[R-390] Ballast Tube Thread

[Bob Camp]

Hi

In defense of what they did it is pretty obvious that these radios got 
used on supply voltages that went well below 100 volts for significant 
periods of time. In that case the ballast tube would have done a lot of 
good.

It is very interesting that they pulled a number of other things out of 
the radio "based on cost considerations"  but still had the very 
expensive ballast in there. The main things they talk about failing 
against the original specification are the ultimate selectivity and 
audio numbers. It seems that the audio specification was changed (or at 
least reinterpreted) late in the program. They seem to have just plain 
missed the selectivity though. Given the ballast tube's location 
swapping it out for another IF can should have been a possibility.

Sure would be nice to have the meeting notes from the monthly program 
reviews. I'll bet they had a *lot* of fun trying to work all this stuff 
out.

	Take Care!

		Bob Camp
		KB8TQ



On Jul 4, 2004, at 12:05 PM, Barry Hauser wrote:

> Ah-hah!  A classical mid-20th century example of CYA engineering 
> philosophy.
>
> Hmmm.. better stock up on some more ballast tubes so my A will be 
> properly
> C'ed.
>
> Uh-oh .. from the notes of the intrepid Three-Star General Torment:  
> "Letsee
> now, the factor of tube aging -- of the 6BA6's -- was unknown, so you 
> guys
> worked with Amperite to come up with a new custom ballast -- with even 
> less
> aging history -- and threw that into the mix?  I see."
>
> Which shows to go you -- even when you think you have your A's well 
> C'ed
> ....
>
> Not to mention that we need to keep this thread going 'til it goes 
> bang --
> it being the 4th and all.  BTW -- anybody have some burnt out ballasts 
> to
> blow up tonight -- assuming they're loaded with hydrogen, not helium.
>
> Barry
>
> PS -- As I write this the History Channel is playing "The Crossing" 
> with
> Jeff Daniels as G. Washington.  Am I mistaken, or didn't he play 
> opposite
> Jim Carey in "Dumb and Dumber"?  Either (a) I don't know how I feel 
> about
> that, being rather fond of the original George and/or (b) Jeff D. has 
> quite
> a range and may qualify as the worlds most underrated actor -- tho' I
> wouldn't mind trading paychecks.
>
>
>
> ----- Original Message -----
> From: "JamesMiller" <jmiller1706 at cfl.rr.com>
> To: <r-390 at mailman.qth.net>
> Sent: Sunday, July 04, 2004 11:11 AM
> Subject: Re: [R-390] Ballast Tube Thread
>
>
>>> From page 15 section 4.2.2.1 AC Power Units of Final Engineering 
>>> Report
> on
>> Radio Receivers R-389 and R-390 Sept. 15, 1953:
>>
>> http://www.r-390a.net/faq-eng-r3.pdf
>>
>> "The filament regulation circuit for the oscillator filaments should 
>> also
> be
>> covered here although this ballast tube is mounted on the IF unit.
>> Considerable work was done with Amperite Corp. in designing this 
>> special
>> ballast tube which feeds a constant 300 mils to the two 6 volt 300 mil
>> oscillator tubes used in the VFO and BFO. These three tubes are 
>> connected
> in
>> series across the 26 volt filament supply. The ballast tube (3TF7)
> operates
>> on a current of 290 to 330 mils and holds this current within ±10 
>> mils for
>> input voltage variations of ±15%. This reduced the 15% variation to
>> approximately 3%. There is some question if a filament regulator is
>> necessary in these receivers since the oscillators are very good even
>> without regulation. However, since the stability was a big factor in 
>> this
>> design and since the factor of tube aging was not known, the 
>> regulator was
>> included."
>>
>>
>>
>>
>>
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>
>
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