[Collins] 30L-1 amp DAHL transformer question

[Dr. Gerald N. Johnson]

One reason might have been to keep the plate voltage in reason with a 
125/250 volt line where the original winding was for 115/230, though the 
best place for that change would be the primary winding to control the 
heater winding also.

There are few tubes that will go in the box, its very compact. The only 
ones that I know will sort of fit have more power capability, the T-200 
or 572B.

My guess is that the lower voltage is partly for line voltage 
compensation (though its not the optimum place for that) and for longer 
tube life running full plate current RTTY. Or maybe a 30L-1 was being 
applied as a power source for a plasma generator running full tilt and 
needed the lower voltage to keep from replacing tubes too often.

Then maybe one day Peter Dahl (a true one man shop) had an emergency 
order for a 30L-1 plate transformer but only had enough copper to wind 
the 550 volt secondary and delivered it that way. Maybe he had that 
emergency order and for the high voltage secondary only had one wire 
size larger and so only 550 volts of turns would fit in the core but the 
DC voltage was close to the original because the larger wire reduced the 
resistive drop and fewer turns reduced the inductive drop of that 
winding. The voltage double rectifier is not a nice sinewave current 
load on a transformer winding, it has big current spikes very near the 
peak voltage and zero current for nearly half a cycle so winding 
impedance has a serious effect on the DC load voltage.

Then its possible different production runs and original transformer 
vendors supplied the two different voltages or a production change was 
made that wasn't reflected in the manual (that was true of the power 
transformer in the 75S receivers over the years, some changes got to the 
manual, some didn't) or 550 vs 650 was a fat finger typo not detected in 
the transformer specifications along the way. I've found several where a 
draftsman slipped a digit on his cricket (Leroy lettering machine) and 
its been in the schematics ever since. I wish for access to the original 
bills of material and a full set of component specifications with 
history of revisions to know the revisions better. A collection of 
change notices would be handy that way too. But I don't know the 
documents exist even for insiders, though there's a slight chance they 
are in the special collections in university library, probably Iowa City.

I'm good at guessing, but I don't have documentation to prove any ideas. 
I thought I might have had a Peter Dahl printed transformer catalog, but 
its not in my filing system where I expected to find it, but much isn't 
filed around here and moving hasn't helped any. I did find a couple 
Harbach era lists in this computer, but nothing older though the windoze 
search didn't turn up those .pdf files either.

73, Jerry, K0CQ, Technical Adviser to the Collins Radio Association

On 6/7/2011 9:25 AM, Bruce H McIntosh wrote:
> On Tue, 2011-06-07 at 08:57 -0500, Dr. Gerald N. Johnson wrote:
>> 30L-1 always had silicon rectifiers.
>>
> Ah, ok, so that speculation is out.  Does lowering voltage to extend
> tube life make sense?  Or was it maybe for a rebuild using different
> tubes entirely?  The world may never know. :)
>