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THE AM BULLETIN BOARD => Technical Forum => Topic started by: WA4WAX on May 08, 2023, 01:34:12 PM

Title: Brit 80 meter CW transmitter
Post by: WA4WAX on May 08, 2023, 01:34:12 PM
From PW.  It is supposed to key nicely.

Title: Re: Brit 80 meter CW transmitter
Post by: w8khk on May 08, 2023, 04:20:59 PM
Thanks for sharing this one, Matt.

Looks nice while transmitting, but I immediately observe two issues, both of which may be fixed by one change.

The oscillator seems to run all the time, which would make receiving rather difficult.  Only the final RF amplifier is keyed.  This is fine for stable keying but you would probably never hear the response to your SEE QUEUE.  

The second problem is the HV switch in the power supply.  It switches the final voltage but not the oscillator voltage.  The potential problem (no pun intended) is that the second valve, when the HV switch is off, receives screen voltage, but no plate voltage, a potentially damaging situation to the little screen in that bottle.

By simply relocating the HT switch from the final HT to the stabilised Osc HT, both issues are resolved.  There is really no need to switch the final HT off, with the cathode circuit open during key-up periods.

Edit: Better yet, move the switch to take all HT off the transmitter during receive periods.  The smallish key-click resistor in the cathode circuit is a bit on the light side to idle the final.

I absolutely refuse to get hooked (again) reading every article in every issue because you linked one reference.  That has been a huge time-sink for me, I got in the rut of reading one after another, and it was fun, but it ain't happenin' agin!  Thanks, anyway, OM!

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