Cossor 4100 'scope - UK Vintage Radio Repair and Restoration Discussion Forum

MotorBikeLes · 28th Mar 2014, 7:21 pm

I have a Cossor 4100 oscilloscope. To be honest, I thought it was a 3000 until I decided to try to sort it out. It MAY be one I bought back in 1987, and it looks as if I have been inside it, but it was dead when I switched it on. No EHT, faulty TIP29A in that section. Replaced with BD939, and it now "works", but needs sorting properly. I found a "service manual" online, but whilst it has the circuits, there is no setting up info.
Can anybody help with setting and calibration info, and possibly spares list as well.
It is a very straightforward and well set out unit; I like all the controls, and it must be one of the easiest dual timebase scopes to learn to drive. No "falling to bits" Tek or HP knobs, and with a claimed 75MHz bandwidth, it should make a very useful addition to somebody's workshop.
Les.

WME_bill · 29th Mar 2014, 7:00 pm

Cossor transistor scopes. The 3100 (originally marketed as CDU160), 4000 (an improved CDU120) and the 4100. Introduced from around 1971-72. I suspect as the last effort to keep some of their dominant post war share of the UK oscilloscope market.
They had produced one of the first all transistor scopes in the CDU100/CDU110 in 1966-67, with later developed versions like the CDU120. A MOD contract produced the CDU150/CT531, a conservatively specified version of the CDU120, and a nice machine. Those were the days when MoD contracts seemed to rotate in turn between the UK manufacturers.
But Cossor had been taken over by Raytheon in 1961 (after the share price had dropped dramatically after they had made huge losses on the Fylingdales Radar contract), and the main company efforts concentrated upon ground radar, aircraft transponders, missile guidance etc. Cossor Instruments became a very small part of the business. The Domestic Radio side had been sold to Philips already.
I have manuals for all the models. Have you decided which model you have, or shall I post pictures of each one. wme_bill.

MotorBikeLes · 29th Mar 2014, 9:20 pm

Bill, definitely a 4100. My confusion was that I thought I had had an incomplete 4100 and passed it on 20+ years ago, and this one was a 3000 in my head. (I had three of those 25 years ago, and THINK this may have been acquired at the same time). I easily found the manual via Google, but actually already had most of the circuits. Unfortunately, nothing on calibration or parts. I can probably manage without parts specs, but it has more "twiddlers" than I can work out without the book. Of course, checking and adjustment order is important as well. All of the PSU voltages are marked, EXCEPT for EHT- at cathode, and EHT+ at PDA.
Interested parties can see one here:-- http://www.youtube.com/watch?v=QT4BITlICE0
Though I see that one is claimed to be a 4100A, if there is any difference. Tidy and self explanatory layout as I suggested in message 1.
Les.

WME_bill · 30th Mar 2014, 12:14 am

Cossor 4100. The PDA voltage is quoted at +18.7kv, with grid at -1.36kv and cathode at -1.26kv. The Maintenance instructions quote the CRT cathode at-1260v, measured with an Avo8 on 2500v range, adjusted by 3R203.
The whole Maintenance (calibration) section is pretty brief - 19 pages. I'll scan them for you. wme_bill

WME_bill · 30th Mar 2014, 6:59 pm

Cossor 4100 75 Mhz DT/DTB oscilloscope. I attach the Maintenance and Calibration section of the manual. The whole manual is too large to post. Please let us know what problems you find and resolve. wme_bill

MotorBikeLes · 30th Mar 2014, 11:08 pm

Bill, many thanks, it is being printed off right now. I have a laptop next to my workbench, but paper is much easier to work from than a screen.
When I replaced the TIP29A in the EHT section, I had cathode voltage in the right area, but no trace. Trace locate showed it was just "hidden" due to triggering. As it warmed up, it began to free run, so once I have checked PSU and EHT voltages as per manual, I can start in earnest. A busy few days this week, but I will find a few minutes to start. I like to work methodically through cal instructions, as they generally lead to faults in a structured way, and if you get to the end, you know all is well. I expect to find a few dirty switches, and the Y1 uncal switch is nbg. Hopefully I will have a suitable replacement.
There is a little bit of blooming on full brill, so the CRT is past its best, but still more than satisfactory. Maybe another 35 years before it needs a boost? Joking aside, I have boosted many CTV tubes, but never a scope tube, though I have blown the odd G-K s/c.
I will report back once I have got it sorted, maybe even shout for help if it gets sticky.
Thanks again, Les.

28th Mar 2014, 7:21 pm	#1
MotorBikeLes Nonode Join Date: Dec 2012 Location: Kirk Michael, Isle of Man Posts: 2,350	Cossor 4100 'scope I have a Cossor 4100 oscilloscope. To be honest, I thought it was a 3000 until I decided to try to sort it out. It MAY be one I bought back in 1987, and it looks as if I have been inside it, but it was dead when I switched it on. No EHT, faulty TIP29A in that section. Replaced with BD939, and it now "works", but needs sorting properly. I found a "service manual" online, but whilst it has the circuits, there is no setting up info. Can anybody help with setting and calibration info, and possibly spares list as well. It is a very straightforward and well set out unit; I like all the controls, and it must be one of the easiest dual timebase scopes to learn to drive. No "falling to bits" Tek or HP knobs, and with a claimed 75MHz bandwidth, it should make a very useful addition to somebody's workshop. Les.

29th Mar 2014, 7:00 pm	#2
WME_bill Octode Join Date: Oct 2007 Location: Exeter, Devon, UK. Posts: 1,554	Re: Cossor 4100 'scope Cossor transistor scopes. The 3100 (originally marketed as CDU160), 4000 (an improved CDU120) and the 4100. Introduced from around 1971-72. I suspect as the last effort to keep some of their dominant post war share of the UK oscilloscope market. They had produced one of the first all transistor scopes in the CDU100/CDU110 in 1966-67, with later developed versions like the CDU120. A MOD contract produced the CDU150/CT531, a conservatively specified version of the CDU120, and a nice machine. Those were the days when MoD contracts seemed to rotate in turn between the UK manufacturers. But Cossor had been taken over by Raytheon in 1961 (after the share price had dropped dramatically after they had made huge losses on the Fylingdales Radar contract), and the main company efforts concentrated upon ground radar, aircraft transponders, missile guidance etc. Cossor Instruments became a very small part of the business. The Domestic Radio side had been sold to Philips already. I have manuals for all the models. Have you decided which model you have, or shall I post pictures of each one. wme_bill.

29th Mar 2014, 9:20 pm	#3
MotorBikeLes Nonode Join Date: Dec 2012 Location: Kirk Michael, Isle of Man Posts: 2,350	Re: Cossor 4100 'scope Bill, definitely a 4100. My confusion was that I thought I had had an incomplete 4100 and passed it on 20+ years ago, and this one was a 3000 in my head. (I had three of those 25 years ago, and THINK this may have been acquired at the same time). I easily found the manual via Google, but actually already had most of the circuits. Unfortunately, nothing on calibration or parts. I can probably manage without parts specs, but it has more "twiddlers" than I can work out without the book. Of course, checking and adjustment order is important as well. All of the PSU voltages are marked, EXCEPT for EHT- at cathode, and EHT+ at PDA. Interested parties can see one here:-- http://www.youtube.com/watch?v=QT4BITlICE0 Though I see that one is claimed to be a 4100A, if there is any difference. Tidy and self explanatory layout as I suggested in message 1. Les.

30th Mar 2014, 12:14 am	#4
WME_bill Octode Join Date: Oct 2007 Location: Exeter, Devon, UK. Posts: 1,554	Re: Cossor 4100 'scope Cossor 4100. The PDA voltage is quoted at +18.7kv, with grid at -1.36kv and cathode at -1.26kv. The Maintenance instructions quote the CRT cathode at-1260v, measured with an Avo8 on 2500v range, adjusted by 3R203. The whole Maintenance (calibration) section is pretty brief - 19 pages. I'll scan them for you. wme_bill

30th Mar 2014, 11:08 pm	#6
MotorBikeLes Nonode Join Date: Dec 2012 Location: Kirk Michael, Isle of Man Posts: 2,350	Re: Cossor 4100 'scope Bill, many thanks, it is being printed off right now. I have a laptop next to my workbench, but paper is much easier to work from than a screen. When I replaced the TIP29A in the EHT section, I had cathode voltage in the right area, but no trace. Trace locate showed it was just "hidden" due to triggering. As it warmed up, it began to free run, so once I have checked PSU and EHT voltages as per manual, I can start in earnest. A busy few days this week, but I will find a few minutes to start. I like to work methodically through cal instructions, as they generally lead to faults in a structured way, and if you get to the end, you know all is well. I expect to find a few dirty switches, and the Y1 uncal switch is nbg. Hopefully I will have a suitable replacement. There is a little bit of blooming on full brill, so the CRT is past its best, but still more than satisfactory. Maybe another 35 years before it needs a boost? Joking aside, I have boosted many CTV tubes, but never a scope tube, though I have blown the odd G-K s/c. I will report back once I have got it sorted, maybe even shout for help if it gets sticky. Thanks again, Les.