Layout for the Music Man iron

[Bob-I]

The Music Man chassis that I bought was altered, cut down about 4" so it's too small for this build. The seller refunded half of my money so I got 2 small chassis, the iron and some F&T caps for $50.

I have a Marshall style chassis that should fit the bill. The front panel controls will have to be staggered a bit to fit, but everything else should work well.

Missing from the layout are reverb control connection, presence control connections and relay supply and switching connections.

This is loosely based on #124 with a one tube reverb added and of course the MM voltages.

Any input is appreciated.

EDIT:
I updated the layout... There will be more updates.

I hadn't thought about the screen resistor size. I'll check my parts bin, I may have some 150R 5W, plus I can reduce the size of the choke replacement resistor as well.

[Structo]

Hmmm, I can't seem to get the image to load.

[talbany]

Bob
Here is the PS..Remember 350 on the screens

[Bob-I]

Bob
Here is the PS..Remember 350 on the screens

Oops, thx for catching that mistake.

EDIT:

You added a 20uF at the screen supply. MM doesn't have that and I wasn't planning it either. The screens come directly off the 250V line, no choke no resistor. There's a cap after for the driver tube node. I added a 1.5K at Andy's suggestion.

I also realized I didn't add the snubbers and LNFB

[talbany]

Bob

Like the schemo the screen supply node get's tapped between the series plate caps which is part of the voltage doubler. AFAIK.. That should give you around 330v.. You neet to filter the screen supply 20uf then the 1k5 or I prefer a choke especially if you plan on cranking her.. Just me.. The 2 22k resistors in series on the schemo should be in your amp a 36 K since your not working with the full 700v (if you want some sag add an 820k dropper here).. From there you could tap off for your reverb transformer (with appropriate dropper) 300v approx on the PI and the standard 2.2k 150k fet sim resistor.. Does this make sense?.. This is AFAIK how very similar to how Dumble does it..

Tony

[ToneMerc]

Mine is similar and too I have a choke the 350V screen supply. I see Tony has done what I was thinking about doing, moving the standby switch to the cold side.

TM

[talbany]

Wrong post..

[ToneMerc]

Tony, the reason I was thinking about doing as that 700VDC+ across that switch makes me a tad nervous.

[talbany]

Tony, the reason I was thinking about doing as that 700VDC+ across that switch makes me a tad nervous. :D

OOPS!!.. You right I was looking at the wrong thing.. Forget it..

Tony

[talbany]

One other thing I forgot.. Since your in no danger of the screens exceeding the plate voltage you can get away with a much smaller screen resistors like 150 ohm..
Hope this helps

[Bob-I]

Bob

Like the schemo the screen supply node get's tapped between the series plate caps which is part of the voltage doubler. AFAIK.. That should give you around 330v.. You neet to filter the screen supply 20uf then the 1k5 or I prefer a choke especially if you plan on cranking her.. Just me.. The 2 22k resistors in series on the schemo should be in your amp a 36 K since your not working with the full 700v (if you want some sag add an 820k dropper here).. From there you could tap off for your reverb transformer (with appropriate dropper) 300v approx on the PI and the standard 2.2k 150k fet sim resistor.. Does this make sense?.. This is AFAIK how very similar to how Dumble does it..

Tony

Yes, that makes since. Thx for the analysis. I NEVER crank my amps so the choke may be unnecessary. If I have space I'll use a choke. Already I have to mount the PT, OT, relay xformer and reverb xformer on top, add a choke and I may be out of space and looking at noise problems.