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

[WA5VGO]

Feedback is established by the 250pF and 50pF capacitors in the grid circuit. If some crystals are sluggish try adjusting the value of the 50pF. The easiest thing to do is replace it with a trimmer capacitor and adjust it until the oscillator keys smoothly. 

73,
Darrell, WA5VGO


> On Feb 12, 2016, at 9:25 AM, David Stinson <arc5 at ix.netcom.com> wrote:
> 
> I think I know why an outstanding transmitter like the TCS, with both MO and Xtal oscillators, never got real traction as a Novice rig (other than the high price at the time).
> 
> 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 values in black are nominally the ones found in the many flavors of this circuit.  The values in red are those found in the TCS transmitter.  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:
> 
> http://home.netcom.com/~arc5/TCS/TCSTXXtalCollinsPreWar.jpg
> 
> With these installed, the oscillator is perky as a pug.  With parallel resistors installed to bring the cathode down to 500 Ohms and the Screen dropper down to 22K,  all properly active crystals I've tried work well and give good drive.
> 
> 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?  Is this why it's easy to find TCS Receiver crystals, but Transmitter crystals are scarce? Curious. Thoughts?
> 
> GL OM ES 73 DE Dave AB5S
> 
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