Music Man Power Supply [was Re: #102 died yesterday :( how,why]

[Bombacaototal]

Another thing which I always been intrigued by is that sometime for very high voltage amps (music man), sometimes people would use one balancing resistor for the power tubes and one for the pre amp tubes, and also a separate choke for the pre amp tubes...I always wondered how to wire an amp as such....

[talbany]

Another thing which I always been intrigued by is that sometime for very high voltage amps (music man), sometimes people would use one balancing resistor for the power tubes and one for the pre amp tubes, and also a separate choke for the pre amp tubes...I always wondered how to wire an amp as such....

You can put the balancing resistors anywhere on the filament supply since they are wired parallel.You just have to put one on each side of the winding. Even if I have a transformer with a CT winding I never used it and always go with the balancing resistors for the very reason that they do give you a level of safety with the fuse-ing effect they provide (1/2 watt resistor) The hope is those go first!, however, since the flyback voltage happens so quickly there is no guarantee that it will always take out the balancing resistors before something else fry's. If a tube goes or you get a heater cathode short or you get a current spike for a longer period of time in most cases the balancing resistors will go. At least this has been what I have found repairing Fenders and other amps through the years. Balancing resistors fried? Shorted tube

BTW. I would imagine a new transformer is more likely to survive a large current spike due vs say one that is 30 or 40 years old where the insulation on the wire is in worse shape.

Tony

[Bombacaototal]

Thank you for clarifying Tony. So in my case you would remove the geen/yellow (PT Heaters ground) from the ground and then add a couple of 100R (1/2W) instead....

And on the high voltage scenario I could potentially just add a couple balancing resistros to each side of the PI tube heaters and just ground them by that tube...

[norburybrook]

valuable knowledge shared here, thanks.

In future I will use the resistors instead of the heater CT.

Raphael you can put them anywhere as long as Tony says you have them on both sides. I've seen them wired on the fender style pilot light for example.


M

[talbany]

Yes ! I would. As for the where to put them? Its generally a good idea to put them down closer to the Power transformer end (not necessary) I generally put a grounding lug on the tubes sockets mounting screws, one on pin 2 and one on 7 of the first 2 output tubes. Don't forget to disconnect and tie off the CT or you will damage the PT. Just a reminder.

Good Luck!

Tony

[10thTx]

On my Carolina Overdrive Special (D-inspired), I have a small turret strip I use for the LED on/off light & 100ohm resistors to ground & as a starting place for the heater wiring to power tubes. NOT saying it "should" be done this way. However, it's been a useful approach for me.

With respect, 10thtx

[rootz]

Thanks for the knowledge here guys. I'm one of those people who always uses the ct on the heater wiring. Now I know balancing resistors or a balance pot have some big advantages.

FWIW 10thTx I believe Two Rock used a tag strip for led and balancing resistors in some amp too. Can't see anything wrong with that approach in general.

Bomabacaototal, not really understand what you mean by balancing resistors in very high voltage amps. You mean balancing resistors over caps to share the load? Schematic/screenshot?

[Bombacaototal]

Hi Rootz, I remember reading somewhere that some high voltage amps (using music man HD130 PT, which had something like 700v on plates) were using not only balancing resistors for the power amp tubes but additional ones for the preamp tubes, and I was wondering why and how to do it. Those amps also had a second choke for the preamp heaters. Unfortunately this is as much information as I have...but wanted to undestand how to wire something as such...just as curiosity..

[sluckey]

I think the balancing resistors you are talking about are the resistors parallel to stacked B+ caps in the power supply and have nothing to do with this discussion. The resistors being talked about in this thread are used for a completely different purpose.

[rootz]

Need to see a schematic about that. I can imagine tapping the screens and preamp supply from the centre tap on a high voltage transformer. And using sharing resistors over the preamp caps like in a precision power supply. That's what you mean?

[Bombacaototal]

Sorry to sidetrack folks, probably I understood wrong, but I thought it was similar to the 100R at the power tube socket another set of 100R at the preamp socket and an extra choke...i am trying to remember where this may come from?!

[sluckey]

Sorry to sidetrack folks, probably I understood wrong, but I thought it was similar to the 100R at the power tube socket another set of 100R at the preamp socket and an extra choke...i am trying to remember where this may come from?!

Show us a schematic.

[Bombacaototal]

I wish I had a schematic, I remember reading this somewhere though...

EDIT: Found the thing about the choke

One Fender style choke, a small 6.3V transformer to supplement the MM PT heater voltage.

https://ampgarage.com/forum/viewtopic.p ... hoke#p3651

[rootz]

That snippet looks like:
-1 choke in the b+;
- extra trannie for the heaters (because the pt wasn’t big enough in that respect).

[Bombacaototal]

That snippet looks like:
-1 choke in the b+;
- extra trannie for the heaters (because the pt wasn’t big enough in that respect).

Ah makes sense now. The extra transformer would be feeding the heaters all the way from the power tubes then to the preamp? Or the PT would feed the power tubes and the extra trannie would feed the pre amp tubes? If the latter probably the second set of balancing resistors makes sense?

Would this extra trannie be wired like a relay transformer?