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Hints, Tips and Solutions (Do NOT post requests for help here) If you have any useful general hints and tips for vintage technology repair and restoration, please share them here. PLEASE DO NOT POST REQUESTS FOR HELP HERE!

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Old 7th Nov 2016, 12:32 pm   #1
David G4EBT
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Default Converting EBL1 valves to EBL31 for use in Ekco A22s

Given the popularity of the Ekco A22, and the scarcity of genuine EBL31 output valves which are needed for the A22, I thought it might be worth mentioning again that the EBL1 side contact valve is identical electronically to the EBL31 and lends itself to conversion. EBL1s seem more plentiful and don’t command such high prices as EBL31s, apart from the fact that NOS EBL31s as offered by UK valve dealers for £25 upwards aren’t genuine EBL31s and are too tall to be accommodated in the Ecko A22. The clue is that they have a tall octal base and a 3/8” top cap. A genuine EBL31 has a ¼” top cap and an octal base and varies in height from the base to the top cap from 115 to 121mm. (4.75”). There is no join in the octal base, which is 16 – 18mm tall and connected directly to the bottle, often with red metalizing overspray on the base.

A non-genuine EBL31 has a join in the octal base where it has been glued over the side contact base of an EBL1 to convert it, still retains the 3/8” top cap, and is 145mm tall (5.75”) – 25mm too tall to fit in an Ekco A22. It is evident that to avoid removing the side contact base, the octal base has been simply glued over the side contact base and cross-wired - hence the tall base.

In recent years I’ve restored three A22s - one for myself, two for my adult son, and over time, I’ve converted several N.O.S EBL1s to EBL31s by cutting off the side contact base and fitting an octal base of the correct height. Admittedly it’s a ticklish job, but with care and a steady hand, it can be accomplished and takes an hour or so. I was lucky enough to recently acquire a new in box Mullard EBL1 from Hornsea Radio Rally which I’ve just converted, so have added some pictures and sketches to show how I went about it.

The first task is to carefully cut around the side contact base as shown using a Dremel type drill fitted with a diamond cutting disk. Cutting the lower part of the base and ;leaving the upper part in place avoids disturbing the metalising or having to remove the whole base, risking breaking the glass. Be especially careful as the wire from the metalizing is very close to the edge of the inside of the base. (The metalizing wire needs to be joined to pin 8 of the octal base, along with the cathode wire). Do not unsolder the pins on the base at this stage, because when the base is removed, the pins spring about in whatever direction they like and apart from the two heater wires, it’s then impossible to know which the other wires are. Hence, once you’ve cut through the base you need to use a needle and thread to tie the thread tightly around each wire and to attach a label to identify what the wire is – anode, diodes, cathode etc. When you’ve fitted the labels, the remnant of the side-contact base can be unsoldered and removed. The wires can be scraped clean and tinned, then various coloured sleeving fitted over each wire to identify it, then the labels can be removed. (You could use the resistor colour code for the sleeving to number the pins).

An octal valve base then needs to be cut to size, 1cm tall. (New high quality valve bases are available on ebay). Then a tinned copper wire about 10 cms long is slipped up each valve pin and bent over at the bottom end so that it doesn’t slip out of the pin. A short piece of silicone sleeving is pushed over each wire and the new wires are soldered to the correct wires emerging from inside the valve making very sure that you have them correct, remembering that from beneath, the valve pins number clockwise, but from above, looking into the base, anti-clockwise. Obvious though this may sound, it’s easy to make a mistake. When all the wires have been soldered, push the base up to the remnant of the side contact base on the valve to make sure it will seat well. If so, use two part epoxy to glue the octal base in place, wiping off any excess. I use ‘Super Steel’ two-part epoxy by Plastic Padding, which I find excellent for many repair and restoration task. Despite its name, it isn’t electrically conductive. It can be held in place by hand till it sets, which is only a couple of minutes. Once set, the wires in each valve can be soldered and the surplus snipped off.

That just leaves the 3/8” top cap to be removed and a ¼” one from a donor valve to be fitted. First melt the solder on the top cap to release the grid wire in the centre. You have two choices then. Firstly, you can turn the valve upside down and rest the top cap in a small container of meths – the cap from the meths bottle will do. This will soften the original cement overnight and the top cap should then come free. Alternatively, if you have a steady hand, you can speed things up by slicing off the top of the cap, taking care not to cut off the grid wire. You can then pour meths into the remnant of the top cap on the valve, and use the tip of a small craft knife to scrape away the old cement as it softens. As long as the metal cap can be removed, any old cement that’s firmly stuck to the glass can be left in place as a good key for the new cement. Slip the new cap into position, fix it with Super Steel and when set, solder the grid wire to the top cap.

That’s it - the valve is ready for testing and use. Admittedly it may sound a bit of a palaver, especially the first time that it’s attempted, and it does require a steady hand, but if for example, you can can’t find a genuine EBL31 at any price, but can find a new in box Mullard EBL1 for a fiver, it’s well worth the effort. Leastways, I think so.

First picture shows an EBL1 before and after conversion to an EBL31.
Second picture shows the lower portion of the side-contact base cut off, with the wires from the valve labelled before unsoldering the base.
Third pic is a sketch of how the new octal base fits over the retained upper part of the side contact base.
Fourth pic shows how the wires from the valve are identified and wired to the octal base.
Firth pic shows the valve wires fitted with coloured sleeving ready to be wired to the octal base.

Some more pics will be added in another post to complete the process.

I hope this might be of interest to A22 owners who are bereft of an EBL31.
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Old 7th Nov 2016, 1:15 pm   #2
David G4EBT
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Default Re: Converting EBL1 valves to EBL31 for use in Ekco A22s

Some more pictures to assist in the conversion.

First pic shows a genuine EBL31 valve, alongside what most UK valve dealers who offer N.O.S EBL31s will supply. Readily identified by the tall octal base and the join where it has been fixed directly over the side contact base of what started out life as an EBL1. Another clue is the 3/8" diam top cap used on an EBL1 as opposed to a 1/4" top cap of an EBL31. These valves are marked 'EBL31' which suggests that they might actually have been factory converted. Fine for use in any other set than the Ekco A22.

Second pic shows new tinned copper wires pushed up into the pins of the new octal base to be soldered onto the electrode wires of the valve.

Third pic shows the old top cap sliced open to add meths to soften the cement and enable removal of the 3/8" top cap and fitting of a 1/4" one from a donor valve.

Fourth pc shows an unmodified EBL1 vale, a genuine ELB31, and an EBL1 that I've converted to an EBL31 as described in this thread.

Fifth pic shows Plastic Padding 'Super Steel' two-part epoxy cement, as used to attach the top cap and octal base.

I hope these notes will be of help and encouragement to fellow Ekco A22 owners who can't source a genuine EBL31 valve. For the first A22 that I restored in 2010, I couldn't find an EBL31 valve anywhere, so I made an adaptor which plugged directly into the octal socket of my A22 to enable an EL84 to be used with two germanium diodes built into the adaptor. It worked very well and tided me over until an EBL31 came along. I posted details of the adaptor on the forum and it also featured in the Summer 2010 BVWS Bulletin.

The A22 is a joy to listen to, both on air and to play my I-pod through via a 'mini-mod' that I constructed.
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Old 18th Nov 2016, 1:24 pm   #3
G4XWDJim
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Default Re: Converting EBL1 valves to EBL31 for use in Ekco A22s

Slightly off topic question - apologies.

Does the 44 volt heater ct8 CBL1 suffer from the same scarcity. I ask because I found one in my stock. Domestic radio valves are not normally my interest but might be of use to someone here.

Jim
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Old 19th Nov 2016, 8:48 am   #4
CambridgeWorks
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Default Re: Converting EBL1 valves to EBL31 for use in Ekco A22s

Hope I don't need to do this, but thank you so much for taking the time to give so much detailed information.
Rob
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