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In Reply to: RE: Jim, what bias setting did you use to achieve 10,000 umhos with posted by hiatt@alaska.net on May 03, 2010 at 10:22:36
Bill,
HS 6 3450 is the switch setting, the bias is set on 10 on the "D" range. Of course it uses 6.3 volts on the heater.
I just now pulled a couple untested EH 7591As at random and they read in the 72-75 area (about 9000 - 9250 umhos) with just a very brief warm up. I've had a few that go over 10K as I mentioned before.
If you only read 28 on your TV-7 you either have a bad tube or a tester problem I'm afraid.
Follow Ups:
A third possibility (bad tube or bad tester) is a bad (sketchy) test condition manual. Besides my USM118 cardmatic, I often test (especially DHT's like my 205D's) on the TV7-D/U because the USM isn't DHT-friendly, as Alan Douglas points out. When I recently (after many months absence) checked cal on my 6L6 reference, which should, according to Dan Nelson read 43, it only read about 28 with the "latest" bias pot setting of 40. Wasted a bunch of time until I fully retraced my steps (seldom have any 6L6's to test)and went back to Nolan Ryan's extensive spread sheet, that points out Rev L specifies 23, Rev M specifies 40 and he questions the validity of the latter. In fact, with a bias of 23, my Nelson-calibrated TV7 reads 43 for the Nelson-calibrated reference 6L6. So 3rd possibility is that the version of the settings manual(or roll chart for other testers) may be obsolete or erroneous for that particular tube. JMO, YMMV.
You mention using the exact chart settings for testing the EH7591, but in a previous post, you mentioned this:
Honestly, I think I just got mixed up or something - it looks like I was describing the EH KT-88 in the prior post!
Sorry, my bad!
....OUCH!
6L6 tube on my calibrated TV-7, and it tested right on the money. The 6L6 was sold to me by Sonny at the Radiola Guy, and it has a value of 42 units on the TV-7.
I re-tested my new EH7591, and I have a correction to make also. They measured 45 units on the TV-7. When I raised the bias to 23(the setting for the 6L6 tube), the EH7591 tested at 32 units. I guess that makes sense actually. So, I am not sure what to do to make the EH7591 measure like a normal, new 7591 tube.
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