ARC vt100mkiii Questions?

I brought one of these 2ndhand lately. The amp had both side boards inside replaced and only the transformers were old. So, it is not broken in. Well, I would like to get advice from other owners about its bass responds. It seems on some music esp. acoustic double bass, the bass is a bit soft and undefined but on others like big symphonies, it sounds quite right with good dynamics. But overall, the bass is not as tight as I would thought it is. I use JBL4425 and Haarbeths HL_5S so to think it is not the speaker’s faults. Does yours have very tight bass? What bias settings were yours set to, mine is set to 60. Thanks.
I only had the Mk1 and no it did not have really tight bass. It had good bass but not what I would call tight. Some recordings did call attention to this. Maybe with a damping factor of 8 or something this is a hint?

First off I do not own a VT100 MK3.

If the boards are new you will need to put some time on the components. Resistors, capacitors, ect. At least 100 hours with signal flowing I would think.

Are the driver and power tubes new? If new they also will need some burn-in time.

If the tubes are old you may want to have them tested. Power tubes maybe nearing the end of their life....

Also you stated the bias for the power tubes was set at 60 mVDC (0.060VDC)..... Is that what the owners manual recommends? Below is a link from AA and the discussion talks about the bias being set at 65 mVDC (0.065VDC). If ARC recommends 65 and you have it at 60 it will cause the amp to sound soft, not much punch...... Try readjusting the bias to 65 mVDC, you will not hurt the power tubes.
Thanks guys for the reply. I was wrong about the bias was actually setted to 55! Too low. I set it to 60 and the bass seems to get better. Yes, it is rounded and not tight but full and quite musical.
I sure hope you are using power tubes from Audio Research.
At 60mA or higher those so-called Black Sable 6550Cs wont last you more than a few hundred hours.
User beware.
I set it to 60 and the bass seems to get better.
12-08-10: Luna
60? Not 65? If you do not have the owners manual you could call Leonard at ARC. He will tell you the proper setting.

Phone 763-577-9700>>
Yes, I knew it should be 65 but as johnsonwu said, the 6550 will last longer if set lower. That is also why the technican set them to 55mv.
Leonard is no longer at Audio Research. If the bass is a bit lacking, I would suggest your output tubes need to be replaced. I always tell customers if your buying a used tube amp don't expect the seller to re-tube it. My guess is your output tubes have come to the end of their life. You might also wish to talk to an authorized ARC service provider in your area so he can have a look at your amp to make sure it's functioning properly. I think the MK3 version of that amp is quite good. They normally don't have bass impact issues. BTW the proper setting is 65mV and I believe it says it on the circuit board right next to the resistor your supposed to measure across.