Hi from a newby and Bush TR82C Distorted at high signal strength

[ppppenguin]

Hi Mike, no upset at all. Happy to help newcomers.

Unless referring to specific historic usage please write 4.7u or 4.7uF or 4u7. 4.7MF literally means 4.7 MEGA farads. (I know it should be a greek lower case mu rather than u but that's a bit too perfectionist).

Mark and I subscribe to the same school of using DMMs and 'scopes. Especially 'scopes bcause they tell you so much. The older school of radio and TV repairers take a different view. Mark has explained it well.

When buying capacitors, resistors etc, buy more than you need for a particular job. Then you will start to build a stock of spares and won't have to order for each job. Perhaps not for big and/or expensive parts - I've just bought a couple of 15000uF 63V caps for about £16+VAT each. I'm not going to buy a spare on the off chance!

[Wanderingfree]

Thank you both for your responses. I completely agree with you both. I was from the era where scopes were not used. I have since bought my own Hitachi scope. It's more complicated than required as its three trace but as you quite rightly say they have their own story to tell. I first started in domestic tv and found that having a screen (crt) it was a bit like a scope as it was very visual. I used scopes at college and they are great all round for analogue as well as logic 1 & 0's. The peak equipment is for conformation of diagnosis as (example) you can have a capacitor which measures ok but the ESR is way off. I'm not sure going round checking every component is the way forward, it's not really fault finding but more change everything to eliminate fault.

Mike

[Wanderingfree]

Hi Guys. As a follow up to my previous post, I have replaced all the Plessey electrolytic capacitors. This involved stuffing the old caps to keep its vintage appearance. The only exception was the AGC cap which was too small to fit another inside but I have used an axial and it looks ok. The cabinet cleaned and reassembled and it looks good. I have one problem. At the same point on the running capacitor I have an annoying microphonic crackle and the sound goes a little distorted. Not sure if it's the running cap or something else. Any suggestions would be very welcome.
Mike.

[Refugee]

There are quite a lot of threads about dealing with tuning capacitors that are crackling.

[Wanderingfree]

Thank you. I took the back bearing off, cleaned and re greased re assembled it's gone from where it was (around Talk Sport) and now seems to be right at the bottom end of the running scale where there are not many channels (if any) so definitely the running cap.

Mike

[boater sam]

Intrigued by your "running cap" for the tuning capacitor, never heard that before.

If it is shorting at one end, examine it closely to see if the gap between all the vanes is equal. It is adjustable by tightening or slackening the back bearing.

See if there is a distorted vane or one with a ding in the edge. Any grit in between?

If there are outer moving vanes obviously bent - beware - if they are touching the fixed vane then alter them but often the outer vanes are bent out away from the  last fixed vane in alignment to minutely adjust the tracking of the capacitor.

[Wanderingfree]

Thanks for that Boater Sam. I spent more time on it having serviced the back bearing and with the problem moving down the scale I decided it was obviously to do with tuning cap. I greased the front bearing, no difference. When I first started on the radio I noticed the clutch on the tuning cap was slack so with that in mind I tightened further, the back bearing by another half turn and wallah the problem solved. There is obviously a slightly out of true vane on the cap and by slight adjustment it centred the vanes and gave more clearance. I had already inspected and brushed and blown out (gently) any dust between them.

Mike

[boater sam]

Glad my advice was of use.

I have found more out of mesh tuning caps in portable radios than table tops probably due to rough handling in the past.

[Wanderingfree]

Yes I think the clutch was loose because of ware due to lots of tuning.