Cossor 1035 MKIII

[Richard984]

I had one of these at the tender age of 14 and it was my first contact with professional oscilloscopes and left me somewhat obsessed with these machines from the hay-day of valves! Some of you will know that I have what I describe as a "Retirement Home For Vintage Oscilloscopes" here in North Carolina and somebody from England recently offered me an example of this machine, I jumped at the opportunity! Having gone through it in depth, I find myself newly impressed, even in the face of Tektronix excellence. I think it is not widely understood that the 1035 may be the first dual trace oscilloscope capable of measuring time and voltage directly?
I would appreciate input on the year the original 1035 was introduced, also the following later models including of course, the MKIII.
Here is my narrative on it:

http://richardsears.wordpress.com/20...or-1035-mkiii/

Best,
Richard Sears

[6AL5W-Martin]

hello Richard,

always amazing to read your site.
That is a wonderful old instrument.

I have a little problem with the application:

EAC 91 cannot be there.

E 6,3v A single diode C triode 91 = 7pins socket

The application looks more like a EBC91,

E 6,3v B double diode , C triode 91 = 7pins socket

greetings
Martin

[Richard984]

Hi Martin.

Yes indeed. That is a straight scan from the book however, the actual implementation in the scope (given further down) is correct.

I added a note under the circuit pointing out the error which must be an ancient typo! I gave you credit for noticing it, thanks!

Richard

[6AL5W-Martin]

hello Richard,

not sure if the application have a mistake in the type or in the picture bec. there is only on diode used, the second ist groundet. So a EAC91 may work at that place also...
EAC91 have one full seperated diode, means both kathode have to be connected extern. EBC91 have 2 diode, common kathode.

So it`s possible in the scope works a EAC91 early version, late version? Sometimes things change in a series.

greetings
Martin

[Richard984]

I included the schematic from the text book because it is of historical interest being the first reference I found to the timebase design in the 1035. If you look under the design notes further down, I have written a detailed description of the timebase operation and included the actual schematic as used in the scope.

Cheers.
Richard

[John_BS]

Richard:

I had one of these in 1972, scrapped from Imperial College. I think it must have been a Mk 1, as it contained EF50's and other octal valves. The Mk 1 circuit was different to the Mk 3, and the Y amp frequency response on A1 was a function of the Y sensistivity setting (a consequence of using switched nfb to define the channel gain). Mine had a leather-clad spring-steel band as the carrying handle: the leather had disintegrated, resulting in a tortuous transport experience! It eventually failed due to an insulation breakdown in the EHT winding.

WME_Bill posted some details of these 'scopes some years ago: see https://www.vintage-radio.net/forum/...ad.php?t=20711

According to Bill, your Mk 3 was introduced in 1959.

John

[emeritus]

This looks similar to the Cossor scope I once had, scrapped from Plessey: in the early 1980's mine also failed due to EHT transformer breakdown. The trace was indeed superb, as sharp and clear as the Tektronix's we used at work. I offered it free for spares in one of the free small ads that "Television" used to provide, and someone came and collected it. I think I still have a Xerox copy of the service manual somewhere. A really heavy bit of kit.

[Richard984]

I hope my unit does not succumb to EHT winding failure too!
On heavy, not really heavy, the big Tek scopes have a good 10lb on it, frankly, it was a relief to work on something smaller and lighter for a while. That's my perspective
Richard