Re: Problem with a Fisher 400

in article 1138519927.923593.206150@xxxxxxxxxxxxxxxxxxxxxxxxxxxx, fourkids
at dearly@xxxxxxxxxxxx wrote on 1/29/06 2:32 AM:

> Well, I hope you guys are still out there....
>
> I have added the 10 ohm resistors...happened to have 4 precision 10
> ohms laying around.
>
> And it turned out that the 5.6k ohm resistor I referenced earlier had
> already been doubled, so I modified it again for a theoretical value of
> 1.3k ohm. This brought my bias voltage down to -20.5 volts, measured
> at each tube.
>
> The voltage over the 10 ohms is .25 to .26, except for one tube: which
> measures .1 volts...I appear to have a bad tube?
>
> OK so my problem: the tubes are still running WAY hot...they are very
> hot in just a couple of minutes. Now maybe I don't understand how hot
> they are supposed to be, but i have nothing to compare it to.
>
> I have already ordered a new quad of 7868EH tubes...should get them in
> a couple of days. The tubes that are in the set now are all
> "Realistic" tubes...not the greatest brand, and probably all bad having
> been run hot for some time.
>
> Anyway, any further wisdom would be greately appreciated.
>
> Dave Early
> Colorado
>



Sounds like you've got a bad tube. Swap it in another position and see if
is still too low.

Tubes are supposed to run very hot. But not so hot that the plates glow
dull orange. Look at them in a darkened room.

Note that most Realistic tubes - which were made by other companies and
banded Realistic - have a lifetime warranty, which they still honor!

.

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