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Leave tubes in phono section if not using it?

Hi,

I just bought a mid 1980's Moscode Minuet preamp (not Minuet in A) on AudioGon. I haven't received it yet, but I think it uses 4 12AX7's (2 in phono section, 2 in line stage).

I don't plan on using the phono stage. I was thinking of just pulling the tubes in the phono section with the hopes of reducing noise/hum and saving myself two tubes. But, I know I could use shorting plugs on the phono imput jacks to possibly eliminate some noise that way.

My question: Is it possible that pulling the tubes can upset some critical design parameter and create a detrimental situation, or even do some damage?

I will not have a manual or schematic for this unit.

Any thoughts would be much appreciated.

Thanks,

Rich
richgib
hifiharv
351 posts
 
I Don't know about Moscode, but I asked Cary about this on my SLP 90 preamp. The answer was, Yes, leave the tubes in place. Replace them with something less precious if they are special. Since your pre is older these days, I wouldn't take any chances.
hifigeek1
770 posts
 
Some preamps not only want phono tubes left in, but if the tubes are not quiet they can cause issues with the power supply and can actually cause problems for your high level/line stage as well. Best bet is to call George Kaye and ask him. Then you will know for sure.
richgib OP
16 posts
 
Thanks, Newbie. I'll just put cheap ones in the phono section. I was wondering if it could affect the line stage, maybe even send the unit into oscillation. I had an early Audible Illusions preamp that oscillated when I unknowingly put in some Hungarian tubes. They even warned about this in their manual. I was just curious if the circuit could be affected in some way, as Hifigeek1 suggested.
robetozian's avatar
robetozian
8 posts
 
Leave the tubes in. If you operate this preamp without tubes in place, it will "un-load" the regulators. Voltages in some places will rise, and may rise above the rating of some components. The repair bill will most likely be higher than the cost of a couple of cheap tubes.
boby
1 posts
 
Gentlemen I need your knowledge
hello possesses a minuet moscode (not in A) and I read that it had four 12AX7 but I have two 12AX7 and two 12AU7
precisions would you please?
so what tubes is dedicated for phono and which are dedicated to the preamp section?
do you know a way to know and tell me how I could understand?
it is a very very good preamp and I love it like working with my MOSCODE 300!
I search the shema of minuet and 300
thank you for your help because I never found anything on this subject and I despair
(anyone know what it is dedicated tube in the minuet in A? this is the same?)
thank you very much
Bob (France)
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