What is the fault with this amp?

analogadikt · 5th April 2011, 02:32 PM

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?

Regards,

analogadikt

hidnplayr · 5th April 2011, 03:20 PM

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.

ke4mcl · 5th April 2011, 03:30 PM

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.
ALPINE/LUXMAN SQ5Bb

analogadikt · 6th April 2011, 02:27 AM

Thanks. Shall replace the capacitors and report back.

Regards,

analogadikt

5th April 2011, 02:32 PM	#1
analogadikt diyAudio Member Join Date: Jan 2011 Location: Mumbai, India	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? Regards, analogadikt

5th April 2011, 03:30 PM	#3
ke4mcl 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. ALPINE/LUXMAN SQ5Bb __________________ certified packrat

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5th April 2011, 03:20 PM	#2
hidnplayr diyAudio Member 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

6th April 2011, 02:27 AM	#4
analogadikt diyAudio Member Join Date: Jan 2011 Location: Mumbai, India	Thanks. Shall replace the capacitors and report back. Regards, analogadikt

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