Bush TV80 14" Transportable

[marc]

The edges might be a problem but have you considered a loose woven fabric, glued and varnished? If you cam get a reasonable colour match it would also replicate the embossed look.

Hi Terry,

That is possible but looking at the edges they are bound over and stitched with what appears to be PVC, It may be possible to tuck the Fablon under this as it's applied thus hiding the edges from view.

Marc.

[marc]

Hi all,

Just when you think your onto a good thing.....Damaged LOPT !
I changed a few rather sweaty looking waxies in the timebase and applied some volts to the set via the variac. By the time 180v was reached I could hear a rather strangled line whistle but by 195v it sounded strong and clean, by 220v it began to sound odd again. there was nothing on screen and a check with my EHT meter confirmed no EHT present at the CRT's A2

I decided to check all around the LOPT for any issues but not being able to see properly found it best to remove it so I could carry out some resistance checks....I didn't have to though as once the LOPT was out it was obvious that someone has been there before, securing screws had no lock washers and one screw head was chewed up a bit, it then looks like the LOPT was forced out of the chassis without disconnecting the wires from under the chassis and broke the LOPT bobbin !
Surveying the damage I'm hoping that the bobbin side can be glued back into place with epoxy resin. If you take a look at the second photo you may just be able to see below the orange lead termination a wire from the winding...it is detached but I should be able to reconnect it with any luck, I'm hoping that this is the reason for the LOPT no working.

Marc.

Spot the damage, looks like the LOPT was yanked without disconnecting 2 wires from below the chassis.

You may be able to see below the orange lead termination a wire from the winding, it's not connected to it's terminal.

[marc]

Hi all,

I've now de-soldered the caps from the LOPT so I can get at the damaged area which is actually worse than first thought, there are three winding wire breaks and a terminal to repair.

Marc.

[Cathovisor]

That's do-able, looking at it. Shall I bring my Skantest for a giggle?!

[marc]

That's do-able, looking at it. Shall I bring my Skantest for a giggle?!

With my luck I'll Skantest my fingers Catho

Anyway back to the plot....
The broken wires are too short to get a reliable joint to their tags so I made three spiral ended extension wires and soldered them on to the broken ones. I've made them long enough to fold over to the front of the LOPT and wrap around the front terminals which have now been epoxied back into place, though I'll leave that while tomorrow once I know the epoxy is fully cured.

Marc.

Made up 3 spiral ended extension wires

Soldered the spirals to the broken wires

The broken bobbin side with terminals now epoxied back into place. The extension wires will be bent over the front and soldered to the tags hopefully giving some extra mechanical supporting strength too.

[marc]

Hi all,

OK so the damaged leads on the LOPT are repaired and the unit is now fitted back to the set but still no EHT.
The EY51 does'nt appear to light up so I removed it and whilst it was out checked for continuity of it's heater winding which was OK, I replaced the EY51 with another and tried the set again, still no EHT. I can draw a spark from the EY51's anode but it is not lit so I wonder if the heater winding is failing.

Marc.

Damage repair complete, the wires now folded over and looped round the tags awaiting soldering once other connecting leads from the front cover are in place.

[Cathovisor]

A suitable silicon diode would be a good "get out of jail free" card: is it possible to do on this LOPT what occiput suggested for the LV20?

[marc]

A suitable silicon diode would be a good "get out of jail free" card: is it possible to do on this LOPT what occiput suggested for the LV20?

Just what I was thinking Catho, what diode would suit best any ideas bearing in mind that the EHT on this set runs at 13kV and where to get one from ?
Shame I haven't got a tripler to try on it.

Marc.

[Terrykc]

... I can draw a spark from the EY51's anode but it is not lit so I wonder if the heater winding is failing ...

If you look at any EHT rectifier heater winding, just about the only way it can fail is if one end breaks away from the eyelet, in the case of an EY51 or U25, or the valve holder pin on anything else.

You've eliminated that so my guess is that the drive is low, resulting in low volts for the heater. Run it up again in complete darkness to see if the EY51 heater really isn't attempting to light.

Also, for 13kV EHT, I would expect you to be able to draw quite a long spark off the EY51 anode connection - I assume you are doing it in the time honoured fashion of holding an insulated screwdriver blade close to the anode. Move the screwdriver away gradually until the spark stops -how long is yours?

[marc]

Hi Terry,

I can't see any light at all from the EY51 (dark room) and the spark isn't very long only about 1mm

Marc.

[Terrykc]

You still have a fault, then Marc, and a stick won't cure it, I'm afraid.

It's a long time since I've done this but, for 13kV, I'd expect, from memory, at least 10 - 15mm - even more, depending on humidity, etc.

Make sure the PL81 isn't overheating and check for a healthy negative voltage on the grid.

Replace C120, if you haven't already done so.

[crustytv]

Recommended reading courtesy of SteveP http://www.oldtellys.co.uk/otltbeht.html full of useful help you will find invaluable. If you're impatient, skip to the "what goes wrong" section.

[Terrykc]

... Shame I haven't got a tripler to try on it ...

I read this earlier and didn't take in the implications initially - what, pray, would you do with a 39kV EHT supply in a 14" TV ...?  :ccf  

[marc]

Hi Terry,

The PL81 is running normally by appearance but I will check the grid voltage later.

I must admit I'm kicking myself here as for some reason I just can't get my head to switch on even though a similar fault was delt with the other day on my Pye B18T

Anyone got a good memory available to fit burk with memory loss

Marc.

[marc]

... Shame I haven't got a tripler to try on it ...

I read this earlier and didn't take in the implications initially - what, pray, would you do with a 39kV EHT supply in a 14" TV ...?  :ccf  

Fit it to the LOP valve as I did with another set with failed overwind....

[marc]

Recommended reading courtesy of SteveP http://www.oldtellys.co.uk/otltbeht.html full of useful help you will find invaluable. If you're impatient, skip to the "what goes wrong" section.

Cheers Chris,

I think because I've not been active with sets until the last couple of weeks I'm missing silly things, it'll come back eventually...I hope !

Marc.

[marc]

Make sure the PL81 isn't overheating and check for a healthy negative voltage on the grid.

Replace C120, if you haven't already done so.

I have -25 on the grid.
C120 ??? what data are you using Terry ? I'm using Trader 1426.

Marc.

[Terrykc]

RTS, which is a copy of the Bush circuit.

[marc]

Hi Terry,

Yes C120 (C64 on Trader) has been changed already.

Marc.

[Cathovisor]

Shall I bring one of my TV80s with me on Friday?

[marc]

Shall I bring one of my TV80s with me on Friday?

It might be worth a spy at
And then when you're not looking I can swap them

But seriously I'm beginning to doubt this LOPT as every thing else seems (loosely said) to be OK.

Just to re-cap (not sure if that's a pun or not !).......
I can draw a 1mm spark from the EY51 anode, if I disconnect the PY81 top cap I get nothing.
I have -25v at the grid of PL81.
Result...still no EHT

Marc.

[Katie Bush]

Hi Marc,

Just thinking out loud here, but does the line whistle sound "right"? Or sound well off, like my TV85, that day some weeks ago? Then, can you draw a spark at either PL or PY top caps? If so, how far can you draw the spark?

Marion

[Cathovisor]

Ring test time. And we can christen the Skantest too

[marc]

Hi Marc,

Just thinking out loud here, but does the line whistle sound "right"? Or sound well off, like my TV85, that day some weeks ago? Then, can you draw a spark at either PL or PY top caps? If so, how far can you draw the spark?

Marion

Hi Marion,

Sparks.....nothing off PY, nothing PL.
As for line whistle it sounds strained a the set warms but then comes on key once settled.

Marc.

[marc]

Ring test time. And we can christen the Skantest too

"Screams and run's for cover"