[R-390] Fw: 3TF7 Ballast Tubes

[Les Locklear]

Ah, my favorite dead horse subject..................

Just about every 3TF7 I ever looked closely at looked as though some eight year old kids made those plates and filaments. Crooked some stretched, others not, and, yes the phenomena Roy mentioned. That's the reason all of the ones I used had either a 39 or 40 ohm resistor in place of the Kielballast Tube. I never tried the 12BA6 mod, but plenty of folks have and it is as simple as it gets. 

One thing I didn't ever notice with the resistor in place, when a light switch was flipped on somewhere else in the house, the frequency didn't change.............<snicker> That is a snarky response to an earlier issue of HSN (Hollow State News), and amazingly enough I could still hear that elusive heterodyne from Pitcairn Island. YMMV

Les Locklear
Gulfport, Ms.
DX'ing Since '57








----- Original Message ----- 
From: Roy Morgan 
To: R-390 List Serve 
Sent: Friday, February 18, 2011 8:43 PM
Subject: Re: [R-390] 3TF7 Ballast Tubes


Ballast Tube Folks,

<Dead Horse Beat Mode ON>

I recently unearthed a Boonton Model 250A RX-meter and poked around  
inside with a voltmeter.  It uses a 6H-6 ballast tube to feed the  
filaments of two subminiature oscillator tubes.  The filament voltage  
should be 6.3 +/- 0.3 volts.  It was 7.7 volts.

The ballast tube was operating, but one of the four segments of the  
filament was glowing quite strongly, with the other three segments  
dark.  Not having a spare 6H-6 handy, I tried a 6V6, 6H6, and settled  
on a 6AG7, which gave 6.6 volts for the filament.

The (next to) bottom line is:  even if the ballast tube is operating,  
it might not be working right. Measure the filament voltage(s) on the  
supplied tube(s).

<Dead Horse Beat Mode OFF>


Roy

Roy Morgan
k1lky at earthlink.net
K1LKY Since 1958 - Keep 'em Glowing!



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