30 year idle MC75's

[Westy56]

Ok Mac vintage tube amp guys, you should always take advantage of Mac`s vintage tube amp`s power transformer`s optional/mandatory(IMHO) primary 125 volt mains tap change over from the sixties default 117 volt tap

A respected Mc guru/forum member told me to use the 117 over the 125 on the MI75's (MC75's industrial brothers).
I forgot why he suggested it. I think there is more current available on the lower tap.

You do have to buck you mains down to 117ACV if you use that tap.

 

[Bill Ferris]

A respected Mc guru/forum member told me to use the 117 over the 125 on the MI75's (MC75's industrial brothers).
I forgot why he suggested it. I think there is more current available on the lower tap.

You do have to buck you mains down to 117ACV if you use that tap.

Well Westy56, IMHO. If the filament`s in a Mac tube amp are running on the high side(~6.7 volts) or higher when powered up at the user`s local I would think it`s best to take advantage of Mac`s foresight by providing the higher voltage tap..
I don`t see where the handful of additional turns of the same gage primary wire used in the higher input tap will have any significant "milliamp"current restricting negative sonic effect, especially when tube amps are already a little spongy to begin with !!

And with some Mac tubers using a tube rectifier/s with often a 50~150 ohm usually high watt B+ dropping resistor post the chassis mounted cap cooking rectum-fryer tube there`s a certitude of much more sponge("warm, AKA Compression") under music dynamics when the amp is used to play at realistic(NATURAL SPL levels...

My line voltage here, when not being stressed by heat waves/strong cold snaps is around 125~7, and that runs my pair of Mac 30`s, MC 225 and (1)MC- 60`s American tube filaments higher than I`m comfortable with when set at the 117v tap as measured here.. YMMV.

My tube amps tend to be trouble free for many, many years.
And that's great, cause I don`t like to have to mess with/repair them after electronically restoring them for many, many years.

I like mine plug and play, and rather be repairing my friends Mac`s, Fisher`s, Dynaco, ect. tube amplification equipment.

Feel free to run your Mac/`s at whatever main`s tap that you wish..

Kind regards, OKB

 

[Westy56]

I use a 30 amp regulator to keep power constant for my tube gear.
Everything but a couple pieces run at 117ACV, so it was a no brainer.

 

[62caddy]

Probably best to select the voltage that is the closest above the AC main for the longest trouble free service.

 

[Bill Ferris]

I use a 30 amp regulator to keep power constant for my tube gear.
Everything but a couple pieces run at 117ACV, so it was a no brainer.
Fair enough Westy56.
I like to keep my variacs on my benches and my older tube amps that are in rotation in the unused fireplace.
Less clutter and their happy too. Plus my HVAC`s thermostat doesn`t mind summertime tube amp tasting !!

 

[cduarte]

would that even apply to my early 60s M series mx110 and C11 and mc225s and my friends perfect time capsule MC240 (his is a very early one with the smaller 240 logo)?

Ok Mac vintage tube amp guys, you should always take advantage of Mac`s vintage tube amp`s power transformer`s optional/mandatory(IMHO) primary 125 volt mains tap change over from the sixties default 117 volt tap rewire for the power transformer for all the older vintage Mac tube amps so current mains voltages are better handled by the Mac tube amp.. Hey !! Your "refurbishing" soldering iron is already warmed up, why not make the amp`s filaments and voltages much happier and closer to spec.. This doesn`t seem to come up often enough on these Mac AK threads as I`ve been reading"/lurking" for around 8~9 months, but I think is very important for the long term well being of the vintage Mac tube amp !! And if not(surprisingly already factory installed) you should install one and or replace the AC in rush thermistor-- CL80/CL90 as the case may dictate.... snipped for brevity, original post is excellent )

 

[cduarte]

My tech just rebuilt a pair of MC60s and converted to SS rectification. Measured power was 99 watts each from 20hz to 20khz and distortion went way down. He was very pleased with the sonic improvement. Hmm, maybe I should trade one of my mc225s for a pair of mc30s...

So do CL-80~90 thermistors inserted in the primary without 4 amps of needless filament PS. transformer/chassis mounted cap cooking dynamic sonic reducing I/R sponging lossy effect tube rectifier effects.. Go your own way !! Cost is not a factor, as I have a big bag full of 5U4`s from decades of tested (recently via a Amplitrex AT-1000) And I assure you Sir. the desirable sonic effects are very real IMHO and many, many other`s whom tasted .. "Tubyness" is still there, just not smeared in the "fastness response" !!!
We like music to be reproduced dynamically as accurate as possible...

Possible from years of experience as a 'real" qualified good, as rated by many others) FOH sound man..
Always trust your ears, for if you like then it`s the best for you....
And in the end that`s all that matters..

Kind regards, OKB

 

[Bill Ferris]

would that even apply to my early 60s M series mx110 and C11 and mc225s and my friends perfect time capsule MC240 (his is a very early one with the smaller 240 logo)?

Thank you cduarte for the kind compliments, I can`t speak for other Mac unit`s you have listed(and most likely the C11 preamp are already SS rectified) other than the MC 225, of which I also own and have rewired for 125 volts mains input..
No tube rectifier in that amp, but it uses a SS rect. voltage doubler which do to it`s design act like a spongy tube rectifier.
I just checked, both C 11 & M series MX 110 are SS rectified and have no 125 volt mains taps.

But if they have had their PS caps replaced should be ok to run above their 115~117 volt with no problem..
My C 22 is run 6 ~8 hr.`s or more once a month for years with no issues and I have yet to recap it since it`s purchase in 2000. Update: the MC 240 has the 125 mains voltage taps and is also using a SS voltage doubler circuit. Take care and enjoy the music. Regards, OKB