UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post

Mike Phelan · 17th Nov 2006, 9:30 am

Sounds good, Adi - a few comments:
If you are using a hexode, it may as well be an ECH?? triode-hexode. Millions of circuits available. Easiest way to go.

If you go a different way, remember that the mixing has to be non-linear; to get the sum and difference of the two frequencies they have to be multiplied, not added.

The reason for the padder is for tracking; often they are adjustable.
C3 is in series with the LC cct, Ct in parallel.
At the HF end of the band, with C2 open, C3 has little effect but Ct great effect, so you adjust the latter; at the LF end, things are reversed - Ct has little effect and C3 a lot.
If C3 is fixed, you would align the coil at the LF end and Ct at the HF end.

Make sense?

17th Nov 2006, 9:30 am	#2
Mike Phelan Dekatron Join Date: Nov 2003 Location: Near Leeds, West Yorkshire, UK Posts: 4,609	Re: superhet Sounds good, Adi - a few comments: If you are using a hexode, it may as well be an ECH?? triode-hexode. Millions of circuits available. Easiest way to go. If you go a different way, remember that the mixing has to be non-linear; to get the sum and difference of the two frequencies they have to be multiplied, not added. The reason for the padder is for tracking; often they are adjustable. C3 is in series with the LC cct, Ct in parallel. At the HF end of the band, with C2 open, C3 has little effect but Ct great effect, so you adjust the latter; at the LF end, things are reversed - Ct has little effect and C3 a lot. If C3 is fixed, you would align the coil at the LF end and Ct at the HF end. Make sense? __________________ Mike.