Ferguson 992T - Page 3 - UK Vintage Radio Repair and Restoration Discussion Forum

Tazman1966 · 15th Mar 2011, 9:07 pm

Nice to see your good results on the Aurora thread. What else do you need to do with this Fergie?

Andy Doz · 15th Mar 2011, 10:05 pm

Watch it

Andy Doz · 17th Mar 2011, 8:49 am

Develops a bit of a hum bar after being on for about an hour ... I'll give some attention to the main smoother I think.

ppppenguin · 17th Mar 2011, 8:58 am

Quote:

Originally Posted by Andy Doz

Develops a bit of a hum bar after being on for about an hour ... I'll give some attention to the main smoother I think.

Could just as easily be HK insulation breaking down in one of the valves as the set gets hot. If you can safely* 'scope the HT rail that will show any increase in ripple. I appreciate that TV repairers of the 1950s would never have used a 'scope for this job, even if they had a 'scope at all. They would probably have bridged extra caps across the reservoir and/or smoothers to prove the point.

*Just because I've got an isolating transformer and know how to use it safely doesn't mean that all our vintage TV enthusiasts are in the same position. Lifting the earth off the 'scope is something that we cannot recommend, even if many of us have done it and got away with it.

Andy Doz · 17th Mar 2011, 3:27 pm

Will do ... never have lifted an earth in my life.

murphyv310 · 17th Mar 2011, 6:51 pm

Hi Andy.
To elaborate on Jeffrey's post, lifting the earth was the norm in some workshops for years. It certainly would be very much frowned upon now and for those less technical it is very much not advised.
As I don't know your skill level, you cannot scope anything in a TV with a "live chassis" (no matter what side is connected to the mains) when it is in direct connection to the mains as the scope is earthed. The only way is to run the set via an isolating transformer.
A qualified engineer who knows what he is doing may do it the old fashioned way but he will have a work area free from any other live equipment, will have an insulated floor and one hand in his pocket and will be 110% certain the TV's chassis is connected to neutral.

Andy Doz · 17th Mar 2011, 8:11 pm

There's a 1.8KVA isolation transformer permanently under the bench. Wouldn't be without it.

It's the Electrolytic BTW. I'll order up something to take it's place. Running a bit low on Higher voltage caps of late ...

The first cap after the rec and before the L is very low in value. That will probably explain the motorboating at low volumes as well.

15th Mar 2011, 9:07 pm	#41
Tazman1966 Nonode Join Date: May 2006 Location: St Albans, Herts, UK. Posts: 2,193	Re: Feguson 992T Nice to see your good results on the Aurora thread. What else do you need to do with this Fergie? __________________ All the very best, Tas

15th Mar 2011, 10:05 pm	#42
Andy Doz Hexode Join Date: Feb 2011 Location: Gloucestershire, UK. Posts: 376	Re: Feguson 992T Watch it

17th Mar 2011, 8:49 am	#43
Andy Doz Hexode Join Date: Feb 2011 Location: Gloucestershire, UK. Posts: 376	Re: Ferguson 992T Develops a bit of a hum bar after being on for about an hour ... I'll give some attention to the main smoother I think.

17th Mar 2011, 3:27 pm	#45
Andy Doz Hexode Join Date: Feb 2011 Location: Gloucestershire, UK. Posts: 376	Re: Ferguson 992T Will do ... never have lifted an earth in my life.

17th Mar 2011, 6:51 pm	#46
murphyv310 Dekatron Join Date: Sep 2006 Location: Kilmarnock, Ayrshire, UK. Posts: 5,422	Re: Ferguson 992T Hi Andy. To elaborate on Jeffrey's post, lifting the earth was the norm in some workshops for years. It certainly would be very much frowned upon now and for those less technical it is very much not advised. As I don't know your skill level, you cannot scope anything in a TV with a "live chassis" (no matter what side is connected to the mains) when it is in direct connection to the mains as the scope is earthed. The only way is to run the set via an isolating transformer. A qualified engineer who knows what he is doing may do it the old fashioned way but he will have a work area free from any other live equipment, will have an insulated floor and one hand in his pocket and will be 110% certain the TV's chassis is connected to neutral. __________________ Cheers, Trevor. MM0KJJ. RSGB, GQRP, WACRAL, K&LARC. Member

17th Mar 2011, 8:11 pm	#47
Andy Doz Hexode Join Date: Feb 2011 Location: Gloucestershire, UK. Posts: 376	Re: Ferguson 992T There's a 1.8KVA isolation transformer permanently under the bench. Wouldn't be without it. It's the Electrolytic BTW. I'll order up something to take it's place. Running a bit low on Higher voltage caps of late ... The first cap after the rec and before the L is very low in value. That will probably explain the motorboating at low volumes as well.