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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
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.
borg7x9 OP
91 posts
 
Gmorris,
Thanks for the info. The guy who gave me the jj tubes has a test bed that I can use. He has offered to go through the adjustment processes with me. I'll do that this weekend. He also has a large collection of tubes that he's offered to lend me to try, which might be interesting.

Myron.
gmorris
351 posts
 
You should also check the 1 Ohm resistors R37/R38 AND R43/R44 (in series with the anodes of the output tubes. (Sometimes they look ok from general inspection, but can be defective.)

Also check the 100 Ohm resistors R39/R40 AND R45/R46 (same comment as above)

I keep a bunch of these resistors (can order from ARC). These are the first to go if there is an arching problem.
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