Music Man 100-RD
Moderators: pompeiisneaks, Colossal
Music Man 100-RD
It's been a while since I've had a Music Man on the bench. This one has 6L6 power tubes. When powered up, hum slowly grows and one tube starts to red plate.
I'm getting my head around the power section. Looks like the signal is fed to the cathodes.
A non-adjustable, fixed bias is fed to pins 5, so I can check for that.
There is a trimmer, TR1, which is also connected to the cathodes--is that a kind of PI balance control? Right now the trimmer is fully CW--how would one adjust it?
Anything else to watch for....aside from the 720vDC on the plates?
I'm getting my head around the power section. Looks like the signal is fed to the cathodes.
A non-adjustable, fixed bias is fed to pins 5, so I can check for that.
There is a trimmer, TR1, which is also connected to the cathodes--is that a kind of PI balance control? Right now the trimmer is fully CW--how would one adjust it?
Anything else to watch for....aside from the 720vDC on the plates?
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I build and repair tube amps. http://amps.monkeymatic.com
Re: Music Man 100-RD
it was few monthis this question.. then how much you charge this repair if you ask for solution on internet?
- martin manning
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Re: Music Man 100-RD
Recent Musicman discussion: https://ampgarage.com/forum/viewtopic.php?f=6&t=36752 that trimmer is the bias adjustment. I’d suspect a failed driver transistor.
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Re: Music Man 100-RD
The 6L6 based amps have less then 600 volts on the plates if I recall right, but non the less be careful.
Turn the amp off and leave the standby switch in the on position and the power supply will drain out in 30 seconds.
Turn the amp off and leave the standby switch in the on position and the power supply will drain out in 30 seconds.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Music Man 100-RD
Hello --
Martin, as usual, on point accusing one or possibly both of those brittle BJTs. Though their failure/death may well have cascaded from surrounding passives. Proactively replacing the electrolytics C19, C20, C21 eliminates obvious probable suspects. A trio of film capacitors would be an inexpensive upgrade/update. That MM bulletin embedded in the prior thread is interesting reading.
Best .. Ian
Martin, as usual, on point accusing one or possibly both of those brittle BJTs. Though their failure/death may well have cascaded from surrounding passives. Proactively replacing the electrolytics C19, C20, C21 eliminates obvious probable suspects. A trio of film capacitors would be an inexpensive upgrade/update. That MM bulletin embedded in the prior thread is interesting reading.
Best .. Ian
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Re: Music Man 100-RD
Totally … if you have to reference an outside source in order to execute a repair then you must lower your prices …because of honor … otherwise harakiri for you !!!
I hope the sarcastic ridiculousness is obvious
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Charlie
Re: Music Man 100-RD
I cannot spot C21 on the schematic...
I build and repair tube amps. http://amps.monkeymatic.com
Re: Music Man 100-RD
The power tubes are driven at the cathodes, and the suppressor/beam forming plates are grounded, but they are internally connected. So how is the cathode modulating the current flow if it's grounded? What am I missing?
Tube junkie that aspires to become a tri-state bidirectional buss driver.
- martin manning
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Re: Music Man 100-RD
Yeah, that's an error. Other MM schematics show it correctly with the internal g3-k connection and no ground.