[Amps] Tube swap
Fuqua, Bill L
wlfuqu00 at uky.edu
Mon Jan 27 23:52:25 EST 2014
The only experience I have had with very soft power tubes produced tungsten oxide, a yellow powder inside the tube.
I have over 20 4-1000a Tubes and a number of 4PR1000A tubes and only a few have been soft. I have glass tubes that
that go back to pre-WWII that still have hard vacuum in them.
I don't know what the white stuff is since these tubes don't have the getters that produce white stuff.
All the oxides of carbon, which is also used in the tubes, are colorless gas.
I guess the strangest thing I had seen is a 304TL half full of water in a high power 20 MHz amplifier.
But that was due to a leak in a water hose that sprayed a stream of water on the 304TL which was just right
to cover the crack that it caused in the envelope. The 304TL and the 3CW10,000A7 were voltage regulars for the
plate supply for a 3CX10,000A7 amplifier. This was a Mobley buncher amplifier for a linear accelerator.
From: Amps [amps-bounces at contesting.com] on behalf of Jim Thomson [jim.thom at telus.net]
Sent: Monday, January 27, 2014 10:45 PM
To: amps at contesting.com
Subject: [Amps] Tube swap
Date: Mon, 27 Jan 2014 21:56:48 -0500
From: "Karel" <kebenstr at bmts.com>
To: "Carl" <km1h at jeremy.mv.com>, <amps at contesting.com>
Subject: Re: [Amps] Tube swap
How do you check if they leaked?
Should there be a whitish discoloration inside the tube?
I will check mine later next month. Right now my amp stuff in under 4 feet
of snow here in western Ontario.
## You will know in 2 seconds flat..when you 1st apply 7.5 vac to the
cathode. I had 3 of em go up..literally like a smoke bomb on the inside of the glass.
They had lost part of their vacuum. Turn on the fil..and all of a sudden, tons of white
smoke billowing round and round on the inside of the tube. The fil went from the normal
white colour to super white..then poof, fil goes out. Event over. The smoke eventually stops,
and deposits itself on the insides of the glass.
## I had picked up 7 more tubes 15 years ago....and tested em one at a time. 3 of em went up
in smoke asap. That is the 1st time I had ever seen a 4-1000 turn into a smoke bomb. A good
4-1000..with 4400 vdc under load of 600ma, will do 1900w pep out with 130 w of drive. The input
Z is 100 ohms..not the 65 ohms of a 3-1000Z......so ur tuned inputs will be out to lunch. The SAME
tube..with 2500 vdc under load of 400ma..and the same 130 w of drive did 600 w pep out. The
4-1000 needs more B+ on it to work correctly. The gain of the 4-1000 goes way up with more B+.
Another tube that will also work is the 4PR-1000A....which is the pulse rated version..rated for 15 kv.
It will drop right in..and function the same as a regular 4-1000.
## IF you are buying used 4-1000s.... make sure you have a provisio that if the tube is no good, you
don’t pay for it. In the old days..back in the 70s... the seller sent the tube..I plugged it in. If I liked what
I saw, I sent a cheque. If not, I sent the tube back. At least get the seller to apply 7.5 vac to the fils for
3 secs.. to make sure you don’t have a smoke bomb. You don’t need a socket, chimney nor blower to do the
2-3 sec smoke bomb test. A soft tube will do like 1100 watts out with 4400 vdc under load. A good one
will do 1900-2000 w out.
## I suspect your 3-1000Z amp only had 3000-3500 vdc on the tube. So even if a good 4-1000 is used, don’t
expect a lot of power from it. IF the input swr is high, power out will drop like a rock on a 4-1000.
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