Ferguson 998T - UK Vintage Radio Repair and Restoration Discussion Forum

matspar · 28th Jun 2018, 8:09 pm

Good evening Gentlemen,

Would anyone happen to have a scan of a Trader sheet for a 1953 Ferguson 998T by any chance? 12" table set.

Did this ever appear on a BVWS CD? My copy only has radios.

Best regards, Matt.

MonochromeMarc · 28th Jun 2018, 8:49 pm

Hi Matt,

I've got a 998T, not a bad set either.
I have scans of the original Ferguson service data.

PM me your email address if you would like a copy sending.

Marc.

matspar · 28th Jun 2018, 8:52 pm

Many thanks Marc PM sent

Boater Sam · 28th Jun 2018, 8:53 pm

For very little money see
https://**********************/Schemat...son&model=998t

Sam.

matspar · 28th Jun 2018, 10:14 pm

Thanks Sam looks very interesting. I'll definitely have some of that. I've never stumbled upon this site before

Heatercathodeshort · 29th Jun 2018, 9:10 am

One of the most reliable models ever produced. The last old style 12" model produced by Thorn. A simple circuit for the service area.

The last production run had provision for very simple Band 3 conversion.

Many of these ran for over 10 years without having the back removed. When I was around 16 I worked with a guy who had been an engineer during the early days of DER. He said that many were working well years past their life expectancy and despite suggestions that the customer should update their receiver, they were more than happy to keep it!

This example was found in a dry basement about 25 years ago and only required replacement of the Dubiliar wax caps and a LOPT dry out to put it back into service. I expect it was still working well when set aside. Took the pics this morning. Regards, John.

matspar · 1st Aug 2018, 9:48 pm

Hello John,

Only just stumbled on your message, not visited the forum for a little while. The 998T was the first 405 set I owned as a teenager back in the early 1990s. I couldn't get it to work so it sadly ended up being pulled apart and wrecked. Found another one all these years later to restore. It has low eht and the EY51 won't light. Fairly decent line whistle however, but no sparks from the top caps of the PL/PY81's. Tiny little spark available from the EY51 anode. This is new as well, and its heater winding is intact.
I'm satisfied that it is not the PL or PY (new ones fitted and even subbed for known good ones to prove a point, but no differences) All voltages are very near to circuit, nice stable HT nothing amiss and all the leaky dubiliers and a few high value resistors replaced.

So, looks like either incorrect line drive or a duff coffin lopt. I'm suspecting the lopt at this point. I have an identical good working one from a fringe version 991T but it lacks the osc feedback winding present on a 998T, so no good unless I'm brave enough to dismantle the pair and experiment with them! Any thoughts?!! the lopt has been sunbathing on a nice bright and red hot window sill over the last few weeks but no improvements...

Matt

Heatercathodeshort · 2nd Aug 2018, 8:22 am

It does sound a bit like the LOPT. The line timebase is self oscillating and this adds a bit of complication when it comes to LOPT substitution.

The space available and the fitting of the coffin gives very little room for experimentation.
It might be possible to add the feedback winding to the limb of the transformer for the 991T but this is a more complicated unit for a 14" 70 degree tube and may not be suitable. John.

FERNSEH · 2nd Aug 2018, 3:18 pm

Hi Matt,
If the line output transformer is proven to be faulty a possible solution is fit the spare transformer and make up a separate line oscillator.
Alternatively, the self oscillating line output stage of the later version of the Ferguson 983T could be considered. Oscillation is maintained by feedback components C23 and R28 which are supplied from a tapping on the LOPTx. See attached circuit diagram.

DFWB.

Restoration73 · 8th Aug 2018, 11:06 am

The Trader index only lists 998T as (near) on sheet 1108, i.e. Ferguson 992T, 994T, 996T
and there is a 992T modifications sheet 1131.

matspar · 8th Aug 2018, 10:55 pm

Many thanks! I have the above trader sheet now, along with the full Ferguson service book. Neither show an exact circuit of the line timebase for the 998T although the factory book does show the component location and list of values. It does seem to be a hard one to pin down.
Thanks John and David, I have been contemplating both approaches. The 991T loptx would be a pure experiment due to the inherent differences.
I have since been offered a correct replacement by another friend and member so fingers crossed I won't have to go down this road!

It's a really nice clean and original set as well, apart from the muck on the tube face!!

matspar · 19th Aug 2018, 5:40 pm

I have obtained a correct lopt and fitted it today. It worked briefly with a nice strong line whistle, the EY51 had a slight glow from the heater (although not as bright as it could be)
Still no screen illumination.
The overwind then became very warm and the pitch 'tyre' began to melt so I suspect this one has developed shorted turns. I'm now back where I started with a weak line whistle and no EY51 heater!!
I'm now thinking of removing the overwind and fitting a solid state tripler to try and get some eht which I've successfully done in the past.

However due to the line oscillator arrangement on the 998T, if I was to do this would the lack of an overwind upset the oscillator feedback winding on the transformer?

Matt

Heatercathodeshort · 19th Aug 2018, 7:02 pm

No I would not think so.
A doubler might be better than a tripler. A maximum of 9KV is required. You can probably construct one on a small square of Paxolin if a doubler proves difficult to obtain.

The Thorn 20" type would be fine or the small screen 1400's. J.

matspar · 20th Aug 2018, 10:03 pm

Thanks muchly John I will experiment with this when time allows!

beery · 21st Aug 2018, 9:22 am

Quote:

Originally Posted by matspar

However due to the line oscillator arrangement on the 998T, if I was to do this would the lack of an overwind upset the oscillator feedback winding on the transformer?

Matt

Hi Matt,
It should be fine, the lack of EY51 heater loading may have more of an effect, but I'm sure it will still be ok. Shame about the overwind though (again!).

Andy

matspar · 25th Aug 2018, 12:22 am

Thanks Andy!

Just my luck again. If anything it's confirmed the original diagnosis. I'll cut the overwind off one of the scrap lopts then and have a little play around with some doublers and triplers, and see what happens! Worked a treat on my Pye VT2 which had an identical fault.

28th Jun 2018, 8:09 pm	#1
matspar Pentode Join Date: Aug 2009 Location: Portsmouth, Hampshire, UK. Posts: 230	Ferguson 998T Good evening Gentlemen, Would anyone happen to have a scan of a Trader sheet for a 1953 Ferguson 998T by any chance? 12" table set. Did this ever appear on a BVWS CD? My copy only has radios. Best regards, Matt.

28th Jun 2018, 8:49 pm	#2
MonochromeMarc Pentode Join Date: Jan 2015 Location: Wakefield, West Yorkshire, UK. Posts: 151	Re: Ferguson 998T Trader Sheet Hi Matt, I've got a 998T, not a bad set either. I have scans of the original Ferguson service data. PM me your email address if you would like a copy sending. Marc.

28th Jun 2018, 8:52 pm	#3
matspar Pentode Join Date: Aug 2009 Location: Portsmouth, Hampshire, UK. Posts: 230	Re: Ferguson 998T Trader Sheet Many thanks Marc PM sent

28th Jun 2018, 8:53 pm	#4
Boater Sam Banned Join Date: Dec 2013 Location: Middlewich, Cheshire, UK. & Winter in the Philippines. Posts: 3,897	Re: Ferguson 998T Trader Sheet For very little money see https://**********************/Schemat...son&model=998t Sam.

28th Jun 2018, 10:14 pm	#5
matspar Pentode Join Date: Aug 2009 Location: Portsmouth, Hampshire, UK. Posts: 230	Re: Ferguson 998T Trader Sheet Thanks Sam looks very interesting. I'll definitely have some of that. I've never stumbled upon this site before

29th Jun 2018, 9:10 am	#6
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: Ferguson 998T Trader Sheet One of the most reliable models ever produced. The last old style 12" model produced by Thorn. A simple circuit for the service area. The last production run had provision for very simple Band 3 conversion. Many of these ran for over 10 years without having the back removed. When I was around 16 I worked with a guy who had been an engineer during the early days of DER. He said that many were working well years past their life expectancy and despite suggestions that the customer should update their receiver, they were more than happy to keep it! This example was found in a dry basement about 25 years ago and only required replacement of the Dubiliar wax caps and a LOPT dry out to put it back into service. I expect it was still working well when set aside. Took the pics this morning. Regards, John. Attached Thumbnails

1st Aug 2018, 9:48 pm	#7
matspar Pentode Join Date: Aug 2009 Location: Portsmouth, Hampshire, UK. Posts: 230	Re: Ferguson 998T Trader Sheet Hello John, Only just stumbled on your message, not visited the forum for a little while. The 998T was the first 405 set I owned as a teenager back in the early 1990s. I couldn't get it to work so it sadly ended up being pulled apart and wrecked. Found another one all these years later to restore. It has low eht and the EY51 won't light. Fairly decent line whistle however, but no sparks from the top caps of the PL/PY81's. Tiny little spark available from the EY51 anode. This is new as well, and its heater winding is intact. I'm satisfied that it is not the PL or PY (new ones fitted and even subbed for known good ones to prove a point, but no differences) All voltages are very near to circuit, nice stable HT nothing amiss and all the leaky dubiliers and a few high value resistors replaced. So, looks like either incorrect line drive or a duff coffin lopt. I'm suspecting the lopt at this point. I have an identical good working one from a fringe version 991T but it lacks the osc feedback winding present on a 998T, so no good unless I'm brave enough to dismantle the pair and experiment with them! Any thoughts?!! the lopt has been sunbathing on a nice bright and red hot window sill over the last few weeks but no improvements... Matt Attached Thumbnails Last edited by matspar; 1st Aug 2018 at 9:57 pm.

2nd Aug 2018, 8:22 am	#8
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: Ferguson 998T Trader Sheet It does sound a bit like the LOPT. The line timebase is self oscillating and this adds a bit of complication when it comes to LOPT substitution. The space available and the fitting of the coffin gives very little room for experimentation. It might be possible to add the feedback winding to the limb of the transformer for the 991T but this is a more complicated unit for a 14" 70 degree tube and may not be suitable. John.

2nd Aug 2018, 3:18 pm	#9
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Ferguson 998T Trader Sheet Hi Matt, If the line output transformer is proven to be faulty a possible solution is fit the spare transformer and make up a separate line oscillator. Alternatively, the self oscillating line output stage of the later version of the Ferguson 983T could be considered. Oscillation is maintained by feedback components C23 and R28 which are supplied from a tapping on the LOPTx. See attached circuit diagram. DFWB. Attached Thumbnails

8th Aug 2018, 11:06 am	#10
Restoration73 Nonode Join Date: Jun 2013 Location: Surbiton, SW London, UK. Posts: 2,801	Re: Ferguson 998T Trader Sheet The Trader index only lists 998T as (near) on sheet 1108, i.e. Ferguson 992T, 994T, 996T and there is a 992T modifications sheet 1131.

8th Aug 2018, 10:55 pm	#11
matspar Pentode Join Date: Aug 2009 Location: Portsmouth, Hampshire, UK. Posts: 230	Re: Ferguson 998T Trader Sheet Many thanks! I have the above trader sheet now, along with the full Ferguson service book. Neither show an exact circuit of the line timebase for the 998T although the factory book does show the component location and list of values. It does seem to be a hard one to pin down. Thanks John and David, I have been contemplating both approaches. The 991T loptx would be a pure experiment due to the inherent differences. I have since been offered a correct replacement by another friend and member so fingers crossed I won't have to go down this road! It's a really nice clean and original set as well, apart from the muck on the tube face!! Attached Thumbnails

19th Aug 2018, 5:40 pm	#12
matspar Pentode Join Date: Aug 2009 Location: Portsmouth, Hampshire, UK. Posts: 230	Re: Ferguson 998T I have obtained a correct lopt and fitted it today. It worked briefly with a nice strong line whistle, the EY51 had a slight glow from the heater (although not as bright as it could be) Still no screen illumination. The overwind then became very warm and the pitch 'tyre' began to melt so I suspect this one has developed shorted turns. I'm now back where I started with a weak line whistle and no EY51 heater!! I'm now thinking of removing the overwind and fitting a solid state tripler to try and get some eht which I've successfully done in the past. However due to the line oscillator arrangement on the 998T, if I was to do this would the lack of an overwind upset the oscillator feedback winding on the transformer? Matt

19th Aug 2018, 7:02 pm	#13
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: Ferguson 998T No I would not think so. A doubler might be better than a tripler. A maximum of 9KV is required. You can probably construct one on a small square of Paxolin if a doubler proves difficult to obtain. The Thorn 20" type would be fine or the small screen 1400's. J.

20th Aug 2018, 10:03 pm	#14
matspar Pentode Join Date: Aug 2009 Location: Portsmouth, Hampshire, UK. Posts: 230	Re: Ferguson 998T Thanks muchly John I will experiment with this when time allows!

25th Aug 2018, 12:22 am	#16
matspar Pentode Join Date: Aug 2009 Location: Portsmouth, Hampshire, UK. Posts: 230	Re: Ferguson 998T Thanks Andy! Just my luck again. If anything it's confirmed the original diagnosis. I'll cut the overwind off one of the scrap lopts then and have a little play around with some doublers and triplers, and see what happens! Worked a treat on my Pye VT2 which had an identical fault.