[Collins] Collins military S line

[Carl]

>
> On 7/7/2014 7:39 PM, Carl wrote:
>> If I had a full run of the tube manual into the 70's Id use a 6EH7 RF,
>> 6ES8 as a Pullen mixer with AGC, 6DC6's in the IF and 6ES8's in the 2nd
>> mixer and PD. Separate AGC loops would handle the different tube curves.
>> This model would have the highest
>
> Many a radio has "delayed" AGC to the RF stage, essentially a voltage 
> divider so it sees less AGC voltage. Probably from use of remote cutoff 
> tubes in the IF stages and a semi remote or sharp cutoff for the RF stage. 
> Adding some threshold effect would enhance the AGC qualities but wreck the 
> linearity of the S-meter reading, just like putting a sharp cutoff RF 
> stage in most receivers.

** Collins uses a lot of sharp cutoff 6AK5's in the RF stage and the poor 
overload performance shows. Of course Hallicrafters followed suit with the 
6CB6 and continued with the 6DC6.
Some sharp cutoff pentodes can provide pseudo semi cutoff by varying screen 
voltage with plate current and reducing gain. Poor mans AGC without having 
to design an adequate circuit.

The old saying was if you want a frequency meter buy a Collins; if you want 
to hear them buy a National. Others added that if you wanted an automatic 
band scanner buy a Hallicrafters.




>>
>> If I was stuck with tubes and circuits available during the different S
>> Line production Id probably choose the 6BZ6 for RF, 12AT7's as straight
>> mixers for early models then upgrade as better choices became available.
>> Drake was smart to continually update the R4 series.
>
> I don't know about tube availability, but I suspect early post war (WW II) 
> designs were encouraged to use surplus tubes because they were available 
> or on hand in large quantities and very cheap. Heathkit got into 
> electronics that way with surplus 5BP1 CRTs and 6SN7s. I expect Collins 
> had considerable quantities of tubes used in the ARC2 and other radios 
> built during the war, which was a period of great manufacturing expansion 
> for Collins. I don't know that to be a fact, though my first boss, Lloyd 
> Winter (badge number 5) told me that in the 50s they had to redesign all 
> the early post war broadcast transmitters because they had used surplus 
> vernier reduction dials but had used up all the supply and couldn't get 
> them any more. I would wonder if there wasn't a machinist in the place 
> that could have made them in the quantities needed or specials couldn't be 
> bought. Probably the cost was high. By then the style probably needed to 
> be updated and Art did like to see style changes, even when they negated 
> his demands for random S-line serial numbers. He didn't always keep his 
> thoughts connected from one week to the next it would appear.

** National built large quantities of the same receivers from before WW2 
with minimal changes. HRO, various variants of the NC-100, 101 and 200 plus 
numerous strictly military designs of all octal tubes. The 1946 NC-240D was 
part NC-200 and part new 240D until 1947 to 49 and all octal tubes as was 
the NC-173, NC-183, NC-57, etc.The HRO-60 was produced 1952-68 and used 
octals everywhere except the 4 miniatures in the front end and a 0A2. Ive no 
idea when they ran out of surplus tubes but they ran the octal since 1936. 
Hallicrafters ran octals into the 60's in some of their lower end sets.


>>
>> In all cases the B+ would be no more than 150V except the audio amp
>> which would be a 6V6 or 6BQ5/EL84.
>
> I have thought it would have been nice thermally to have had a couple 
> small (like 6AQ5 or 6AK6) tubes in pushpull so they could be run class AB 
> or class B and have a significantly lower idling current than the single 
> ended amps running class A.

** You dont wnt to run PP beam tetrodes or pentodes in Class B. It is  AB1 
for low distortion and AB2 for more peak power....and distortion as used in 
the 32V series, Johnson, Heathkit, and others. The 6AK6 was an obsolete 
pentode with little changed since the 41 of 1932.


>   Costs a tube and a socket, and an extra wire on the output transformer 
> plus s phase splitter and a couple extra coupling components.

** The phase splitter could also be the audio driver and a simple 6SJ7, it 
saves the cost of a 6SN7 and extra filament current. Just dont let the 
output stage draw grid current. There are comparable tubes right into 
Compactrons

The audio quality and the heat dissipation
> would have been detectably better by ear and hot finger.

** If you want heat grab a 6F6 in the early Super Pros, driver and PP output 
all inefficient triode connected. Or a 6L6 or 4 digit versions, and 5X4; all 
guaranteed to remove skin.

 Carl
 KM1H


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