Bush VHF box.

[Danndad]

I have a bush vhf70 and I’d like to know how voltages are taken on the ECC85 vhf valve please?, also is it possible to get in to the vhf box to check components without removing the whole unit and disturbing the tuner cord etc. 

Regards Danndad.

[boater sam]

One side of the box comes off in situ without disturbing anything. The trimmers in there are known to go short circuit.

[Danndad]

You were absolutely spot on with that Sam thanks, one half of the box came away leaving fairly decent access to do some checks.
My reasons for wanting to get in there was I thought I had a noisy resistor as when it was switched to VHF there was a lot of scratching and rustling .
The trimmers were responsible for the scratching and rustling, after exercising them and a liberal dosing of servisol its now fine.
The other thing now is that I have a 100k grid leak resistor on the UCC85 that measures 130k, its buried at the back of the box with the tuner cord near it.  I’m a bit concerned about getting in there to replace it, I have visions of catching the tuner cord with the soldering iron ETC so is it ok to leave it as it is for now?
   

[Mike Watterson]

130k instead of 100k is fine.

[Danndad]

OK, thanks Mike.

[boater sam]

130K will be close enough but if it concerns you consider shunting it to bring the resistance down. In a VHF tuner you need to think about position and wiring as it will affect the tuning.

[PerdioPal]

130k will be fine, any good design should cope with at least 50% tolerance on components. OK there is perfection and working, working does it for me.

[Danndad]

Thanks for all the replies, I'm going to leave the resistor as it is for now.
Under what circumstances would the dual 30r resistor be used as heater droppers in this radio??
The radio had been run by me for quite a while whilst try to track down other faults, til it was spotted. I have replaced it with a pair of 200r 5w resistors which was what was supposed to be in there, would there be any long term damage to valve heaters?
   

[boater sam]

Probably not. Over-running by 10% or so may just liven the cathodes up a bit.

Good that you have corrected it though.  What voltage tapping was it set to originally?

[Danndad]

Voltage was in the 245v position.
The radio has had an enormous amount of components replaced(not by me) but to me the soldering on that dual 30r looked original.