Anyone recognise this ancient CRO?

A bloke's contacted me in the hope that I might know something about a simple oscilloscope his late father built many years ago. It's got a 2" RCA CRT and only four (octal) valves.

I've uploaded the photo he sent me, to

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One of the visible valves looks like it could be a 5Y3G and another a

6J7G. A lot of the visible capacitors look like those yellow Philips polyester(?) ones from the 1960s but his father quite likely replaced original waxed papers caps with them.

Does anyone recognise it?

Cheers, Bob

Reply to
Bob Parker
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Perhaps it is one of the designs that were in the ARRL Handbook 30 - 35 years ago.

Reply to
Rodwell

I believe it dates back a lot further than that

have a look at examples from the 30s through to the 50s.

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some brand names, some home brew diy.

Cheers Don...

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Don McKenzie 

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Reply to
Don McKenzie

"Bob Parker"

** Bloody heck !!

The chassis looks like something Radio & Hobbies mag could have published circa 1940 - then, in the early 70s, it was refurbished with new hardware & film caps.

The AC tranny must be remote, to keep 50Hz mag fields away from the CRT.

Many details remind me of my own Electronics Australia, 3 inch CRO from May

1966 - but that has 5 x 9 pin valves, all of them twin section, plus silicon diodes. It has the same knobs as that black one down the bottom.

** How can you even make a CRO with just four single valves ?

Is the CRT a 2AP1 ??

** I doubt anyone alive still does.

.... Phil

Reply to
Phil Allison

Yep less actually, we had to make one as an exercise in our apprentice scheme. It had a DG7 tube; two EF91s , and a rectifier, possibly a 6X7. The EHT rectifier was a selenium one. It wasn't exactly a Tektronix.

We would have definitely got a failing mark though if it looked like that.

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Reply to
keithr

Indeed. I got a start in electronics about 35 years ago and by then valves had well and truly disappeared from the hobbyist scene (yes, there were a very few devices still being made using valves, but easily 99% of all kits and published schematics were solid-state).

I'd say it'd easily date back to the 50s, possibly earlier - though hobbyists were still building their own oscilloscopes in the '60s, by then there were far better CRTs available, for likely an equal or lower price than the older models. This page shows three RCA CRTs which are similar in appearance to the one used, and all were released during the '40s;

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Bob Milutinovic 
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Reply to
Bob Milutinovic

It starting to look like a chassis that had holes drilled-punched for yet another project, and with the above chassis components, I would doubt that it was a kit of any description.

Possibly home brew from just a schematic. I remember buying my first transistor in 1959? so I figure a valve CRO could be anywhere from about 1935 to 1965.

CRO tube could have been war surplus, maybe even an ex radar part.

Don...

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Don McKenzie 

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Reply to
Don McKenzie

I remember seeing several DIY 'scope designs base on WWII surplus tubes, particularly the VCR139A . By the mid 1960's when I could afford to build something like that, VCR139As were getting scarce, but I did manage to find one somewhere, to use in a design from one of the UK mags. I think is was from PE, the original mag is probably still buried in a box here, if only I knew which box...

I used the DIY scope for a few years, but when I got some money for my

21st birthday, I blew the lot on a 10MHz Philips PM3200. I gave the still working DIY scope to somebody else in 1979.

The PM3200? It is now over 40 years old and I still use it occasionally. Besides the CRT it has one tube, ECC83, which has only been replaced once. I also had to replace the bridge rectifier in the power supply, and the BNC socket on the front panel which simply wore out.

Andy Wood snipped-for-privacy@trap.ozemail.com.au

Reply to
Andy Wood

** No I didn't.

.... Phil

Reply to
Phil Allison

Thanks for the link Don.

The RCA model 151 from 1936 onwards is pretty well described in its advertisement at

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It too has four valves in it, namely a pair of 6C6 + an 80 + an 885 thyratron for the timebase. The RCA 151-2 CRO is the same except it's got a 2AP1 CRT.

The one in the picture I was sent looks like it's got a 6J7G which has similar characteristics to the 6C6 + either an 80 or its octal equivalent 5Y3G, and what looks like a thyratron on the other side. Quite likely the valve we can't see is another 6J7G.

Maybe this bloke's late father cloned the RCA 151-2 design onto a chassis he originally made for something else? I wonder where he got the power transformer from.

Thanks everyone for all your helpful replies. Did you see the specs for the RCA 151 in the ad?

1.75V RMS for 'full scale deflection'

Flat response from 30Hz - 10kHz

Timebase 30Hz - 10KHz

Things have changed a bit since then. :)

Cheers, Bob

Reply to
Bob Parker

I wouldn't have thought so either, but it is possible to make a CRO with only four valves.

Have a look at the schematic of the RCA 151 which looks a lot like the one I've been asked about, at

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Bob

Reply to
Bob Parker

When I was a kid and TVs were rare luxury items, the guy from up the road who was a radar tech built his own. He used a CRT from a radar display, interesting picture, bright green and the persistence turned any moving object into a smear across the screen.

Reply to
keithr

"Bob Parker"

** Positive ground system with the 6.3V heater run left floating = OK.

CRT plates near ground or grounded with the cathode linked to the floating

6.3V supply ?

Most CROs have high, negative voltages applied to the cathode, but this is whacky.

.... Phil

Reply to
Phil Allison

It looks like the CRT cathode + one side of the 6.3V heater supply (CRT pin 2) connects back to the bottom end of the Intensity pot. I was starting to wonder how it could work...

Reply to
Bob Parker

I saw part of the 56 Olympic games in a techs shop window in Williams road Windsor (Vic) on a 5" green ex radar tube.

Don...

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Reply to
Don McKenzie

Bob, Sean Clarke from the back shed forum, provided this link:

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A pdf of the CRO project Jim Rowe did in 1963 in R, TV & H

Cheers Don...

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Don McKenzie 

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Reply to
Don McKenzie

** Despite being a 1.5MB jpeg, that scan has low resolution so the existence of dots is ambiguous.

BTW:

I once paid $25 for a service manual ( a B&W booklet ) with multiple schematics that lacked ANY dots - when the manual was prepared somehow they all failed to print.

The manual was for the EV " 2.0kW" power amplifier featuring dual SMPSs and an unusually high component count.

It was real fun trying to work out where the dots should be and put them in....

.... Phil

Reply to
Phil Allison

The mid-1970s Yamaha service manual circuit diagrams had random dots and errors galore in them. Whoever drew them didn't have the slightest knowledge of electronics. I'd often waste more time trying to work out what was really connected to what, than finding the cause of the fault.

Reply to
Bob Parker

I remember a bloke in the early 1960s who built a TV using a 5BP1 CRT, complete with a beautiful black and green picture. Who said we didn't have colour TV until 1975?

Bob

Reply to
Bob Parker

Thanks, Don. I hadn't looked at that site for a while. The CRO looks like the 1963 unit Phil built.

I've gotta say that Jim Rowe is one incredibly knowledgeable bloke and he's still going >50 years later.

Bob

Reply to
Bob Parker

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