In a message dated 10/11/2006 11:23:30 A.M. Central Daylight Time,
w8ji@w8ji.com writes:
>I just bought a 8877 on Ebay advertised as new...I just
>tested it on my
> hipot and found it draws 40 microamps(Cold) at
> 4000vdc...Comments from amps
> guys? Guy says to return and he`ll refund my money if it`s
> not DOA!
> Wow,screwed Huh? Jim K7RDX..
Hi All,
A couple of years ago a friend gave me a never used still in the box 8877
with a date code from the late 80's. A quick check showed internal leakage
starting with only 1600vdc with the tube cold.
After running the filament only with a fan blowing on the tube for cooling
for about a week, the leakage was improved to about 3000vdc before seeing
current. I plugged the tube in a 2m amplifier and it blew the plate fuse as
soon
as hv was switched on. I reconnected the primary of the plate transformer to
120vac instead of 240vac for half plate voltage. I ran the tube at idle
current for a couple more days like that and retested the leakage. It had
improved
to about 6kv so I returned the power supply to full voltage.
At this point the tube blew another plate fuse that was replaced. I have
since operated the amplifier at full rated power on many occasions with no
problems at all. If I were more ambitious I would pull the tube and check the
leakage again but the time never seems available.
So, I would say that yes, your tube has a defect. But, it may well be quite
usable with a bit of TLC in bringing it up to power.
73,
Gerald K5GW
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