There are currently at least 24 of these Luxman MQ-60 PP amps on ebay, the reason being that they use uber rare and expensive 50v heater Matsushita output tubes which are no longer a practical proposition. The transformers are excellent and this amp is crying out for a swap of the output tubes. There is already one modified for 6550 tubes and the EL34 would be another choice since the OPTs are 5K. The 6550 modded amp uses a bigger A3700 mains transformer which doesn't really fit, and my choice would be an outboard power supply with one 115/230V step-down transformer for the 100V Japanese voltage and one 6.3V transformer for the output tubes. This would use a 4 pin umbilical e.g. a Speakon connector or something like that. A fairly simple modification, and in my view worth it for the quality of the original transformers.
Anyone tempted?
https://www.ebay.co.uk/itm/115981686756?
Anyone tempted?
https://www.ebay.co.uk/itm/115981686756?
I'd love to snag one of those amps cheap and run a high heater voltage Compactron tube. Really like the layout and look. 
jeff
jeff
It's brilliant isn't it!!! A real Japanese classic just waiting for a facelift and some standard output tubes. The cheapest are around $900
https://www.ebay.co.uk/itm/285539046029?
Tube type stereo power amplifier completed as an independent amplifier based on the main part of SQ38F.
NEC's 50CA10 is adopted as the output tube like SQ38F.
・Consecutive output: 30W/30W (4, 8, 16Ω)
・Total harmonic distortion 0.1% (at 1W output) 0.3% (at maximum output)
・Frequency response 15Hz to 60,000Hz -1dB
・SN ratio: 90dB or more
・Residual noise: 0.7 mV or less
・Damping factor: about 15 (1kHz)
・Load impedance: 4Ω, 8Ω, 16Ω (switch switching)
・Semiconductors used, etc.
Vacuum tubes 4x 50CA10: 2x 6DT8/6AQ8: 2x 6267/EF86
Semiconductors (5 pieces): DS16A: 4 pieces, DS16C: 1 piece
・Dimensions: Width 410x Height 160x Depth 205mm
・Weight: 13.8kg
https://www.ebay.co.uk/itm/285539046029?
Tube type stereo power amplifier completed as an independent amplifier based on the main part of SQ38F.
NEC's 50CA10 is adopted as the output tube like SQ38F.
・Consecutive output: 30W/30W (4, 8, 16Ω)
・Total harmonic distortion 0.1% (at 1W output) 0.3% (at maximum output)
・Frequency response 15Hz to 60,000Hz -1dB
・SN ratio: 90dB or more
・Residual noise: 0.7 mV or less
・Damping factor: about 15 (1kHz)
・Load impedance: 4Ω, 8Ω, 16Ω (switch switching)
・Semiconductors used, etc.
Vacuum tubes 4x 50CA10: 2x 6DT8/6AQ8: 2x 6267/EF86
Semiconductors (5 pieces): DS16A: 4 pieces, DS16C: 1 piece
・Dimensions: Width 410x Height 160x Depth 205mm
・Weight: 13.8kg
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The kit version, KMQ60 are a bit cheaper at around $750. Even with int. shipping, that would less than a grand.
I'd love to hear one of these amps with the original NEC output tubes.
jeff
I'd love to hear one of these amps with the original NEC output tubes.
jeff
With my friends of Fiat transformer here in Roma have rewound from original Luxman MQ3600 with 100 volt trafo and the results was great
It is a hard job but can de done
Walter
It is a hard job but can de done
Walter
I was looking at these a couple of years ago but I wasn't into push pull amps at that time. Do the opt tubes test strong in these? Are the driver tubes easily available? Can one enjoy the original using a step down/isolation transformer before hacking it away? I was looking at some schematics it shows 80mA/channel on the output triodes but I am not sure if these have a OPT with ultralinear tap or not. The schematics are a mishmash of redrawn schematics. Would you keep the triode configuration or going for pentode? These have grounded cathode and -50V for the bias, any mods needed there?
There would be no reason to have a UL tap. I found a small schem. in an old AK thread, post #1.: https://audiokarma.org/forums/index...or-schematic-service-manual-etc.688474/page-2 The OY15-5 OPT doesn't show a UL connection.
jeff
I'm not planning to modify one of these right now, I'm resisting temptation! No idea of the state of the output tubes in the 24 amps for sale. One of the listings from Japan has a box of spare tubes which looks unopened. The input tubes are EF86 and ECC85/12BH7 so no problem there. All the listings state the amp is working, so at least you'll have sound with the right step-down. I haven't seen any schematics myself. You're on your own with the modifications, but maybe others on the thread can chip in and help.
Hi Jeff,
that was a great link! Apparently, I was looking at a clone schematic.
that was a great link! Apparently, I was looking at a clone schematic.
50V heaters and 5k transformers, I'd look at PL36 as replacements for the output tubes.
It seems that with 50V filaments, two of them in series would allow them to power the filaments directly off of Japan's 100V power mains.
That would free the power transformer from having to power the output tube filaments.
I could not look at the schematic to see if they did that; but why not do that?
There are auto transformers to take 120V power mains to power the 100V filaments. The rest of the amplifier can still run off of the amplifiers secondaries for safety reasons.
How much do the 'golden obsolenium' tubes cost! . . . $$$
Modifying the amplifier may cost more in parts and in labor (labor is not free, time is money even if you do it yourself).
Good luck, however you get them up and running well.
That would free the power transformer from having to power the output tube filaments.
I could not look at the schematic to see if they did that; but why not do that?
There are auto transformers to take 120V power mains to power the 100V filaments. The rest of the amplifier can still run off of the amplifiers secondaries for safety reasons.
How much do the 'golden obsolenium' tubes cost! . . . $$$
Modifying the amplifier may cost more in parts and in labor (labor is not free, time is money even if you do it yourself).
Good luck, however you get them up and running well.
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