UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Television and Video

Notices

Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc.

Closed Thread
 
Thread Tools
Old 20th Feb 2005, 11:39 am   #1
af024
Octode
 
Join Date: Jan 2003
Location: Ashby-de-la-Zouch (it's not by the sea)
Posts: 1,254
Question Pitch-covered LOPTxs

I have one of those bitumen (pitch?) -covered LOPTxs that has great chunks of covering missing (flaking off) and the windings are now exposed. I was hoping to re-cover it with something suitable which:-

(a) has the same look and finish
(b) similar electrical insulating properties (or better)
(c) won't melt under normal operation
(d) spreadable with spatula or brush (to apply)
(e) something which won't attack the exposed windings

Does anyone know what might be suitable? Is there anything in a tin that I could buy from (say) a builder's merchants? How about genuine tar?

Looking forward to a reply.

Many thanks in anticipation.


Andy
af024 is online now  
Old 20th Feb 2005, 9:37 pm   #2
Ed_Dinning
Dekatron
 
Join Date: Jan 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 8,171
Default Re: Pitch-covered LOPTxs

Hi Andy, I believe the windings were originally "dunked" in pitch, you could probably get some form your local roofer, but use it at a temperature at which it has just melted. The various "brushable " compounds for DIY shops may present problems as they all contain solvents that may attack the enamel on the wire. I have often used paraffin wax, which will dissolve pitch and melts at a lower temperature as well as looking black. It can even be brushed on in its molten state.

HTH ED
Ed_Dinning is offline  
Old 21st Feb 2005, 7:24 pm   #3
af024
Octode
 
Join Date: Jan 2003
Location: Ashby-de-la-Zouch (it's not by the sea)
Posts: 1,254
Smile Re: Pitch-covered LOPTxs

Thanks Ed - I appreciate that.

I was (am) really worried about solvents attacking the windings, so I shall go and hunt down some tar from somewhere. I suppose I could always leave well alone altogether? Would that be a mistake do you think?

Will parafin wax melt during normal operation? I can't say that I know what I'm looking for here to be honest.

Regards,


Andy
af024 is online now  
Old 22nd Feb 2005, 9:46 am   #4
Ed_Dinning
Dekatron
 
Join Date: Jan 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 8,171
Default Re: Pitch-covered LOPTxs

Hi Andy, the LOPT itself should not run that hot, but conducted heat from other sources may cause it to warm up. The paraffin wax will penentrate the windings and give protection as it is less viscus than pitch. The surface wax may well drip off, but should do no damage.

HTH Ed
Ed_Dinning is offline  
Old 22nd Feb 2005, 5:49 pm   #5
af024
Octode
 
Join Date: Jan 2003
Location: Ashby-de-la-Zouch (it's not by the sea)
Posts: 1,254
Smile Re: Pitch-covered LOPTxs

Thanks again!

What product am I looking for - is there a brand name or something I can seek out?

[As regards the heat issue, my LOPTx and two large valves are encased in a metal tin affair. I was worried about the nearby heat plus any that my be generated in the LOPTx itself - all combined]

Many thanks,


Andy
af024 is online now  
Old 1st Mar 2005, 6:47 pm   #6
af024
Octode
 
Join Date: Jan 2003
Location: Ashby-de-la-Zouch (it's not by the sea)
Posts: 1,254
Default Re: Pitch-covered LOPTxs

Just a quick view (not the worst side!) for those of you who'd like to send sympathy ...

Cheers,

Andy
Attached Thumbnails
Click image for larger version

Name:	Bush TV24 LOPTx (1).jpg
Views:	255
Size:	95.9 KB
ID:	299  
af024 is online now  
Old 2nd Mar 2005, 9:24 am   #7
Ed_Dinning
Dekatron
 
Join Date: Jan 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 8,171
Default Re: Pitch-covered LOPTxs

Hi Andy, I've seen them worse than that and still working!
The problem may be the core. It looks rusty, a common fault, which can cause it to swell and split the former. It might be worthwhile taking all the pitch off to see the state of play (leave in a cold place and chip off carefully). It could then be re-impregnated with wax.

Ed
Ed_Dinning is offline  
Old 2nd Mar 2005, 12:17 pm   #8
Aerodyne
Octode
 
Aerodyne's Avatar
 
Join Date: Jun 2004
Location: Hampton Vale, Peterborough, UK.
Posts: 1,698
Default Re: Pitch-covered LOPTxs

It is possible that the rusted core is acting as a shorted turn: it looks as though the TX has been very hot! I would support Ed's suggestion that you strip it down to check things out.

As far as wax goes, how about black shoe polish wax? It might be stiffer than candlewax.
-Tony
Aerodyne is offline  
Old 2nd Mar 2005, 7:57 pm   #9
af024
Octode
 
Join Date: Jan 2003
Location: Ashby-de-la-Zouch (it's not by the sea)
Posts: 1,254
Default Re: Pitch-covered LOPTxs

Thanks for your replies guys.

The thing actually works ok - BUT, it might well be getting hotter than it should. It's a pain to remove, but it would be even worse to repair further damage I suppose.

I don't know about the boot polish idea, the stuff I use (once in a blue moon!) is very flakey. I don't suppose it would stick to anything. Might give a nice smell though ...

If the core looks ok and it's just a case of cracked pitch, would black-coloured silicon do the job? Mind you, it's not exactly an authenic material is it! BUT I can buy it (always a bonus).

I'm worried about running the thing with exposed windings and even more worried about using a covering material that is not inert.

Seriously, was it really the stuff that road menders use? If so, how did they dip the thing into a hot tub of the stuff and not crack things - especially the EY51? They were clever these Bush folk weren't they ...

Cheers,


Andy
af024 is online now  
Old 3rd Mar 2005, 9:42 am   #10
Ed_Dinning
Dekatron
 
Join Date: Jan 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 8,171
Default Re: Pitch-covered LOPTxs

Hi Andy, you need to be very careful with silicone as some brands give off acetic acid as the cure. This would couse havoc with the windings!!!
The EY51 would be added after it had been dunked into pitch. The pitch would be nominally the same as used on roads and for roor repairs, it starts to melt at about 50C, but is laid at much higher temps so it is really liquid.
The transformer should not run to hot in use so wax is possibly the best option, despite requiring removal to do it (it was done this way originally).
I hope to get the winding details of this LOPT shortly so it may be possible to replicate.

Ed
Ed_Dinning is offline  
Old 3rd Mar 2005, 6:53 pm   #11
af024
Octode
 
Join Date: Jan 2003
Location: Ashby-de-la-Zouch (it's not by the sea)
Posts: 1,254
Default Re: Pitch-covered LOPTxs

Thanks for that Ed - perhaps I need to go and see the council ...

Funny about the EY51 though - before I cleaned the gunge off it (using WD40 and a cottom bud), it looked just like the same black pitch that covers the LOPTx. I suppose it could have simply been 50 year old muck eh.

I shall steer clear from the silicon for sure.

Now it's a toss-up between wax (from a common household melted candle?) and good old-fashioned tar from the council. I wonder if you can get black candles (now there's a question).

By the way, what are the laminations like - is the thing simply a single stick?

Regards,


Andy
af024 is online now  
Old 4th Mar 2005, 9:58 am   #12
Ed_Dinning
Dekatron
 
Join Date: Jan 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 8,171
Default Re: Pitch-covered LOPTxs

Hi Andy, Black candles may contain Graphite for colouring, not a good idea as it is conductive. Standard candles should be OK. Pitch from the local roofing contractor or trace the guys when you small it and they are doing your neighbors roof!
The gunge was know as "black jam" a combination or grease, dust, grot and smoke particle from coal fires.
From memory the lams were a single stack that was held together by the bobbin and wer probably interleaved with thin paper. Some later models used an early Ferroxcube (ferrite) bar.

Ed
Ed_Dinning is offline  
Old 4th Mar 2005, 7:28 pm   #13
af024
Octode
 
Join Date: Jan 2003
Location: Ashby-de-la-Zouch (it's not by the sea)
Posts: 1,254
Default Re: Pitch-covered LOPTxs

Thanks again Ed.

Time to track Murphy's down methinks ....

Regards,


Andy
af024 is online now  
Old 6th Mar 2005, 4:19 pm   #14
af024
Octode
 
Join Date: Jan 2003
Location: Ashby-de-la-Zouch (it's not by the sea)
Posts: 1,254
Unhappy Re: Pitch-covered LOPTxs

Please don’t laugh ... AND don’t do this at home children.

I couldn't find any Murphy's roadworkers anywhere.

So here I am again. The saga continues .....

I decided to go and seek some melt-down tar. Several builders’ merchants later I finally found one that stocked the stuff. The only one they had was something described as ‘Ruberoid Bitumen Grade 95/25’ and came in a 40kg keg! Well it was all or nothing basically, so yes, you guessed it, such is my drive to get the job done properly that I purchased a keg (and a physio session for the back later!).

On my way back home I popped into to Woollies and bought a tall metal container that I thought would be useful when melting the stuff and dipping the LOPTx.

When I got home, I man-handled ‘the thing’ into the garage and hacked a lump off with a lump hammer. Bits flew all over the place (good job I had the goggles on I suppose).

I initially tried melting some in the container I bought by placing it in an old saucepan of boiling water (a bit like the technique used when your mother used to melt cooking chocolate). This had no impact – it simply sat there grinning at me. I then saturated the water with salt to raise the boiling point a bit and this had no affect either. Great!

I then lost my patience and put the pot directly into the burner of a camping stove. Literally ¾ hour later (and nearly an empty gas cylinder) the stuff had pretty much melted. Now considering that I only had something like 1.5 pints (maybe 2) I thought that this was very hard going. I feel for the like of Murphy’s now!!

What was particularly worrying is that the words on the side of the keg talk about the flash pint only being 250 degC! I have no idea whether I got anywhere near as I have no mean of monitoring temperatures above 100 deg C. Anyhow, as it happened, despite the odd snap crackle and pop I did survive the experiment and I did not have to call the fire brigade!

I found that I had to get it really hot before it became anywhere near workable, and, presumably because the source of heat was localised UNDER the pot, the top of the mixture seemed to want to stay rather crusty. This seemed to cause a bit of a problem when dipping something into it to get a nice coating. As the crust wanted to grab the item on the way out again!

Nevertheless, the finish is pretty much the same as the original stuff on LOPTx so from that perspective it looks promising. I have not tried to measure it’s electrical resistance yet (which is probably a good idea before I go for it for real).

I do have some issues though ...

(a) If I remove the EY51 before dipping, there would be no way to re-locate the terminals after dipping.
(b) I could dip the whole thing with the EY51 fitted, but I suspect that this would crack the valve glass envelope (although I did dip a duff EF80 and it didn’t crack)
(c) 50 deg C was mentioned as the melting point, but this didn’t happen for me – it’s obviously different from stuff already referred to. If I dip it at the elevated temperature will I wreck the thing altogether? Is it best to simply leave well alone and run it with the windings exposed etc?

I then decided to seek a possible alternative.

I came across something called ‘Bitumen Paint’ for £3.99 (in a tin). It contains ‘White Spirit’.

I dipped the other end of the duff EF80 into this and let it dry for several hours.

It doesn’t set as hard as the other stuff and it’s not as thick in one coating (so whether I should go for multiple dips is anybody’s guess).

BUT what is worrying is that it says, ‘avoid application to tar-based substrates’. Does this mean that it will attack whatever original coating I leave on the LOPTx?

What is ‘White Spirit’ anyway? It is paraffin-based?

I don’t know about its electrical insulation properties as yet.

So, let’s see, I have two products (one of which fills up the garage) and I’m still not much further forward. Bah humbug ...

Who said that the love of all electrical/electronic vintage things makes us do daft things ...

Where now folks?

Regards,


The mad one

PS The stuff gets everywhere – including the cat and carpets. So be warned – it’s worse than the residue off TCC wax caps!!
af024 is online now  
Old 6th Mar 2005, 6:28 pm   #15
Paul Stenning
Administrator
 
Paul Stenning's Avatar
 
Join Date: Dec 2002
Location: Cardiff
Posts: 9,060
Default Re: Pitch-covered LOPTxs

With some help from google I found the manufacturer's website here http://www.ruberoid.co.uk/ and in due course found a couple of datasheets:

Health & Safety data sheet
http://www.ruberoid.co.uk/netbuildpr...=187&BLOBID=89

Product data sheet
http://www.ruberoid.co.uk/netbuildpr...D=187&BLOBID=7

The product data sheet says that the normal working temperature is 240C and that it must not be heated above 260C. Incidently the product is a bonding bitumen intended for roofing.
__________________

Paul Stenning
Forum Admin/Owner and BVWS Webmaster
Paul Stenning is offline  
Old 7th Mar 2005, 1:48 pm   #16
Ed_Dinning
Dekatron
 
Join Date: Jan 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 8,171
Default Re: Pitch-covered LOPTxs

Hi Gents, this roofing stuff soundslike a very high temp compound. The compound used by electrical manufactures was a lower temp than that, try and locate some old electrical equip and you may get some from there. this type would start to soften in strong sunlight at about 50C. Try the local electricity board yard. Solder leads to the EY51 terminals and ues them to lower it int the pitch, it can then be cracked off when cool to reveal the connections.

Ed
Ed_Dinning is offline  
Old 7th Mar 2005, 4:27 pm   #17
mjizycky
Retired Dormant Member
 
mjizycky's Avatar
 
Join Date: Dec 2002
Location: London, UK.
Posts: 69
Default Re: Pitch-covered LOPTxs

I thought some of the encapsulation compounds sold by the likes of Farnell/RS/CPC/Maplin would be useful here... hang on though, they're epoxy based (do a search on "encapsulant"). I agree with Ed though, you definitely need the electrical grade bitumen stuff - if you're going to use bitumen.
mjizycky is offline  
Old 7th Mar 2005, 6:00 pm   #18
Ed_Dinning
Dekatron
 
Join Date: Jan 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 8,171
Default Re: Pitch-covered LOPTxs

Hi Gents, in the old days they used lots of this stuff as it was a very cheap form of insulation. As a young engineer at Reyrolle one was encourages to use it all the time, the only cheaper insulant was air and that took up too much space !!
Modern encapsulants are based on epoxies, they work well but are not what is required here.
A scrap yard may yeild some old electrical switchgear that would contain the correct stuff in its cable terminal chambers.

Ed
Ed_Dinning is offline  
Old 7th Mar 2005, 8:23 pm   #19
af024
Octode
 
Join Date: Jan 2003
Location: Ashby-de-la-Zouch (it's not by the sea)
Posts: 1,254
Default Re: Pitch-covered LOPTxs

Thanks guys. Goodness knows where I would go around here to find the electrical lower melting point variety though!

Any thoughts on the other stuff in the tin? It's certainly more user-friendly for sure!

Can anyone use a 39.9kg lump of tar?

Cheers,


Andy
af024 is online now  
Old 7th Mar 2005, 9:15 pm   #20
pmmunro
Octode
 
Join Date: Jul 2004
Location: Dundee, UK.
Posts: 1,797
Default Re: Pitch-covered LOPTxs

Before epoxy materials were in common use, as recently as the 1970s certainly, pitch was used by cable jointers to fill joints. It came in the form of large cakes bound in brown paper into which I assume it had been poured for dispatch. It was heated in galvanised cans with a pouring spout, usually on a gas ring. Presumeably the pitch was an electrical grade. Pure pitch, as supplied is rather like industrial grade toffee.

A squirrel natured, ex Post Office or regional electricity authority jointer would be a good contact. I would even try asking the inmate of a red and white striped tent if he, maybe even she, knows anything about pitch. If an old joint was being dug up - they're usually just abandoned - that could be a possible source. Again if your local BT telephone exchange has been in the same place for a very long time there might be some old-stock pitch althought the joys of "Quality Control" probably make this unlikely.

Another use was for the sealing of the tops of lead-acid batteries when these were made of hard rubber. If there is an auto-electrical business which has been in the same premises for a very long time its just possible that they may have some if it can be found under the dust.

Pitch is also used for deck caulking on boats and ships and may be available from a ship chandlers or boatyard.

This link, http://www.pavingexpert.com/setts05.htm#pitch, describes the use of pitch to set setts in paving and shows how it is used - unfortunately they mention 25Kg blocks of pitch and there is some implication the it is bitumen/pitch compound rather than pure pitch.
pmmunro is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 6:06 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.