[Amps] 8877 hipot

[TexasRF at aol.com]

In a message dated 10/11/2006 11:23:30 A.M. Central Daylight Time,  
w8ji at 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