gdaught6@stanford.edu wrote:
> On 24 Nov 2005 at 9:14, k7fm wrote:
>
>
>>The actual resistance is not material. Filaments are basically,
>>either open or shut. If you measure resistance, they are not open.
>>Many of the inexpensive meters have at least a few tenths of ohms of
>>resistance in the leads and often the connection will add resistance.
>>So, whether it measures 1 ohm or 3 ohms, it means the filament is good
>>and you can move on to the next step in the investigation.
>
>
> That's close. It could have continuity and still be bad (but not
> likely); and remember that the resistance goes up a lot when the
> filament gets hot.
Measuring the heater current would likely prove it one way or another.
It's worth doing tests both in and out of the amp if you can - that
might show some oddity in the connections. Out of the amp, give the tube
a good shake and thump, and invert it in case there's something
intermittent.
I have two 8877s which have intermittent heaters - when the contact is
good, they behave just like others, but positions much off vertical, or
inrush current, can send them open until a tap closes the circuit again.
Steve
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