Bush TV22 restoration questions.

[lloydwells]

Having now become slightly addicted to old TV's I have bought a TV22. The set works sort of, one of the power resistors on the frame board is overheating which I'm putting down to a dodgy smoothing cap? What value are these and what are suitable replacements? Also I have two 2uf electrolytic caps on the underside of the main chassis do these need to be electrolytic? Another question I have another more derelict TV22 the outside of this one's CRT is flaky. Is this aquadag and is this recoatable?

[Argus25]

Hello Lloyd,

It would be helpful if you could identify the capacitors in their exact locations in the circuit or with their reference numbers. As far as I can tell there were at least two "trader" service sheets, or circuit diagrams, these listed the components with L, T, R and C numbers. The sheet numbered 1091/T38 which covered the TV22, and another 1003/T15 with minor differences and the part numbers had different C and R numbering.

In any case if you are restoring a set I would recommend all the electrolytic caps be renewed. Since vintage electros were relatively large in physical size, if they have a low uF range, usually less than 5uF or 10uF, it is often possible to replace them with non electrolytics of similar uF and voltage ratings. If this can be done it is far superior because the non-electrolytic has a lower ESR, less leakage better reliability and a much longer life and will not go physically or electrically leaky in the future.

For example the electrolytic capacitor has five failure modes 1) Shorted out due to insulation between the foils failing. 2) loss of uF value due to drying out 3) internal corrosion of contacts to the foils & goes open circuit 4) electrical leakage and 5) physical leakage of corrosive electrolyte material to destroy/damage surrounding objects.

If electrolytic caps can be avoided, as space constraints allow, then its always better to choose a non electrolyic option.

Electrolytic capacitors have become the "tool" modern equipment manufacturers use to "life cycle" their equipment. The new generation surface mount electros generally leak after a decade and destroy surrounding surface mount parts and tracks. Ones in heat stress environments usually dry out in 5 years or less.

The main filter electro in the TV22 can be rebuilt, here is a very brief article which shows a photo of this at least, from a TV22 I restored in the past, its simply a matter of machining a new base out of phenolic or similar material and adding some screws/lugs to fit new capacitors inside the original large metal canister:

http://worldphaco.com/uploads/BUSH_TV22.pdf

If you are working on one of these sets I would strongly recommend an isolation transformer in case the chassis is accidentally live.Working on mine I used an isolation transformer and earthed the chassis to help with the attachments of oscilloscopes & test generators etc.

You can clean of all the flaky external aquadag on a CRT and instead use a high voltage doorknob style filter capacitor of 500 to 1000pF on the EHT feed. Or you may be able to find some genuine aquadag paint. Conductive paint is available for circuit board repairs and other applications, though I'm not sure of the price.

Hugo.

[Freya]

I wouldn't mind betting it capacitor c28 0.75uF that's causing the resistor r30 1.2K on the frame board to overheat, component references from genuine bush sheet.
graphite spray here https://www.rapidonline.com/kontakt-...-200ml-87-0695

[lloydwells]

That's the correct resistor any problem.with using a 1uf here instead ?

[wd40addict]

You can just disconnect the capacitor for now.

It reduces the ripple on the HT line from about 0.7v rms to about 0.15 rms. The set will work fine without it, but you can see the picture expand and contract slightly as the Aurora generated 50Hz beats gently with the mains 50Hz. With it in circuit this effect becomes virtually invisible.

However given the amount that the picture size varies anyway with scene brightness it's not essential. If you do replace it ensure adequate voltage rating. It has ~185vdc on one side and ~200vac rms on the other. so must be able to tolerate (200*1.4) + 185 = 465vdc. Which is the worst case during a negative AC cycle.

[Freya]

Needs to be 1000v rating using 0.47uF in parallel with a 0.22uF.


crossed post with wd40addict

[lloydwells]

On the service sheet I have covers tv22 24 and tug24 its main deck c3 c21 and I think c24 its not very clear which is in the deflector unit under tc2 these are the ones in wondering about replacing with non electrolytics

[Freya]

No real reason why not, most prefer to fit like for like replacements and 200volt 2uF are not exactly expensive for the C21 boost and C24 DC blocking , C3 is a 25v 22uf cathode bypass.

If the sets working why not leave it as is ?

[KeithsTV]

I replaced the two 2uF electrolytics on mine with non electrolytics as I wasn't sure that the ripple current rating of the modern electrolytics was up the line scan current.

Check the 16uF C25 as well. If this fails it can cause line tearing and hum on sound and vision.

Keith

[lloydwells]

@ Freya it works of a fashion I have a decided lack of width even with the control at full the top of test card C is bent to the left theres the already mentioned overheating issue I have a very nasty thin white lime ripping diagonally back and forth across the picture and all the electrolytics are rather furry at the end. If it was behaving itself id be leaving well alone. When bough the receiver chassis was jiggered ive sorted that.

[lloydwells]

ok up and running no longer on fire however wobby top of picture

[KeithsTV]

Assuming you are using an Aurora for the testcard, check that the equalising pulse option is turned off. The 405 line spec never had equalising pulses unlike the 625 line spec. The TV22 was designed to work without these pulses. If they are present they can cause the symptoms you see.

See this thread for more details

https://www.vintage-radio.net/forum/...ad.php?t=50425

Keith

[lloydwells]

Erm how do you turn them off / on

[KeithsTV]

It's all in the manual (attached). I'm assuming that you have a version 3.0 or 3.1 where the user settings are changed using the function (switch option 3). Earlier versions had internal DIL switches.

Note that the difference between versions 3.0 and 3.1 is that the equalising pulse settings are reversed. See this thread for more details.

https://www.vintage-radio.net/forum/...ad.php?t=50425

The label on the underside of the converter will have the details of the version.

Keith

[lloydwells]

Its ok managed to download the manual problem now solved