Tale of a Cossor CDU110 from my Bedroom Stash!

[Chris55000]

Hi!

Almost ten years since this tale of the Cossor CDU110 with poor brightness intensity was written:–

https://www.vintage-radio.net/forum/...t=78108&page=2

Guess what – I've just dug one out from under the stash in my bedroom and it's got exactly the same fault on it!!

Anyway I have one of those RBM EHT meters, so I'll get busy on it and see how mine compares voltage–wise with those the OP got with his unit documented in the post linked above!

My CDU110 book is suffering badly from the brown sellotape curse afflicting old paper manuals, so I'm making some new diagrams for the board layouts, that will be added to this thread as I complete them!

Chris Williams

[WME_bill]

CDU110.
Chris, I know you like re-drawing board layouts ( it is a good way of learning the circuit tricks), but I have an original manual quite unsullied, and can make you a copy of any of the board layouts or circuits onto A3 as in the original if you would like them.
Did we ever get an explanation for the dim trace referred to in that posting in 2012 which we debated at the time.
wme_bill.

[Chris55000]

Afternoon Bill!

I must confess I didn't realise you had a pristine book, I'll be in touch by PM in due course regarding this!

I believe the OP in the post I linked found either a dry–joint on the capacitors C55 & C57 or one of the rectifiers faulty (MR 46, MR 47 and MR 48) but it wasn't clear exactly which!

Like your and other Member's experiences, I've found it's rare to find a really bad Oscilloscope CRT from any of the reputable old manufacturers, the only exception being the modern Chinese mono–accelerator ones, which are only good for a few tens of hours usage before the focus goes bad!

(When I worked at Dowding & Mills and sold a few of the Chinese 10 MHz cheapo scopes, we had to get them all replaced under warranty because of C.R.T. failure!)

I do have at least three oscilloscopes that definitely will need books drawing out tho', as I know of none in existence for:–

1) The Mitte D47/Dartron D17 ;
2). The Enertec 5072 Analogue Storage Scope ;
3). The Advance Bryans DSO1526 Digital Storage Scope.

Chris Williams

[MotorBikeLes]

Cris, generally most of the well known scopes with positive EHT had good tubes, though I have come across those damaged by mechanical means (dropping, post etc.) but I do have one here which should be pretty good, except for the CRT. Also a Cossor, a 4100. a continental made CRT (the make on the tip of my tongue, so maybe before this is finished.
The 4100 is rather a difficult one to calibrate, "working towards" perfect calibration seems to elude me, and a few compromises were necessary.
Anyway, I would be more than happy to have it set up on my bench, if the CRT was not "double humped" with low brightness.
I have seen the same problem on a couple of TQ D83s, with the big, expensive in house TEK CRT.

[Chris55000]

Evening Les!

The 4100 has a D14–220GH of Telefunken manufacture, and for some strange reason this CRT was specified with a 7.0V 240mA heater (the one in Frank's Electron Tube Data is quoted as being a standard 6.3V 0.3A heater!) – it's not a misprint in the data because the '4100 PSU circuit quotes the transformer secondary as 7V as well!

There doesn't seem to be a "double–hump" in the action of the brilliance control of my CDU110, just not a lot of it!

Chris Williams

[Chris55000]

Hi!

I've got an Erie 1n8 4kV wkg. disc ceramic capacitor n.o.s. and five of those Chinesium 2CL–etc., 5mA e.h.t. rectifier diodes coming, but I will be meticulously inspecting the G board round C55 and C57 as well!

I've also discovered that Cossor thoughtfully left out that part of the power supply layout drawing covering the 40250 series pass transistors and the 5W chassis–mounted zener diodes associated with these from their handbook, so that's another drawing project added to a very long list!

Chris Williams