CT 52 'scope repair - UK Vintage Radio Repair and Restoration Discussion Forum

Hermit6345 · 21st Aug 2008, 9:02 pm

Not sure if this is a success story, but it is for me anyway. The CT52 has resided in the bottom of my cupboard for the last 25 years. The dates on the various electrolytics indicate that it was made in, or after, 1963. The main problem was the Y input spring clip that was hanging out and broken. I could never seem to find a replacement. Anyway, I have acquired a 3343 Ganging Oscillator and wanted a valve scope with a large sweep output to drive it.
I decided to repair the CT52. A request for a couple of replacement terminals on this forum resulted in a kind member (Thanks Ant!)sending me a couple.

I decided to power up the scope via a Variac. As I brought up the voltage, valves began to glow and I was rewarded with a very non-linear X trace. With the sync control in Single Shot I was getting a timebase trigger every few cycles. All supply voltages were in spec. All are provided by metal rectifiers or equvalent.

To get at the input and output terminals, the front panel must be hinged down. To hinge down the front panel, the tube has to come out. The tube seemed to be very well fixed but eventually it gave in. To my horror, the tube had left it's metal base behind! I managed to re-unite tube with base thanking my stars that the DG7-5 tube has a glass base like an EF50 with the pins protruding through holes in the metal base. In order to refix the metal base I had to find out which pins went through which holes. I decided the best way was to use an AVO to locate the heaters and then fix the metal base so that these two pins (1 snd 9) were either side of the metal spigot on the metal base. Phew!

With the front folded down I could clearly see all the Visconol paper caps for the Miller timebase section of the scope. They were all oily, sticky and electrically leaking as well. All the Visconol caps in the scope were in the same state so I decided to change them all. Whilst I was at it I changed the two electrolytics but left the main smoothers as they were fine (Oddly)

The terminals arrived and I set about replacing them. What a job. I finally resorted to holding the front part of the terminals in place with a large elastic band wound round adjacent terminals, whilst I worked through wiring looms and switch wiring on the back parts. I am sure when they built the scope the first thing they put in were the terminals. It was an absolute p*g of a job. A nut driver and angled pliers were essential tools.

Anyway, I decided to check all the resistors behind the front panel as I did not want to have to take the tube out again. Only one was out of spec, a 100k that was 125k. It was replaced. Front panel folded up and secured, tube replaced and scope fired up. pretty linear timebase trace, sync working properly. Tube rotated so that timebase trace was horizontal. All the knobes were removed and attacked with soapy water and a toothbrush.

So now I have a working scope, though to be honest it's not a lot of good for much except looking at waveforms. The timebase is totally variable, the Y gain via the internal amp is totally variable and the calibration voltage is 100 volts p-p. However, it does work as intended and I have other "proper" scopes which I can use to measure things properly.

An old codger brought back from a long sleep..now onto to the 3343!

Ian.

Keith · 21st Aug 2008, 11:28 pm

Well done Ian,

Sounds like it was quite a challenge. This was the first scope I ever had when I was at college back in the early seventies - bought at the local surplus shop in Portsmouth. Luckily it worked OK without any intervention being required. It was just about fast enough for looking at DTL waveforms!

Brased · 22nd Aug 2008, 9:19 pm

It looks very successful to me. You have clearly put a lot of work into it and got it working as its maker intended. You have saved it from the skip so well done!

Edward

Top Cap · 23rd Aug 2008, 4:46 am

We used to use these in the Navy for monitoring various waveforms around the main radar transmitter. The timebase accuracy was not really required as all waveforms were fixed to the prf of the radar. The terminals on the front were wired to a piece of coax with a post office jack plug for inserting into various stages like the trigger pulse to the modulator or magnetron drive pulse. The latter much attenuated as it was something like 27kV at 26 Amps

.
At least it prepared me for working on 25kV colour tellies

.

Hermit6345 · 23rd Aug 2008, 10:53 am

Thanks for your kind comments Keith and Edward. Keith, I am sure that I have some DTL chips around in my junk!

To Top Cap, I seem to remember one of these fitted in the 965 radar rack, connected just as you described. Perfect for looking at pulse waveforms like that with a relatively low prf. It even has a delay line to enable the pulse being monitored to be in the centre of the screen. I checked the timebase ranges with an accurate AF oscillator and they are more or less as detailed on the top front of the case. In the free running mode, on range 6, the timebase is switched off, which is handy for measuring frequencies using Lissajous figures.

Ian

21st Aug 2008, 9:02 pm	#1
Hermit6345 Rest in Peace Join Date: Oct 2006 Location: North Wiltshire, UK. Posts: 638	CT 52 'scope repair Not sure if this is a success story, but it is for me anyway. The CT52 has resided in the bottom of my cupboard for the last 25 years. The dates on the various electrolytics indicate that it was made in, or after, 1963. The main problem was the Y input spring clip that was hanging out and broken. I could never seem to find a replacement. Anyway, I have acquired a 3343 Ganging Oscillator and wanted a valve scope with a large sweep output to drive it. I decided to repair the CT52. A request for a couple of replacement terminals on this forum resulted in a kind member (Thanks Ant!)sending me a couple. I decided to power up the scope via a Variac. As I brought up the voltage, valves began to glow and I was rewarded with a very non-linear X trace. With the sync control in Single Shot I was getting a timebase trigger every few cycles. All supply voltages were in spec. All are provided by metal rectifiers or equvalent. To get at the input and output terminals, the front panel must be hinged down. To hinge down the front panel, the tube has to come out. The tube seemed to be very well fixed but eventually it gave in. To my horror, the tube had left it's metal base behind! I managed to re-unite tube with base thanking my stars that the DG7-5 tube has a glass base like an EF50 with the pins protruding through holes in the metal base. In order to refix the metal base I had to find out which pins went through which holes. I decided the best way was to use an AVO to locate the heaters and then fix the metal base so that these two pins (1 snd 9) were either side of the metal spigot on the metal base. Phew! With the front folded down I could clearly see all the Visconol paper caps for the Miller timebase section of the scope. They were all oily, sticky and electrically leaking as well. All the Visconol caps in the scope were in the same state so I decided to change them all. Whilst I was at it I changed the two electrolytics but left the main smoothers as they were fine (Oddly) The terminals arrived and I set about replacing them. What a job. I finally resorted to holding the front part of the terminals in place with a large elastic band wound round adjacent terminals, whilst I worked through wiring looms and switch wiring on the back parts. I am sure when they built the scope the first thing they put in were the terminals. It was an absolute p*g of a job. A nut driver and angled pliers were essential tools. Anyway, I decided to check all the resistors behind the front panel as I did not want to have to take the tube out again. Only one was out of spec, a 100k that was 125k. It was replaced. Front panel folded up and secured, tube replaced and scope fired up. pretty linear timebase trace, sync working properly. Tube rotated so that timebase trace was horizontal. All the knobes were removed and attacked with soapy water and a toothbrush. So now I have a working scope, though to be honest it's not a lot of good for much except looking at waveforms. The timebase is totally variable, the Y gain via the internal amp is totally variable and the calibration voltage is 100 volts p-p. However, it does work as intended and I have other "proper" scopes which I can use to measure things properly. An old codger brought back from a long sleep..now onto to the 3343! Ian. Attached Thumbnails

21st Aug 2008, 11:28 pm	#2
Keith Heptode Join Date: Jan 2003 Location: Tewkesbury, Gloucestershire, UK. Posts: 693	Re: CT 52 'scope repair Well done Ian, Sounds like it was quite a challenge. This was the first scope I ever had when I was at college back in the early seventies - bought at the local surplus shop in Portsmouth. Luckily it worked OK without any intervention being required. It was just about fast enough for looking at DTL waveforms! __________________ Keith Yates - G3XGW VMARS & BVWS member http://www.tibblestone.com/oldradios/Old_Radios.htm

22nd Aug 2008, 9:19 pm	#3
Brased Hexode Join Date: Mar 2005 Location: London, UK. Posts: 318	Re: CT 52 'scope repair It looks very successful to me. You have clearly put a lot of work into it and got it working as its maker intended. You have saved it from the skip so well done! Edward

23rd Aug 2008, 4:46 am	#4
Top Cap Octode Join Date: Mar 2006 Location: Watford, Hertfordshire, UK. Posts: 1,270	Re: CT 52 'scope repair We used to use these in the Navy for monitoring various waveforms around the main radar transmitter. The timebase accuracy was not really required as all waveforms were fixed to the prf of the radar. The terminals on the front were wired to a piece of coax with a post office jack plug for inserting into various stages like the trigger pulse to the modulator or magnetron drive pulse. The latter much attenuated as it was something like 27kV at 26 Amps . At least it prepared me for working on 25kV colour tellies . __________________ Whether the Top Cap is Grid or Anode - touching it will give you a buzz either way!

23rd Aug 2008, 10:53 am	#5
Hermit6345 Rest in Peace Join Date: Oct 2006 Location: North Wiltshire, UK. Posts: 638	Re: CT 52 'scope repair Thanks for your kind comments Keith and Edward. Keith, I am sure that I have some DTL chips around in my junk! To Top Cap, I seem to remember one of these fitted in the 965 radar rack, connected just as you described. Perfect for looking at pulse waveforms like that with a relatively low prf. It even has a delay line to enable the pulse being monitored to be in the centre of the screen. I checked the timebase ranges with an accurate AF oscillator and they are more or less as detailed on the top front of the case. In the free running mode, on range 6, the timebase is switched off, which is handy for measuring frequencies using Lissajous figures. Ian