Vintage oscilloscope info

[mikemike]

Hi, I'm trying to get a great little vintage scope going.

I've powered it up slowly and it seems to be generating the right sort of voltages across the various smoothing caps but no hint of a trace.

It's labeled 'Industrial Electronics' on the back and I would guess 1940/50s vintage, judging from the octal valves.
The tube looks like a ACR10 to me. The 2 rectifier valves are 6X5 (double diodes) and the other valves are 4 off 6SH7 and a T41.

Look on the net but all I could find was a vintage advert, suggesting it may be a model 1200B.
Does anyone recognise this unit and have a circuit diagram for it?

Regards - Mike

[Diabolical Artificer]

A labour of love there Mike. First off have you got heater glow? Next have you got EHT or whatever the CRT works on? Next if that's all ok your trace might be hiding so you need to measure whether brightness, focus are working and the X & Y plates. Brightness changes the grid voltage, Vgk negative less bright trace, VGK +, trace brighter. X & Y plates need to be at the same potential for a center trace.
No idea re the timebase and you have no trigger, not a practical scope really.

Andy.

[barrymagrec]

T41 suggests a Thyratron timebase, should be fairly easy to see if it is running.

http://www.r-type.org/exhib/aat0007.htm

[factory]

I've got one of these in my collection, it's a little newer & uses some top cap valves, some of which are war surplus parts.


It did produce a trace when I acquired it, I expect some capacitors need replacing to get it working properly, i.e. the X-shift control is set all the way to get the trace centred.


Did you remove the CRT shield to see if there is heater glow, or was it missing?

David

[factory]

Some info on Industrial Electronics here, "greentrace" was the website of forum member ScopeMonkey, it's now only accessible on the web archive.
https://web.archive.org/web/20160115...anic/2300t.php

Jonz Valve Page has the later 2300T, that was also made by Industrial Electronics for EMI.
http://www.thevalvepage.com/testeq/emi/2300/2300.htm

David

[mikemike]

Hi guys
Many thanks for the replies and info, much appreciated.
Yes it's very much a labour of love, but I hate to see these thing non fuctional. No idea what I'll do with it when its working. Display for a panadapter perhaps!!

The adverts say it's DC to RF (3MHZ) so I possibly there is a differential amplifier using 2 pentodes (6SH7), who knows??

Yes I removed the Mu metal shield, and yes the tube heaters are working.
The T41 is a thyratron, used to generate the sweep sawtooth.

Lots of different heater xfmr windings as the tube and the T41 are 4V, the rectifiers are 5V and the 6SH7s are 6.3V. But all the heathers are working.

As for the tube voltages; The ACR10 / VR139A tube is specified with max anode of 1500V but I've seen circuits with only 700V. In many designs the chassis seems to often sit at a middle potential so the tube cathode is at something like -300V and the plates are at a sensible voltage W.R.T. the chassis.

The -V rail (oil/paper cap) has -294V and the +V rail (electrolytic cap) has +315 so maybe a look a bit low.

The tube anode voltages look way too low, with A3 only having 146V, so something has probably failed.

As for the deflection plate voltages (just to confuse you the tube is fitted 90 degrees round so the 'Y' plates are actually the sweep ones).
Horizontal 1 = +20 to +194V, depending on X position control.
Horizontal 2 = +280V
Vertical 1 = +50 to +240V, depending on Y position control.
Vertical 2 = 155V

The T41 valve gets a lot hotter than all the others, not sure what you'd expect from a thyratron?

Really could do with a circuit. Probably going to have to work it out from the wiring - eek.

Cheers Mike

[Graham G3ZVT]

Is the thyratron glowing like a neon lamp (apart from the heater glow).

[mikemike]

Hi Guys
Well spent a bit more time on the scope. The negative HT rail seemed low to me so I started tracing out the circuit.

The plus HT rail uses an eletrolytic cap, although wierdly the minus end isn't taken to chassis. I measure +440V on this so think it's ok.

The minus HT rail uses 2 metal can caps (oil filed, paper?) with a 220k series resistor between them. Someone has added another resistor across this, which rang alarm bells with me. These caps are jamed behind the transformer and required major surgery to get out. The cans were bulging and when tested and there was significant leakage.

I replaced them with a chain of 3 rubycon 33uF 250v electrolyics with 330k balancing resistors. I put a 150k resistor in series with the rectifier at first but only got -440V, so I reduced it to 30k and got -650V.

This has got the scope working after a fashion. I get a trace now although the time base doesn't work on all ranges (probably more leaky caps).

Still a result. I even cleaned up the front panel.
Just need to think of a use for it now!

Cheers - Mike M0CAA

[Diabolical Artificer]

Good progress Mike though the TB doesn't look linear, as you say leaky caps or off spec resistors or both probably.

Use? I met a valve amp tech once his entire test gear suite consisted of a old scope like this and an Avo oh and probably his ears, his bench looked really empty.

Andy.