G'day,
My SB220 is currently operating on HF and 6m (10 band was pinched and
realigned) but was not optimised - gain is around 7x on 6m.
This exceeds the max in ZS when driven by an IC-746 so there was no incentive
to optimise the output power.
The input tuning was changed and on the output a piece of copper tape run to
the tune cap. Details fuzzy - it was done 11 years ago during the last solar
max...
Possibly there was insufficient inductance on the output.
Stability is good and there are no problems.
However, the 70 MHz transverter to be used outputs only 30W and the intention
is to up this around 9-10x in the SB220.
I am happy to say goodbye to HF with the SB220.
Please advise on the following:
1. The grids will be grounded using copper tape.
2. The suppressors will be changed to around 33 ohm/2W carbon film with a
couple of turns of thin copper wire. Or should I just rewind the existing
suppressors with fewer turns?
3. The 10m output coil will be replaced with one of about 2-3 turns with 6m
tapped at the hot end and 4m tapped around 1.5 turns.
4. The TUNE capacitor will replace the LOAD capacitor.
5. A 33 pF wide spaced variable (used) will replace the TUNE capacitor.
6. The existing T/R relay will be retained - I have a used Jennings 26.5v
vacuum relay lying around.
7. A "pulled" CRL 850 anode capacitor will replace the existing stock anode
capacitor. I have several CRL 850's ranging in value 12-140 pF and believe
these are good for 5 kV and the RF current.
8. To switch between 6m (10m) and 4m (15m) the band switch will be retained for
better or worse.
9. 15m input realigned to 70 MHz.
End of proposed mods.
Advice appreciated,
73.
Ian ZS6BTE
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