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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 26th May 2020, 4:06 pm   #1
jonnybear
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Default Lockdown EBL31 project

Working on a old PYE 48A which was a wreck, doing some experiments with various valve line ups, came up with a lockdown EBL31 which preforms really well, it uses a high gain 6CH6 valve and a EB91 double diode, the 6CH6 valve has slightly higher gain than the EBL31 so volume levels are not diminished. mounting on a sub chassis will not demean the radio in any way and can be easily reversed, and finally wired with a recovered 9 pin octal base.
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Old 26th May 2020, 4:17 pm   #2
HamishBoxer
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Default Re: Lockdown EBL31 project

Clever stuff.
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Old 26th May 2020, 4:45 pm   #3
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Default Re: Lockdown EBL31 project

What did you use for the valve top cap?

Did you consider using an OA91 diode instead of the EB91?
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Old 26th May 2020, 4:46 pm   #4
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Default Re: Lockdown EBL31 project

"9 pin octal base"?

I've come across "11 pin" ones for relays but not 9 pin ones......

Neither is octal anyway!
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Old 26th May 2020, 6:08 pm   #5
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Default Re: Lockdown EBL31 project

I think I have come across (or at least heard of) a 9 pin plug/socket similar to Octal (I do not mean the B9G base of things like the EF50). Wasn't there a radio (Murphy?) with optional wired remote control where the control unit which fitted on the bottom of the set connected by such a plug to a socket on the bottom of the radio chassis?

As for the 11 pin one, I've seen it called 'B11A'. A couple of days ago I was working on a device that used a 'valve' on such a base, so it's not just for relays. I put 'valve' in quotes, it's actually a photomultiplier, the device is a transmission densitometer (so probably not really on-topic for this forum).
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Old 26th May 2020, 6:19 pm   #6
jonnybear
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Default Re: Lockdown EBL31 project

Quote:
Originally Posted by Herald1360 View Post
"9 pin octal base"?

I've come across "11 pin" ones for relays but not 9 pin ones......

Neither is octal anyway!
Fat fingers pushed the wrong tab on keyboard should have been 8. thanks for pointing it out.
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Old 26th May 2020, 6:23 pm   #7
Sean Williams
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Default Re: Lockdown EBL31 project

I Like the Bootlace Ferrule for the "Top Cap" connector
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Old 26th May 2020, 6:23 pm   #8
jonnybear
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Default Re: Lockdown EBL31 project

Quote:
Originally Posted by Silicon View Post
What did you use for the valve top cap?

Did you consider using an OA91 diode instead of the EB91?
I did but wanted to keep it thermionic + the EB91 is indestructible and I thought it would be good to recycle.

The top cap plug is a large cable ferrule used in wiring panels with stranded wire, this one has a screw soldered to it and a insulating washer at the bottom.
John
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Old 26th May 2020, 6:29 pm   #9
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Default Re: Lockdown EBL31 project

Quote:
Originally Posted by Sean Williams View Post
I Like the Bootlace Ferrule for the "Top Cap" connector
You sussed that one out, make do amens.
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Old 26th May 2020, 6:40 pm   #10
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Default Re: Lockdown EBL31 project

I would put a date on it for future historians "What's this lockdown thing?"
 
Old 26th May 2020, 8:08 pm   #11
David G4EBT
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Default Re: Lockdown EBL31 project

Neat job John.

Genuine EBL31s are virtually non-existent - even good used ones.

The only 'new' EBL31s sold be dealers are clearly EBL1s (electrically identical) with the side-contact base left in place and an octal base wired on and glued over the side-contact base. Really, a rather clumsy bodge and I wonder if they were done at the factory as they're stamped 'EBL31'. These tall so-called 'EBL31s' work fine if the valve is to be mounted vertically and there's enough headroom, but often the EBL31 is needed for an Ekco A22, where the valve lies horizontally and the rear of the set won't fit back on.

What's more, the 3/8" EBL1 top cap has been left in place rather than replaced with the correct EBL31 1/4" top cap.

I only discovered that the EBL31s offered by dealers were non-genuine 'bodgertronics' converted EBL1s after I'd fobbed out £25.00 for one back in 2010. While I continued my quest to find a genuine EBL31 of the correct height, I decided to have a go at making an adaptor using an EL84 valve and two OA91 diodes, which worked very well. I fitted a 1/4" 'top cap' on the side of the Octal base. By cross wiring the EL84 valve-holder to the Octal pins to suit the EBL31 valve holder layout on my A22, it enable me to plug in the adaptor and EL84 with no changes to the valve holder on the chassis. Although it looked rather incongruous, it did the job fine till a genuine EBL31 came along.

I wrote it up in a thread entitled 'EBL31/EL84 Adaptor' here:

https://www.vintage-radio.net/forum/...=EBL31+adaptor

I then came across some reasonably priced NOS EBL1s, which I converted by partly cutting off the side contact base and fitting a cross-wired Octal base of the correct height, also removing the 3/8" top cap to fit a 1/4" one. (Valve base and top cap cement easily dissolves if soaked in meths. AKA 'de-natured alcohol').

I wrote up the process in Post #14 in this thread 'Converting an EBL1':

https://www.vintage-radio.net/forum/...=EBL31+adaptor

I have one Ekco A22 and my younger son has two, so over the years, whenever I've come across NOS EBL1s, which are usually £10 - £12.00, I've bought them and converted them. (EBL1s seem more plentiful than EBL31s).

I guess that as the years pass, we'll be faced with more of these situations.
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