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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 your replies Guys,
I bought this amp on the weekend second hand. It came re-valved with 6h30's so not my doing. They have only been in there a couple of weeks so hopefully no damage has been done. I work in the Telco industry and there is someone here that I can borrow 8xmatched 6922's off and give them a go. Should be fun. However .....

Common sense tells me that this circuit should work best with the tubes for which it was designed. I just hope that no permanent damage has been done.

I think the Mklll not the Mk11 had the toggle balanced/single ended switch. see:- www.arcdb.ws/VT100/VT100.html

I'll give Leonard a call in the morning and see what he has to say.

Thanks for your excellent advice.

Myron.
hammertone_audio
16 posts
 
Just a word of wise. The VT100 Mk 2 requires a 2 stage bias set up. You must bias the 6922's prior to inserting the 6550's and then set up final bias. Leonard will be able to send you the biasing imformation which does not come with the original manual.
But all things said, congratulations on your purchase.
rlips
105 posts
 
Yes, be careful, the bias scheme for the 6922 is involved.

Go Here: http://mycollins.net/audio/artube1.html

very good article on this.

Cheers,

Ron
borg7x9 OP
91 posts
 
Thanks again guys. I tried to talk to Leornard this morning but he's not in untill Tues. :-) I'll give him a call tonight.

Any thougts on the single ended operation without the balanced jumper pins ?? Should I perhaps be thinking that connections have beed internally modded as the single ended inputs work without the jumpers in place ??

I really hope its not been internally modified and that everything is as it should be.

Thanks agian,
Myron.
gmorris
351 posts
 
I am currently using an ARC VT100 mkII in my system. The 6H30 tubes are used in the VT100 mkIII amp. As mentioned previously, you need a set (8) 6922 tubes. Upscale audio sells the 6H23 (NOS 6922) with the required tolerance/balance that are necessary for the VT100 MKII. Poorly selected input tubes will cause your 6550C output tubes to arc and take out the bias resistor.

The above article by Collins is excellent in providing guidance in setting the bias of your amp correctly.
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