[ARC5] When a "Good" Tube, Ain't- AN/ARC-2 Success (long)

[Richard Knoppow]

----- Original Message ----- 
From: "Kenneth G. Gordon" <kgordon2006 at frontier.com>
To: "Glen Zook" <gzook at yahoo.com>
Cc: <Arc5 at mailman.qth.net>
Sent: Friday, March 21, 2014 9:00 AM
Subject: Re: [ARC5] When a "Good" Tube, Ain't- AN/ARC-2 
Success (long)


>> I do have several tube testers but seldom use any of 
>> them.
>
> Likewise here.
>
> Ken W7EKB

     I must disagree about the usefulness of tube testers, 
IMO they can be quite useful although, of course, the final 
test is if the tube works in circuit.
    Oscillator drift with filament voltage variation seems 
to be quite common. For instance, the SP-600- will drift 
quite noticeably with line voltage despite having a 
regulator in the B+. The regulator eliminates drift when the 
RF gain changes but does not affect filament voltage. The 
frequency moves slowly and will come back when line voltage 
comes back. I noticed this first when using a receiver on 
the same line as an electric heater with a thermostat on it. 
Some receivers have ballast tubes to regulate filament 
voltage to sensitive circuits.
    On a tube tester its interesting to lower the filament 
voltage a little and watch the meter. On a good tube the 
indication will usually go _up_ a little and then come down 
while on marginal tubes it just goes down. I am not sure of 
the mechanism of this test but it does seem to work.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com