Burndept screen grid 4

[unrealdave]

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

[unrealdave]

Here are some pics.  I am going to take a look inside if I can get it apart! 

[unrealdave]

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!

[Ed_Dinning]

Hi Dave, it looks pretty clean, a nice set. The I/V transformer can easily be rewound if you cannot find a good one. If you post a pic of the grid leak I may have one from that period.

Ed

[unrealdave]

Hi Ed

The pic is attached - it say 3 on it so I assume its a 3meg grid leak, I was going to leave it but if you've got one like it that's 2 or 3 meg then yes please.

[Ed_Dinning]

HI Dave, 1 or 2 meg was the normal value, I will have some. I suggest that you try running it with a mosern resistor in place, see what value is best, then I'll find you one

Ed

[unrealdave]

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.

[LymanDar]

That's awesome that you got it working Dave.

[peter scott]

It's a beautiful looking set.

Peter