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

[Jim Thomson]

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