Cossor 3339 Oscillograph(Scope).

[David Simpson]

Further update :- Friday's 339 chassis now stripped bare of all components & fittings and scrubbed & scrubbed in hot water & Cif cleaner. What grime came off !
The Cossor technicians 70 years ago must have had private investments in tin & copper mines, going by the huge blobs of solder on every tag & connection. All the wiring was at least 16swg, and going by IEE Tables for 1.5mm s/c wire(nearest to 16swg), had a current carrying capacity of 14.5A ! And, capable of only 44mV/A/m drop at 70deg.C ! Then every tag was wrapped at least twice, sometimes thrice!
Thus, sadly,(this'll upset the purists), those lovely big 2W b/t/s resistors could not be saved due to their short tails, and had to be cut away. And most of the cloth/rubber ins circuit wiring. However, although the cloth looked pristine, much of the inner rubber insulation was cracked or perished.
Purism - well, back in the 60's I once completely rewired a 13A scope. But no-way could I go to the RAF stores & demand 1930/40's cloth covered replacement wiring. PVC insulated tinned c w was what was in use by then. And of a size suitable to it's proposed current carrying capacity. More like 26 or 24 swg at most. So, once the 339's donor parts have been cleaned up, the 3339 rebuild will continue - with pvc wiring.( I have an abundance of ex oil rig high spec cabling to strip down).
The big 8uF/750V electrolytics are connected to my re-forming rig, and are up to 500V, on a slow trickle since yesterday.

Regards, David

[Sean Williams]

David,

Do you need anything else for this project - I am about to strip an old 339 that has seen better days....

Sean

[David Simpson]

Further update.
3339 now half-way rebuilt. HT & EHT circuitry installed & working. Its larger sibling - the 339 is my template, despite it being 2.5" longer. Going to be a tight squeeze.
Two small H/duty turntables would be great for this sort of work. However, smooth cardboard or piece of wood underneath the chassis' rotate quite easily on a varnished ply workbench. Rear connection board must be protected with foam or similar padding, though.
Note - must take care to avoid too many eddy currents falling out of mains T/F & chokes.

Regards, David

[AC/HL]

Is it just me, or do other people get as much interest from the rest of workshop photograph as from the subject itself. This is a very well organised one too!

[Phil G4SPZ]

I enjoy looking at other people's workshops too, and yours David is a credit to you. It puts mine to shame, as does your 339 which looks as new. It will be good to see the 3339 when it's finished, and I hope you'll post a Success Story.

[David Simpson]

Bill & Phil, If it wasn't for the great help from yourselves & other kind Forum guys I wouldnt have been able to get started on the project in the first place.
Folks, apart from repairing the mains transformer, rewiring some of the HT & EHT circuitry, removing the front panel for a respray, and tarting up all the knobs - the credit for the 339(donated by Phil) being in full working condition should go to Phil. My thanks again to him for the 339 & the 343 Ganging Oscillator. When the 3339 is complete, what a trio they'll make.
Luckily I was able to aquire, dirt cheap off ebay, a 339A which is donating many components & bits & bobs.
I dont know about a credit-worthy workshop. I'm forced to keep it tidy due to very limited workbench space. What you see is just about 4' x 1.25' working area at a decent height. There is another 4' x 1.67' space at right angles, but its lower down & just used for spreading out spares & stuff in old ice cream/margarine tubs.

Regards, David

[David Simpson]

Folks,
Hopefully I can cease 3339ing at last ! Its been a long haul, and couldn't have been completed without great help from several Forum folk. Once again guys, many, many thanks.
With Phil Harris's 339 as a template, I've managed to get the 3339 rebuilt. Sadly,due to someone else's attempts to originally turn it into a primitave TV(see old pictures), its been rebuilt with 339 & 339A spares. Hellua sod to do with the chassis being over 2" shorter than a 339. The 339A which I bought cheap off ebay provided the most important huge rear mounted paper/oil double capacitors C's 2,29,30,31 (10C/13050) and several missing double pots & multi-wafer switches. Sadly, many of the 339A's 2 & 3W big old b/t/s resistors were knackered or seriously out of tollerance, and I was unable to source original replacements.
I manufactured my own component boards with paxolin & tags, and all wiring was carefully loomed & laced where practical. New or newish pvc insulated wiring was used throughout, and double insulated or HV sleeving used for EHT circuitry. Also, the x-section was reduced to 1.5,1.0 or 0.5 mil, where safely practical, from the original vir/cloth insulated hard-drawn wire of nigh on 2 or 2.5 mil. Anyway, most of the gash 339A's wiring was pretty well perished. Also most of its big electrolytics were weeping or knackered.
Without the double Mu-metal screening of the crt, mains interference was seriously apparent. However, once fitted again, an untroubled display was seen.
So hopefully, this 73 year old classic scope(Oscillograph), with Cossor valves & crt, will plod on for many years to come. Making a great trio with Phil's donated 339 & 343. Also importantly are spare mains T/F, crt's, and original 339 & 3339 diagrams & hand book.
I'll try & attach as many completion pictures as permissable. But can attach to emails for those other keen Cossor repairers/renovators who get in touch.

Regards, David

[Radio Wrangler]

Perhaps the quality of workmanship in the chassis-bashing is a guide to whether it was an official modification?

The 3339 and 339 only had to last until the beginning of the 50's when the Hartley came along and made it fairly pointless trying the improve the old scopes. I had a 339 as a schoolkid and I remember how bad the distortion was from the single ended deflection. 09D certainly rings a bell. Mine definitely had one 807 per channel. The handbook waxed most eloquently over O.S. Puckle's hard valve timebase. I think you are more likely to have a homebrew attempt at a TV receiver than a ministry attempt at improving the 3339. UNLESS you've come across a prototype mule in the development of Cossor's later scopes.

I took my 339 apart for the HT/EHT transformer for my homebrew VCR97 scope in about 1967, it was just disappointing in performance.

I saw a 339 or 3339 (I didn't look closely) looking very prettily restored on a matching trolley last Thursday, so there is a possibility that someone has a manual.

David

[David Simpson]

Aye David, If you scrole back a few thread posts to 6th Aug 2010, you'll see the sad state of the 3339's chassis. Well hack-sawed !
I have heard from one or two folk that 3339's & 339's were aquired from exWD sources by homebrew enthusiasts in the 50's for primative TV construction projects.
After a lot of cleaning & rubbing down & respraying, the chassis turned out quite nice. (Again, see previous thread pictures).
Right enough, its display isn't as good as the 13A(which I know well), nor the 13A's eventual replacement - the CT436 from Hartleys. However, judicious adjustment of the Brilliancy & Sync controls greatly dims the anoying flyback trace. The multi-wafer Condenser yaxley switch assembly on both sets is well worn, and requires gently tweaking to counteract the tendency to burst into wibbly/wobbly Lissajous figures. But hey, I remember many well worn 13A's not much better.
As I said, I do have all the documentation & diagrams, including an original 1939 3339 Manual, a nice p/copy of their original 3339 pamphlet dated April 1939, and an original Cossor factory diagram, approx A3/A2 size, for the 339. In the Manual, Cossor wax lyrical about their trend setting Puckle timebase circuitry.
My plan now is to, sometime in the future, build a replica of Cossor's Oscillograph/ 343 Wobbulator mounting panel(Called a "Radio Service Rack"). And also keep a look-out for Cossor's 3330 35mm Camera assembly.
Thanks to very generous donations from guys previously attributed, and plenty of bits & bobs fron the gash 339A - I should be able to keep these 70 odd year old Cossor items working for many a year.
If, David, you can find out who restored that trolly-mounted 339 or 3339, please put me in touch. Just so we can compare notes, so to speak.

Regards, David

ps. Just remembered, I've been saying today that the gash spare scope was a 339A - - but in fact it was a 339 that Mark & Rob kindly FCS'd up to Scotland.(the ebay owner had mistakenly described it as a 339A).

[HamishBoxer]

Let me say,its looks superb.Still sat here on a 339+339A both needs attention and one is missing a switch or pot.Though one is mint and the other v/good.

[Phil G4SPZ]

Hi David,

You've done a wonderful job, and converted that basket case into a rare working example of oscilloscope history. I'm glad 'my' 339 came in useful, and that you were able to fix it as well as using it as a template. Did you put the "Harpic blue" tube from the 339 into your 3339?

Along the way, you must have acquired quite extensive knowledge of Cossor's oscilloscope developments in the late 1930s/early 1940s. A nice project to write up over the winter months, and definitely worthy of a Success Story on the Forum!

Well done. I'll drop you a PM with my e-mail address as I would like to see more photos.

Kind regards,

Phil

[David Simpson]

I'd like to say that without Phil's generousity, and (HB)David's encouragement, this project would never have got off the ground. Knowing that another Forum guy in Scotland also has a 339 & 3339 to renovate, I guess spurred me on a bit.
Yes Phil, the 339's blue tube went into the 3339, as a nice comparison to the other green ones. So I chose one of the two mint condition NOS green tubes that Bob Worsley very kindly donated to go in your 339. The original one from the 3339 was as dim as a TocH clock,(thats why, I guess, someone had fitted a 6.3V T/F to boost the worn out 4V crt heater or cathode).
I dont know about how extensive the knowledge I've gained on Cossor 339/3339's is, or wheather its sufficient to write up a sucess story. If someone has similar plans, then just print off the cumulative posts from this thread & slip them into a wee A4 folder for reference. Or get in touch for a natter.
Hopefully I'll be able to meet up with the other Davids again at Norman's next Scottish Swap-Meet.
Quite frankly, such a rebuild requires more mechanical/workshop skills than deep electronics knowledge. Once the bare chassis has been tarted up,the circuitry & component layout easily falls into four seperate mini projects. ie - the HT & EHT circuitry & components, the CRT cir. & comp., the Timebase c & c., and finally the Amplifiers. Each one can be thoroughly tested before going on to the next.
I dare say that the purists would condem my mounting quite a few components on tagboards, and using more modern pvc insulated wiring. But I just do not like the higgledy piggledy spiders web of (un-colour coded)(perishable) vir insulated wiring & random placement of components. But lets not digress.

Regards, David

[Radio Wrangler]

I thought that wiring harness was very neat indeed.

There is an ambiguity of purpose in handling anything old. Do you want to make it so it still looks very old, or do you try to make it look like it did when it was new? Only the latter transports the viewer back to the heyday of that instrument and gives a feeling of what it was like to use it. Back in 1940 they weren't using 70 year old oscilloscopes.

The screwed skirt B9A sockets were often used with the EF50 series. They didn't need screening, of course, but they got screwed retaining collars in airborne equipment.

Cheers
David

[HamishBoxer]

A case were rescue is much more important than originality.

[Mark James]

At last the 339's are on the bench. Due to David's generosity I had 2 bare chassis to prepare before starting assembly and also a pile of components from Fruittool's chassis and my complete 339B plus another scope built during WW11. I am hoping to build 2 out of 2½ which may be a challenge as some components are missing from Fruittool's Type 10 and the WW11 chassis is in very poor condition - extensive corrosion and the electrolytics will not reform better than 3mA leakage at 450v.
I will start on one of the chassis and build that according to the 339 wiring diagram. Both spare chassis have been shot blasted and sprayed as per David's recommendations for colours etc. I have attached a photo of progress to date. I have fitted NOS valve bases and am currently reforming the 8µF 750v electrolytics - they seem to level out at a 1mA leakage at 520v which is as high as my reformer will go.

A point of interest - when I removed the CRT from my 339B I found that it was fitted with the blue 09J tube as was suggested in this thread:-

https://www.vintage-radio.net/forum/...reply&p=561250

According to the literature I have seen, the blue tube in the later versions was to special order - perhaps they numbered the scopes as "B" when built to identify them.

Mark

[David Simpson]

Mark, what a lovely looking chassis. I'm glad that my humble advice & help has helped another 339 enthusiast.
I've been told in the past that there were loads of surplus 339's in the late 40's/early 50's. However, now in the early decades of the 21st century, I reckon there is only a small handful of them in full working order.
I'm still on the look-out for the camera attachment. But despite recently hounding a couple of vintage photography enthusiasts, still no joy.

Regards, David

[Phil G4SPZ]

Originally Posted by Mark James

According to the literature I have seen, the blue tube in the later versions was to special order - perhaps they numbered the scopes as "B" when built to identify them.

One of the 339s that I owned for a time was fitted with a blue tube - "Harpic blue" as I seem to recall David calling it. A most apt description.

It's great to see these old Cossor 339s being rescued and rebuilt. Somewhere in my shack, I'm sure I have a spare tube, complete with mumetal shield. If it would be any use to you, Mark, you are welcome to it.

[RogerWalker]

I don't think the OM5 was varimu - more like the straight EF36/VR56 I believe. I have lots of good VR56s [sadly mostly with disintegrated metallising] and could probably sort out a few IO skirted bases and cans/caps if you needed them. I will have a rummage for a manual on the 3339.
Kind regards
Roger

[Mark James]

Thank you all for your offers of help. Sean Williams kindly let me have several NOS CRTs so I should be OK for them. I actually bought an original 339 manual from a bookshop in New Zealand via the internet. Very reasonably priced and it arrived within the week! Along with all the help from David and his rebuilds I have a lot of information. My main problem at present is that the donor 339A I have which has capacitors which are dated 1944 is in far worse condition than I realised. The 3 "engraved" plates riveted to the front panel are really too coroded to use and the electrolytics will not reform adequately so I expect to have to look for another donor to finish the project. Still plenty to be going on with. Will post some more pictures as I progress.

Mark

[WME_bill]

Cossor 339 3339.
Following up RogerWalkers comment about the valves. I have always understood that Cossor OM6 was same as Mullard EF39, i.e. var-mu.
My Wireless World data table for 1958 gives OM5B similar to EF36(VR56) and also gives OM5C as special version for DC amplifiers, which suggests it is similar to EF37. Interestingly, there is no mention of the OM5 in any earlier WW data books, (1954, 1949) though the OM6 appears in them all.

If anyone has the full manual for the 3339, I would very much like a copy please. As this was a pre-war model, it uses video output pentodes for the amplifiers (42SPT) with much higher gain than the 807 (5.7ma/v) used in the war time 339. I suspect the overall performance was much better, with much more sensitive Y channels.
It has always intrigued me that the Hartley 13A, which was about the same period, uses video pentodes again (Philips AL60, CV9 14.5ma/v, which was very similar to the 42SPT 11ma/v).
Or was the Hartley post war. Does anyone know?
And congratulations to David Simpson and Mark James on rebuilding their versions. It should spur me on to do something. wme_bill m0wpn