2. amps-preamps
  3. 1241558275

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
11 responses Add your response
riley804
1,224 posts
 
what was wrong with the answers that were given here ?

http://forum.audiogon.com/cgi-bin/fr.pl?aamps&1241496763
newbee
4,767 posts
 
Riley804, what Rich wants is someone with intimate knowledge of this pre-amp who can tell him whether or not operating on only 2 of 4 tubes will cause him any problems.

I don't have a clue with this pre-amp - for me it would be easier to stuff in $20 worth of cheap tubes (actually he could go even lower) in the phono stage and forego having to take the word of folks who would just be guessing or otherwise worrying about it.

But, he is seeking knowledge and that is a good thing isn't it?
clio09
3,355 posts
 
If he is seeking knowledge he should just call George Kaye and get a direct answer.
mechans
3,048 posts
 
I like the cheapo tube idea. I have a few stock tubes that arent worth the glass the're made of. Just buy some 5 buck Sinos and don't worry about unless a friend wants to try a TT on your pre.
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)
Ag insider logo xs@2x
mr_moscode
2 posts
 
The Minuet will be fine if you pull the 2 phono pre tubes out. They are the ones on the left looking at it from the front.
knghifi
1,668 posts
 
My VAC Sig MKIIa has a pair of 12au7 for tape and a pair 6922 for linestage. I don't use tape but found the 12au7 position very sensitive to tube rolling. All VAC owners that roll 12au7 had similar results.

Listen before removing or replacing with inexpensive tubes.
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