R1155/T1154. Improvements.

[PaulDent]

Since I cut my teeth on the 1155/1154 in the ATC before I got my ham radio licence I have been in love with them ever since. Their known deficiencies for modern use can be eliminated.

The 1155 had the problem that the LO was FMed by the signal making SSB reception poor. The cure is simple: Take the AGC off the mixer tube and use a fixed bias of about 3V. I took the grid circuit to ground and put a 3V Zener in the cathode (decoupled).

It is simple also to drastically improve the selectivity. 560kHz ceramic resonators were available for pennies on eBay and I put a network using a two of them to couple the two coils inside the first two IF cans in place of the 1pf top capacity coupling. I now have 3KHz BW with steep skirts. It's slightly disconcerting, as when tuning, you get no hint that a signal is coming until you're on top of it.

You can also get rid of the 1154 chirp, which is caused by the 1200V HT being dropped through a resistor to give the oscillator 250V. But it rises to 1200V on key up and falls back down on key press. Those little triodes were specially spec'ed to take 1200 on the anode at zero current. The solution is to power the oscillator from the 1155's 220V HT

[GW3OQK Andrew]

Hello Paul
I've done same to narrow the IF.

I once tried stabilising the MO HT and chirp became worse. With the low HT the oscillator took longer to come to frequency, but with full HT it comes to full oscillation rapidly and quite acceptable small chirp on 80m, with a gentle drift during an over.

I've never yet made a Transatlantic QSO with the '54 but would like to try when winter comes.
73, Andrew

[cnpope20]

Originally Posted by PaulDent

It is simple also to drastically improve the selectivity. 560kHz ceramic resonators were available for pennies on eBay and I put a network using a two of them to couple the two coils inside the first two IF cans in place of the 1pf top capacity coupling. I now have 3KHz BW with steep skirts. It's slightly disconcerting, as when tuning, you get no hint that a signal is coming until you're on top of it.

Could you say a little more about the networks using the ceramic resonators?

Thanks.