RCA BTA 1MX Conversion

[KA3EKH]

I have a RCA BTA1MX that I am looking at operating on 160, although it’s a 1 kW transmitter I am looking at removing one of the 833 tubes in the PA and operating it as a 500 watt transmitter, unfortunately I will  have to use the 1kW rated modulation transformer, reactor , chokes and 3.1 kV plate transformer. Being that C21 and 22 along with  C23,24 and 25 all have to be changed anyway with the original frequency being 1360 I wanted to know if anyone knows the correct value for C23/24 and 25, the capacitors on the output side of L7 and if at 160 meters you need any capacitor for C21? The manual shows no capacitor being in place on the 500 watt version and 100 pf for the two tube 1 kW version for C21. Also are there any ideas on what the value for C20 the feedback capacitor should be? I know that R10 changes between the signal tube and two tube version and C51 decreases in size but do not know if that necessary and last but not least have others used the interlock circuit to control between transmit and standby or built up more complex transmit standby systems using additional relays and bias systems?
Ray Fantini KA3EKH

[KB5MD]

I have a BTA 1R1 transmitter and it has 250 watt, 500 watt and 1kw taps on the plate transformer.  Have  you checked yours for the same type of setup?  If that is the case, use one of the other taps to lower power and readjust your modulator bias according to the manual.  When I converted to run in the ham bands, I removed all the output components and replaced them with a pi-output.  I do have to switch in an extra 1000pf to load for 160.  You can put a 240volt variac in the plate transformer primary to make the B+ adjustable also.  The transmit is controlled by switching the B+ on and off via the "interlock" circuit as you suggested.  I hope this helps.