon resistor and this ties to the filament supply and a 240ohm resistor to ground.I measure 27vt on the cathodes.I have seen this befor on a Silvertone but don't understand it.Could I still use 1ohm resistors to measure bias or shunt the trans.

[stokes]

The amp cathode biased so you cant use the 1ohm bias resistor.I assume the filament supply is not the twisted pair config.,in other words one leg of the fil.winding is supposed to be grounded,but instead of being grounded it is connected to the cathode of the power tube via that 39ohm res, to raise its ground potential to 27vdc above ground,its an old hum reducing trick.As for the screen resistors,I would feel safer with the 250ohm 5w than a 150 ohm 1/2 watt,you can go to 470ohm or even 1k on these without hurting your sound.

[Teleman55]

Thanks Stokes,The amp filament is as you describe.If the Output tube bias had to be adjusted what component is the key-The 39 0hm resistor,the 240 ohm,or the combination.I tried adding a bypass cap with no change to the sound.I used values from 10mfd to 330mfd bypassing each resistor and the combined resistors.This must function differently than standard cathode bias.
By the way I was very impressed with this amp.It sounds great and the owner is thrilled.The tremelo problem was a bad 6SN7 tube.I hope he can find a replacement,I only have one and I use it for testing as I did here.

[stokes]

I couldnt find the schem for a Twin 12 but the Twin 15 seems to have a dc filament to just the 12AX7's.The dc is generated at the junction of the 240 and 39 ohm resistors.So it is not a hum reduction technique as I first said.One end of the filament is connected at the junction of the 2 resistors and the other is connected to ground.This schem shows a 20uf bypass cap.I wouldnt mess with the bias resistors or you will have to be sure the ratio between the 2 are such that the filament volts stay the same.