[R-390] Ballast Tubes

Sat Jul 3 10:14:48 EDT 2004

Hi

There is mention of the ballast tube in the Collins reports on the 
radio. They did not seem to feel it was a major part of the radio. The 
report more or less says it's unclear weather it was needed or not.

If your line voltage goes down to 95 volts then the tube will help. 
However the rest of the radio may not be doing very well at 95 volts.

The ballast was set up for about a 110 volt nominal line voltage and 
regulation over a +/- 5 to +/- 10% range. It seems to work fairly well 
from 105 to about 115 VAC. Past that it starts to fall off in 
regulation. I doubt it will do much for a 122 to 125 volt change.

Since it's a thermal part it will do it's thing on the order of 
seconds. The tube works about the same way. Very fast changes will not 
affect things but sags that last for > 10 seconds are an issue.

The only significant effect on the tube from the filament voltage is a 
small variation in transductance when the tube cools off. I suppose the 
geometry may change when the tube cools and thus the capacitances but 
if they do it's not a documented effect. Since oscillators limit cycle 
based on gain the frequency of an oscillator will change a bit when the 
gain changes. A receiving tube with the filament up to temperature has 
such a small variation in transductance that the change even in a VFO 
should be nearly impossible to detect. The B+ change may on the rest of 
the stuff in the radio probably does more to move things around as long 
as the filaments are up to temperature.

Bottom line - ballast tubes are an optional part ...

	Take Care!

		Bob Camp
		KB8TQ

On Jul 3, 2004, at 8:52 AM, Barry Hauser wrote:

> I've read most all the posts over the years, but still don't know.
>
> The general word -- consistent with Chuck's account -- is that the 
> ballast
> tube was needed for military and naval installations where power sags 
> were
> common and extreme.
>
> I've monitored the power line voltages here.  Basic voltage levels run 
> on
> the high side -- about 126 -- lower on average during the summer, when
> brownouts can drive it down to as low as 95 something.  Due to cycling 
> AC,
> electric dryers, refrigerators, etc. I see a fluctuation of about 3-4 
> volts
> regularly on a fairly rapid basis -- on the order of seconds.  The 
> meter
> will read 125 for a few seconds, drop to 123 for a second or two, pop 
> back
> up, etc and that will continue.
>
> Is this the type of fluctuation/sag that the ballast tube would dampen 
> out?
>
> As the 6BA6 filaments are resistive heaters, don't they have some 
> damping
> characteristics of their own?  There may also be some latency and 
> damping in
> the transformer, any capacitors, etc.  Would there even be a 
> fluctuation in
> the heat output in those two tubes without benefit of a ballast?
>
> Either way, under what circumstances does a ballast tube smoothen 
> things
> out?
>
> With all the past threads, I don't recall ever reading anything on 
> this.
>
> Barry
>
>
>
> ----- Original Message -----
> From: "Chuck Ochs" <jmerritt2 at capecod.net>
> To: "Bob Camp" <ham at cq.nu>; "Forrest Myers" <femyers01 at bellsouth.net>
> Cc: "r-390" <r-390 at mailman.qth.net>
> Sent: Friday, July 02, 2004 9:49 PM
> Subject: Re: [R-390] Ballast Tubes
>
>
>> One must keep in mind that the R-390 was a "general purpose" receiver,
> which
>> saw extensive shipboard use by the Navy during it's heyday. Power 
>> aboard
>> ships tends to be anything but stable. I know. I was a shipboard
> electrician
>> on an LST during that nasty little war back in the sixties. We had 
>> these
>> radios on board, as did nearly every other ship in the Navy at that 
>> time.
>> Using a ballast tube in the oscillator filament circuits was, at the 
>> time,
> a
>> clever way to maintain stability during all those periods where the 
>> line
>> voltage sagged from operating such heavy electrical loads as gun 
>> turrets.
>> The regulation of ships generators of the period was very slow by 
>> today's
>> standards. IMHO, there is little ( probably NO) need for this 
>> regulation
>> scheme given a radio running on modern "shore power".
>> A few years ago, the ballast on my VERY early R-390 died, and I simply
>> replaced it with a resistor. I did not notice any change in operation
>> whatsoever. It has been running this way for several years now.
>> Chuck N1LNH
>>
>> ----- Original Message -----
>> From: "Bob Camp" <ham at cq.nu>
>> To: "Forrest Myers" <femyers01 at bellsouth.net>
>> Cc: "r-390" <r-390 at mailman.qth.net>
>> Sent: Friday, July 02, 2004 7:24 PM
>> Subject: Re: [R-390] Ballast Tubes
>>
>>
>>> Hi
>>>
>>>  From what's been said here they are still available for something in
>>> the $30 to $60 range. Not quite a price that would encourage me to 
>>> grab
>>> a couple dozen.
>>>
>>> One modification that has not been mentioned as part of this thread 
>>> on
>>> ballast tubes is probably the oldest of the batch. Grab a plug that
>>> looks like a tube base and wire a resistor to it. The value needs to 
>>> be
>>> right to get the filaments to run right but that's about all there is
>>> to it. It pulls no more power than the ballast tube and it's a 
>>> totally
>>> reversible mod. When the bottom drops out of the ballast tube market
>>> you can plug one of those two dollar ballast tubes in there and 
>>> nobody
>>> will ever know what you did.
>>>
>>> Somehow I doubt that ballast tubes will get cheap again unless there 
>>> is
>>> a Chinese factory we know nothing about making them by the ton. They
>>> are not terribly high tech so it is a possibility. There may be a 
>>> long
>>> forgotten warehouse in South East Asia with a few hundred thousand of
>>> them sitting on the shelves - stranger things have happened.
>>>
>>> If it was my radio I think I would do one of the re-wire mods to
>>> eliminate the beast. The filaments would be un-regulated but there
>>> would be less heat and no additional stuff inside the cabinet.
>>>
>>> The function of the ballast tube in the radio is questionable. With
>>> modern wall voltages the original ballast is running at best on the
>>> edge and at worst over the edge of it's ratings. It's not doing a 
>>> real
>>> good job of stabilizing the filament voltages on a radio plugged into
>>> 120 to 125 VAC. Fortunately for all of us the filament voltage has a
>>> pretty small impact on the tubes in the radio. It's my belief that 
>>> the
>>> problem comes in on the low voltage end of the equation. If you try a
>>> radio on 100 VAC then the ballast is probably a good idea.  Don't see
>>> much of that coming out of the wall outlets around here ....
>>>
>>> Take Care!
>>>
>>> Bob Camp
>>> KB8TQ
>>>
>>>
>>>
>>>
>>>
>>> On Jul 2, 2004, at 4:17 PM, Forrest Myers wrote:
>>>
>>>> Hello All,
>>>>  Came into the shack and found my r-390a dead. A quick check found 
>>>> the
>>>> ballast tube was shot. I've seen a lot going by on ballast tubes 
>>>> these
>>>> past
>>>> few days but am interested in getting a real ballast tube, if I can
>>>> afford
>>>> it, back into the radio.
>>>>  Anyone have a source for a 3TF7?
>>>>  If I must, I'll put in a mod to get around the 3TF7 but would 
>>>> rather
>>>> not.
>>>>
>>>> Thanks,
>>>> Forrest Myers
>>>> AG4ND
>>>>
>>>> -------------------------------------------------------------------
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>>>>
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