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Old 15th Oct 2019, 5:36 pm   #1
Helder Crespo
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Default Bush TV22 Mk2 - first approach using a variac

Hi
This is my very first post in the forum. I recently got a TV22 Mk2 in very good original condition, i.e., the cabinet looks great and will only require some light polishing and waxing, the chassis is solid, as are the wood side panels, there are no signs of major overheating anywhere, corrosion/rust spots are minimal, the tube looks great by eye (still has original sticker on), the rubber wiring is mostly very good and bright, apart from the two mains dropper wires (a common issue), and all components (including all valves) seem to be in place and original. I gave the chassis a first clean (mostly dusting and some degreasing). The focusing mechanism (the lever is intact) was initially very hard due to dried out grease, but some cleaning with WD40 solved this perfectly and it now works very smoothly.

I went through the many great posts in the forum devoted to repairing and restoring these sets, and clearly there are many possible approaches that can be followed prior to plugging it into the full mains. One thing I'd like to try is to use a variac to hopefully reform the electrolytics (after removing and noting all valves) at least to the point of doing a crude test with all valves in place with the hope of seeing first light (while paying attention to the valve heaters and with a quick finger on the mains switch) prior to starting a full recapping (frame output stage first, RF stage last). From my readings here in the forum, I understand that some of you may not advise such an approach at all, but on the other hand there are several reports of successful "slow waking ups" based on using a variac or a bulb limiter. I intend to post photos and details of any relevant progress as I move on. I would really appreciate any advice on this from the many experienced forum members.
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Old 15th Oct 2019, 7:13 pm   #2
stevehertz
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Default Re: Bush TV22 Mk2 - first approach using a variac

Change all wax capacitors on sight. Remove all valves and clean their bases and pins using proprietary switch cleaner, similarly all switches, pots and connectors. Replace all electrolytics. That's what I'd do before anything else, because if you do this you will have removed a very large proportion of the faults that will exist in that TV.

I have an EF80 TV22 in excellent condition that is patiently awaiting (for the past 30 years) restoration and that's what I'll do. Others like to address faults piece meal. I don't see the point of that when the end goal (for me anyway) is to get the set working with as little risk as possible and also wanting to avoid future failures as a result of iffy components giving up the ghost or performing way out of spec.

Best of luck!
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Old 15th Oct 2019, 8:15 pm   #3
Helder Crespo
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Default Re: Bush TV22 Mk2 - first approach using a variac

Many thanks for your quick reply. This makes a lot of sense to me too. Even though I understand and appreciate the concept of patience - and you surely made a point there too, as proven by your own EF80 TV22 - sometimes it takes someone else's opinion to counteract one's gambler's mentality.
I'll do a shopping list for all caps. Do you have any recommendations regarding a supplier? I know that Just Radios in Canada sells polypropylene caps with unusual values (by today's standards), such as 5 nF, but we obviously can get by with the usual 4.7 nF plus or minus 10%. Regarding the electrolytics, I'm not really into restuffing the old cans, not even the dated ones (I'll keep them though, together with the waxies, as part of the history of the set), but it would be great to get new ones as close as possible in size and appearance as the originals. Many thanks once again!
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Old 15th Oct 2019, 8:27 pm   #4
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Default Re: Bush TV22 Mk2 - first approach using a variac

Personally I like to ‘compartmentalise’ a restoration project ie on a ‘two deck’ set such as TV22 starting with power supply & timebases (disconnecting HT from RF deck) I’d replace electrolytics to get you going (you can always restuff later if you’re feeling enthusiastic) - the risk with ‘shotgun’ replacement of capacitors is that if you make a mistake it may take a long time to diagnose and correct

But everyone to his/her own - I know of quite a number of totally successful ‘blanket replace’ restorations - I just don’t have enough confidence in my own eyesight/concentration for this approach.

Anyway best of luck with whatever approach you take - I’ll follow with interest

Kindest regards

John
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Old 15th Oct 2019, 10:13 pm   #5
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Default Re: Bush TV22 Mk2 - first approach using a variac

Before supplying the set with power from the mains it might be a good idea to apply the warm up technique to the line output transformer.
Connect up 20 to 30volts DC between the EHT winding and the top cap connection of the line output valve.
I assume your set is the version with the line timebase compartment on the right side of the chassis.

DFWB.
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Old 15th Oct 2019, 10:26 pm   #6
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Default

Thanks John. I'll definitely replace the electrolytics too. I recently got a working DAC90A still running on its original caps (including the mains waxie and the infamous That Capacitor), and the fact that it nevertheless works made me think that I could skip a blanket replacement at this stage, but the added complexity and EHT of the TV22 are surely less tolerant to capacitor leaks, so I'll try to play it as safe as possible (within the limits of my own inexperience).

Thanks DFWB. Yes, the line timebase compartment in on the top right of the chassis (as seen from the back), but don't all TV22s share this characteristic, regardless of Mk? This is a photo of my set as I got it, prior to any dusting and cleaning.
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Old 16th Oct 2019, 3:26 am   #7
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Default Re: Bush TV22 Mk2 - first approach using a variac

Sounds like you landed a great set.

It is good that everybody generally agrees the better move is to replace the waxies and electrolyic caps before powering the set. Also checking cleaning the valve sockets, checking resistors are in spec etc and replacing what is necessary.

In the case of the LOPTY, if pitch coated and you can see cracks extending down to the overwind, I would not power that until the pitch was dissolved away and the Lopty varnished (there are other threads about doing this)

It is tempting to want to power the set to see what happens, but its much safer to replace the parts first and make sure everything is as sound as it can be. Once that is done there is also no need for a variac, it is needed when the capacitors are old and in a risky condition, so if you reach for the variac with a notion of re-forming old electrolytics it is worth thinking twice if you should be doing that in the first place.

There is a picture in this article of rebuilding that large dual electrolytic in the TV22:

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

Last edited by Argus25; 16th Oct 2019 at 3:34 am.
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Old 16th Oct 2019, 7:28 am   #8
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Default Re: Bush TV22 Mk2 - first approach using a variac

Quote:
Originally Posted by kan_turk View Post
Personally I like to ‘compartmentalise’ a restoration project ie on a ‘two deck’ set such as TV22 starting with power supply & timebases (disconnecting HT from RF deck) I’d replace electrolytics to get you going (you can always restuff later if you’re feeling enthusiastic) - the risk with ‘shotgun’ replacement of capacitors is that if you make a mistake it may take a long time to diagnose and correct

But everyone to his/her own - I know of quite a number of totally successful ‘blanket replace’ restorations - I just don’t have enough confidence in my own eyesight/concentration for this approach.

Anyway best of luck with whatever approach you take - I’ll follow with interest

Kindest regards

John
I'm not really understanding your fear of "shotgun" replacement of capacitors as you put it. One doesn't cut out all the caps and then put new ones in. Each cap is replaced one at a time. So for example, you snip out a 4.7uf cap and replace it immediately with a 4.7uf cap. Surely anyone capable of restoring a relatively complex piece of vintage valve equipment can do that without putting in the wrong value? Then you replace the next one, and so on.
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Old 16th Oct 2019, 7:32 am   #9
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Default Re: Bush TV22 Mk2 - first approach using a variac

I use Cricklewood components for capacitors. They have a wide range suitable for vintage restorations.
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Old 16th Oct 2019, 9:17 am   #10
Helder Crespo
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Default Re: Bush TV22 Mk2 - first approach using a variac

Hi stevehertz
Thanks for the tip on Cricklewood components. Their webpage is very good, and they're based in London, which is very convenient for me.
Helder
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Old 16th Oct 2019, 9:32 am   #11
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Default Re: Bush TV22 Mk2 - first approach using a variac

Quote:
Originally Posted by Argus25 View Post
Sounds like you landed a great set.

It is good that everybody generally agrees the better move is to replace the waxies and electrolyic caps before powering the set. Also checking cleaning the valve sockets, checking resistors are in spec etc and replacing what is necessary.

In the case of the LOPTY, if pitch coated and you can see cracks extending down to the overwind, I would not power that until the pitch was dissolved away and the Lopty varnished (there are other threads about doing this)

It is tempting to want to power the set to see what happens, but its much safer to replace the parts first and make sure everything is as sound as it can be. Once that is done there is also no need for a variac, it is needed when the capacitors are old and in a risky condition, so if you reach for the variac with a notion of re-forming old electrolytics it is worth thinking twice if you should be doing that in the first place.

There is a picture in this article of rebuilding that large dual electrolytic in the TV22:

http://worldphaco.com/uploads/BUSH_TV22.pdf
Hi Argus. Thanks for the tip regarding the LOPT. Next time I'm in London (that's where my set is) I'll inspect the pitch to see if a full strip and varnishing are required. I understand that this can also help with heat dissipation, but I still find the pitch removal procedure a bit risky. I've read reports of two different approaches: thermal (put it in the oven) and chemical (dip it in some solvent).
I am aware of your great article, which is part of my small collection of TV22 tech notes. Again, I'm not much into restuffing right now, but may end up doing it once the TV is back in operation.
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Old 16th Oct 2019, 10:40 am   #12
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Default Re: Bush TV22 Mk2 - first approach using a variac

Quote:
Originally Posted by Helder Crespo View Post

Thanks DFWB. Yes, the line timebase compartment in on the top right of the chassis (as seen from the back), but don't all TV22s share this characteristic, regardless of Mk? This is a photo of my set as I got it, prior to any dusting and cleaning.
Hi Helder,
In 1952 Bush introduced the model TV22A which has completely redesigned timebases. The frame blocking transformer oscillator used in the earlier sets was replaced by a cross coupled multi-vibrator and the line timebase employs a self oscillating output valve.
From the Radiomuseum, info about the TV22A:
https://www.radiomuseum.org/r/bush_tv22atv_22.html

DFWB.

Last edited by FERNSEH; 16th Oct 2019 at 10:46 am.
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Old 16th Oct 2019, 10:53 am   #13
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Default Re: Bush TV22 Mk2 - first approach using a variac

The idea of getting it going (first light) with minimal component replacement is to prove the critical parts, CRT and LOPT for example, are all working. I am not sure how experienced you are but fault finding a set where the wiring may have been disturbed or replacement components accidentally wired to the wrong pin is very difficult.

I would go for the minimum of parts replacement in the line and frame stages and try it, just don't leave it running for long. Once you have a reasonable raster you can complete the full restoration.
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Old 16th Oct 2019, 11:02 am   #14
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Default Re: Bush TV22 Mk2 - first approach using a variac

Hi Helder,

We meet again! Glad you've posted on this board and you're going to have a go yourself. You'll find here a useful store of experience and knowledge - and enthusiasm!

You'll probably also seen my own example of a TV22 restoration HERE. This also used 'replace all waxies and electrolytics' technique - though only one at a time!

There are different views held about doing this. In my case, it was the best option because the restoration was a commercial one. Time was of the essence and I wanted to achieve a set with as many as possible of the faults removed, as quickly as possible and with minimal effort.

However, if you are electrically competent, aware of the various safety hazards and yes, ideally have a variac, then you 'should' learn much more by gradually bringing the set to life as you fix each fault - one at a time. Although for the beginner, there may well be episodes of despair during the learning process! Some experienced folk may find doing things this way quicker and more efficient than doing a 'blanket replacement'. It's also time-efficient, because they often know the faults they'll find before they check and they can 'read' the raster (for example) for clues.

As regards the TV22 LOPT, I know there are those here who may consider my method of warming and pulling off the pitch excessively 'brutalist'. Again, in my case, this was simply much quicker than leaving it for days to dissolve in olive oil. As has been suggested elsewhere here, thoroughly drying out the windings by passing a current through them can be a good idea and improve the performance later. I invite opinions as to whether the direction of flow of the warming DC makes any difference as regards polarising the core...

Once in its cabinet, a TV22 can run rather warm when left on for a long period. On occasion, I have fitted a small fan into a circular hole cut into the top of the LOPT cover.

The rubber insulated multicore wiring from the RF/IF tray and the internal mains wiring can perish inside even when it looks OK outside. It's nice to keep the looms looking as original as possible externally when replacing their internals. In my case, working commercially, I always replaced all the mains wiring regardless of apparent condition.

Again, some would throw up their hands in horror when in this case I didn't seek out a new 'correct' mains connector but wired in a new mains lead directly, with strain-relief and a grommet. I drew comfort from my understanding that the original-style connectors today are only legal up to 50v.

So there you have it Helder. Enjoy getting to know your new TV22 - a recognised style icon that can work jolly well too. You'll find plenty of support available here.

Steve
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Old 16th Oct 2019, 11:11 am   #15
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Default Re: Bush TV22 Mk2 - first approach using a variac

There is one thing to look out for which I haven’t seen mention of yet, there are some wax caps decoupling the valve heaters on the RF deck, which if not at least disconnected before attempting a power up can short out and over run some of the valve heaters and the CRT heater. They don’t normally short out right away either, so you think you have got away with it until next time you power the set up and notice it only took 10 seconds for the line whistle to start, then look round the back of the chassis to see some valve heaters not lit at all, and the ones that are lit are glowing like light bulbs!

Regards
Lloyd
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Old 16th Oct 2019, 1:32 pm   #16
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Default Re: Bush TV22 Mk2 - first approach using a variac

Quote:
Originally Posted by Helder Crespo View Post
I understand that this can also help with heat dissipation, but I still find the pitch removal procedure a bit risky. I've read reports of two different approaches: thermal (put it in the oven) and chemical (dip it in some solvent).


As pitch ages the lower molecular weight hydrocarbons leave the pitch via evaporation. This shrinks the volume of the pitch and causes it to be less viscous and more brittle. So it hardens and cracks. These cracks & crevices in the material allow atmospheric water vapor to enter the windings. It also encourages corona discharges.

In addition, another reason for failure of this LOPTY is that the PL38 can acquire a positive grid bias due to the g1 coupling cap going leaky. This further heats the transformer.

Once the pitch has lost its low MW hydrocarbons and has become brittle, heating it won't cause the pitch to melt or flow. If you stick the transformer in the oven, or use a heat gun on it, all you will achieve is to further harden the pitch and bake it on and heat stress the transformer's insulation.

It is much better to place the transformer in a bath of solvent (mineral turpentine is the superior product) and let the pitch soften and dissolve over a few days, and then use a multiple varnish dip after that, either professional transformer varnish, or I have found that marine grade spar varnish is perfectly fine. (PS olive oil will not dissolve hardened pitch in your lifetime)

Never pick at the pitch, it will damage the windings, especially on the fragile EHT winding or "over-wind".

It is possible that the pitch coated transformer in your set might not need any restoration, check it for crevices and cracks in the pitch surface.
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Old 16th Oct 2019, 1:40 pm   #17
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Default Re: Bush TV22 Mk2 - first approach using a variac

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... heating it won't cause the pitch to melt or flow. If you stick the transformer in the oven, or use a heat gun on it, all you will achieve is to further harden the pitch and bake it on and heat stress the transformer's insulation.
Not my experience. The pitch softened and could be gently peeled off. Only gentle heating was used though.

Quote:
Originally Posted by Argus25 View Post
Never pick at the pitch, it will damage the windings, especially on the fragile EHT winding or "over-wind".
This has never happened to me, though I agree that there is a risk and the 'dissolving' method is intrinsically gentler and safer.

Steve
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Old 16th Oct 2019, 1:45 pm   #18
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Default Re: Bush TV22 Mk2 - first approach using a variac

You might have been lucky. It does depend on how hardened the pitch has become. If it is not too brittle it still may flow well with heating. Fresh pitch for example does melt and flow quite well with heating.
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Old 16th Oct 2019, 2:10 pm   #19
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Default Re: Bush TV22 Mk2 - first approach using a variac

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Originally Posted by stevehertz View Post
I'm not really understanding your fear of "shotgun" replacement of capacitors as you put it.
Hi Steve,
I think the point is, is that if you a new to television restoration then it can be very hard to diagnose a self created fault. If one capacitor is changed at a time (testing the set after each one) then you can easily spot if you make a mistake and learn about how each component is linked to particular fault symptoms.

However, I would say that the Bush TV22 is much neater in terms of component placement than say a PYE of the same period. Also, the TV22 does have some really fragile wound components such as the frame oscillator transformer and the line output transformer which can be damaged by powering the set with leaky wax caps (the Metrosil is also easily damaged). So for the TV22 I do think changing all the capacitors in one go is probably the best way to go.

Cheers
Andy
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Old 16th Oct 2019, 2:32 pm   #20
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Default Re: Bush TV22 Mk2 - first approach using a variac

Hi Helder Crespo,
welcome to the world of the TV22. For all the jokes I make about these sets, my own TV22 probably gets used more than any other set in my collection.

A bit of advice...

Powering up the set with no valves in is a no no. Unlike most valve radios, TV sets such as the TV22 have a series heater chain, so removing any valve can result in heater cathode breakdown of other valves in the chain.

The chassis is connected to one side of the mains.

Re-forming with a variac is not a great idea for a TV, but if you do, then you need to make sure that the main HT feed is disconnected from the set since you can't remove any valves. Applying a low HT to the timebases can result i damage to the wound components.
With no HT load you must not wind the variac up to 100% as you may well exceed the voltage that the smoothing capacitors saw in service. If I reform electrolytic caps I disconnect the HT output first and then power them from a dedicated capacitor re-former. There are many circuits on the internet for these. There is more chance of success if you re-form a capacitor to the HT voltage quoted in the manual than to try to re-form it to the voltage rating written on the capacitor itself.

The main smoothing can usually re-forms ok, but the 16uF capacitor on the underside always seems to be low in value.

Before you think of powering it up, make sure you cut one end of the big waxie at the front (0.75uF) and one end of the 0.1uF class X capacitor (next to the mains dropper).

Cheers
Andy
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