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April 22, 2021, 06:54:11 PM

Author Topic: Monamour 45???  (Read 485 times)

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Offline kevner21

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Monamour 45???
« on: August 05, 2020, 12:59:33 AM »
Can a monamour be changed to a 45 tube output?

Online Paul Birkeland

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Re: Monamour 45???
« Reply #1 on: August 05, 2020, 05:19:23 AM »
It could, but the output transformer impedance isn't ideal for the normal range of #45 operating points.  If you want to run the #45, the Stereomour II has some documented modifications to allow this and uses different iron that better supports the #45.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Brissie

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Re: Monamour 45???
« Reply #2 on: March 31, 2021, 07:39:40 PM »
Hi Paul,
I am thinking of converting my MonAmour amps to #45 tubes as I have quite a few good pairs laying around.
I have a spare set of OT2 transformers (I think they are 4K?) which are probably a good match for the 45?
What other changes would need to be made to be able to run a #45 tube in the MonAmour amplifier?
I assume the changes are similar to what you already recommended in the Stereomour II 45 Conversion thread but I suppose the MonAmour is a bit different circuit.
Thanks, Steve

Offline Paul Joppa

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Re: Monamour 45???
« Reply #3 on: March 31, 2021, 08:32:58 PM »
Sounds possible. Let me give some thought to the operating point. A big resistor will make more heat under the chassis; PB may have some ideas about that.
Paul Joppa

Online Paul Birkeland

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Re: Monamour 45???
« Reply #4 on: April 01, 2021, 05:10:42 AM »
You'll need to change a bunch of resistors and figure out how to mount the OT-2s to the chassis. Don't forget to increase the filament dropping resistor to bring the filament voltage down and to replace the parallel feed capacitor to either a 6.8uF or 8.2uF part (you could probably leave the 12 for testing, but it would make sense to get an 8.2uF Solen to see if that makes much of a difference).

I don't know what you would do with the switch, as it could no longer serve any purpose that I could think of.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man