-----Original Message-----
From: measures <2@vc.net>
To: Steve Thompson <rfamps@ic24.net>; AMPS <amps@contesting.com>
To: <amps@contesting.com>
Date: 17 September 2000 13:21
Subject: Re: [AMPS] Hipot tests
>
>>
>>I'd be interested in comments on the following results. The polarities
given
>>are correct. All tests are between anode and control grid.
>>
>>I bought a pair of 8877, I'm fairly certain they are industrial machine
>>pulls. One blew its heater the first time I powered it up.
>
>Was one side of the heater not hard-wired to the cathode when the heater
>blew?
>Was either side of the heater grounded?
I don't know for sure, as it was someone else's amp that I was fixing, and I
took the opportunity to check my tubes. Looking at the design I think was
copied, I'd expect the heater to have been fully floating with rfcs and no
connection to the cathode. There were no visible anode or grid meter
twitches as the HT came on, and no standing current when put into tx. I'm
prepared to accept it as 'one of those things', maybe from lack of current
limiting. Diagnosing the heater failure wasn't the intended purpose of my
post, but it does mean that the tube can be opened without any loss.
>
>>The other works fine in a 6m PA.
>>
>>Blown one (8722 date) anode+, grid- 10uA at 10kV. Anode -, grid+ 10uA at
>>5kV.
>>
>>Good one (8705 date) anode+ 10uA at 13kV, anode- 10uA at 8kV.
I was interested in the increased leakage with the anode negative. Any
ideas, anyone?
Comparison figures were to verify that the hipot system was working ok.
Steve
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