Marmac Super 60

[g1]

I just lifted the leg on the larger resistor and it still measures 100.7K. The underside was damaged as well so I’ll need to replace that one for shure.

If it's that close then I agree it must be 100K. The yellow band must have browned from heat.
This unit looks so much like Hiwatt that I would look to Hiwatt schematics in case there is a match. There is a good chance it is a copy, or at least parts of it.

[vintagekiki]

Help us
If it's not a big effort, look and draw¹⁾ where the wires go from pwr amp (less) pcb.

https://music-electronics-forum.com/filedata/fetch?id=921927&d=1609963221

The end left and right power resistors are certainly Rg2 (470 or 1k), the two yellow capacitors are the transfer capacitors PI / g1 power tubes ... ...

[C Upp]

I’m on it. Trying to trace and draw up the power amp. I just haven’t had very much time this week ’cause of work and zoom meetings. Weekend looks like I’ll have more time so I’ll try to get something drawn up tomorrow.

really learning how hard it is to wrap my head around these things without a schematic. Love learning though.

[C Upp]

Ok. So I drew this up of the small board and PI. I find it really hard wrapping my head around it all. Thankful for all the help.

[Helmholtz]

Ok, what I see is an input amplifier ("common cathode" circuit, right side triode) followed by a cathodyne PI (left side triode): http://www.valvewizard.co.uk/cathodyne.html

I recommend to start any schematic by drawing a lower ground bus line and an upper B+ line. Then place the tubes including power tubes between and see what connects where.

[vintagekiki]

Minor errors probably exist. Compare the schematic with the power board lay.
From the attached I did not infer positions for resistors 390, 1.5k and 6.8k
Try to determine where they belong on the schematic.
thanks
vk

[vintagekiki]

Just to informatively, ask how the restoration is progressing, is help needed?

vk

[C Upp]

Sorry. I’ve been very busy working so I haven’t really had that much time to put into this yet. Got the new electrolytics in and built the limiter. Started it up on the limiter and it looked good. Stable voltages and no smoke. Put in some new tubes and it does amplify signal so I suppose the transformers are ok and that’s awesome.

I will need to order some new resistors to replace the ones that are damaged before I take it off the limiter and try it out at full power. Thought I could get them locally but that place went out of business last year.

Thanks for everything so far. I really appreciate the help. I know I’m an annoying newbie, and that I move slowly but I really hope to learn more from this. Will be another 2 weeks of a lot of work before I can get into this amp more. I really don’t wanna do anything after a stressful day because I’ll just break something. Will keep you posted.

[vinyvamos]

Hi folks, it is I who has the Atomic Analog page on Facebook and I who has a rather rough schematic of said amplifier here for your eyes and minds to get confused upon :-P :-). The OP contacted me directly and although I will send this to him I also thought it useful to post it here also. Marmac amps earn a warm place in my heart, even though they are not so reliable. Mine also had two burnt up resistors which were in fact the upper and lower resistors of the phase splitter. Mine were still conducting and measured 63k (upper) and 59k (lower) and I probably replaced them with the closest values.

https://www.facebook.com/atomicanalo...05616319597105

[vintagekiki]

https://www.facebook.com/atomicanalog/photos/a.877179665774113/1805616319597105