07-17-2017, 07:12 AM
Hey folks!
I have just completed a recapping of my 38-116 code 121. I replaced all capacitors including electrolytics and micas. I also replaced all resistors. I took the RF sub chassis apart and replaced all caps and resistors hiding there too as well as the caps in the bakelite blocks. I installed a fuse and a CL--90 and a safety cap on the line cord circuit. I have checked all tubes out on my Hickock tube tester (and purchased a new 5X4 rectifier).
With all the tubes out, I slowed powered the chassis up on my isolated variable AC power supply (a BK precision 1653). Got it up to 110 and dial lamp worked well and was drawing right amperage of 1.4 amps. I checked all the tube filament voltages and they all read 6.3 VAC as the should.
I next measured the B+ voltage on the filter caps - these too read correctly about 390 vdc from positive to the can ground and about 315 vdc from positive to chassis ground. I next put the rectifier tube in and then measured the filter caps again - it started off in the right range but then once the tube warms up it goes down to about 210 vdc for the reading that should be 385 and then about 180 for the reading that should be 315. I put in the rest of the tubes and still had the same low readings on the filter caps - however all tubes glow.
A couple other observations:
--the main dial light works (on at all times)
--the 4 magnetic tuning lights work when magnetic tuning switch it on
--the mixer tube should be a 6L7G (pentagrid mixer) - but it came with a 6K7G (remote cutoff pentode) in its spot and I have not replaced it yet.
--there is no noise from the speaker - not even a hum.
--I had a bad audio interstage transformer which I had replaced with custom made one from heybour.
Any ideas on why the voltage across my filter caps be reading low?
I have just completed a recapping of my 38-116 code 121. I replaced all capacitors including electrolytics and micas. I also replaced all resistors. I took the RF sub chassis apart and replaced all caps and resistors hiding there too as well as the caps in the bakelite blocks. I installed a fuse and a CL--90 and a safety cap on the line cord circuit. I have checked all tubes out on my Hickock tube tester (and purchased a new 5X4 rectifier).
With all the tubes out, I slowed powered the chassis up on my isolated variable AC power supply (a BK precision 1653). Got it up to 110 and dial lamp worked well and was drawing right amperage of 1.4 amps. I checked all the tube filament voltages and they all read 6.3 VAC as the should.
I next measured the B+ voltage on the filter caps - these too read correctly about 390 vdc from positive to the can ground and about 315 vdc from positive to chassis ground. I next put the rectifier tube in and then measured the filter caps again - it started off in the right range but then once the tube warms up it goes down to about 210 vdc for the reading that should be 385 and then about 180 for the reading that should be 315. I put in the rest of the tubes and still had the same low readings on the filter caps - however all tubes glow.
A couple other observations:
--the main dial light works (on at all times)
--the 4 magnetic tuning lights work when magnetic tuning switch it on
--the mixer tube should be a 6L7G (pentagrid mixer) - but it came with a 6K7G (remote cutoff pentode) in its spot and I have not replaced it yet.
--there is no noise from the speaker - not even a hum.
--I had a bad audio interstage transformer which I had replaced with custom made one from heybour.
Any ideas on why the voltage across my filter caps be reading low?
Andy Sorrell
Palmyra, Virginia
