[Hammarlund] Beware Russian 6SN7

[Carl]

Did you check all the socket grounds, sounds like some corrosion under a lug 
or three.

Carl
KM1H


----- Original Message ----- 
From: "Richard Knoppow" <1oldlens1 at ix.netcom.com>
To: <hammarlund at mailman.qth.net>
Sent: Thursday, December 09, 2010 8:45 PM
Subject: [Hammarlund] Beware Russian 6SN7


>     The 6SN7 in my HQ-129-X measured weak on one side so I
> got a couple of Russian made ones from my tube supplier to
> replace it. They test fine in both my tube testers, an old
> Weston and a TV-7B/U but both have 60hz hum. Note 60hz not
> 120hz so its coming from the heaters somehow. I got another
> 6SN7GTB today, this one made by General Electric, works fine
> no hum. I don't know what the Russians are doing wrong but
> there must be some heater to cathode leakage, both tubes
> were identical.
>     Another instance of a hummy tube was the 6K8 converter.
> Hum modulation on the higher frequencies. I got two
> replacements, I think both old RCA tubes, one a military
> one. One has some hum, the other is perfectly clean. All
> three test good on both testers.
>     I checked the power supply before changing the tubes,
> its almost ripple free. I think the new 6K8 may have
> affected the frequency calibration but have not redone that
> yet.
>
>
> --
> Richard Knoppow
> Los Angeles
> WB6KBL
> dickburk at ix.netcom.com
>
>
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