[Amps] high drive/low output QRO HF-2500

[Steve NR4M]

Thanks for you cautionary input, Jim,

I have the two originals, here, on my desk.
Two of the non-pedigreed spares are in the amp now, with no HV, cooking.

I plan on also using my 'never-before-used' hi-pot tester on the new 
ones. I figure I need be good at 6 kv plate to gnd.

Steve

On 3/4/2015 17:25, Jim Thomson wrote:
> Date: Wed, 04 Mar 2015 16:26:27 +0000
> From: Steve NR4M<steve at nr4m.com>
> To: Carl<km1h at jeremy.qozzy.com>
> Cc: amps at contesting.com
> Subject: Re: [Amps] high drive/low output QRO HF-2500
>
> Happy 'Hump day' to all,
>
> I did a little investigation based on suggestions from members of the group.
>
> In preparation for running the amp with only one tube, and then the
> other tube, figured I would do some simple resistance checks of the
> tube.  I was looking for an open filament.  I pulled both tubes out to
> check one against the other.  (I really do hate putting these tubes back
> in their sockets...)
>
> Trying to understand the Svetlana pin out info for this tube. /Assuming
> /in their 'bottom view' that the gap in the pin symmetry is at the six
> o'clock position.  That is, pin 1 (G1) is at 7 o'clock and pin 7 (H) is
> at 5 o'clock.  I also located the 3 connected pins for the cathode (K)
> at pins 2, 4 and 6.  This, then, seems to make sense to me.
>
> First tube I pulled measured an open across pins 7 and 3 (H)  I am
> supposing 'H' is the designation of the filament.
> The second tube showed 1.4 ohms across the same two pins.  Therefore, I
> believe the first tube has an open filament.  This would explain the
> 'not working correctly' vs catastrophic event of a short somewhere.
>
> I have a couple of spare tube I got several years ago.  I do not know
> their pedigree, but supposed to be NOS.
>
> Any issues with freely mixing tubes, or is the performance of this tube
> such that a pair of tubes MUST be matched, or at least recommended, to
> be matched for getting the operating bias/quietens current of each tube
> the same?
>
> Comments welcomed.
>
> 73 de Steve, NR4M
>
> ###  DON’T  MIX THEM UP.   IE:  keep track of which is bad, which is
> the oem good original.     and the 2 spares, since u don’t know if they will
> work , not work, both good, both bad,  1 bad, 1 good.   mark em somehow
> like with a jiffy marker.  1-2-3-4
>
> ##  dunno if they have to be matched or not.  Unless  u can read individual plate
> + screen currents, u would never know anyway.
>
> Jim  VE7RF
>
> Jim
>
>
>
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-- 
73 de Steve, NR4M