I would rebuild MC-30 as it was!
It's not a common amp!The OPTs are for unity coupled configuration.Maybe they'll work as UL,too.But it's very difficult to find these days such kind of OPTs so, it's a nice idea to try unity coupled.
The only thing that I'd search about is to bias it at class AB or A.
And this because MC-30 as I remember is biased in class B.But you must be sure if transformers can handle more current.
It's not a common amp!The OPTs are for unity coupled configuration.Maybe they'll work as UL,too.But it's very difficult to find these days such kind of OPTs so, it's a nice idea to try unity coupled.
The only thing that I'd search about is to bias it at class AB or A.
And this because MC-30 as I remember is biased in class B.But you must be sure if transformers can handle more current.
Yes, rebuild it as an MC-30; there was a thread here quite recently that gave a site with full McIntosh diagrams:
http://www.berners.ch/McIntosh/de/Frame_Matrix.htm
I had a quick look and note that the MC30 uses 12AX7 and 12AU7. As you would be starting from scratch, you might want to consider using 6SN7 in place of 12AU7 and 6SL7 in place of 12AX7. The 6SN7 draws more heater current, so you might decide to use a separate heater transformer (always a good thing to split heaters off from rectification).
It all depends on how keen you are. The output transformers are designed for a very specific use, so you don't have any choice there - it's only in the details that you have choice.
http://www.berners.ch/McIntosh/de/Frame_Matrix.htm
I had a quick look and note that the MC30 uses 12AX7 and 12AU7. As you would be starting from scratch, you might want to consider using 6SN7 in place of 12AU7 and 6SL7 in place of 12AX7. The 6SN7 draws more heater current, so you might decide to use a separate heater transformer (always a good thing to split heaters off from rectification).
It all depends on how keen you are. The output transformers are designed for a very specific use, so you don't have any choice there - it's only in the details that you have choice.
Hi Markp,
I've rebuilt many McIntosh amps in the past. I think I have an MC30 schematic I can send you if you need, just pm me.
With modern components, this amp should sound better than it did. First build it as it was designed, then try to increase the bias current to see how it sounds. The phase splitter had matched resistor I think, around 12K. Increase the wattage rating on these over stock. I recall using 2W resistors.
If the cases are rough, have them re-plated. I did some in a semi-gloss brass with black xformer covers. That looked really sharp. My cases were badly rusted so there was no question of retaining the cosmetic value.
-Chris
I've rebuilt many McIntosh amps in the past. I think I have an MC30 schematic I can send you if you need, just pm me.
With modern components, this amp should sound better than it did. First build it as it was designed, then try to increase the bias current to see how it sounds. The phase splitter had matched resistor I think, around 12K. Increase the wattage rating on these over stock. I recall using 2W resistors.
If the cases are rough, have them re-plated. I did some in a semi-gloss brass with black xformer covers. That looked really sharp. My cases were badly rusted so there was no question of retaining the cosmetic value.
-Chris
Hi Markp,
Try first with the tube rectifier, that's stock. MC-40 's used solid state rectifiers. The supply will have a smother rectified DC (no HF spikes). For outputs, have been using Electroharmonix lately. I've been pretty happy with these and the cost is much more for something better.
-Chris
Try first with the tube rectifier, that's stock. MC-40 's used solid state rectifiers. The supply will have a smother rectified DC (no HF spikes). For outputs, have been using Electroharmonix lately. I've been pretty happy with these and the cost is much more for something better.
-Chris
The MC-30 has very nice output iron...
Depending upon the condition of the chassis you might want to just build one up as it was... it is a pretty nice design. It works well.
I had one on the bench for 20+ years as the bench amp... Have a 50-W2 in that role now. Cooler looking but actually the MC30 works a bit better overall.
They used the 1614 steel cased 6L6 style tube.
And no it won't work as an ultralinear transformer...
You could substitute in almost any tube that ends up with the requisite plate impedance and power level...
Of course having only one of them sort of limits you as to what you can do with it.
If the chassis is in good shape and you have the bottom cover, it has some collectors value that way. Something to consider.
So, I wouldn't gut and drill the original chassis if ur planning on a different input circuit... the Japanese or someone with a rusty chassis would like to own the one you have and will pay for it.
If ur gonna do a new input design or use different tubes, lay it out fresh on a new chassis...
my 2 cents...
_-_-bear
Depending upon the condition of the chassis you might want to just build one up as it was... it is a pretty nice design. It works well.
I had one on the bench for 20+ years as the bench amp... Have a 50-W2 in that role now. Cooler looking but actually the MC30 works a bit better overall.
They used the 1614 steel cased 6L6 style tube.
And no it won't work as an ultralinear transformer...
You could substitute in almost any tube that ends up with the requisite plate impedance and power level...
Of course having only one of them sort of limits you as to what you can do with it.
If the chassis is in good shape and you have the bottom cover, it has some collectors value that way. Something to consider.
So, I wouldn't gut and drill the original chassis if ur planning on a different input circuit... the Japanese or someone with a rusty chassis would like to own the one you have and will pay for it.
If ur gonna do a new input design or use different tubes, lay it out fresh on a new chassis...
my 2 cents...
_-_-bear
I'm gonna keep it pure then. The only thing might be the sold-state rectifier path like my MC-225 has. The MC-30 actually give me three channels of vintage Mcintosh with the MC-225 so it might be the from setup in an all tube surround system with my old ST-70 on the rears!
I've ordered 7591EHs for my 225 outputs and I have good input/drivers for it all vintage but my MC-30 will need all new tubes.
I've ordered 7591EHs for my 225 outputs and I have good input/drivers for it all vintage but my MC-30 will need all new tubes.
Just be aware that there are two PS circuits. One of them has a tap of reduced voltage for the negative rail, the other has its source directly on the end of the HV secondary. The former has a 250 VDC capacitor, and the other a 450 VDC filter cap( in between the last two couping caps at the 5U4 end of the circuit board).
regards,
Douglas
regards,
Douglas
They go here yesterday and my initial impressions are good. They are much larger than the old original 7591 Westinghouses they are replacing but have no 'bases', its all glass. The sound is very full and powerful in the bottomend and clean highs. I'm going for another pair now that I like these.anatech said:
My ST-70 has vintage 6CA7s with the coke bottle shape in it and some Russian 7199s that are just OK. I replaced all the resistors with metalfilm and upgraded all the caps in both the circuit and the ps. The only bummer is my power transformer is on its way out, I need a new one. The rebuild made it totally quiet, no hiss!anatech said:
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