Marconi TF2202 Dual Beam scope.

[Diabolical Artificer]

Having a look at this for a recently joined forum member. We've go a trace and all seems to be working but there's a high pitch whistling I'm wary of. I presume this is the oscillator in the invertor for the EHT.

So far I've only brought the scope up on a variac to about 180v mains AC, maybe the whistling will stop with full mains applied, but as mentioned I'm wary. Is this whistling normal or a sign of a potential issue?

Lastly I can't find anything about this scope, certainly no manual. It looks very similar in construction to a Telequipment D43, in that it has two TM6962 vertical plugins, a removable TB and delay module. It's a dual beam delayed TB scope, maybe 10mhz tops.

It looks to be a very handy scope for HV work having a 200v/div Y setting, also x1, x 10 & x100 attenuation. The trigger seems to be pretty stable too.

Any info tips welcome, Andy.

[Dickie]

I have a manual for it. The PDF is about 7M so PM me an email address and it's yours.

[Diabolical Artificer]

I have a manual for it

Brilliant, that'll make life easier, PM sent.

Andy.

[Chris55000]

Hi!

My friend swapped a laptop for one this morning so that's me in the book Q as well!

PM sent.

Has anybody seen the funny transistor symbols used in one or two E.M.I. books?

I remember there was some (slightly heated!) discussion in the Letters Column of W.W. Magazine regarding point–contact and junction transistor symbols during the late 1950s and early 1960s, and I think the funny E.M.I. symbol was one of those discussed!

Chris Williams

[Diabolical Artificer]

Managed to do some investigation on this scope yesterday and think I've found the source of the whistling, it's VT605. What VT605 does I'm not really sure. VT605 seems to drive VT606 which is an off board TO3 Q which is housed in a metal box on the back of the scope.

At a guess I'd say the power supply instead of consisting of a mains tfmr with a primary and secondaries is, in this case is a mains tfmr with a tapped LV secondary, this is rectified and smoothed and powers our board - TM6888, some sort of oscillator which is amplified and drives another tfmr, so like invertor. But for the life of me I can only see one tfmr in the scope, which can't be right.

This scope design is really odd, complicated by the possibility of powering the scope from a battery. Although I now have a manual, it's not a Tektronix or HP manual that's for sure. No waveforms shown, no voltages throughout the circuit, it's a bit of a nightmare to decipher. What is it with British manual'? They are usually very sparse and badly written.Technical service manuals; one thing we English can't knock the Yanks for.

Anyhoo, back to VT605... AFAICT all power supply rails are about right. I've found a few duff electrolytics and rails with high ripple and have tacked in temporary replacements for now, but apart from that I can't see anything wrong.

The scope works fine, but just has this high pitched whistling. I have it powered on a variac at present at about 180v AC, so rails are a bit low. Applying full mains doesn't make the whistling go away.

Apologies for the rambling nature of this post, just setting my thoughts down so far, hopefully the fog will clear as we go on.

Andy.

[Keith956]

Looks like it's a DC-DC inverter with VT609/10 as the oscillator driving the high voltage supplies. I would guess the whistle is the oscillator frequency you're hearing. VT606 might be part of some sort of regulator as it's providing the supply to the transformer CT.

That transformer TR604 may not be all that large - certainly not as big as I suspect the mains one is, which looks like its supplying 24V or so at 5A.

[Radio Wrangler]

The scope can run off battery power or off mains. It'll need an EHT supply oscillator for the electron gun and accelerator anodes. But typical electrostatic deflection plate sensitivities will also need more volts than the battery to power the Y and X amplifiers. So there is a need for a power inverter.

David

[WME_bill]

Marconi TF2202.
It is a dual trace scope, using a 4inch split beam tube. 6Mhz bandwidth, and with trigger delay The tube is the Etel 1960 prototype CR157, became E10-11 or Mullard DHM10-10. Date about 1963, an early all transistor scope.

Solartron produced a valve scope at the same time with similar performance, the CD1183 but all mains, which turns up more frequently. Also uses the same split beam tube, which perhaps was specially developed for this application. Split beam is cheaper than a twin gun tube which was used in the CT436 or Telequipment D43 or that huge seller, the 1970 workhorse, Solartron CD1400 series.

I suspect both originally developed for an MoD contract, perhaps to replace the 1962 valve Solartron CT436 dual beam, 6 Mhz.

But it seems that the TF2202 did not sell well, and the manual you have is the "preliminary" version, and was never updated to a final version.
Uses a strange selection of germanium and silicon transistor types, including twenty of the germanium OC170, which tend to suffer from the whisker disease.

A whistling power supply used to occur often. Due I believe to magnetostriction of the transformer laminations. Designs were improved later to avoid this, by using a ferrite core transformer or by raising the frequency.

The SE Labs SM111 (or Marconi TF2204) of 1969 appears to have been the replacement for the CT436 in front line service. 18 Mhz, all silicon, mains or battery. Yet it can have a bad whistle also.
While my Solartron CD1642 of 1965, another early mains/battery, all silicon 15Mhz transistor scope, is nicely quiet. It uses an odd CRT, Brimar D13/46, with the more sensitive deflection for the X plates, presumably because of limited availability of high frequency, high voltage medium power transistors for the X amplifier output stages in the early 1960's.

I attach the CRT data so you can see the operating voltages.
I have the manuals for all scopes mentioned if you want to compare the design approaches used.
wme_bill

[WME_bill]

TF2202.
Herewith the CRT data for the Etel CR157/DHM10-10/E10-11 omitted in error.
wme_bill

[MotorBikeLes]

When i read the bit about whistling, i immediately thought of the SELabs scope.
I once had one, modified by the GPO if I remember. It had possibly 20M of wire leading from it, and whilst I don't recall its exact use, I think it was a poor man's Time Domain reflectometer* for detecting faults in telephone leads.
That had one transformer doing everything, and it needed a big 12v battery to power it. I wonder how much power disappears generating that whistle.
I seem to recall that Telequipment made one as well, either a D54U or an S54U.
I don't think I ever had one of those.
Les.

[Diabolical Artificer]

I suspect both originally developed for an MoD contract

That makes sense, it has a military feel to it and also somewhat of a prototype feel too. It's not an easy scope to work on, stuff jammed into inaccessible holes or tucked into walled off enclosures. I found the missing tfmr tucked into one of said nooks. The PDF manual Richard sent has two copies of every (or most) schematics,can't see any differences so far. Thanks for all that background Bill, you know your old scopes, hats off.

Okey, so the whistle could be normal, I suppose one could live with it. It sounds like small fan run at higher than spec volts or a mosquito with a small megaphone. Curious as to the mechanics of the sound which I presume to be VT605 vibrating; do trannies have aural capabilities? Or is it a piezo effect?

It looks like all I can do with this scope is change damaged electrolytics and check for tin whiskers. a full restore is a daunting prospect. Thanks all, Andy.

[TonyDuell]

I would guess the whistle comes from the transformer. The core will change dimensions slightly as it magnetises and demagnetises (so-called magnetostriction I think) and that's what you hear. Same as the line whistle in TV sets.

[Radio Wrangler]

It's a self-oscillating inverter, and core saturation usually plays a part. This is just asking for significant magnetostriction and sound output. You also get noise from the wire in the windings unless it is carefully impregnated with varnish.

David

[barrymagrec]

I`m fairly sure this is the scope we had back in the early seventies at a broadcasting organisation I worked for.

If so I seem to remember it almost always whistled....

[Diabolical Artificer]

I used a scope probe unconnected to sniff around and got the highest amplitude next to VT605, but as the tfmr is very close it could be that, I'll have another sniff around.

A