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In Reply to: RE: Testing a 211 in an 845 amp posted by Blackdog on March 16, 2014 at 17:48:59
Hi Dan, I changed a pair of the ps caps in the voltage doubler circuit. There was popping sounds and the one pair of caps were getting noticeably warmer than the other pair. I installed some Kemet caps which I think have a higher surge rating than the originals.
The amp is an Antique Sound Labs 845 with fixed bias , so I do have some adjustment leeway. What is the bias necessary for the 211? regards, Dak
Follow Ups:
You need about half the negative voltage for the 211. It also has a lower plate dissipation. This is an AQ1006 I assume. You grid, is probably around -125 VDC, you would need to lower it to around -60 I'm guessing. Atleast the 211 will be running light. So you won't damage anything. The other way around you risk over current.
Dan Santoni
Hi, on the amp is a milliamp meter. Right now it is set to about 700ma. So, just to be clear, I would have to turn down the bias adjustment to around 350ma if possible. regards, dak
That's actually reading 70ma even though it says 700. I had a pair of these amps for a while. there's not enough adjustability in the fixed bias to get it anywhere near that low for 211s. Additionally, the output transformers will not have the primary inductance needed to properly load 211s. You could see if they light up but that's probably about it.
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