My TV22 Projects

Hi.

Since I have been away I thought I’d bring you up to date with some of my projects and repairs. This thread is about the Bush TV22 that has now turned into a project set.

Background

I first saw this set way back in 2004 when I was approached by a chap in Glasgow. Hew had bought the set some years before to use as a main set, he didn’t of course realise that it was 405 lines and the transmitter and standard were long gone, he then got a TV62 with a portable 625 line chassis fitted. By the time I came on the scene the TV62 transplanted innards were well and truly due for the bin.

The TV22 when I got it to restore was very tidy with a lovely shiny chassis and super clean inside with a mint cabinet, he did pay a lot for it though. The restore was easy enough with mostly caps troubles and a duff frame blocking oscillator transformer. Once done the picture was very good indeed. I had to supply an Aurora from Darryl directly and a Freeview box. The total bill was around £400. I kept in touch with him after delivery for some years and the set must have run for 8 years with no problems. I think around 2012 he left a message to say it had no picture, I picked it up one day I was working near his home, on inspection the anode load for the line oscillator had gone O/C, a decent metal oxide resistor fitted in 2004, so a quick repair, a three day soak test revealed no other faults.

Again I didn’t hear from him for a few months then got a call moaning the odds it had broken down, well I ask you it lasted 8 years with no service calls and the last repair was a resistor!!!

The Faults

On picking it up I was shocked to see what happened, the LOPT was bereft of its pitch and wax, the PZ30 & PL38 were sucked in and the spanking CRT has a cracked gun glass. The set had massively overheated, the customer initially didn’t own up he left the set on for a very long time unattended, possibly the Aurora had shut down and no raster was seen or perhaps something initially had failed…. Who knows, he did though tell me later that he came in drunk from the pub the day before he found out the set wasn’t working. I told him there was little I could do with it as it needed a CRT, LOPT and perhaps more as well. I suggested he look on eBay for another and I could make one out of two. That was the last I heard from him for some time. In the meantime I obtained another TV22 from Ian (IJK2008) it too needed work with a duff LOPT so no good for a donor set but it was with Ian’s set that I initially tried a Thorn Jellypot LOPT.

There was good reason for not going for a rewind, I had previously had one rewound for a TV24, it was a customer set and the results really were a compromise between width and EHT, the tuning cap value had to be changed for this and the value was considerably different to the original. Ian too had a rewound LOPT in his set and it was worse, the thought of spending quite a bit of money on a project set or even on the burned out set and not getting paid was a bit off putting.

I had one of the early 950 red bodied Jellypot transformers, these were allegedly the worst ones Thorn made as they didn’t use a low output overwind, they could supply 16Kv right of the winding via a single EHT stick, I knew the Bush would only need half that and deduced that the transformer would be reliable at that level.

In the meantime

I had a stroke of luck which was purely by chance, I had been returning from a job in Glasgow and was passing through Dalry when I spied a skip and a bloke throwing an old Mullard box into it, I promptly stopped and after asking a couple of questions the unopened Mullard CRT box and also a Mazda one was in the van. Later on I was gobsmacked to have found out that I got two NOS tubes, an MW22-16 and a CME1702.

This hastened on the work on Ian’s Chassis, I followed loosely the Bush circuit, I had to add in a Blocking oscillator for the line stage, I managed to still use the PZ30 and PL38 but eventually changed that to a PL36 with slight change to the valve base wiring, for good width and 8Kv EHT the line stage only needed 85v HT. I didn’t add in any regulation or any other refinements. Width and linearity were still handled by the original controls, picture was excellent with a much brighter result at higher brightness and contrast without defocussing, The HT to the line stage was fed via a potential divider from the 205 volt line.

Around this time unfortunately I was paid off from my job for no reason, It caused a lot of distress at the time as I was advised to go to a tribunal, I was of course suffering with heart issues and dodgy knees, added to that severe stress when I was dismissed, I decided not to go through the stress of the tribunal. The next few months though were difficult and I was told I needed a Heart Bypass. This kind of restricted my projects but after I had the bypass done at the end of March 2016 I began to recover. The original problems were resolved but it has left me with some other issues and the knees are still not done.

Fast forward to late last year

Lo and behold the owner of the first set came on the phone, after many e-mails and texts from me to say if he didn’t get in contact I’d scrap the set. I’d already given the cabinet away and was using Ian’s cabinet for the experiments. Fortunately I was able to get the cabinet back and after a bit of discussion I decided the best plan was to get the set back to him repaired. This actually came at the right time as Anne had just been through a Hysterectomy in February of this year, she had to stop all the work she did for clients so money was tight. The set went back with its NOS Tube and the Thorn 950 LOPT, the picture was stunningly good and the customer was over the moon and was happy to pay my price. The set had been here though for 6 years, Of course it was actually Ian’s chassis in the customers cabinet.

Here is a YouTube of the set working just prior to the time it went back, the striations were put right before delivery

Line Standard Experimentation

After Anne was feeling better a bit I then started on the original chassis, it is the earlier deck with EF91’s. I decided I wanted to play around with older lower definition standards on this set. Bob has a good stock of Jellypot’s all NOS so I was able to get another red 950 LOPT. I decided to take a different approach with this and do away with the PL36 & PZ30. In their place I used PL36, PY800 & PY33. There is plenty of room on the chassis for extra bases and the dinky Thorn LOPT. I also felt that HT stabilisation might be needed for 180 & 240 Lines. On the other set It was obvious that these LOPT’s are very efficient so a CRT with half the deflection angle and half the EHT requirements would mean again the line stage would be running in starvation mode. I was not keen on using Thorn’s stabilised EHT/Width arrangement due to getting the correct balance and of course if any part of it failed giving rise to double EHT etc. Again a Line blocking oscillator was needed, the Bush width and linearity coils were dispensed with this time as well.

Initially I used a variable PSU for tests on the lower standards as it was easier to monitor width and EHT. On 405 HT was around 105v, 240 only 90v, 180 down to 85, going to 120 actually required a little more and was back to just over 90 volts. Results were OK ish, the frame timebase will run at 25Hz but tends to cramp at the bottom, fiddling around with the resistors on the height and linearity improves matters as does fitting a 30PL1 which is a pluggable replacement in the TV22, the set though suffers with linearity drift and still does, I’m convinced it is the valve base that is to blame because every thing has been replaced, unless it is the use of a different frame blocking oscillator transformer, drive is spot on though.

Eventually I decided on just 180 lines and 240 lines and added in a shunt HT stabiliser this hugely improved the sag on HT with high brightness and remember I was using a 7BP7 Radar CRT for this project. Results were good but I needed to make the stabiliser able to be switched to accommodate the different HT required for the standards changes. It was at this time I thought I’d use avalanche diodes to stabilise the EHT and this idea has worked brilliantly , 6, 1Kv diodes were wired in series between EHT and ground brightness was adjusted to a little over what you’d go on a peak white raster and HT was set so there was no sag and 6Kv reducing the brightness the EHT remained at 6Kv so we had a solid 6Kv at all beam current levels, after that I removed the shunt stabiliser for HT, in effect the the whole system is stable, width also remained fairly reasonable between 180 & 240.

I got bored with 180 and 240 lines, even on the long persistence 7BP7 the flicker was grim you couldn’t watch a program in the tube anyway so I ditched these standards, I went back to 405 line only and started doing other things like adding in the flywheel sync circuit from the Thorn 1500, changing the video amp from an EF91 to 30FL1 with a cathode follower, that made a big improvement to video drive and contrast, I moved off the ECL80 line oscillator and sync separator to again a 30FL1, this gave me more line drive and stopped LHS foldover. Eventually I tried the CRM93 from my TMB272, increased the EHT to 9Kv and got a beautiful bright picture that has to be the best I’ve seen on a 9 inch round CRT.

CRT Substitution Experiment

The last bit of madness was to try a Sony TV9-90 CRT out of a scrap set with scan coils etc, It actually worked first time and amazingly well, supplies were needed for focus but that was easy enough from the boost line.

On the 7BP7 & CRM93 I had to arrange some way of controlling width and line linearity to a degree as I dispensed with the original controls. One method that works on these tubes is a home made width sleeve. I had some thin copper foil and after a good few attempts I managed to get this to work and reduce the stretched picture on the left. I sandwiched the foil between masking tape and slid it into the scan coils, really fiddly and time consuming but an effective answer. The thin neck of the Sony TV9-90 tube though is not easy so I’ve not pursued the idea. I would like to try and obtain a CRM93 for the set as this hopefully will be the last thing to do once of course I sort out the frame linearity drift. Overall it has been an eventful few years with these TV22’s, I could probably draw out the TV22 circuit off the top of my head now. Both of these TV22’s were in real terms scrap but with a few mods they can be fixed up.

I’ve not gone into specifics too deeply, the article would take an age to do and could get boring, perhaps others might have a go with a set that’s destined to the bin, it’s fun and rewarding and keeps the grey matter going.

Have fun!!

Some further YouTube videos and pictures: