What's the function of these caps and resistors please?

[spec]

No probs CW. I have now recovered from the alcohol and Earl Grey.

No RS232- that simplifies things.

And, from what you say, no key input either- is that correct?

Is it also correct that the 'signal' that you refer to is the 272 KHz clock square wave (is it a square wave)? If so is the 272 KHz simply turned on and off to provide the output signal. If so can you describe the rate of turning the 272KHz on and off?

spec

 

[Chris Wilson]

The key input is just grounded to keep the amp "on", I don't do any manual, hands on a key, CW stuff. I would like to keep the RS232 input though, as software generated, very slow Morse is a method used on LF for communication that I have previously used on a different amp.

As for the "signal", yes the 272 kHz square wave is derived from either the newly built U3S device :

https://www.qrp-labs.com/ultimate3/u3s.html

or the Kenwood Ts-590, pre amp and frequency doubler. The signal is present as soon as the software begins a TX sequence. WSPR gives just under 2 minutes continuous, OPERA has a few seconds TX, then stops for a few seconds, then on again, for a 32 minutes long TX sequence.

As the U3S seemingly has cured the randomly occurring start up oscillation or whatever it was, I may stick with it, it's cheap as chips and frees up my expensive TS-590 for SSB voice (yes, I do actually speak with other amateurs as well as use this funny digital stuff.... ). As such I am going to investigate a firmware option to have 180 degree out of phase, (mirrored) outputs generated by the Si5351a device. I am thinking this might drive the FET driver IC directly? I need to look at the levels, and see if one output is held high when no signal is being created. If so capacitive coupling will still be needed.

Finally, is the groups decision final that C1 and C2 with their associated 15k resistors are there to help stop both FET's being briefly turned on together?? And if so would their continued presence be desirable between the Si5351a outputs and a driver IC, should I be able to make the idea work?

Thank you spec!! I am expecting a call from RS Component's marketing team asking why I am no longer buying dozens of FET's

 

[Chris Wilson]

I just wanted to pop back and say thanks again, especially to "spec" who tirelessly assisted and this amp is now 100% reliable and last night again made 7 successive contacts on 137.550 kHz from here in the UK to East coast United States. My sanity and finances have recovered immeasurably. Thanks!!!

 

[schmitt trigger]

The pins 10,12 are sensitive to the drive level of 74F74 since TTL only sources 2.5V @ 2mA ( yet sinks 20mA~0.5V).

I hadn't seen an F-series "fast" TTL chip used in a design since the mid 1970s.
They were extremely power hungry, and thus had been largely superseded with S and LS series chips.

 

[Tony Stewart]

I hadn't seen an F-series "fast" TTL chip used in a design since the mid 1970s.
They were extremely power hungry, and thus had been largely superseded with S and LS series chips.

I agree yet D-K still stocks them for those who can't afford to change the design for something needing <1ns differential output skew in lower power range of CMOS.

 

[schmitt trigger]

Which BTW, in the project presented by the OP, is not really required.