Hi, John H, Skip and David F,
Thanks for your collective inputs regarding the TL911.
The TL911 does use the tubes in the gounded grid configuration and has 10
ohm resistors in the cathode leads.
I am also sceptical about the 2KW PEP max input rating but did not intend
to run the amp anywhere near this level - our legal limit is 400W PEP
output ????.
I have never actually had this amp on the air. It was obtained via several
parties and included five supposedly new (boxed) 6JE6s. The first job was
to remove the old tubes and check the circuit for any obvious signs of
component failure. Next all operating voltages were checked and all seemed
ok. The "new" tubes were inserted and the set up procedure carried out.
This mainly consists of setting the idle current of each tube to 15mA. The
maximum I could get, and this was from one tube only, was about 12mA the
rest were all below 10.
I decided to apply a little RF and see what kind of output I would get -
nothing - one tube had a grid to cathode short. I eventually inserted each
tube individually, including the old ones, to see if I could find five
tubes which would give the recommended idle current- again none met this. I
selected 5 tubes which gave me approximately the same idle current with
more or less the same grid bias and tried again. With a dummy load on the
output and an in line wattmeter between rig and
amp I applied drive until, at about 150 watts output from the amp, there
was a spectacular flash from within one of the tubes a dimming of shack
lights and howls of complaint from the TV watchers upstairs. At this point
hurling the thing through the shack window was looking like an attractive
alternative!!.
A colleague of mine, Greg ZS5K, suggested I try this forum for advice and
so far the response has been great.
Rather a long story but maybe some one will note whether I have overlooked
something very basic.
I have noted the suggestions regarding alternative tubes and will scout
around and see what I can find. Unfortunately (or fortunately ??) TV was
only introduced into this country in the 70s and all sets were solid state
so the only place your likely to find a TV sweep tube is in a science
museum.
Thanks again to everyone who has responded with suggestion and advice.
Eric ZS5EWM
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