07-06-2015, 06:12 PM
I'll tack this post onto this old thread as the title is correct and it is of similar content.
Acquired a fair VHF64 last winter whilst I was away and having looked at it sitting on the to do shelf for long enough decided to make a start on it last week.
Both brights were missing off he knobs but I can soon knock out 2 from brass sheet and the hardwood dies that my mate Brian produces. Both scale lamps are missing.
All 3 speakers seem to be in good order, cabinet is very good, no worm. The rubber wiring is also good enough to leave intact. The 2 core mains lead will be replaced with 3 core and a proper earth made to the chassis.
All the valves look like the originals, there is no sign of any repairs having been made. The FM aerial plug on the back was squashed as is usual but it has straightened out OK. Tuning cord is fine.
So a quick check over with the ohm meter, transformers OK, no shorts, spider skeletons evicted and on to the variac for some power.
No drama, filaments all up, Hum on the finger in gram position, some good reception on L, M, and S AM bands. Check the EL84 grid, whoa, 7 volts! So its that cap out off the tag board, gut it and fit a new one into the sleeve. Refit and test, that's better, only 0.06v, good for an old EL84.
Ah, totally useless on FM, motorboats like a good 'un as soon as the volume pot comes off the stop.
That will be capacitors I assume. Magic eye fully driven on FM so chances are that its IF instability not audio stage. Eye looks good and bright too.
So I started disconnecting the Hunts caps from the front end, ECH81. Mmm, as expected, every one of the first 5 are useless, reading just a few pf. So start replacing with new, 0.047 uf, 0.01uf 0.022uf etc. Try it on the mains after every 2 or 3 replaced, still motorboating.
Then, eureka, 1st EF89 IF transformer decoupler to chassis, it has never been soldered to the IF transformer pin! There are 3 HT wires on this pin, the cap is the lowest wire ie first one fitted when it was built and the solder has just not made it down far enough.
Power up and all is now quiet on FM even with full volume. No popping but I can hear the electrons hissing through the valves, no reception even with an aerial fitted.
Check valve voltages and find that the ECC85 in the FM head is drawing next to no current on either triode. A substitute produces a good clean reception across the FM band. Success!
So it will be complete the re-capping and clean and polish to finish, another lovely Bush preserved.
I do like these sets, not difficult to work on, well engineered, but what a shame about Bush using the Hunts. Cost engineering I assume.
Acquired a fair VHF64 last winter whilst I was away and having looked at it sitting on the to do shelf for long enough decided to make a start on it last week.
Both brights were missing off he knobs but I can soon knock out 2 from brass sheet and the hardwood dies that my mate Brian produces. Both scale lamps are missing.
All 3 speakers seem to be in good order, cabinet is very good, no worm. The rubber wiring is also good enough to leave intact. The 2 core mains lead will be replaced with 3 core and a proper earth made to the chassis.
All the valves look like the originals, there is no sign of any repairs having been made. The FM aerial plug on the back was squashed as is usual but it has straightened out OK. Tuning cord is fine.
So a quick check over with the ohm meter, transformers OK, no shorts, spider skeletons evicted and on to the variac for some power.
No drama, filaments all up, Hum on the finger in gram position, some good reception on L, M, and S AM bands. Check the EL84 grid, whoa, 7 volts! So its that cap out off the tag board, gut it and fit a new one into the sleeve. Refit and test, that's better, only 0.06v, good for an old EL84.
Ah, totally useless on FM, motorboats like a good 'un as soon as the volume pot comes off the stop.
That will be capacitors I assume. Magic eye fully driven on FM so chances are that its IF instability not audio stage. Eye looks good and bright too.
So I started disconnecting the Hunts caps from the front end, ECH81. Mmm, as expected, every one of the first 5 are useless, reading just a few pf. So start replacing with new, 0.047 uf, 0.01uf 0.022uf etc. Try it on the mains after every 2 or 3 replaced, still motorboating.
Then, eureka, 1st EF89 IF transformer decoupler to chassis, it has never been soldered to the IF transformer pin! There are 3 HT wires on this pin, the cap is the lowest wire ie first one fitted when it was built and the solder has just not made it down far enough.
Power up and all is now quiet on FM even with full volume. No popping but I can hear the electrons hissing through the valves, no reception even with an aerial fitted.
Check valve voltages and find that the ECC85 in the FM head is drawing next to no current on either triode. A substitute produces a good clean reception across the FM band. Success!
So it will be complete the re-capping and clean and polish to finish, another lovely Bush preserved.
I do like these sets, not difficult to work on, well engineered, but what a shame about Bush using the Hunts. Cost engineering I assume.
Boater Sam.
