Bush TV56 find - UK Vintage Radio Repair and Restoration Discussion Forum

ediz1999 · 17th Feb 2017, 10:54 am

Hi all, I came across this Bush TV56 on the way home at a junk shop, which I just had to pic up. The back cover is missing, and upon inspection, some of the valves have fallen out of their sockets. Some of the wires would need to be changed, and both the power board and RF board which would need to be sorted out. The casing seems fairly good for it's age too. The tuning knobs are missing, but volume and tone (?) knobs are there. LOPT looks okay, I mean it hasn't crumbled away and there's no noticeable massive chunks missing from it so I think we can assume for now that it's decent. Although I'm afraid this has been kept in a damp environment, on some of the valve pins, there's this egg blue coating of what looks like rust? CRT looks decent too, although the base seemed lose so I secured it with some electrical tape. I'm looking for a circuit diagram for the set. Where should I go looking?

ukcol · 17th Feb 2017, 11:32 am

The following may help.

There are 6 pages of data on the TV56 in the 1955-56 Radio & TV Servicing series of books starting on page 259. It is also covered by Trader sheet 1236/T97

FERNSEH · 17th Feb 2017, 11:33 am

Before attempting to supply mains power to the set start off the restoration by warming up the line output transformer, there will be moisture in the windings. The method I use is to pass a current of 20mA though the EHT overwind. A 15 to 20 volt DC supply will be sufficient to drive the current through the windings.

DFWB.

ukcol · 17th Feb 2017, 11:59 am

Quote:

Originally Posted by ukcol

........It is also covered by Trader sheet 1236/T97

I have just looked and it turns out that I have a paper copy of this sheet. If you PM me with your email address I will scan it for you.

ediz1999 · 17th Feb 2017, 1:10 pm

Thanks for the suggestions. Pming you now Ukcol.
I've started with just replacing some of those frayed wires.

Freya · 17th Feb 2017, 1:16 pm

It may be worth mentioning that if the frayed wires are connected to the dropper resistors then normal pvc covered wire will not be suitable due to heat generated by the dropper. Silicone covered wire is much better suited to this position.

Duke_Nukem · 17th Feb 2017, 2:14 pm

On the underside of the power chassis there is probably a single board with components mounted on it. If so, check underneath it, there are a number of wires running along its length and then popping up through a hole in the chassis onto the top of the chassis. On my TV62 (very similar chassis) these were badly cracked and almost certainly would have shorted where they bend through the chassis.

For the valve pins, I recommend getting a fibre pen which will clean them up nicely.

TTFN,
Jon

ukcol · 17th Feb 2017, 3:36 pm

Hi "ediz1999"

I have just emailed the scan of the Trader sheet to you.

ediz1999 · 17th Feb 2017, 8:29 pm

Thanks for the suggestions everyone. I had to replace one wire which the pvc had decayed that went to the dropper resister. I had also checked and changed a couple of valves which look like they had their vacuum broken, and I also cleaned the pins on the other valves also. I made another quick visual check before I applied power. I used a lamp limiter for the first power up. I only had the two borers connected, I had disconnected the deflection coils and focus ring as I was previously cleaning them. The fuse in the holder was open so I changed it, and then plugged it in. The lamp limiter lit up brightly. The valve filaments didn't light though. Could there be a short? Or a duff valve? I'm sure they're a few shorted or indeed open valves but surely if so, the limiter wouldn't light at all?

ukcol · 17th Feb 2017, 8:47 pm

Quote:

Originally Posted by FERNSEH

Before attempting to supply mains power to the set start off the restoration by warming up the line output transformer, there will be moisture in the windings. The method I use is to pass a current of 20mA though the EHT overwind. A 15 to 20 volt DC supply will be sufficient to drive the current through the windings.

Have you taken David's advice as above Ed? If you don't you could turn a salvageable transformer into one that will need a rewind. I don't know how long this heating method needs to be applied, I would imagine at least 24 hours but David may put me right on that.

You won't have done any damage (yet) because you haven't had the line timebase running.

HamishBoxer · 17th Feb 2017, 8:48 pm

Cap across the mains input leaky?

Freya · 17th Feb 2017, 8:55 pm

Which fuse was open, you have two, one for the heaters and one for the HT.

I suggest you trace the AC voltage from F2 through the droppers and then the heater chain, when it disappears you will have found the issue.
Don't be tempted to rush this restoration, the advice on the Lopt overwind should be adhered to.

FERNSEH · 17th Feb 2017, 11:22 pm

The EHT overwind has a resistance of 375 ohms. When 20 volts is supplied to the winding the power dissipated will be only slightly over 1 watt.
Leave the transformer for at least 24 hours to drive out any moisture.
Current through the overwind will be 53mA. (0.053A) If you have any qualms about passing this current though the overwind then reduce the voltage to say, 15V
DFWB.

ediz1999 · 20th Feb 2017, 3:55 pm

I've been busy with work lately but now I have a bit of time for this.
Both fuses were blown, so I'll be taking your advice with the LOPT when I get in tonight. Thanks for the advice. Thanks to 'UKCol' I now have a trader sheet with all the diagrams and such. I'll update the thread with my progress as I go on.

17th Feb 2017, 10:54 am	#1
ediz1999 Retired Dormant Member Join Date: May 2016 Location: London, UK. Posts: 27	Bush TV56 find Hi all, I came across this Bush TV56 on the way home at a junk shop, which I just had to pic up. The back cover is missing, and upon inspection, some of the valves have fallen out of their sockets. Some of the wires would need to be changed, and both the power board and RF board which would need to be sorted out. The casing seems fairly good for it's age too. The tuning knobs are missing, but volume and tone (?) knobs are there. LOPT looks okay, I mean it hasn't crumbled away and there's no noticeable massive chunks missing from it so I think we can assume for now that it's decent. Although I'm afraid this has been kept in a damp environment, on some of the valve pins, there's this egg blue coating of what looks like rust? CRT looks decent too, although the base seemed lose so I secured it with some electrical tape. I'm looking for a circuit diagram for the set. Where should I go looking?

17th Feb 2017, 11:32 am	#2
ukcol Rest in Peace Join Date: May 2003 Location: Harlaxton, Lincolnshire, UK. Posts: 3,944	Re: Bush TV56 find The following may help. There are 6 pages of data on the TV56 in the 1955-56 Radio & TV Servicing series of books starting on page 259. It is also covered by Trader sheet 1236/T97

17th Feb 2017, 11:33 am	#3
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Bush TV56 find Before attempting to supply mains power to the set start off the restoration by warming up the line output transformer, there will be moisture in the windings. The method I use is to pass a current of 20mA though the EHT overwind. A 15 to 20 volt DC supply will be sufficient to drive the current through the windings. DFWB.

17th Feb 2017, 1:10 pm	#5
ediz1999 Retired Dormant Member Join Date: May 2016 Location: London, UK. Posts: 27	Re: Bush TV56 find Thanks for the suggestions. Pming you now Ukcol. I've started with just replacing some of those frayed wires.

17th Feb 2017, 1:16 pm	#6
Freya Octode Join Date: Jan 2009 Location: Falmouth, Cornwall, UK. Posts: 1,989	Re: Bush TV56 find It may be worth mentioning that if the frayed wires are connected to the dropper resistors then normal pvc covered wire will not be suitable due to heat generated by the dropper. Silicone covered wire is much better suited to this position. __________________ Stephen _________"It`s only an old telly" ___

17th Feb 2017, 2:14 pm	#7
Duke_Nukem Octode Join Date: Jan 2003 Location: Birmingham, West Midlands, UK. Posts: 1,268	Re: Bush TV56 find On the underside of the power chassis there is probably a single board with components mounted on it. If so, check underneath it, there are a number of wires running along its length and then popping up through a hole in the chassis onto the top of the chassis. On my TV62 (very similar chassis) these were badly cracked and almost certainly would have shorted where they bend through the chassis. For the valve pins, I recommend getting a fibre pen which will clean them up nicely. TTFN, Jon

17th Feb 2017, 3:36 pm	#8
ukcol Rest in Peace Join Date: May 2003 Location: Harlaxton, Lincolnshire, UK. Posts: 3,944	Re: Bush TV56 find Hi "ediz1999" I have just emailed the scan of the Trader sheet to you.

17th Feb 2017, 8:29 pm	#9
ediz1999 Retired Dormant Member Join Date: May 2016 Location: London, UK. Posts: 27	Re: Bush TV56 find Thanks for the suggestions everyone. I had to replace one wire which the pvc had decayed that went to the dropper resister. I had also checked and changed a couple of valves which look like they had their vacuum broken, and I also cleaned the pins on the other valves also. I made another quick visual check before I applied power. I used a lamp limiter for the first power up. I only had the two borers connected, I had disconnected the deflection coils and focus ring as I was previously cleaning them. The fuse in the holder was open so I changed it, and then plugged it in. The lamp limiter lit up brightly. The valve filaments didn't light though. Could there be a short? Or a duff valve? I'm sure they're a few shorted or indeed open valves but surely if so, the limiter wouldn't light at all?

17th Feb 2017, 8:48 pm	#11
HamishBoxer Dekatron Join Date: Aug 2007 Location: W.Butterwick, near Doncaster UK. Posts: 8,932	Re: Bush TV56 find Cap across the mains input leaky? __________________ G8JET BVWS Archivist and Member V.M.A.R.S

17th Feb 2017, 8:55 pm	#12
Freya Octode Join Date: Jan 2009 Location: Falmouth, Cornwall, UK. Posts: 1,989	Re: Bush TV56 find Which fuse was open, you have two, one for the heaters and one for the HT. I suggest you trace the AC voltage from F2 through the droppers and then the heater chain, when it disappears you will have found the issue. Don't be tempted to rush this restoration, the advice on the Lopt overwind should be adhered to. __________________ Stephen _________"It`s only an old telly" ___

17th Feb 2017, 11:22 pm	#13
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Bush TV56 find The EHT overwind has a resistance of 375 ohms. When 20 volts is supplied to the winding the power dissipated will be only slightly over 1 watt. Leave the transformer for at least 24 hours to drive out any moisture. Current through the overwind will be 53mA. (0.053A) If you have any qualms about passing this current though the overwind then reduce the voltage to say, 15V DFWB.

20th Feb 2017, 3:55 pm	#14
ediz1999 Retired Dormant Member Join Date: May 2016 Location: London, UK. Posts: 27	Re: Bush TV56 find I've been busy with work lately but now I have a bit of time for this. Both fuses were blown, so I'll be taking your advice with the LOPT when I get in tonight. Thanks for the advice. Thanks to 'UKCol' I now have a trader sheet with all the diagrams and such. I'll update the thread with my progress as I go on.