Re: {Collins} 51S-1

["Charlie T, K3ICH" <pincon@xxxxxxxxx>]

Hello Steve.

Yes, the 7543 is a special low hum version of the 6AU6.  I believe a 6133 is 
also the same tube as the 6AU6.

However, I am curious as to why you found so many tubes that showed shorts. 
This is not a typical failure mode in the 51S-1.  In fact, I have seen 
51S-1's where some of the 6EA8/6U8's showed virtually no emission at all on 
a transconductance tube tester, but the radio still worked.  I know the two 
tube conditions may not be related, but shorted tubes are not as prevalent 
as weak ones.

If it does occur, a filament to cathode short especially in that PTO tube 
will cause a hum in the audio.  It effectively injects the 6.3VAC filament 
signal into the cathode to plate current.

73, Charlie k3ICH


----- Original Message ----- 
From: "Steve Wender" <tobiebw2@xxxxxxxxxxxxx>
To: <collins@xxxxxxxxxxxxx>
Sent: Wednesday, November 19, 2014 11:58 PM
Subject: {Collins} 51S-1


> Hi All,
>
> I am trying to bring a 51S-1 back to life.  I have tested the tubes and 
> found many showing shorts and I replaced them.  The 7543 oscillator tube 
> is also showing a short and I replaced it with a 6AU6.  How bad is that? 
> It seems to work.  Should I bother buying a 7543?  They don't seem too 
> expensive. What are your thoughts?
>
> Thanks,
>
> Steve
> KC5WN
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