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Audio Research vt100mkll question

I wonder if someone has experince of this ??

Two questions really.

I've just bought a vt100 mkll and am running it with single ended input from the source , with-out the pins in the balanced input. It seems to work ok just wondered if there was any down side to this ?? Should it work at all ??

Also My amp has been re-valved with 6h30's instead of the original 6922s. Is this a good thing as the 6922's are a lot less current hungry than the 6h30's ?? Will it work properly ??

Over-all the amp is proving harsher than I expected on leading edge vocals and sounding a touch bright. (could the valve be causing this ??) I'm driving proac 3.8s . Bass is good and some things sound very, very good.

Any opinions would be appreciated.

Thanks for your time.
borg7x9
gmorris
351 posts
 
Borg

I think it is important to note again that the VT100 MKII requires input tubes with closely matched tolerances. You may encounter problems with arcing of the output tubes with a loss of the bias resistors if the tubes are not properly pre-selected.
9rw's avatar
9rw
318 posts
 
Still, the previous owner may at some point have used the 6h30 tube (or done something else equally stupid) and damaged the amp. I'd be very suspicious. I recommend that you send it to ARC -- or someone familiar with the amp -- to make sure everything is OK. Otherwise, you'll always wonder if you're hearing the amp as it should sound. And it really is a superb amplifier.
borg7x9 OP
91 posts
 
Thanks for all your advise guys.

Just to let you know that the person who supplied my tubes has matched/supplied them up in relationship to their use in the circuit described in the schematic that Leonard sent me(together with the original biasing instructions).

I'm going to do the job this weekend, I'll let you know how I go. Thanks for your interest and comments.

Myron.
borg7x9 OP
91 posts
 
Ok just in case anyone is still checking this..............

DISASTER NOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO

I warmed up the amp and tested across the resister on the Power valves (130Mv) and was only able to adjust to 98 Mv max on right channell and 122mv max on left channell. they'd both been adjusted to 98 mv.

Adjustment on the input output valves were shot too. I adjusted these to within the tollerances specified (60v on relevant testing points)without any drama's but this didn't influence the output of the power vlves at all.(expecetd)

So I guess the short story is that the guy who sold me the amp fibbed about the recent Valve replacement ( bad bad man ).

So my plan is to ship the amp to the local distributor who will revalve and service My amp. It will end up having cost me 4000 USD in the end. So while I'm a bit negative about the experience overall, if I end up with a smooth, lovely sounding amp I still think I will have done OK.

Thanks all for your time. Any encouraging comments would be appreciated :-).

Myron.
gmorris
351 posts
 
Borg:

If the input tubes are not properly balanced and adjusted you will not be able to adjust the output tubes to the specified 130 mV.

I would first re-checek the input tubes before shipping off the VT100 for repairs.
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