Ekco A22 repair started at last.

[CambridgeWorks]

I have had this A22 a few years now, sitting on top of a record storage cupboard in the back bedroom alongside a Marconi AC42.
Waiting inspiration on both I suppose.
In that time, neither have been powered up.
Today, I dug out the A22. Taking the back off, I remembered a few things from years ago. There was a resistor attached to the top of the output valve (which was not original) with pvc tape and the mains transformer was not original, though maybe as old as the radio. A 5Z4 metal rectifier was fitted, to match the 5v transformer winding.
The choke had been moved to where the dial bulb access plate should have been and an old TCC main capacitor was fitted, boasting a reformed label.
It passed a megger test fine.
Firstly, I looked for the grid coupling capacitor and replaced with a mullard mustard 47nF 400V.
I brought up mains slowly in stages with my variac to 200V and nothing nasty happened, but just got a faint crackle when changing wavebands.
The o/p valve had been replaced with a 6B8G that had just a short stub wire where the top cap should be. The IF was a EF37A, not EF39.
I took the chassis out and looked around underneath after removing the dial.
Most parts looked original.
Using my sig gen on 465KHz I found the EF37A was very low gain.
I thought, ok, put a EF39 in to try. Those are buried in my garage and it is cold! However, on my shelf above the work bench was a box with 2 ME1400 and one EF37A. This I fitted and very soon had a lot more noise from the speaker. Stations heard on MW and LW as well. Audio level is quite good, considering the 6B8G output maximum audio capacity. Sufficient for me.

To summarise, it needs the wax capacitors changing and resistor values checked to see if way out of tolerance, if not they will remain. The wavechange switch needs cleaning and the tuning gang shorts near full mesh.
Some rubber insulation requires attention as well.
The case has no cracks or bits missing, just needs a good clean.

I dug it out at first for disposing of it, but think I may now just keep it. It is years since I did any domestic set restoration or repair work and I find it quite fun, at the moment!

I will post some pictures in a day or so, as it is time now to help in the kitchen!
Rob

[radiolot]

Now why on earth would you do something else instead containing such danger - such as helping out in the kitchen.
The A22 is one of my favourite radios, a set of visual perfection, especially the ever incredible double-back pressure point of the little legs of the case molding. I think I've only seen a handful which have not shown fatigue signs in the area. Go for it, best of British luck on the work sir.

[vinrads]

Wen I replaced the wax capacitors on mine I found the innards came out quite easy ,clamped one wire in the vice a bit of heat on the other wire ,then pulled with a pair of pliers , then re stuffed with new ones, I don't go to this much trouble normally ,but the A22 deserves it , Mick.

[CambridgeWorks]

Thanks. I did notice that happened with mine. However, a 400v one is too big. 160v one may fit.
I will check the circuit as I think I measured just a very small voltage there.
It is only worth me attempting that provided all the hv decoupling type ones will take a 400v one if needed.
Rob

[Ian - G4JQT]

Beautiful sets - if electronically unremarkable.

I've completely rebuilt three now, and once properly aligned they give a very good account of themselves. I hope you have something they can tune in to for a loud and clear signal!

[CambridgeWorks]

I used the remains of my g5rv antenna, about 18 ft outside. Really good signals with little qrm.
I will align it fully when done, as I did notice less noise at hf end of MW when tuning around.
Just need to swot up on bakelite cleaning and polishing out small fine scratches.
Because of previous replacement parts fitted, I will aim for a reliable repair with quality parts rather than trying for 100% originality.
Rob

[mark pirate]

Just need to swot up on bakelite cleaning and polishing out small fine scratches.

I get excellent results using T-cut followed by a good quality wax, a fair bit of effort, but the end result is stunning!


Mark

[stevehertz]

Originally Posted by mark pirate

I get excellent results using T-cut followed by a good quality wax, a fair bit of effort, but the end result is stunning!


Mark

Having just repolished a number of bakelite radios my procedure is a good going over with Greygate number 5 polishing compound, then similarly with Brasso, then finally with shoe polish. A long laborious job, but like yourself, stunning results.

[CambridgeWorks]

Thanks for the bakelite advice. T cut is something I have not used for years! So another dig in the garage is needed.

Here are some pictures, showing "as is" but with my af coupling Mullard capacitor fitted.
Note the 5Z4 metal, the 6B8G in place of the EBL31, the 6K8GT and EF37A, which is faulty. As I said before, fitting a replacement EF37A and it worked with a respectable audio level at maximum. The 6B8G is designed as a low level af pentode, but has the same pinout as the EBL31, just no pin for metalising. The previous repairer had just dropped it in with the bodge where the top cap should be. He didnt do anything about the screen max voltage being just 150V!. But it does work.

Today I spent nearly 2 hours sorting through boxes in my garage. I found what I was looking for, a used EBL31 looking very clean. I was fairly sure I had one, and it was in the second from last box of maybe a dozen or more. It also tested around 100%. I also found some EF39 and ECH37 as well, plus a 5Z4G.

This afternoon, I started some cleaning up. I also altered the wires from transformer primary to suit 240-250V, nearer to our actual supply. It was set to 230V.
One thing I don't like is the 3 core mains lead terminating on the small 3 way paxolin tag strip near the chassis edge. I may use a quality type of choc block or similar for extra safety. I will have to see what I have that will do the job. The modern plastic ones would look out of place. The small tywrap anchoring the mains lead is my temporary measure to stop any pulling.

The transformer is by W A Bryce and company, printed on a nice brass plate and this rating plate gives 250-0-250 @ 80mA, 6.3V & 5V both at 2A, so plenty of current.
The dial bulb is on the 6.3V winding. I will probably fit a resistor to drop it a couple of volts.

I removed the loudspeaker and o/p transformer so as not to cause any accidental damage to them.
There are some wires with crumbling insulation needing attention as well.

I also dug out a couple of large boxes of resistors and capacitors whilst in the garage.

Rob

[Sideband]

EF37A is an audio pentode. Won't work very well as an IF amplifier and it's not vari-mu either so the AGC won't work properly. EF39 is a vari-mu RF pentode and is correct for the radio. Someone must have tried an EF37A thinking it was near enough but the gain would have been low and I doubt the AGC would have worked very well.

Didn't the 6.3V dial bulb go onto the 5V winding originally?

[CambridgeWorks]

Original used a 4V AZ41. This has had a different transformer fitted in the past. Wiring has been changed to the 6.3V heater circuit.
Rob

[Leon Crampin]

The original A22 rectifier was an AZ31 (octal base). The original mains transformers nearly always fail, as the HT windings are wound with very thin wire - note the DC resistance values.

I suspect a 6.3V 0.3A dial lamp at full voltage may overheat the lamp housing or scale - hence Ekco's use of a 5V tap for the lamp. If a replacement transformer without the tap is fitted, it may be beneficial to fit a series resistor to the lamp.

Leon.

[CambridgeWorks]

I agree Leon. First, will look through my bulb stash before fitting a resistor.
Today, I will try various liquids to try to clean the chassis, but a quick go with a cotton pad yesterday and various liquids didn't really do much. Neither did a tooth brush with these liquids.
May just have to accept it will have to stay dirty looking, as I am not going to spend lots of time or dismantle it to clean things up.
Rob

[CambridgeWorks]

Just a couple of hours so far today. I tried some cleaning inside a small area of the cabinet. I used cotton pads with a small amount of white spirit. I also tried some spray furniture polish of a minor brand. Both seem to work at cleaning.
I also have tried various fluids cleaning a small area of steel chassis, with no effect.
I have some rust remover to try sparingly on one or two items as well.


I must say, I am enjoying my "restoration" of the A22. My first domestic one for decades, as most previous work has been fixing test gear.
It started off the other day, when I decided that just 3 or 4 items I had stored in a spare bedroom and that were of value, I could offer on here as I had lost virtually all interest since start of covid and 2 spine operations in the past 15 months.
It needed more work than I first thought. I started that work, and very soon enjoyed what I was doing once more.
My wife agrees it can have a place in the lounge when done. She is very pleased that I have also rekindled some interest in the hobby. A pantry transmitter will be next, probably a mongrel made up from various circuit ideas and articles. Just for the fun of it.

Rob

[CambridgeWorks]

A bit more work done today. Mostly rewiring around the ebl31. I found the cathode decoupling capacitor was a 250uF, not 25uF! Whether the previous repairer thougt this better for the 6B8G he had fitted I don't know. I fitted a 25uF 25V. I did some wire replacement as well, due to the fragile original rubber insulated wire being rather crumbly. Although I have 1000s of capacitors here, I could not find direct replacement for the 0.04uF 500V AC across the op transformer primary, nor the 0.0025uF between anode and cathode, that I do not know the voltage rating of. I found a 0.047uF 1000V and 2x 0.0047uF 250V AC to use in series.
I hope these will be ok.
I have limited the wire replacements to those that could have insulation problems in the future.
My mission is to get it working as it should and have components and workmanship for reliability. I gave up restuffing capacitors when faced with the 0.04uF 500V AC as the case was not very big to accomodate a combination in series of stock capacitors I had to achieve the voltage rating.. The same for the 2 modern 0.0047 in series.
I also experimented on the cabinet inside, cleaning different areas with a furniture polish aerosol in one part and white spirit another. Both followed with brown shoe polish.
Both look very good. I will post some pictures tomorrow maybe.
Rob

[mark_in_manc]

Originally Posted by robinshack

It needed more work than I first thought. I started that work, and very soon enjoyed what I was doing once more.
My wife agrees it can have a place in the lounge when done. She is very pleased that I have also rekindled some interest in the hobby. A pantry transmitter will be next, probably a mongrel made up from various circuit ideas and articles. Just for the fun of it.

Rob

I am sorry to hear you have had health issues, but your description of 'getting over the hump' and finding enjoyment in something again, is very familiar to me too. I do hope you continue to have fun!

(I use a 'minimod', much utilised on this forum. It's great, and it was so exciting (I know, I don't get out much) when I could play a record in the front room and listen to it on the radio in the back I use a small aerial on the modulator next the stereo, and clip the radio aerial elsewhere to the central heating as the front room radiator seems to sink a bit of RF power! And the longwire in the attic picks it up, too).

[Herald1360]

The 6B8G is interesting as an EBL31 sub. If you can live with maybe 1W audio output (plenty for domestic radio listening, most early trannies and valve portables managed with around 200mW) then it could get a set back on air for rather less than the real thing. It would probably fit in the sets where the crudely rebased EBL1s won't as well.

[paulsherwin]

Originally Posted by Sideband

EF37A is an audio pentode. Won't work very well as an IF amplifier and it's not vari-mu either so the AGC won't work properly. EF39 is a vari-mu RF pentode and is correct for the radio. Someone must have tried an EF37A thinking it was near enough but the gain would have been low and I doubt the AGC would have worked very well.

The EF37A did start off as the EF36 which was intended for use at RF/IF frequencies. As you say, the AGC may not work very well, but the performance may well be adequate if the valve is in good condition - easy enough to find out. See http://www.r-type.org/addtext/add008.htm

[stevehertz]

I have just finished - how shall I word this? - a 'partial restoration' on an A22. It was a working set when I got it, but as per usual the work wasn't the best and there were still about six wax capacitors in there that needed changing, yes they were leaky. There's still a few 'not so brilliant' rubber coated wires wires in there, I did change some, but a full, much more time consuming restoration I will undertake at a later date. What I wanted to say is, I am very surprised at the performance of this little set. I've read varying reports about how good or average they are but I found this one to be excellent. Being familiar with the performance capabilities of pre and just post war radios, I was quite surprised at how well and clear it pulled in stations on medium wave and particularly, on short wave. Not to forget the few stations on LW of course. I also like the way that Ekco seem to have beefed up the knobs on this post war set compared to their pre war offerings. The knobs have a substantial brass insert, a much larger grub screw and an altogether more solid feel to them.

BTW, mine has a brown dial scale which at first I wondered if it had 'yellowed' with UV exposure but on full examination it clearly is a brown scale, or whatever the proper colour name was - amber perhaps. Is one more common than the other - ie white or brown?

And finally, doing a bit of research on round Ekcos in general, I discovered that no two models had the same diameter! I always knew that the A22 was smaller, but to be factual, here we go:

A22 - 13"
AD75 - 14"
AD36 - 14.5"
AD65 - 15"
AC76 - 15.7"