>
>A friend of mine is looking at purchasing a used Titan from an estate sale.
>It's not been used in a while. The seller claimed to have recently tested
>it at 1KW out. He did state that there appeared to be a problem on 15
meters.
>I did notice that the factory installed collar to keep one from turning the
>band switch to 10M had never been moved from the blocking position.
>
>When first turned on the amp blew the PS fuses (think they were not slow
>blow).
// I worked on a 425 that suffered from this problem. I did the
Funderberg gold-sputter test on the 3CX800A7s, Both tested positive for
loose gold meltballs. By tapping firmly on the tops of the anode cap
with the flat side of a 4oz ballpeen hammer, I was able to safely park
the meltballs in the bases of the tubes. Leakage was reduced in both
tubes to c. 5uA at +5kV. To reduce the chance of another parasite
evaporating more gold plating from the grids, I installed lower
VHF-Rp/lower VHF-Q parasitic suppressors. The only thing that these
3CX800A7s would no longer do is to operate inverted in an acrobatic
aeroplane.
- One of my customers had a similar problem. He installed lower VHF-Q
suppressors and it apparently cured the problem that Ten-Tec had been
unsuccessful at fixing. He happily wrote to Ten-Tec and told him that
he had been successful with the type of suppressors described in the
October, 1988 *QST* article on parasites. Ten-Tec said that they had
tried the suppressors described in the article, but they got hot during
10m operation, so they abandoned their use. Naturally, VHF suppressors
that do not get hot at 28MHz, aren't likely to be doing the needed job
adequately at VHF.
> When it started up without blowing the fuses, and it came off the 3
>minute warm-up, it showed .3 amps plate current without being keyed. The
>amp was opened up and tubes pulled, blown out, visually inspected and some
>corrosion on the plate cap connections was removed. When turned back on, amp
>starts up normally (like mine), HV seems right and it seems to be keying
>correctly in QSK with a TT Omni 6 with the amp feeding a dummy load.
>
>The problem - no output with 20-30 watts in, no movement of the grid current
>meter or plate current meter, no dip in HV supply when keyed in CW. Input
>SWR on 20 was 2 (mine is 1.1-1.2) .
>
>I've set the amp down next to mine and compared the two. Other than a few
>component changes (mine's probably a few years older), we could not see any
>significant differences. The amp did not perform any differently on my PS
>than it did on it's own (and yes - my PS still works).
>
>Is there any easy way to tell if the tubes are shot?
>
// Surely - use a high-potential tester to see whats up. A hammering
could save ur wallet from taking a hammering.
good luck, Ralph.
>Can the amp be run with just one tube at a time to test each tube?
>
>How much risk am I taking if I try my good tubes in his amp???
>
>Any ideas of what else to look for?
>
>I've owned about 10 different used amps with various tubes and never had any
>significant trouble. Can't say that for the numerous used HF radios that
>I've bought!
>
>73
>Ralph N4TG
>ralry2001@aol.com
>
>--
>FAQ on WWW: http://www.contesting.com/FAQ/amps
>Submissions: amps@contesting.com
>Administrative requests: amps-REQUEST@contesting.com
>Problems: owner-amps@contesting.com
>
>
- R. L. Measures, 805.386.3734, AG6K, www.vcnet.com/measures.
end
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