MV-45 bias voltage range and current

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highfigh
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MV-45 bias voltage range and current

Post by highfigh »

I replaced the bias supply caps and after checking the voltage at all of the pins, I can't get the bias LEDs to illuminate with the tubes in place. The range I'm seeing is 24VDC-35VDC, plate and Grid 3 are 525VDC, heaters are 6.2VAC and DC resistance to chassis on the cathodes is 20.2 Ohms- these readings are the same on all four sockets.

I contacted C-J a while back regarding a power switch and was informed that the amp could be sent in for repair, but they aren't in the business of selling parts. I had received the schematic a few years ago from them but it seems that they don't want to reveal any other service info.

If anyone has more info WRT the correct voltage, bias current, etc, I would appreciate seeing it.

Thanks, in advance.
Last edited by highfigh on Sun Nov 08, 2020 9:58 am, edited 1 time in total.
highfigh
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Re: MV-45 bias voltage range and current

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Buehler, Buehler, anyone?
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AnotherJohnson
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Re: MV-45 bias voltage range and current

Post by AnotherJohnson »

Past advice on a similar question was that it may be related to your mains voltage being out of the expected range. I suppose the LEDs could have failed too ... Mv45 is no spring chicken.

FWIW, I assume the amp sounds normal since you don’t say otherwise. I don’t know the specifics for the MV45, but those voltages look “normal” for typical tube amps.
Last edited by AnotherJohnson on Sun Nov 08, 2020 3:49 pm, edited 1 time in total.
It’s just stuff. I like mine. I hope you like yours. I probably like yours too.
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roberto
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Re: MV-45 bias voltage range and current

Post by roberto »

Hola highfigh,

Are all the tubes new and fresh? Are all the tubes acting equally? Check the bias resistors, usually with a value of 20 ohms and 5 watts. These resistors must be at the exact value. The new value for power dissipation of these resistors are 7 watts.

The values that you are sending are and looks ok. I can not think for what else to do. Put fresh tubes and try.

Happy listening!
ML CLX BF-210 Stage X Motion 4. CJ 120SE amp ET7V2 pre, Holo May Kte Dac. Mac Pro. Power Cond. BPT Signature+ 3.5, Gaia II Feet. USB Lush^V3. Nordost SPM IC and Spk. Shun Mook, BCanto CD2 CD3. Linn LP-12/Unitrack tonearm/Denon DL103R MC.
highfigh
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Re: MV-45 bias voltage range and current

Post by highfigh »

Thanks-

I have the schematic but hadn't seen anything about the higher bias resistor power rating- maybe the old ones are out of spec from being treated like a farm animal. Tubes are fresh (as of the original post), all tested very close to each other. I have another set but if this goes off the rails and wants to red plate them, I'd rather use older but good tubes. In the meantime, I got some vintage EL-34 that had been in a Dynaco ST-70 and I may try them in one channel (one of the four was bad) and the ones I have in the other.
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Re: MV-45 bias voltage range and current

Post by roberto »

What really bugs me, is that you have all the tubes with the problem...when a bad tube is gone, the LED does not lit or could be on all the time. But having all four at the same time, that is very odd.

Happy listening!
ML CLX BF-210 Stage X Motion 4. CJ 120SE amp ET7V2 pre, Holo May Kte Dac. Mac Pro. Power Cond. BPT Signature+ 3.5, Gaia II Feet. USB Lush^V3. Nordost SPM IC and Spk. Shun Mook, BCanto CD2 CD3. Linn LP-12/Unitrack tonearm/Denon DL103R MC.
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