Burndept screen grid 4 - UK Vintage Radio Repair and Restoration Discussion Forum

David Church · 28th Mar 2017, 9:58 am

Does anyone have a circuit diagram for a Burndept screen grid 4?

I’ve just got an early one (valves are 6 volt with a double ended valve S625) but it’s not working.

Cheers

Ed_Dinning · 28th Mar 2017, 8:42 pm

Hi Dave, nice set and should work well when fixed.

Note that there are equivalent valves available at 2 and 4 volts that can be used here (but not sure about the SG). DO NOT OPERATE It without GB connected even for a short time. Main enemy here will be corrosion on terminals and contacts.

Ed

David Church · 28th Mar 2017, 9:36 pm

Quote:

Originally Posted by Ed_Dinning

DO NOT OPERATE It without GB connected even for a short time.

Hi Ed

Why not?

AC/HL · 28th Mar 2017, 11:18 pm

Essentially the same as a dodgy "that cap" of notoriety hereabouts.
Lack of bias could cause excess anode current, possibly damaging the valve and output transformer. Not worth the risk at this age.

David Church · 29th Mar 2017, 9:17 am

Quote:

Originally Posted by AC/HL

Lack of bias could cause excess anode current, possibly damaging the valve and output transformer. Not worth the risk at this age.

Yup - I get that - what I should have said was is there something about this particular model/circuit that makes it especially susceptible?

I will open it up soon and see what's inside, I will post some pics.

David Church · 29th Mar 2017, 3:56 pm

Here are some pics

Ed_Dinning · 29th Mar 2017, 8:20 pm

Hi Dave, nice looking set.
Most sets that use GB are liable to the same problem, without bias the anode current rises dramatically.

Ed

greenstar · 29th Mar 2017, 8:31 pm

Wow, that's a beauty. Love that double ended valve.

Radio Tech · 30th Mar 2017, 8:53 am

I too love that double ended valve, a beautiful set without a doubt and certainly well worth the effort to get it working again.

Best wishes

Ken

David Church · 30th Mar 2017, 9:53 am

Well I opened it up - 4 screws on the bottom held it in the case.

There is a tin plate fixed to the bottom of the case and the back had turned up so caught up the back of the set making it tricky to slide the set out.

Some of the wiring is going to need changing as the rubbery stuff is crumbling.

There is a Ferranti transformer that is o/c - type AF 3

There are two ww resistors showing in pic 2 that look like a napoleon hat, 1 says 70k and is o/c but there is a dubilier one across it so its been out the case before.

In the second image you can just see some green caps - there are three and the show between .3 meg and .4 meg

The grid leak is showing 4.3 meg

I got the transformer out now just need to find another one!

Boater Sam · 30th Mar 2017, 10:13 am

Should rewind quite easily, they are getting a bit scarce.

David Church · 3rd Jun 2017, 9:50 am

Well I finally got this going. I found an old Ferranti AF3 that was rusty but in circuit. I changed the case over which is an easy job with these transformers. Also the windings are in sections so it’s possible to find the section that’s broke and bypass it but that’s another story.

I put new caps in the old cases and put the tar back on top. The original ones leaked badly.

The SG valve is working but unfortunately weak. I am hunting another one down.

The biggest pain was the aluminium cover – getting it back on was really difficult and I had to leave a couple of screws off.
Anyway it now sounds good as well as looking great.

28th Mar 2017, 9:58 am	#1
David Church Banned Join Date: Feb 2011 Location: Romford, London, UK. Posts: 331	Burndept screen grid 4 Does anyone have a circuit diagram for a Burndept screen grid 4? I’ve just got an early one (valves are 6 volt with a double ended valve S625) but it’s not working. Cheers

28th Mar 2017, 8:42 pm	#2
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,194	Re: Burndept screen grid 4 Hi Dave, nice set and should work well when fixed. Note that there are equivalent valves available at 2 and 4 volts that can be used here (but not sure about the SG). DO NOT OPERATE It without GB connected even for a short time. Main enemy here will be corrosion on terminals and contacts. Ed

28th Mar 2017, 11:18 pm	#4
AC/HL Dekatron Join Date: Nov 2003 Location: Heckmondwike, West Yorkshire, UK. Posts: 9,642	Re: Burndept screen grid 4 Essentially the same as a dodgy "that cap" of notoriety hereabouts. Lack of bias could cause excess anode current, possibly damaging the valve and output transformer. Not worth the risk at this age.

29th Mar 2017, 3:56 pm	#6
David Church Banned Join Date: Feb 2011 Location: Romford, London, UK. Posts: 331	Re: Burndept screen grid 4 Here are some pics Attached Thumbnails

29th Mar 2017, 8:20 pm	#7
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,194	Re: Burndept screen grid 4 Hi Dave, nice looking set. Most sets that use GB are liable to the same problem, without bias the anode current rises dramatically. Ed

29th Mar 2017, 8:31 pm	#8
greenstar Octode Join Date: Jul 2011 Location: Leicester, Leics. UK. Posts: 1,684	Re: Burndept screen grid 4 Wow, that's a beauty. Love that double ended valve.

30th Mar 2017, 8:53 am	#9
Radio Tech Nonode Join Date: Dec 2012 Location: Bocking, near Braintree, Essex, UK. Posts: 2,071	Re: Burndept screen grid 4 I too love that double ended valve, a beautiful set without a doubt and certainly well worth the effort to get it working again. Best wishes Ken

30th Mar 2017, 9:53 am	#10
David Church Banned Join Date: Feb 2011 Location: Romford, London, UK. Posts: 331	Re: Burndept screen grid 4 Well I opened it up - 4 screws on the bottom held it in the case. There is a tin plate fixed to the bottom of the case and the back had turned up so caught up the back of the set making it tricky to slide the set out. Some of the wiring is going to need changing as the rubbery stuff is crumbling. There is a Ferranti transformer that is o/c - type AF 3 There are two ww resistors showing in pic 2 that look like a napoleon hat, 1 says 70k and is o/c but there is a dubilier one across it so its been out the case before. In the second image you can just see some green caps - there are three and the show between .3 meg and .4 meg The grid leak is showing 4.3 meg I got the transformer out now just need to find another one! Attached Thumbnails

30th Mar 2017, 10:13 am	#11
Boater Sam Banned Join Date: Dec 2013 Location: Middlewich, Cheshire, UK. & Winter in the Philippines. Posts: 3,897	Re: Burndept screen grid 4 Should rewind quite easily, they are getting a bit scarce.

3rd Jun 2017, 9:50 am	#12
David Church Banned Join Date: Feb 2011 Location: Romford, London, UK. Posts: 331	Re: Burndept screen grid 4 Well I finally got this going. I found an old Ferranti AF3 that was rusty but in circuit. I changed the case over which is an easy job with these transformers. Also the windings are in sections so it’s possible to find the section that’s broke and bypass it but that’s another story. I put new caps in the old cases and put the tar back on top. The original ones leaked badly. The SG valve is working but unfortunately weak. I am hunting another one down. The biggest pain was the aluminium cover – getting it back on was really difficult and I had to leave a couple of screws off. Anyway it now sounds good as well as looking great. Attached Thumbnails