Curious about circuit mods

T0rch

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Hi guys. I just recently got a ‘77 1959 Superlead that was modded to run only two tubes. There’s a few things altered in the circuit that I’m curious if anyone can explain to me. I want to bring it back to full 100w.

At some point the power tranny blew up and was replaced by a Canadian Hammond one. But there’s also a 100ohm resistor across the number one & number eight pin on both of the tube sockets that are being used, and also a resistor across one of the 10u caps. Are these to make the amp more stable with 2 tubes or are they something else entirely? Is it safe to just remove it back to stock when I put it back to four tubes?
 

neikeel

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We might need some pics.
Are you sure 100ohm vs 1R or 10R for setting bias via cathode current method (I=V/R).
The resistor across the 10uF bias caps could simply be an adjuster?
Pics please?
 

T0rch

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Sorry I meant to attach them, I guess it didn't work. Here:
 

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rockgod212

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the resistor on the tube socket should be 1ohm not 100ohm and its for bias readings. not sure what that resistor is doing jumped over the bias cap like that though as its not normal to do so. you better take it to a tech or make sure your transformers are for 100watt amps and not 50watt before switching to 4 tubes. someone could have stuck 50watt transformers in it, you never know.
 

T0rch

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The resistors measure 100 ohm and for some reason they are not from pin 8 to ground, they're from pin 1 to pin 8. Transformer isn't original, it's a Hammond direct replacement for the 100w laydown Marshall transformer that was originally in there. The resistor across the electrolytic is a 120k.
 

Matthews Guitars

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Yeah, looks like someone tried to put in bias sense resistors and just got it all wrong.

Itt's pins 1 and 8 together, connected thru a precision 1 ohm resistor, to the ground lug.

What you have there is just nonsense. You've now got the cathode 100 ohms above ground and the suppressor grid as well.

Either take the resistors out and ground pins 1 and 8 or get the 1.000 ohm resistors and install them correctly.
 


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