>
>
>-----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.
A floating, RF-choked heater, jumpered to the cathode is the safest
way. Some guys take the shortcut.
>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.
A heater has much less inrush current than does a filament. Very few
heater type tubes need heater inrush protection.
> 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.
>>
I don't understand the question.
>>>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?
>
I have never seen such a case. With gas leakage, the +/- currents are
equal.
cheers, Steve
>
>
>
>--
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>
>
- Rich..., 805.386.3734, www.vcnet.com/measures.
end
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