w5jo at brightok.net
Thu Jun 24 09:43:16 EDT 2004
When I find I have replaced a tube the second time, I go for the schematic
and read voltages and resistances. In all cases this has not been a
problem. It just seems to me that the tube does not last long.
The most recent example is in an HRO 60. Agreed they run the plate with,
what I call, excessive plate voltage---250 volts. I am sure they followed
the tube manufacturers specs on it, but like the Collins situation, they
could have reduced it. The screens are at 85 volts.
----- Original Message -----
From: "Brett gazdzinski" <Brett.gazdzinski at mci.com>
To: "'Discussion of AM Radio'" <amradio at mailman.qth.net>
Sent: Thursday, June 24, 2004 6:55 AM
Subject: RE: [AMRadio] 6BE6
> I don't know.
> But some tubes always test on the weak side on my tube tester, I think
> it's the settings for that tube type being off, as every tube does maybe
> 70% tops.
> Other tube types may get up to 90%...
> Running tubes to hard will cause them to fail, excessive plate voltage,
> screen voltage, plate current.
> Cathode resistors going low, shorted/leaky cathode bypass caps?
> Funny, because I have found the small tubes in receivers to work fine
> At 100 volts or less, no need to strap them.
> The 6C4 in my homebrew receiver (local osc) works fine as low as 30 volts!
> I run it at 105 volts, but don't need to, and above about 75 volts
> gives very little extra output.
> Collins used to advertise they ran the 75s series at 150 volts to reduce
> heat and
> extend the life of the tubes...
> Maybe run a test, and see just what the tubes are running at voltage and
> current wise...
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