My Telequipment S31's

[britishrocket]

Ladies and Gents,

Hello my name is Carl. This is my first post. I have been interested in electronics from childhood and I have always had a particular fascination with valve circuitry. As a teenager I got hold of a copy of the Van Valkenburgh, Nooger and Neville text "Basic Electronics". This was all valve based and never left my side. I used to scrounge old TV valves from the local repair shop - PL's, DY's - you know the type of thing. My attempts at making anything with them were sometimes successful, using rectified mains as Ht - and sometimes less than successful. I guess the fact that I didn't kill myself was part of the success.

I must be hankering after my youth because last year I bought two Telequipment S43 scopes off ebay. I had one when I was 17, bought at the electronic fleamarket shop near the college where I was doing my C&G.

Well, I have two so I hope to get at least one going. Haven't powered them up yet as I do not have a variac, but reading these pages I see lamp droppers seem a good alternative.

I've got quite a lot of electronics experience generally but not much with valve kit. Obviously there are some big slumbering giants of electrolytic caps in there - I have reformed big caps in motor drives and I see schematics on the net. Is it advisable to desolder them all and do this, or just leave the unit powered up "on a low light" so to speak, thereby reforming them?

I imagine someone here has one of these scopes. Are there any known problems to watch for? I have heard about a selenium rectifier for eht that goes. What else?

I appreciate these are all probably noddy questions for you guys and gals. I spend a lot of my time fiddling with fibre optics and surface mount stuff. So you are helping me get back to real electronics.

I have a somewhat younger Telequipment scope too!

Thanks in advance,

Carl.

[Diabolical Artificer]

Welcome to the forum Carl. You're on the right track, reform the caps, start it up through a lamp limiter and check the big red diodes if you don't get a trace.

There's a lot of caps in these, when I did mine I used a simple cap reformer, see attachment and did each cap one by one, which takes a while as a lot have two caps in one can. You can do the whole scope but you really need a variac to it and IMO isn't as sure fire as the one cap at a time approach.

It's a good idea to give a the valves a wiggle to make sure they have good contact with the bases and on start up set the scope up as in the user manual, first time start up procedure.

One other handy bit of kit to have is a EHT probe to check very high voltages. You can make these yourself by stringing a load of 10meg or similar resistors together to form a potential divider. Take care, there's some nasty voltages inside these, clip your meter probes on, then switch on.

If you need any spares I have a few Telequipment scope bits.

Good luck, Andy.

[britishrocket]

Thank you for that very warm welcome and informative reply. Thank you also for the offer of spares.

Taking out the electrolytics and reforming them individually was the way I had envisioned doing things, to be honest. Thanks for the info on the cap reforming circuit. I've been looking at the circuit diagram and I see all the metal rectifiers in the HT and EHT supplies.

One of the S43's I have looks to be in far better condition than the other. I haven't had the back off either of them yet, they have been sitting on a shelf in my workshop for 18 months waiting for me to get a hold of that elusive yet useful piece of kit called a "round tuit". That said, through the ventilation grilles of one I can see loose wiring and other signs of hamfisted tomfoolery. So maybe that one will become the spares donor.

Thanks again for the help. I will be sure to post some pictures, once I get a hold of the above mentioned erstwhile tool.

Cheers,

Carl.

[MotorBikeLes]

Don't confuse the odd pair of stiff wires (usually red) sticking up but going nowhere. They constitute a neutralising capacitor.
There are TWO versions of the S/D 43 series. The early one has three pairs of push buttons on the timebase module, whilst the later one had two sets of three push buttons. Quite a few differences between the two. Good 'scopes to work with, and decent pictures to be seen on the screens. The CRT is a high voltage PDA type, so a bright well focussed spot is normal.
Those brown selenium rectifiers are probably low efficiency by now. I never had a "failure" in the sense of fully O/C or S/C. They just go high resistance and the EHT falls below specified. Use any HV diode (BY182 I think I used) but add say a 4K7 resistor in series with each one. 15MHz bandwidth for the types A and J vertical amplifiers, but a wide choice of alternatives. B, C, G, K and some even have Y-delay lines CD(?), JD.
The J and JD are actually 25MHz amplifiers, but not in a 43 mainframe, only in the 53 series.
Les

[Diabolical Artificer]

You don't need to take the caps out, just unsolder the positive leads. Be carefull though, the insulation has a habit of melting. You may find it easier if there's enough wire length to snip the wire near to the cap terminals, strip back the wire and do the connection from scratch. If yours are like the ones I've worked on the terminals will be mucky, a good clean with a fine file and some extra flux helps to get a good joint.

Re the big red EHT diodes, you can't test them with a diode checker on a DMM. There's an article online somewhere that describes the process. I used Vishay BYX10GP-E3/54 off ebay as replacments.

There may be two big EHT capacitors too in the EHT PSU, I've found these are usually ok even though they're paper in oil or similar.

Good luck, Andy.

[britishrocket]

Hello Les and Andy,

Many thanks for the helpful information. As I say, I haven't had the chance to get in and about the two scopes yet. My job takes me away from home and I do a lot of mechanical and hydraulic stuff as well as electronics and fibres.

Anyway, I decided that I would simulate part of the circuit of the capacitor reformer in the "Big Bang" article that Andy so graciously gave me.

Here is a screen shot of the simulation running, I use Livewire. Using the notation in the circuit diagram in the article, you can see that a 10K resistor as R16 gives as near as damn it 500V at point M.

Cheers,

Carl.

[britishrocket]

Well, I have an update for you regarding my S43's, and it's a big one. They aren't S43's at all. They are S31s! Replete with full wave diode in the Psu.

OK so I am not perfect...

[AC/HL]

Thread title corrected.

[britishrocket]

Thanks for that. It's an EZ81 in the Psu. Multiplier with selenium rectifiers for the eht.

[MotorBikeLes]

A lot of the things I said in another thread a few days ago about the S32 applies to the S31. Valve rectifier not selenium as you noted. However, these have a monoacclerator CRT, not a PDA type. The last one I touched (maybe 30 years ago) needed very little attention, but it was full of the brown German caps, especially on the time cm switch which ALL go leaky or S/C. I replaced those and it worked. I think the Selenium rectifiers sticks in the EHT- are E1500. Can be replaced with an HV silicon type with a bit of series resistance, but I have a few new ones here. The FIRST affordable TRIGGERED 'scope on the market, 5 or 6MHz bandwidth, capable of anything the Radio and TV engineer of the day could ever need.
Les.

[Diabolical Artificer]

The "Big Bang" reformer uses a voltage doubler circuit to get the required voltages needed to reform big smoothing caps as seen in scopes etc. You start off at 50v say and work your way up to the capacitor's working voltage, EG 350v.

"OK so I am not perfect..." No one is, we all make mistakes. : )

Andy.

[britishrocket]

Thanks for all the great advice. Noted Re the German caps. I am home now and have assembled the parts for the cap reformer. I will try to post some pictures of the scopes in the next few days.

Thanks,

Carl.

[britishrocket]

Quick update. I am about half way through building the big bang capacitor reformer. Assembling the components on tag strip (such a joy!) and building the whole into a die cast case. Will try to post some pictures soon.

Carl.

[britishrocket]

Here is a picture of the capacitor reformer underway.

[MrBungle]

Thanks for posting this. I love to see things people have built from scratch.

[trh01uk]

Originally Posted by Dr Wobble

There's a lot of caps in these, when I did mine I used a simple cap reformer, see attachment and did each cap one by one, which takes a while as a lot have two caps in one can. You can do the whole scope but you really need a variac to it and IMO isn't as sure fire as the one cap at a time approach.

Glad to see that article I wrote up so long ago is still proving useful! Mike Hazell, who came up with the basic idea, is still going strong.

Richard

[britishrocket]

More to come. Did some more construction yesterday. Meantime, here is one of my scopes.

[britishrocket]

Two transformers back to back give the HT for the reformer.

[britishrocket]

Thank you Mike and Richard for this design.

[britishrocket]

Cap reformer 12 way switch was fiddly to assemble...