Bottlehead Kits > Mainline

Mainline BIAS Issue

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Mike V.:
Hi guys, long time no chat, Finally I´ve dicided to build my Mainline kit that I bought in Dec'14. I have completed the kit, all messurements were correct, the 275V is 300V in my Reading. the rest of ohms and volts are perfect.

The issue I got is adjusting the BIAS of the A side. The B side I set it at 145V, but the A side is stucked at 80V if I rotate the switch I can get up to 81 or down to 74V until I start listening a click every turn I do. I switched the tubes and I was able to set BIAS at the B side at 145V, but The up I could get on the A side with the other tuve was 97V.

I have inspected all the soldering joints, and look fine, all leds are lighting. the only issue I guess I have is one Capacitor ZU5 that I solded it to close to its body.

Please help me!

Paul Birkeland:
OB on the center board is the adjustable bias voltage for the A side.  What voltage do you have on OB at each end of the trimmer pot rotation? 

Mike V.:
Sorry the side that I don't get the correct bias is the one of the C socket.

The OA measurements are the following: 3.7v - 0.69v

Mike V.:
I already re heat and solder all the C side, I get the same 97v

Mike V.:
I have checked and compare all voltages from both C4S boards, and all are equal except the one related to the bias 145v - 96v. I guess that will take me to the tube socket and after I have resolder everything, maybe the problems is with a ZU5 or a 1/8w resistor that I have blown  or is defective?

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