[Collins] Collins archives and 4A transmitter

[Dr. Gerald N. Johnson]

While searching for copies of 30s vintage Collins Signal, I stumbled
onto an archive in special collections at the University of Iowa. 42
boxes, including blue prints and internal reports as well as apparently
equipment manuals for many decades. It could be a gold mine of vintage
equipment information, though the several boxes about the C System
probably won't improve anything today.
http://www.lib.uiowa.edu/spec-
coll/msc/ToMsC850/MsC814/CollinsRadioCompanyRecords.html Its something
that will have to be viewed personally, the contents have not been
scanned and probably they won't copy for any price.

The reason I was looking was because I was at the Pavek Museum of
Broadcasting in the twin cities last week and they have an early model
of the 4A transmitter, with bakelite panel. And it has no provisions for
shutting down the crystal oscillator on receive. Stephen Raymer, the
managing director, asked my why that was. I sent him the following
yesterday? Are there other opinions about that?


> I looked for a schematic of the 4a, but all I found was a description
> in
> the August 1933 Collins Signal that is on line at the CCA web site
> archives. In the March 1933 issue they had a more extensive article
> with
> schematic on the 32A/B which used four tubes and it had the same
> characteristic of keeping the oscillator on all the time. Then in the
> December 1934 issue they reported the 32A/B (B for AM or CW, A for CW
> only) had a new capability. "Provision is made for switching off the
> crystal oscillator to permit reception on the crystal frequency." So
> they saw that as an innovation.
> 
> Thinking back to my novice days in 1955, where crystal control was
> required, we didn't expect an answer to our CQ on our frequency, we
> tuned the entire novice band looking for that answer. Similarly on 2m
> in
> the early 1960s where the standard was crystal control, we tuned. It
> was
> unusual (but not impossible) in either case to get an answer on our
> own
> frequency. So I'm guessing that in 1933 it was even less likely to get
> an answer that stayed on your CQ frequency so that leaving the
> oscillator on wasn't a big problem and probably helped keep the
> receiver
> on frequency. That was before the stability of the HRO receiver or the
> self controlled transmitter.
> 
> Then too, I suspect that oscillator tube capable of a few watts out
> was
> running lots of crystal current and there was drift if it was shut
> down
> from heating the quartz, even that big hunk of quartz. So when shut
> down
> for receiving, it drifted noticeably when powered back up for
> transmitting, so it performed best when left on.
> 
> In the 32A/B circuit, there is a meter switched between the PA cathode
> and the sum of the oscillator and buffer cathodes for tuning and
> neutralizing the buffer and PA. It was switched with a DPDT switch
> where
> one pole moved the meter (the other side grounded) and the other
> closed
> the circuit with the meter out. Simply replacing that switch with a
> center off switch would allow turning the oscillator off for
> receiving,
> a simple mod. But the 4A doesn't have that provision with one meter
> switched between the PA grid and cathode (or plate, can't be sure
> without a schematic).
> 
> The later picture of the 32A shows one more switch on the power supply
> section. Its not good enough to read the labels.
> 
> Your 4A with the bakelite panel is definitely an early one. Its
> possible
> later 4A had a switch to kill the oscillator too, but I have nothing
> to
> prove that at this point. I suppose one could turn the primary power
> off, but the 80 and 83 are slow to heat (probably a lot slower than
> the
> RF tubes) and that would slow the response time.
> 
> 73, Jerry, K0CQ
> 
> 
-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer