Dead channel and very bright glowing 6080 [resolved]

nicari · 1388

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Offline nicari

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Hello.
Yesterday I finished building my Crack. One of the first times I powered it up for testing the 6080 tube glowed very bright (like a light bulb) in a single spot of the filament. After some power on and off, I connected the input RCAs and the tube returned to glow normally and the amp worked as it should.
Today I installed the Speedball upgrade and when I turned it on for the first time I had the same problem until I connected the input RCAs and tried to turn it on again.
The problem is that even the tube glows normally the right channel is dead. I checked all the connections and they are ok, but not the voltages, terminals 1, 7, A6, B1 and B3 all measures about 170V instead of 90~100V. The two LEDs on one of the small Speedball boards don't emit light (already checked polarity).
Before starting to desolder: have you any idea of what could be the problem?
« Last Edit: July 10, 2015, 07:03:48 AM by Caucasian Blackplate »

Andrea Stefanello


Offline Paul Birkeland

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Reply #1 on: July 09, 2015, 07:33:46 AM
Did you measure the voltages and listen to the amp before you installed the Speedball?

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline nicari

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Reply #2 on: July 09, 2015, 07:35:33 AM
Yes, I did. It sounded perfect without speedball (after the tube started to glow normally) and voltages where ok (apart from A1 that measured 74V insted of 90V, but it's not a huge difference).

UPDATE: I decided to start desoldering. Without Speedball the amp returned to work perfectly. The problem must be in the Speedball boards.
« Last Edit: July 09, 2015, 10:12:01 AM by nicari »

Andrea Stefanello


Offline Paul Birkeland

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Reply #3 on: July 09, 2015, 10:17:54 AM
Check the R1 values to be sure they are correct, check the 2N2907 and 2N2222 transistors to be sure they are in the correct places.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline nicari

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Reply #4 on: July 09, 2015, 01:18:39 PM
Thanks! I had switched 237Ω with 31.6Ω resistor.
Solved the problem! Now is working!

Andrea Stefanello