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Old 5th April 2011, 02:32 PM   #1
diyAudio Member
Join Date: Jan 2011
Location: Mumbai, India
Default What is the fault with this amp?

Hallo tube amp experts,

I require help on this.

Am trying to revive a vintage tube integrated amp that I picked up from the flea market last year. This is a LUXMAN SQ5B. I have not been able to find the schematic for this one on the net. The tubes are 3x12AX7/ECC83, 2x6AN8, 4x6BQ5/EL84, 1x5AR4.

I installed the ECC83 and EL84 in another amp to confirm that they work properly as I do not have access to a tube tester. The 6AN8 are NOS.
When I switch on the amp there is no sound output irrespective of the input selected. All the tubes light up and #2 power tube shows an orange glow inside from top to bottom. This happens at the same position even when tubes are swapped. When I measured the voltages at all the heaters and anodes, the anodes show both ac and dc current. Is this ok? What could be wrong with this amp?


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Old 5th April 2011, 03:20 PM   #2
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Join Date: Sep 2008
Start by replacing the electrolytics. (the big capacitors)
The 2 tubes are glowing orange because bias is not correct, inspect the bias circuit..

Most of switches and potmeters might need cleaning too.
Real tubes have top-caps
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Old 5th April 2011, 03:30 PM   #3
ke4mcl is offline ke4mcl  United States
diyAudio Member
Join Date: Apr 2009
Location: miami, fl
sounds like a bias issue just as hidnplayr said. most of these japanese tube amps used oil capacitors that are failing. they must all be replaced. failed coupling caps will cause the issue you are referring to.

i found some info on your amp.
certified packrat
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Old 6th April 2011, 02:27 AM   #4
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Join Date: Jan 2011
Location: Mumbai, India
Thanks. Shall replace the capacitors and report back.


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