Baird T5 restoration project.

[FERNSEH]

Remember the shelf that carries the timebase and sound and vision chassis assemblies on which the fixing screw recesses were drilled on the wrong side of the board? The upper side instead of the underside.
Well, last week I decided to the put things right. The errant holes were bored out further with a 5/8inch drill and 21mm dowel pieces inserted.
That done, the screw recesses were drilled out on the correct side.
The repaired shelf is a much better fit in the cabinet and slight correction of the positions of the holes for the chassis screws has improved the fitting and removal of those units.

DFWB.

[FERNSEH]

Before the CRT can be reinstalled some sort of connector must be made for the base of the tube.
Yesterday, I attempted to make a ring type connector for the four side contacts on the CRT base. So far without much success. Contact resistances are too high for the tube filament connections, the directly heated cathode draws >2A current @ 2.5V.
An alternative is to attach a B4 valve base to the end of the tube. However, it must be taken into consideration that the 5KV anode connection is also on the tube base.

DFWB.

[Rich Woods]

Wouldn’t it be better to hard wire the tube once in situ, or am I missing something?

[FERNSEH]

"Wouldn’t it be better to hard wire the tube once in situ, or am I missing something?"
Hi Rich,
It might well come to that but the fact is it is not a pleasant task refitting the vertically positioned tube with wires dangling about when passing the CRT neck through the focus coil and that six inch long rolled metal tube.
Also, the CRT base connections are close to the cabinet base.
It was a scary enough business lifting the tube out, those wires got in the way of what should have been an easy task.

DFWB.

[Rich Woods]

Originally Posted by FERNSEH

"Wouldn’t it be better to hard wire the tube once in situ, or am I missing something?"
Hi Rich,
It might well come to that but the fact is it is not a pleasant task refitting the vertically positioned tube with wires dangling about when passing the CRT neck through the focus coil and that six inch long rolled metal tube.
Also, the CRT base connections are close to the cabinet base.
It was a scary enough business lifting the tube out, those wires got in the way of what should have been an easy task.

DFWB.

Yikes, good point! Looking at the B4 valve base, you could also run some shrink down over the EHT pin after soldering with maybe a non conductive (non silicon based) sealant where the shrinkdown meets the valve base.

[FERNSEH]

Decided to keep faith with the side contact CRT socket. Have added plastic shims behind the brass contacts.
Excellent results, contact resistance now reduced to an acceptable figure. 0.1ohms.

DFWB.

[FERNSEH]

At last the special connector for the Cathodevisor CRT has been completed.
The white plastic bar was made from a microwave oven door latch. It fits perfectly. For the EHT connection a 10mm valve top cap will soldered on to the isolated contact. The CRT will be positioned in the cabinet with the EHT connection towards the front of the receiver.

DFWB.

[Rich Woods]

Good practical solution. The microwave part could have been made for the job!

[FERNSEH]

Hi Rich,
the oven door latch was a legacy part left over from the days I used to sell microwave ovens.
DFWB.

[FERNSEH]

Just one more job to do and then the CRT can be reinstalled. The Baird T5 has a vision receiver local oscillator adjustment on the control panel. A rubber coupling between the remote drive and the worm gear was used to rotate the tuning capacitor. The original part was completely perished. The possible replacement part being considered is from a Seeburg juke box. But a method of attaching the new component must be found.

Might even consider employing Meccano parts.

DFWB.

[FERNSEH]

The only item holding up the completion of the Baird T5 restoration was the flexible coupling between the vision receiver local oscillator tuning mechanism and the control cable.

On Tuesday I finally managed to remove the remains of the flexy coupler attached to the worm gear. It was hoped that the securing pin could be driven out the shaft. That task proved unsuccessful. The only answer to the problem was to cut off the remains of the old coupler and drill out the end of the worm gear. This has been done so now a new stub shaft must be made to adapt the 3mm worm gear to 6.35mm for the replacement coupler.
Also, another adaptor stub shaft for the other end of the flexible coupler, 6.35mm to 9mm.

DFWB.

[beery]

Hi David,
That job is a pain.
I believe that the retaining pin is a tapered one, so it only comes out one way. However, after all this time it probably won't budge.
The original coupling was rubber and the triangular part was mounded into it.
I once considered using this type of thing on a T5-
https://uk.rs-online.com/web/p/anti-...s/1263944?gb=s

Cheers
Andy

[radiomobile]

Alloy flexible shaft couplers for CNC machines are available on eBay in many configurations including 3mm to 6.35mm (1/4") for around £3 each. Of course there is no electrical isolation and they may be too bulky...not sure what the OD is.

[FERNSEH]

This week I was hoping that the CRT would be reinstalled, but that won't happen until I'm fit enough to do the job. I've suffered damage.
However, parts have been made for the oscillator tuner coupling.
The coupling shafts have been turned down to 6.35mm.
Just a matter of finding a different flexible coupler.
It's unlikely the one shown in the attachment will be used.

DFWB.

[Panrock]

Sorry to hear you've suffered damage. I hope you'll recover soon.

Steve

[peter_scott]

Originally Posted by Panrock

Sorry to hear you've suffered damage. I hope you'll recover soon.

Steve

+1

Peter

[FERNSEH]

Hi Steve, Hi Peter,
thanks for your concern. It's not a serious injury.
What happened on Sunday morning I experienced severe cramps in the right leg, something that happens quite often with no ill effects. However, this week I wasn't so lucky. On Monday the pain was tolerable, but on Tuesday the pain got worse. Then the other leg became painful. Confined to the house.
Feeling much better today.

Need to be really fit for the reinstallation that huge Cathodevisor CRT. It's not heavy but extreme care is required handling this fragile tube.

DFWB.

[murphyv310]

Sorry to read this David.
Hope you get the problem investigated, a sudden onset of pain when fitting that CRT doesn't sound so good.
Take care.

[FERNSEH]

Legs are still a bit wobbly so the CRT remains in it's cradle until I'm better.
In the meantime a 10mm ex-valve top cap connector has been fitted to the CRT base. The CRT will be positioned so that the EHT connector is facing the front of the cabinet.

DFWB.

[McMurdo]

check for woodworm, it gets the legs first

Get well soon, your installments are better than watching telly