[Collins] Collins S line help?

[Dr.Gerald Johnson]

Changes in S-Line receivers have been subtle, often more in front panel 
controls than in schematic specifics.

The S-1 was fundamental, the S-2 was exactly the same (in transmitter and 
receiver) except the S-2 had the second crystal board. There was a kit to 
make that conversion in the field.

Later receivers had the dual time constant AVC and a modified gain 
distribution. Later receivers had plug in filters instead of solder in filters. The 
use of plastic cased filters in early S3B lead to noise modulated by hum from 
the magnetic field of the power transformers. That was cured by a mu-metal 
shield over the filters. The 6EA8 provided a bit better mixer noise and signal 
handling performance over the 6U8. The use of plug in filters allowed several 
options for CW and RTTY filtering. CW filters were offered in bandwidths of 
200, 300, and 500 Hz. The 500 Hz filter was mechanical, the narrower filters 
were crystal filters that prevented using the mu-metal shield because of their 
size. My mu-metal shield that I made shields only the plastic filter.

I think it was the S-3 that added the AVC change and made provision for a 
different BFO for CW. The S-3A was a 3 with the second crystal board.

I know the S-3B/C (C having the second crystal board) had a front panel 
tunable BFO option that was handy for using the CW filter on narrow shift 
RTTY though I found it clumsy. Later production runs of 3B/C had changed 
signal levels at the mixers to improve dynamic range and the mu metal shield 
on the mechanical filters to reduce noise. The Q-multiplier notch filter is 
definitely a handy tool. I've made several modifications to my S-3B to 
significantly improve strong signal handling and to make the variable BFO 
feature more handy to use.

In transmitters the 32S-1 and 32S-2 are identical with the addition of the 
second crystal board in the 2. The 32S-3 and 3A, I think, have the same 
relationship.

The stock 32S-1/2 has a double diode balanced modulator for which there is 
a factory service bulletin making it into a four diode circuit for better carrier 
suppression and better longevity of that suppression adjustment. The 1/2 
generate CW by keying the 1800 Hz side tone and passing that through the 
transmitter audio. If the carrier suppression isn't quite perfect, there is the 
probability of transmitting the carrier 1800 Hz from the desired output. Unless 
one wishes to copy CW at 1800 Hz (most prefer 400 to 800 Hz) this makes the 
single dial transceive mode of operation impractical on CW. Spotting the 
transmit frequency to the received signal requires turning the operation 
mode switch to spot.

The 32S-3/3A create CW by passing carrier around the balanced modulator 
so the side tone generator is only used to allow keying monitor. There is a 
separate spotting switch for setting transmitter to receiver frequency.

There is little different in the transmitters for use on SSB, though the later 
production units of the 3/3A will have different PA neutralization components 
with wider range allowing the use of 6146B and late 6146W PA tubes.

One can't determine production sequence by serial number because S-line 
serial numbers were issued in random order, by edict from Art Collins. 
Sometimes one can determine vintage by MCN (manufacturing change 
number) or by looking for date codes on tubes, crystals, and electrolytic 
capacitors or subtle schematic changes. Changes in model nomenclature 
and change from winged to round emblem do make markers for vintage, 
somewhat defeating Art's edict. And many of the changes came from other 
edicts, such as styling changes that came down from "above."

I've not looked at the used equipment list to the end at Burghardt lately, but 
they have had some S-line crystals (mixed in others from Collins). Surplus Sales 
in Nebraska has listed S-line crystals. Good crystal makers can make new 
crystals to work in the S-line such as International Crystal in Oklahoma City. I 
don't know where or what spare parts are in Australia.

73, Jerry, K0CQ, Technical Advisor to the CRA

-- 
Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.