Bush TV24C

[Murphyv310]

Yes indeed.
I always wonder how long these sets have been unused.
The interesting thing with this set is the good condition of the main smoothing capacitors, bang on capacity and good ESR.
The warm up time is very long. Monitoring the voltage on the CRT heaters is odd. They rise to 3.1v in around a minute then they slowly rise to 3.8v then drop back to 3.5v then slowly rise to 5.6v maximum. There is a raster at 4v and the picture shows around 4.8v. Warm up time to 5.6v is nearly 5 minutes. I suspect the thermistor is the problem so if I have one I'll replace it and see.
5.6v on 6.3v heaters is bit too low, all the valves look dull, I've not checked the full chains voltage or current as of yet.

[ppppenguin]

Could be the thermistor. Otherwise has somebody been mucking about with the dropper? But the thermistor is more likely.

[Murphyv310]

I'm sure it's the thermistor, its common on most of the Bush sets of the era. Low heater current is as bad for valves as much is over running them. Take for example a rectifier. Low heaters, will result in low HT and increase the dissipation in rectification increasing heat. This is far more noticeable in a TV than a radio. In fact in this set the HT is below the spec, bringing up the heater voltage to its correct level increases HT by 15v. Later last evening I realised the HT drops slowly after the initial warm up. With the correct heater current this gradual sag doesn't happen and the reduction in width is cured.

[ppppenguin]

It's amazing how good that CRT is, even with only 5.6V on the heater.

How important is the thermistor? I know it reduces the switch-on surge but plenty of TVs managed without one. Presumably you'd need a bit more dropper resistance if you bypassed the thermistor.

[`FRANK.C]

Hi Trevor
That heat up time sounds to be about the same as mine.
I have never measured the heater voltages.

Frank

[Murphyv310]

Hi.
I simply bridged out one of the 66 ohm sections on the dropper the CRT heater voltage is now between 5.95v and 6.1v depending on where the mains is floating to.
Now have stable width and sensitivity is up. Warm up time still takes 4 minutes a little better than before, I'd still prefer to use a thermistor, but this method will do till I find one.

[LENINGRAD T2]

During the 1940's and early 1950's, television broadcasting times were quite short. So the picture tubes were wearing out slowly. Looking at the different types of cathode ray tubes from that period, I come to the conclusion that today they are usually good or very good. CRTs that are damaged most often have lost their vacuum or have mechanical damage. It is rare for them to have poor emissions due to wear and tear. For example, I have several models of German TV with a round cathode ray tube B30M1 / Rembrand, Rubens, Iris, Weissensee /. All these televisions retained excellent cathode ray tube emission.

[Murphyv310]

Hi.
When I started in the trade in 1970 as an apprentice CRT changing was common place. In my first company (British Relay) we handled a lot of Murphy sets. Even then there were a lot of V310, 410, 510 & 659s out on rental. If the customer was happy with the set a regun tube was fitted from Renvu Tubes in Renfrew.
Many of them were on the original CRT not bad for up to 12 years of most likely hard use.
After 1955 we had two channels in the UK so with more choice the sets were used more often. BBC2 started in 1964 on 625 lines but many customers wanted to hold onto their 405 line only sets even into the early 70's, a lot didn't like the choice of programmes on BBC2 and being in Scotland wouldn't waste money on something that would hardly be used. Things did change when later our local transmitter opened improving the UHF signal, by 1974/5 there were very few 405 line sets in service.