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Maurizio 30th June 2006 12:03 PM

Help on a LUXMAN MQ 3600
Hello all,

I've a Luxman Mq3600 to modify for the 6550 tubes.

Anyone have the original and modified scheme to send me?

Thanks for your help.


audiohead 1st July 2006 07:48 PM

Hi There:
here is the link for the schematic:


Alain Dupont 1st July 2006 10:52 PM


Here it is:



Maurizio 2nd July 2006 11:23 AM

Hi art,

I can't open the link you send me..This is the modified version?

Can you help me about?


Alain Dupont 2nd July 2006 01:25 PM


what I did find on:

AFAIK, an 8045G IS a 6550 wired as a triode (by jumpers in the base).

Most of the "8045G" labelled tubes I've seen were US made 6550's
with jumpers added in the base.

| This may be a difficult and expensive
| change, though less expensive than finding new 8045Gs.

Wiring the socket for a 6550 or KT88 is not difficult,
nor should it be expensive.
Ned Carlson Triode Electronics Chicago,IL USA

Then connect about 100 ohm, a couple watt resistors from pins
| 3 to 4.
| With no output tubes installed, fire it up (preferably with a
| Variac, but *SAFETY FIRST* in any case - allow no children or
| pets in the room).
| Observe voltages at points marked "C1" and C2". Adjust the 30K
| ohm bias pots for maximum voltage.
| Power off. Observe all supply voltages and wait until they've
| fallen to a low level, maybe a coupla volts.
| Install your new matched quad of Svetlana or maybe JJ power tubes.
| Fire it up again and observe. Everything OK?
| Bias is measured at the cathode pins (pin 8). I'd run modern
| tubes at between 50 and 70 mA (500 mV and 700mV on pin 8).
| The 10K ohm pots are to balance the current in each pair.
| Try various bias currents and use the least that doesn't affect
| sound quality. And no more than 80mA.

Hope this will help.


audiohead 3rd July 2006 12:43 AM

2 Attachment(s)
Hi Maurizio:
here is the schematic, copied from yahoo luxman group:

Maurizio 3rd July 2006 07:39 AM

Thanks a lot ART.

Tell me, the OY 3.6k of MQ3600 have ultralinear taps?

Cause in the original scheme with 8045 doesn't appear.



audiohead 3rd July 2006 03:55 PM

hi maurizio:

I don't know. Never owned one, should not make any difference for switching to 6550. the schematic I copied from luxman yahoo group.
may be you should consider joing the group.

al2002 3rd July 2006 04:18 PM


Originally posted by Alain Dupont


AFAIK, an 8045G IS a 6550 wired as a triode (by jumpers in the base).



The NEC 8045 was actually a TV sweep valve, internally triode connected.

6LF6 or similar valves should work well, don't know what the going price is now.

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