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Old 7th Dec 2017, 5:51 pm   #21
Voxophone
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Default Re: Bush TV22 spares availability?

Quote:
Originally Posted by Keith View Post
Thanks for the further advice and encouragement - I'm going to have another look at it tomorrow. It's at a sort of upmarket antiques emporium. From a quick look inside, both chassis looked clean. Didn't notice the LOPT condition (although the rear half of the shield was missing). I don't know if the proprieters will allow me to take the back off, but worth a try. Is it possible to probe the CRT heater pins through ventilation holes, I wonder?
From memory the heater pins aren't accessible through the vent holes (unless the back is in really bad condition). The heater pins are the two closest to the lug on the CRT base.

As has been said, the heater will probably be fine, but checking it does no harm and at least rules out one potential source of a completely dead tube.

Also take note of what model the set is. If the lower deck has mainly EF91 valves it's a Mk 1; EF80s and it's a Mk 2. There's also the TV22A which has a somewhat different design, and aparrently a much more reliable LOPT than the other models.

You might also be able to make out a label identifying the CRT type. It would be worth bringing a maglite or something to look inside if you can. MW22-18 tubes (fitted to some Mk 1 sets only) are more succeptible to ion burns since they have an inline gun and no ion trap. MW22-16 has the gun off centre and should have an ion trap magnet clamped to the neck (check for this).

Don't worry too much about how the LOPT looks. Both of mine looked horrendous but ultimately work ok. Looking at what others have come across this appears to be the norm.

Good luck

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Old 7th Dec 2017, 9:03 pm   #22
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Default Re: Bush TV22 spares availability?

Hi Argus, no need to remove the pitch from the overwind.
Unsolder the leads from the 6 tags at the base of the former, some gentle heat and the core complete with pri will slide out.

Turns data was posted on the forum some time ago, but note that there are 2, tapped windings and their relative positions are important (self/ mutual cap) to the tuning and correct operation of the transformer.

I have also seen transformers that were wound in the "opposite" direction (all windings so it did not matter), presumably from different suppliers.

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Old 7th Dec 2017, 9:58 pm   #23
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Default Re: Bush TV22 spares availability?

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Originally Posted by Boom View Post
You are far more likely to get a screen damaged by Ion burn than an open heater. This is something you won't see until you have restored the set and all timbases etc are running.
I agree with this. Most but not all of the troubled CRT's I have, the gun still has reasonable emission, they have either gone soft focus or the phosphor is ion burnt or has simply darkened and lost efficiency all over, this is easy to see on round face tubes where the raster was scanned and some unused phosphor at the periphery is still normal.

This is why a tube gun rebuilding service on its own is only a partial solution, the tubes to be re-built properly must be re-screened.

I once attempted to re-screen a CRT myself, but it failed. But over 25 years ago now the particular tube, a 12LP4 was re-screened and re-gunned, by Thomas Electronics in the USA, they aluminized it too, turning it into a 12kP4. I didn't know how lucky I was at the time that the service existed.
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Old 7th Dec 2017, 10:04 pm   #24
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Default Re: Bush TV22 spares availability?

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Hi Argus, no need to remove the pitch from the overwind.
The pitch on the overwind on mine had "failed" due to the extent it had hardened and shrunk and developed large crevices in it so deep I could see the overwind in quite a few places in the bottom of the cracks. So the lopty certainly would have failed if I had left it like that I think. The pitch has to go in my opinion, using the slow mineral turps method. Plus once its removed its much easier to work on the transformer without putting any stress on the wires that lead to the windings.

Do you know where the data/link is that shows the taps ?

Its also important that the phase/winding direction of the overwind is correct wrt to the primary (plate connection) so the peak primary voltage adds in phase to create the correct EHT.
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Old 7th Dec 2017, 10:45 pm   #25
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Default Re: Bush TV22 spares availability?

Hello.
I have been reliably informed that other line output transformers can be substituted into this set. I have a Bush TV22 that has been languishing in my loft for a very long time. I would think it is now time to do something with it.
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Old 7th Dec 2017, 11:08 pm   #26
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Default Re: Bush TV22 spares availability?

Interesting the notion of being reliably informed. If that was true, I imagine it would only be for other Bush TV sets with similar circuit designs and or CRT sizes/deflection angles, like TV24, or that were direct Bush clones.

Generally the design of the lopty's overall inductance, turn's ratio, winding taps, winding DC resistance, coil mutual inductances, operating voltage and design of deflection yoke it operates with, is pretty specific to the particular manufacturer & set model or close model to it. Unlikely you'd get a drop in replacement for one from another manufacturer's set, unless it was just the same set re-badged.

Do you have a list of makes/models that used an identical transformer ?
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Old 8th Dec 2017, 10:40 am   #27
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Default Re: Bush TV22 spares availability?

Quote:
Do you have a list of makes/models that used an identical transformer ?
The TV22 LOPT was used only in 9" & 12" models, such as the TV24/TUG24.
The later TV22A model used a different type, in fact the top chassis was entirely redesigned using the more modern PL81 & PY81 and was used in the 14" TV32 and it's relatives.

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Old 8th Dec 2017, 11:07 am   #28
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Default Re: Bush TV22 spares availability?

If you are paying good money for it and there is no guarantee offered, you should be entitled to examine it carefully. You would not buy a car without opening the bonnet.
You need to make sure it is complete with all valves, and still has getter flash and therefore vacuum in the tube at the very least.
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Old 8th Dec 2017, 11:57 am   #29
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Default Re: Bush TV22 spares availability?

Sadly, on removing the back and having a good look, it turns out that the CRT heater is o/c. Needless to say I declined to buy it! Hey ho...
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Old 8th Dec 2017, 12:53 pm   #30
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Default Re: Bush TV22 spares availability?

A better bet would be to buy one from a forum member who would know what condition is is in, less nasty surprises that way.
Buying blind is OK but the price has to reflect the risk.
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Old 8th Dec 2017, 1:24 pm   #31
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Default Re: Bush TV22 spares availability?

Sorry to hear that. At least you spotted it before parting with any of your hard-earned cash!

There are quite a few on eBay at the moment, but more of a gamble involved there and they usually won't be cheap.

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Old 8th Dec 2017, 2:57 pm   #32
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Default Re: Bush TV22 spares availability?

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Originally Posted by Argus25 View Post
Interesting the notion of being reliably informed. If that was true, I imagine it would only be for other Bush TV sets with similar circuit designs and or CRT sizes/deflection angles, like TV24, or that were direct Bush clones.

Generally the design of the lopty's overall inductance, turn's ratio, winding taps, winding DC resistance, coil mutual inductances, operating voltage and design of deflection yoke it operates with, is pretty specific to the particular manufacturer & set model or close model to it. Unlikely you'd get a drop in replacement for one from another manufacturer's set, unless it was just the same set re-badged.

Do you have a list of makes/models that used an identical transformer ?
I believe Fernseh converted a TV22 to use a Ferguson Potted Line transformer quite a long time ago and also my friend Trevor has done this as well.
He recently has been expeimenting with other television line standards on a TV22.
You will find all you need to know here: http://golbornevintageradio.co.uk/fo...d.php?tid=6537
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Old 8th Dec 2017, 3:31 pm   #33
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Default Re: Bush TV22 spares availability?

That's a shame! I bought one with a partially shorted CRT heater, it would light up like a light bulb with 2v on the heater, and draw a fair bit of current, it was useless in the series heater chain, and it finally went O/C while I was restoring the set. It was also the same set whose Lopty failed in! Shame really as the CRT had a lovely bright crisp picture despite the partial short. I borrowed a CRT from another unrestored set to keep the restoration going. The Lopty failed after 4 years, it even survived working 8 hours solid on display at the Festival of Vintage at York racecourse!

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Old 8th Dec 2017, 5:02 pm   #34
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Default Re: Bush TV22 spares availability?

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Originally Posted by D Cassidy View Post
I believe Fernseh converted a TV22 to use a Ferguson Potted Line transformer quite a long time ago and also my friend Trevor has done this as well.
Yes it is quite possible to re-design a line output stage and replace the EHT generator with other systems/parts, but that is quite different to dropping in a substitute transformer and having it work off the bat with the existing circuitry and no other design changes. The only way to have this is to use the exact transformer.

In American designed sets, many with what are known as RF EHT generators, they suffer from similar problems with the transformers, in this case the EHT drops with time. So one solution to those has been to add in modern plastic potted EHT generators. The only thing is, its a bit of a bodge and it leaves the system far from original.
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Old 8th Dec 2017, 5:47 pm   #35
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Default Re: Bush TV22 spares availability?

......I could have also mentioned on the topic of Lopty compatibility between different TV sets. In many/most sets the design of the line deflection is such that the H oscillator is independent from the line deflection/output stage, except for feedback for synchronization.

In the TV22, a tap on the LOPTY is used for feedback to create the line oscillator. So the exact properties of the LOPTY are important in determining the line (H) operating frequency too as was found in the cited thread:

http://golbornevintageradio.co.uk/fo...d.php?tid=6537

apart from the other parameters previously noted which ensure the deflection width and EHT are simultaneously correct.

So a substitute or non standard transformer for a TV22, even if it had some winding tap available, likely would have an operating frequency issue requiring significant circuit design changes to have it operate satisfactorily. Probably it would require moving to a separate H scan oscillator.

So using a non standard LOPTY in the TV22, the entire design of the line output stage/oscillator would need to altered which is very messy.

It is better to replace it with the exact part or rewind it.

Last edited by Argus25; 8th Dec 2017 at 5:58 pm. Reason: repeat link
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Old 8th Dec 2017, 6:18 pm   #36
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Default Re: Bush TV22 spares availability?

Hello.
Thank you very much for your comments. I will discuss this with my good friend over the weekend.
I do know that he did another TV22 a few years back with either the same type or similar one with great success. I have seen the pictures, they are stunning. I also believe that the original valves were used and only an extra transformer was required in the line oscillator. He has told me that rewinds are around 150 which is a lot of money if you are doing the hobby on a shoestring. I'm not a TV man by any means though, so really can't comment.
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Old 8th Dec 2017, 9:12 pm   #37
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Default Re: Bush TV22 spares availability?

Hi Gents, not sure where the quote of 150 for a rewind came from, but the are considerably less than that.
LOPT is the most expensive, then frame and sound outputs, then blocking osc.

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Old 8th Dec 2017, 9:38 pm   #38
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Default Re: Bush TV22 spares availability?

Hi Argus, there was an article in Radio Bygones in Autumn 2016 that gave the winding details.

Totally agree about the pitch cracking and removal, but not necessary to remove it ti get at the primary. Note that some transformers have the EHT heater winding on a separate ceramic tube, glued on with pitch.
The overwind connects to pin4 and the PL38 anode: 1040 turns, tap (pin 5) for metrosil then 310 turns and the line lin coil (pin 6)

pin 3 boost anode, 630 turns tap pin 2 to width coil, 60 turns pin 1 to HT

A wire 0.25mm dia

Note that there is an offset start or finish on one winding and this together with the amount of insulation used can affect the coil self capacitance.


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Old 8th Dec 2017, 10:42 pm   #39
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Default Re: Bush TV22 spares availability?

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He has told me that rewinds are around 150 which is a lot of money if you are doing the hobby on a shoestring.
I did not know these were so expensive, but I guess given the "one off" nature of the job and the time consuming nature of it, it doesn't surprise me. probably this would be with the repairer stripping the old transformer and keeping the original former & core.

It would be good to have a bulk batch of the coil assemblies made, at least 30 to 50 units by a transformer company arranged with a new former for the EHT coil & tags and a primary winding such that the old iron core could slip into it. This might get the cost for the coil assembly down below 30 pounds at a guess.

In fact it might be worth a vote. I would buy such a spare part/coil assembly now, if it were for sale, given the unreliable nature of the original part.

It might be possible if enough TV22 owners would do it too, we could all front up the money to get them professionally wound.

I wonder how many TV22 owners are "out there" and what % would want to buy a spare coil assembly, assuming a reasonable cost ?
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Old 8th Dec 2017, 11:02 pm   #40
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Default Re: Bush TV22 spares availability?

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Originally Posted by Ed_Dinning View Post
The overwind connects to pin4 and the PL38 anode: 1040 turns, tap (pin 5) for metrosil then 310 turns and the line lin coil (pin 6)
pin 3 boost anode, 630 turns tap pin 2 to width coil, 60 turns pin 1 to HT
A wire 0.25mm dia
Ed,

Thanks for that data.

On this thread:

https://www.vintage-radio.net/forum/...ad.php?t=37396

he used 0.22mm wire. It might be that this refers to the wire without the enamel.

It looks like the bulk of the tuning capacity is across pin 1 & 3 , the 470pF, so probably this could be adjusted to allow for different overall self capacitance or slightly different insulation etc of a rewound transformer.

Can I ask Ed, if you had this set with a failed Metrosil on pin 5, what component/s would you replace it with as an electrical equivalent ?

Hugo.

Last edited by Argus25; 8th Dec 2017 at 11:12 pm. Reason: ask question
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