using two Mcintosh MC2102 in mono parallel mode


I'm considering getting another MC2102 amp and running them in the parallel mono mode; my speakers have quite a low impedance (0.7 ohms above 6KHz). Does anyone have experience with this setup, or with another Mcintosh tube amp set up that way?

Here are some of the things I'm concerned about:

Will it work well if one amp is 4ys old and one is new?
Do the tubes on the two units need to be matched?
Does the amp input impedance change?
Does the amp sensitivity change?

Thanks for any advice on this,
Steve, 0,7ohm looks incredibly low to me. R U certain of that figure? If so, you'll have to mod the amp to take that sort of load (unless this has been provided for already), and, geberally, tube amps are extremely unhappy with very low loads.

I'm not sure what parallel mono mode is; if it's bridging each stereo amp to amplify mono then the load impedance the source will see will be halved UNLESS Mcintosh has a different design provision (which they'll specify).

Amp sensitivity: shouldn't change, but again, I don't know the effects of bridging on yr amp (McIntosh probably specs this in the manual).

Matching the tubes: let's not go overboard:) As long as the tubes on the old unit aren't severly tired, it'll be OK. In any case, you'll hear the differences if any. UNLESS you mean, should the two amps be using the same brand of tubes -- in which case the answer is yes.
The folks at mcIntosh Labs are very helpful. Give them a call. I own the 2102 and I am very happy with it.
what kind of speakers are you running that dip that low & what is their rated nonimal impendance? when you go paralell with the mc2102 the impendance drop's from 16, 8 & 4 ohm's to 4, 2 & 1 ohm's,i would think that your speaker's would reek havok on a mc2102 running it in stereo mode due to the low impendence dip,even if your running them from the 4 ohm tap the dip you mentioned is extremly low & cant be an easy load for that amp,does your current single mc2102 handel such a dip well?

if your speaker's truly dip that low then your probably on the right track getting another amp & running them in paralell because in paralell you can try your speakers on the 2 ohm tap or even the 1 ohm tap without putting such a demand on the amp.

i dont think ive ever heard of a speaker that dip's down to 0.7 ohm's are you really sure that figure is correct?

Thanks for the replies. I did call Mcintosh directly, they are indeed helpful (the input impedance does not change in mono mode, and they agreed there is no need to match the tubes or age of the amp).

Re the speaker impedance, yep, I'm sure about the number. The speakers are Martin Logan Summit electrostat hybrids. ML specs say 4ohms nominal, min 0.7ohm at 20KHz.

now you've peaked my interest in this,what did mac say about running 2 of them in paralell & will it help any issues with the low impendance?
Hello Bigjoe,

When I talked to Mcintosh Labs Tech Support, they said that using mono parallel would be the right way to go. The MC2102 has two mono modes: parallel and bridged. As I understand it (might not be technically correct), in parallel mode the left and right amplifier circuits are used in parallel and can supply more current, while in bridged mode the L&R circuits are stacked somehow and can supply more voltage. Parallel mode is recommended for driving low impedances, bridged for low-sensitivity speakers.

At least, this is how I understood it.

thank's steve,i ran my mc2102 in bridged mono but i never had a reason to run it in paralell,good info to know though.