Hi
A friend of mine has asked me to fix his Mactone MH-300B.
Problem is it has been at a very unprofessional repair shop that has cut all the resistors and capacitors out and they are now in a plastic bag.
It is a PushPull 300B with 4x300B 2x12bh7 1XECC82 so it is probably a very common topology with fixed bias, but it would be easier for me , if I had the original schematic.
I do not have the amp in house yet, but if the schematic is impossible to get hands on, I will post the measured values of all the resistors and capacitors, and then hope we can agree on how the amp should be ..
A friend of mine has asked me to fix his Mactone MH-300B.
Problem is it has been at a very unprofessional repair shop that has cut all the resistors and capacitors out and they are now in a plastic bag.
It is a PushPull 300B with 4x300B 2x12bh7 1XECC82 so it is probably a very common topology with fixed bias, but it would be easier for me , if I had the original schematic.
I do not have the amp in house yet, but if the schematic is impossible to get hands on, I will post the measured values of all the resistors and capacitors, and then hope we can agree on how the amp should be ..
"I will post the measured values of all the resistors and capacitors, and then hope we can agree on how the amp should be .."
Hopeless business.
Why not ask manufacturer?
https://mactone-com.translate.goog/お問い合わせ/?_x_tr_sl=auto&_x_tr_tl=en&_x_tr_hl=en
: 24-11 Koshino, Hachioji-shi, Tokyo 192-0361
Mactone Co., Ltd.
info@mactone.com
TEL. 03-3394-0131
FAX . 03-3394-0351
Hopeless business.
Why not ask manufacturer?
https://mactone-com.translate.goog/お問い合わせ/?_x_tr_sl=auto&_x_tr_tl=en&_x_tr_hl=en
: 24-11 Koshino, Hachioji-shi, Tokyo 192-0361
Mactone Co., Ltd.
info@mactone.com
TEL. 03-3394-0131
FAX . 03-3394-0351
Oh dear, that's quite a challenge. There's a photo of the interior here, if that eventually could help at all:
https://6moons.com/audioreviews/mactone/300b.html
https://6moons.com/audioreviews/mactone/300b.html
If you achieve HiFiengine site (dumb operators prohibits our country) try to download it:
https://www.hifiengine.com/manual_library/mactone/mh-300b.shtml
https://www.hifiengine.com/manual_library/mactone/mh-300b.shtml
Most of the audio manufacturers won't supply the schematic with the users. I believe the circuit is quite simple and won't be too difficult for trouble shooting.
Johnny
Johnny
It appears to be not a question of "troubleshooting," but complete reconstruction. If I understand the OP correctly, the "tech" ripped everything out, then gave up.
Look at the power tubes and you will see... it is not 300 b. I made tube amplifiers for fifteen years. But why did I post this? People will notice the works of this Japanese . Color based on old altech amps.
The box is made for three 9-pin tubes and four power tubes. The power transformer can not work for the 200-watt sound. The sound character of these two amplifiers is completely different. The output transformers must also be replaced. This matching is not possible.but good circuit😳
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I wrote about topology.
Small manufacturers usually do not like to change proven solutions, so the principle structure of this amplifier may be similar.
Small manufacturers usually do not like to change proven solutions, so the principle structure of this amplifier may be similar.