Pennine Amplifiers 'Scout' Radiogram.

[pwdrive]

Hi Joe, I was assuming that the pentode section of the EBL31 was the output stage and that it's G! input wasn't derrived from the anode of a preceeding stage but direct from the detector diode via the usual filtering and vol. control.
I might have read it all wrong , if so my appologies...it's an age thing.....

Lawrence.

[Joe]

Thanks, all.

I've just been looking up the valves and they do seem a bit exotic. Maybe a small manufacturer using what they could get. Things look un-messed with but a closer look in decent light is called for.

- Joe

[Steve_P]

No PWDrive, that's right. There is no AF stage.

Cheers,

Steve P.

[pwdrive]

Hello Steve I thought that might be the case. i guess that if the ouput valve grid coupling capacitor goes leaky then the valve will not do the same amount of overtime as in a triode pentode audio output stage with capacitor coupling.

Lawrence.

[Yorkie]

The valve line up is exactly the same as the Ekco A22.

Hopefully the EBL31 will be OK, because if not, they're both difficult to get hold of, and expensive (£25 - £30). Furthermore, none of those that are on offer from valve dealers are genuine EBL31s - they're impostors - EBL1s, which was a side contact valve, which have been adapted by fitting an octal valve-base over the 7-pin base. Though that's been neatly done (you can see the tell tale join), the valve then becomes too tall to fit in an A22, s the valves lies horizontally and protrudes too far to fit the back on. Apart from that giveaway, the other indication of a non-genuine EBL31 is that the converted EBL1s have a 3/8th top cap (grid), whereas a genuine EBL31 has a 1/4" top cap. It's a double diode pentode, with the diodes taking care of the AVC and detection, and the pentode, the AF amp.

The additional height of the converted EBL1s wouldn't matter in your Pennie set Joe as you have the height, but would need to change the top cap clip to 3/8".

When I needed an EBL31 for an A22 I was restoring for my son, I couldn't get a genuine one anywhere, so I made an adaptor using an octal valve base, a B9A valveholder, two germanium diodes and cross-wired the octal valve base to suit an EL84 to create a 'virtual EBL31' that would fit in the A322 till I eventually found a genuine EBL31, as I did. The adaptor with an EL84 perched on top looks ridiculous in comparison, but it worked well, and had the merit of requiring no alterations to the wiring of the valveholder on the radio. The details were published in the BVWS Bulletin some time ago, but I've attached a pic of a genuine EBL31, a 'pretend' EBL31 (converted EBL1 as sold by dealers), and the EL84 adaptor.The EL84 is close enough in characteristics to the pentode section of the EBL31 for it to work as a reasonable substitute, with the two germanium diodes in the adapator base. On the side of the adaptor, is the 'top cap' connector.

I've since obtained two EBL1s, and have converted one properly, by cutting off the 7-pin base with careful surgery (or you cut through the metalising connection) and fitting an octal base, (as well as removing th 3/8" top cap and fitting a 1/4" one). Very tricky and not for the faint hearted as you must label every connection before lifting off the 7pin valve base. The wires inside otherwise spring out, and aren't in a circle but in a line in the glass pinch, so apart from the heater, you haven't a clue which wire is which.

I've also set about trying to fit an octal base directly over the 7-pin base EBL1 base but at a lower height than those 'pretend' EBL31s offer from dealers, to make it a simpler job to convert an EBL1 for A22 owners who may not be adept at cutting off the valve base with a Dremel, but that project stalled due to other priorities. (Another potential Bulletin article that didn't make it to Carl Glover).

From left to right in the picture is the EL84/EBL31 style adaptor that I designed, a genine EBL31, and a so called EBL31 (converted EBL1) as offered for sale by valve dealers. The two clues that give the converted valve away are the larger top cap, the increased height due to the octal base glued over the 7pin EBL1 base, and the joint on the valve base.

Sorry to take this thread a bit off track Joe.

Best of luck with the Pennie 'Scout' - with a large speaker in a large compartment and if the EBL31 is up to it, it should sound great!

[Joe]

Thanks for the tip-off about it being like an A22 - it's as close as I'll get to one of those!

I like that EL84 arrangement, I'd been having similar ideas myself if the need has arisen but so far so good. It''d be interesting to see the Bulletin article if you've got a copy.

I'll be mixing shellac and sawdust to sort the 6K8GT out soon.

- Joe

[Yorkie]

Thanks for the tip-off about it being like an A22 - it's as close as I'll get to one of those!

I like that EL84 arrangement, I'd been having similar ideas myself if the need has arisen but so far so good. It''d be interesting to see the Bulletin article if you've got a copy.

I'll be mixing shellac and sawdust to sort the 6K8GT out soon.

- Joe

The two-page article was in the Summer 2010 Bulletin Joe. (Vol 35 No 2). It would breach BVWS copyright to post it on the forum, but I'll happily either scan it and e-mail it to you or pop a copy in the post. I don't think that would be a hanging offence!

Shellac and wood flour was the original compound generally used to secure valve bases, and can be dissolved with meths to either remove it (which is how I removed the 3/8" top cap from the EBL1 valves after having unsoldered the wire at the top of the valve, and used shellac and wood flour as an adhesive to fix the 1/4" one on). Sometimes with loose valve bases, you can get away with dribbling meths into the gap around the glass at the valve base then using masking tape or plastic insulating tape warped over the valve base and top of the valve to hold the base firm while the meths dissolves the original shellac and re-bonds it to the glass. (If you are lucky, that is!).

Wood flour is preferable to sawdust, which is a bit coarse. You can soon get a pile of flour by sanding any old piece of wood (tree wood is best:-) with 80 grit sandpaper.

As to A22s, what a pity they aren't as ubiquitous as DAC90As and about the same price!

[Joe]

If somebody has re-wired the socket with the 6K8GT in they've done a miraculously good job, especially if they were only a 'fiddler':-

   

I'll print the valve data in a bit and see if I can trace just what is going on.

The only sign of previous work is the screws which hold the deck in the cabinet and the ones which hold the motor to the deck being a bit chewed. The turntable is noisy which seems to be caused by the rubber tyre on the idler being rock-hard; it's also got a dip where it's been pressing on the motor spindle. Putting a rubber band 'round it quietens it, at least until it flies off. I'm not worrying myself over-much about that as I can't see myself using it.

I've re-wired the dial lamp and needed to take the EBL31 out. This rattled and there's a lump of metal loose within which looks roughly the size and shape of the +ve connector on a PP9 with a bit of wire on. It still works though.

Cheers

Joe

[Joe]

I checked the output valve grid and found 2.5V on it. I changed the relevant cap which got it down to 12mV.

There were seven 0.1 mfd capacitors in all which I've changed. Before Mark starts muttering into his beer about scatter guns I tested them all. Two caused the neon in the AVO Test Bridge to flash, two made it glow dim and steady and the other three lit it up like a search light. It's certainly louder now and I'll change the 0.05 mfd ones when I get some.

The cabinet has polished up nicely too.

As far as I can tell the 6K8GT is connected like this (I suggest right-clicking and selecting 'Open in New Tab'):-

   

- Joe

[Yorkie]

To be in keeping with the era Joe, you just need a Gracie Fields 78RPM of 'Sing As We Go' to test the record deck!

http://www.youtube.com/watch?v=rSWcWGC6BEE