[R-390] 3TF7 replacement from Germany

[frankshughes at aim.com]

http://www.schmid-mainz.de/Flyer.pdf  (Dr. Kurt Schmid, DH3PJ)


I also use these wonderful devices from the professor in my 390A and 390.


73 KJ4OLL





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To: r-390 <r-390 at mailman.qth.net>
Sent: Sat, Feb 19, 2011 7:01 am
Subject: R-390 Digest, Vol 82, Issue 20


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Today's Topics:

   1. Dead Horse Beat mode - ON (Paul Galpin)
   2. Re: 3TF7 Ballast Tubes (Drew P.)


----------------------------------------------------------------------

Message: 1
Date: Sat, 19 Feb 2011 15:38:53 +0200
From: "Paul Galpin" <galpinp at absamail.co.za>
Subject: [R-390] Dead Horse Beat mode - ON
To: <r-390 at mailman.qth.net>
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I was lucky enough to get two R390s, each with its 3TF7 apparently working.

These were tested by monitoring the output current from a variable Bench supply 
from about 2 volts to the maximum rating. As
expected, the current rose with the voltage to about 9V, and then stayed 
constant up to about 20V then started going up again.
Stopped immediately this happened.

For one of them, the constant current section was 0.32A, for the other 0.37A. 
The high current one got retired to the emergencies
only box, and was replaced by a 47R resistor.

So, for any voltage between 9 and 20 across the barretter, the current is 
constant. In the R390A, the voltage is a nominal 12.6.
Since the same current flows in the 2x 6BA6 oscillators, their heater current is 
constant.

What this proves, though, is that your 3TF7 may be working, stabilising heater 
current, but it might not be the correct value of
current!  FWIW, I've seen the same stabilising effect in filament globes, but 
never a convenient value.

Please, don't anyone say "but it's different with AC"!

Paul Galpin
ZS2PG



------------------------------

Message: 2
Date: Sat, 19 Feb 2011 08:14:13 -0800 (PST)
From: "Drew P." <drewrailleur807 at yahoo.com>
Subject: Re: [R-390] 3TF7 Ballast Tubes
To: r-390 at mailman.qth.net
Message-ID: <769635.84523.qm at web38505.mail.mud.yahoo.com>
Content-Type: text/plain; charset=us-ascii

Ben Loper ignited yet another grand reversal of Equine Entropy when he 
proclaimed:

> I came across some NOS 3TF7 Amperite tubes. 
> Should I make an offer on 
> > them
> > or is the conventional wisdom to replace them with a
> 12BA6 tube

Once again, we all benefit greatly from Wei-Li's tireless labors of distillation 
and compilation of the wisdom coursing through this forum over the years, in his 
masterpiece "Pearls of Wisdom".  This will be found at r-390A.net.  Following is 
the direct link. 

http://r-390a.net/Pearls/index.htm

Once there, click on "Ballast Tubes".  You will learn more than you ever wanted 
to know about ballastubes and all other aspects of our beloved R-390x series.

Drew




      


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End of R-390 Digest, Vol 82, Issue 20
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