Ekco A22's with 5 valves

[Robert Darwent]

Back in 2009 I started the following thread on UKVRR: Round Ekco A22 Chassis Variations?

Today, another UKVRR forum member has kindly made me aware of a further A22 with 5 valves instead of the usual 4. The extra valve is mounted on top of the bulb inspection cover and the screws mounting the valve socket can be seen in the images.

It was suggested in the earlier thread that the extra valve was added as a modification by someone, but this latest set is now the third I've seen with 5 valves and provides the clearest images - all three can't be explained away as modifications surely?

Regards

[pwdrive]

What's the extra valves function Robert?

Lawrence.

[Robert Darwent]

No idea Lawrence, I'd like to know too - only got the photographs.

Regards

[pwdrive]

If I'm looking at the extra valve correct it's the one between the can cap and the output valve?

Regulator? or extra audio?

Lawrence.

[Robert Darwent]

Yes it's the valve next to the large electrolytic can and sits on top of the dial bulb inspection plate in the usual 4 valve set.

Not sure what its there for but extra audio output would be my first thought - very odd though!

Regards

[ed731pdh]

Some early sets had an extra valve as a preamp for fringe areas, might be the reason why.

[Robert Darwent]

Some early sets had an extra valve as a preamp for fringe areas, might be the reason why.

Are you referring to early A22's or early sets in general?

With regards the A22, a pre-amp would seem unlikely. The signal flow on the chassis goes from RF at bottom right then anticlockwise to the output valve. The component strip follows in a similar fashion around the edge of the chassis.

The extra valve is located after the normal output valve so quite a length of screened cable would be needed to feed the signal back to the lower right if it was a pre-amp - no evidence of that and it would make the set prone to instability/hum.

Regards

[Robert Darwent]

I've also got this thread running on UKVRR and someone suggested that the extra valve may be due to problems sourcing the EBL31 valve usually fitted in the A22. Then I noticed in the images that the valve in position V3, where the EBL31 usually sits, is too small in diameter to be an EBL31.

I now believe Ekco, for whatever reason, substituted the EBL31 in some of the chassis for say an EBC33 and an EL33. If correct the valve line-up would have been: ECH35, EF39, EBC33, EL33, AZ31

The A22 was released just after the end of WWII and possibly valve shortages at the time forced the production of a limited number of chassis with the fifth valve. I know for certain Ekco did the same sort of thing with the AD75 round Ekco which can be found with a chassis having either a CBL31 or Pen453DD output valve and/or side-contact valve substitutes in some of the other valve positions.

Regards

[Joe]

It seems as likely as anything but it's odd that the device info doesn't mention it.

- Joe

[AlanBeckett]

I now believe Ekco, for whatever reason, substituted the EBL31 in some of the chassis for say an EBC33 and an EL33. If correct the valve line-up would have been: ECH35, EF39, EBC33, EL33, AZ31

I bet that caused some panic in the Engineering Department - 'And where the very Devil do you think I'm going to put it Sir?'. They were more polite in those days.

Pye did some CT/Octal jiggery-pockery during that period, but very rapidly settled on the B8As - not necesarilly the best choice in retrospect.

Alan