Ferguson 992T

[space_charged]

I have just acquired a Ferguson 992T. Originally I had thought of it as a CRT "donor" for another project, but it is in such good condition that I want to restore it. I have the service sheet for it, but does anybody have any experience of this set? I'd welcome any tips, beyond the more obvious things we know about (caps etc).
Chas

[Heatercathodeshort]

Good reliable Ferguson 14" table model. One of the 99x series from 1953.
No real problems as such. Simple efficient circuit. Worth checking the condition of the MW36-24/44 tube with particular reference to the heater. These Mullard tubes tend to develop partial shorts dropping the voltage to around 4v when in a series chain.
LOPT is generally OK but may need drying out for a couple of months in the boiler/airing cupboard. I like these receivers and many thousands, probably hundreds of thousands were sold. The diode/rectifier in the cathode of the video amplifier [not all models] mounted on the rear chassis rail can give some odd symptoms when they go O/C.
Band 3 conversion is nice and tidy depending on the schedule [A B C etc] Note the tuner is Band 3 only. The set reverting to band 1 with the normal aerial socket for BBC.
The ganged 5 channel tuning adjustment knob can give trouble. The three iron dust tuning coils rust up and get stuck in their formers. When retuning the adjustment rods break away from the cores giving no/odd tuning so be careful here. They are a fiddle to repair but not impossible. Good luck with it. You will be surprised at the results. Regards, John.

[space_charged]

Hi John,

Thanks for the information. Yes I've read about the heater shorts in the Mullard MW36-24/44.
I'll test mine with a 300Ma constant current supply (limited to 6V) shortly. [ Ha ha, hope the pun doesn't come true ].

My set has a rather obviously added turret tuner added to it,, bypassing the original RF and mixer stage. As it was added a long time ago, I'll leave it there and try to get it working as it is now.

I've played with B/W TVs since I was 14, all my sets being acquired from my school's radio club. I've restored a Philips 17TG100U to working order recently and in that set as you may know the LOPT is plug replaceable. I put it on top of a radiator in my house for several weeks before doing anything else! The Ferguson is in my living-room now so should be drying off nicely.

I've ordered various capacitors for it, top of the list being boost reservoir cap and will do basic checks before anything else.

Usually I run a new set up on an isolating transformer and through a variac while monitoring the volts on the main smoothing electrolytic. With my Philips 17TG I left the volst on the main caps at 50V for 10 hours, then ramped it up very slowly. The low voltage
on the heaters of the PY82s makes the valves act like a high resistance in series with the caps limiting the current while they (hopefully) reform.

Thanks for the tip about the semiconductor in the cathode of the video output valve. I'd seen that in the circuit diagram. What would you suggest replacing it with? I'd guess its not too critical, as in "any old silicon diode"?


Chas

[space_charged]

I've just tested the CRT heater using a power supply set to .3A and 6V. The heater lights and the volts come up to 6V at .3A, so no internal heater shorts. No H/K shorts either.

Also there was a space charge between the cathode and first grid, so the cathode is emissive. Obviously that doesn't mean it will supply beam current required for a good picture. It does mean the vacuum is probably OK and the cathode not completely dead.

[space_charged]

Question about the CRT in this set:

The CRT in my set seems to be an MW36-44 whereas the service sheet shows it to be an MW36-24, the former being a pentode gun and the latter a tetrode. Does that mean my set has had a replacement tube or were some vertions of the 9922T fitted with the pentode gun tube?

[Heatercathodeshort]

The MW36-22/24 was the original Mullard 14" rectangular tube released around 1952. The MW36-44 is a later tube that replaced the earlier one. A photo of the label will give a rough idea of it's age. J.

[space_charged]

OK, photo of the label on the tube attached to this. The label had fallen off the tube and was inside the set.

[Heatercathodeshort]

Definitely a later replacement I guess from around 1958/9. I expect the original went S/C heater! J.

[Restoration73]

No label on the tube in my 991T, but it is marked "made in Holland" on the rim.
Every corner joint on the cabinet has failed !

[space_charged]

Thanks John,

Yes I too thought the tube must have been replaced, so hopefully a better chance that the tube will be OK.

[Heatercathodeshort]

Originally Posted by Restoration73

No label on the tube in my 991T, but it is marked "made in Holland" on the rim.

The 991T is one of the 99xT series and the most interesting chassis.Twenty two valves, flywheel sync, loads of gain but lacking vision AGC.
The early MW36-24s were manufactured in Holland and if the early 9" tubes are anything to go by certainly had the edge over the UK produced ones.
Just as a guide. The Ferguson model numbers ending even [992T] are service area models. Uneven [991T, 990T etc] are fringe models with flywheel sync. John.

[FERNSEH]

The MW36-44 employs a pentode gun assembly. The design of this gun according to Mullard is said to offer uniform focus across the whole screen area. The extra electrode (A2) is connected to pin 7. Connect pin 7 to various potentials, e.g. the first anode, ground or the cathode to obtain the best results.
The Ferguson 992T is worthy of a restoration project rather than just a donor set for components. I'm sure you will be pleased with the results from this resto project.

DFWB.

[space_charged]

Hi all,

Yes I'm aware the MW36-44 is a pentode gun tube and it was claimed to have better focus.
I'm hoping my tube will be OK so I can see for myself if that is true!

I'm slightly worried to see that there is NO connection to pins 6 or 7 on the base of my CRT to the set. Just leaving it "floating" wouldn't be all that clever IMHO. I'd expect it to build up a fair negative charge in the electron beam. Maybe leakage would let enough of it discharge so as not to be a problem. Looks like when it was replaced, somebody thought it was a drop in replacement!

Originally I thought of the Ferguson as a "donor" for my Peto Scott restoration project, but seeing how good the the condition of the Ferguson is, I'm going to restore it.

Chas

[space_charged]

On this age of set, the base of the CRT projects out beyond the back-plate
is enclosed in a sort of "cup". This appears to be made of some sort of
plastic.

On my set, it is distorted and I wonder if it could be heated to restore its
original shape. Does anybody have any thoughts on that?

[Restoration73]

I would avoid heating old thermoplastics in case of cracking or splits developing.
If there is insufficient length it could be attached to the rear of the case. It has to
protect and tube from knocks and the user from shocks. There are a wide range of
cup type structures that could be found in diy, food, or garden outlets.

[space_charged]

Thanks for the ideas to replace the cup. Yes garden and diy shops might provide something.

The original looks like a thermosetting plastic as it resembles bakelite. In that case it wouldn't melt anyway.