[Milsurplus] TCS Transmitter: OK Smart People; Why?

[Mike Morrow]

Dave wrote:

> Those familiar with crystal-controlled transmitters of the 40s 
> and 50s will recognized this pentode oscillator circuit:
>
> http://home.netcom.com/~arc5/TCS/TCSXtal.jpg
>
> ...The TCS values bias harder and reduce the screen voltage considerably.
> As a result, crystals like FT-243, CR-1, HC-6 and even large-blank FT-241
> will not reliably function or fail to oscillate altogether.  However- I
> have a couple of pre-war, Collins-made large-blank transmit crystals:
>
> ...
>
> The engineers knew what they were doing and what the result would
> be.  Why did Collins do this?  Were they trying to ensure only
> crystals bought from them would work?

That seems improbable to me, because Collins crystals apparently often did NOT work.  Collins and several contractors made the nt-40068 crystals.  Hamilton manuals also refers to nt-40130.

There is an inherent design problem that can occur even when using the proper crystal unit.  Section 4.6.1.1 in the manual for Collins-made sets discusses CW "keying problems" that can result when USING CRYSTAL CONTROL.  Keying will likely be  unsatisfactory above 20 wpm, and some crystals will cause unsatisfactory keying at any speed.  The manual states that this is inherent to the crystal and is not the fault of the transmitter.

That's a shabby way to address a real problem!

I assume that the uncharacterized problem is sluggish frequency stabilization.  Obviously this is from a deficient Collins design that was easier to just acknowledge than it was to fix.

> Is this why it's easy to find TCS Receiver crystals, but
> Transmitter crystals are scarce?

I find just the opposite.  I've collected TCS crystals for 20 years and have found receiver crystal units to be very rare, compared to transmitting units.

Mike / KK5F