[R-390] 3TF7 Ballast Tubes

[Richard W. Solomon]

I have a large quantity of 50 ohm 10 watt Dale Ceramic 10% resistors.
I used one in my R-390A in place of the Ballast Tube and it worked fine.

Anyone need any, I'll mail 3 of them postpaid in the USA for $4.

Address OK on QRZ.com.

73, Dick, W1KSZ


-----Original Message-----
>From: Randy and Sherry Guttery <comcents at bellsouth.net>
>Sent: Feb 19, 2011 8:10 PM
>To: Les Zwiebel WB6ORZ <wb6orz at pacbell.net>
>Cc: R-390 at mailman.qth.net
>Subject: Re: [R-390] 3TF7 Ballast Tubes
>
>I'm sure that I'm going to get shot at for this - but - in 
>the interest of completeness - I'm going to "stick it out 
>there"...
>
>On 2/19/2011 6:31 PM, Les Zwiebel WB6ORZ wrote:
>>      It's comforting to know that the alternative installations probably yield the same amount of heat, so that a plate of kielbasa can be kept warm on top of any 390-A.
>Actually - there is a way to drop that voltage *without* the 
>heat...  I'm not necessarily recommending as a "fix" for 
>R-390As - but it is an "option" for replacing "ballast" 
>tubes / resistors in other radios.   Several of us also 
>restore "vintage" and even "antique" radios.  While ballast 
>tubes weren't commonly used - they are not exactly "rare" 
>either.  And much more common (and much more serious to 
>address) were radios with "curtain burner" power cords - 
>which literally had a third "resistance" wire in the power 
>cord to drop voltage to feed a series filament string.  Once 
>AA5s (who's tube's filaments add up to line voltage) became 
>common - curtain burners weren't made any more - but many 
>examples survive today.  Obviously from the kick-name - no 
>sane person is going to retain a curtain burner cord on a 
>radio that will be used. The most obvious "fix" is to 
>replace the resistance power cord with a power resistor.  
>The problem often run into though - and a reason that wasn't 
>done in the first place --  is because these are usually 
>VERY compact radios - and putting that much "extra" heat 
>inside can be not only hard on the other components - but a 
>fire hazard as well.  Another solution is an "outboard" 
>resistor - mounted in something like a "brick on a leash" 
>power supply box - with adequate ventilation so as to not be 
>a hazard.  A similar solution - one that reduces the heat 
>but is still a "room" issue - is to use a "bucking" 
>transformer.
>
>There is, however - a much more elegant solution - a 
>capacitor.  By correctly calculating the capacitance 
>reactance - a capacitor can be used in place of the ballast 
>tube - and while it will *not* provide any regulation (but 
>then neither does a resistor - or using 2 12BA6s) - it drops 
>the required 12.6 volts with nearly zero heat...  Granted 
>that's a "savings" of a little less than 4 watts - but then 
>again - go hold a 4W incandescent night light in your bare 
>hand for a while...
>
>just my .02  (and donning my flame-proof britches)....
>
>-- 
>randy guttery
>
>A Tender Tale - a page dedicated to those Ships and Crews
>so vital to the United States Silent Service:
>http://tendertale.com
>
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