'The Beast!' Textronix RM502A - UK Vintage Radio Repair and Restoration Discussion Forum

Tractorfan · 12th Jul 2021, 11:23 am

Hi,
A friend of ours travelled down from the Netherlands and presented me with an old oscilloscope that was destined for the scrap.
I was very pleased to have it (my mrs. is delighted!), but what I didn't expect was this monster of an instrument!
It's a beautifully built Textronix RM502A dual beam 'scope. US in origin and connected for 220 volts with a NEMA 5-15 inlet. I wondered why it had a large fan on the back, and found out when I took the covers off. It sports 39 valves, no less! So, might be a good workshop heater.
Not had a chance to power it up yet, but if your street lights go dim, you'll know why.

Cheers, Pete.

Craig Sawyers · 12th Jul 2021, 12:16 pm

That is in really nice condition, and well worth saving. The 502A is listed in the 1963 catalogue and was $1050. The RM502A is listed in the 1964 catalogue and was $1150 ($25,000 in today's money).

Maximum sensitivity is 100uV/div albeit at 50kHz bandwidth. So think of it primarily as a sensitive and useful audio frequency oscilloscope.

The user and service manual can be found easily on line.

Craig

Craig Sawyers · 12th Jul 2021, 12:32 pm

Just spotted that this is a true dual beam oscilloscope. The CRT has two guns and vertical deflection systems. There is a single horizontal deflection system and one timebase. So the number of display selections is limited to the vertical amps only.

Just as well. The much later 7844 had two entirely independent guns and deflection systems in the same CRT. With two timebases and two vertical amps, there are at least 16 different selectable displays. You really have to keep your wits about you with that one.

Craig

John_BS · 12th Jul 2021, 10:27 pm

Run it up first on a Variac to reform the main HT smoothing caps.

Enjoy!

John

joebog1 · 12th Jul 2021, 11:55 pm

You really have to keep your wits about you with that one.

Craig

Ill put 100 quid on that comment!! I bet its 50 times easier and simpler to operate than my entry level digital scope

Joe

jamesinnewcastl · 15th Jul 2021, 6:15 am

Hi

What a strange position to put the CRT. I know it's rack mount but did they anticipate such a tall rack that the screen would need to be lower?

I looked through the Wiki pages for no reason at all and found another of the little characters that Tektronix liked to put on the circuit diagrams. So nice to have a really professional company show that there is a place for humour!

Cheers
James

Tractorfan · 15th Jul 2021, 9:26 am

Hi,
I thought it odd too that the tube was low down. When my friend sent me a photo of what to expect when he arrived, I thought he'd posted it upside down!
It has swivel brackets on each side which, I presume, allows it to be tilted when it is trolley mounted. And it needs a trolley, it's a heavy lump!
Love the little character, but couldn't find him inside the case!
Cheers, Pete.

Craig Sawyers · 15th Jul 2021, 10:08 am

Quote:

Originally Posted by jamesinnewcastl

Hi

What a strange position to put the CRT. I know it's rack mount but did they anticipate such a tall rack that the screen would need to be lower?

I looked through the Wiki pages for no reason at all and found another of the little characters that Tektronix liked to put on the circuit diagrams. So nice to have a really professional company show that there is a place for humour!

Cheers
James

Yeah - there are a whole bunch of them from that era. That the schematic draughtsman(probably man) was allowed to get away with that is testimony to the positive management ethos of Tektronix in the 1960's.

https://w140.com/tekwiki/wiki/Tektronix_Cartoons

Craig

Craig Sawyers · 15th Jul 2021, 10:14 am

That doesn't count the ones that they put on the circuit boards!

turretslug · 15th Jul 2021, 1:08 pm

I have a hunch that "unknown (Pilot Light)" is from the 1481R TV waveform monitor, but wouldn't swear to it.

Radio Wrangler · 15th Jul 2021, 1:28 pm

There probably was much laughter in Beaverton from the thought that every time someone came across a photo of it, they'd think it was upside down.

David

MotorBikeLes · 15th Jul 2021, 8:37 pm

Craig, loads of stuff there I have not seen before, but I am sure I recall a spider hanging down off the end of a circuit rail, not in that list.
Or was it somewhere else?
Les.

turretslug · 15th Jul 2021, 9:11 pm

That rings a bell here too Les, but I'm darned if I can remember which Tek device it was!

Colin

factory · 15th Jul 2021, 9:39 pm

Quote:

Originally Posted by Radio Wrangler

There probably was much laughter in Beaverton from the thought that every time someone came across a photo of it, they'd think it was upside down.

David

It does look very odd, but looking at the internal pictures & comparing them to my 502A it's clear they rotated the standard scope by 90 degrees.

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Mine is in quite poor condition, several valves & the neon ref tube had gone to air through storage in a damp environment, the intensity pot had been snapped off inside too, the only suitable replacement I had was a slightly higher value part I found in my HP spares.

Last time I worked on it the trigger failed, seem to remember changing a failed diode twice, then the 2N2043 transistor died, still haven't got back to that one.
Hopefully I'll sort it one day, also it is the only CRO here with a dual-beam CRT.

David

Radio Wrangler · 15th Jul 2021, 10:58 pm

In the manufacturing dyeline master for one board of an HP product (said quietly, the manager of that product may be listening...) I had a 8 bit latch wired as 8 delays of a single bit line, so the schematic looked like a square spiral around the latch. There is a spider hanging off a bit of line from one bottom corner, labelled 'Boris the spider's delay line', of course. Must be 35 years ago.

David

Tractorfan · 9th Aug 2021, 10:07 am

Hi,
Well, I had a bit of time spare over the weekend (quelle surprise!) so I thought I'd fire up the 'Beast'.
I couldn't resist taking a couple of photos of the myriad valves glowing merrily within. (I didn't get a shot of the electric meter spinning like a top, alas.)
One small round white component was puzzling me, and I thought that maybe it was some sort of inductor. I finally realised what it was. Can you?
One little thing that surprised me was that, considering it's built like the proverbial masonry outhouse, there are no valve retaining clips fitted. Maybe they're not needed due to the high quality valve holders.
Cheers, Pete.

IanG3XYV · 9th Aug 2021, 10:16 am

Silver solder supplied with scopes of that vintage?

IanG3XYV · 9th Aug 2021, 10:32 am

Great looking trace by the way.

karesz* · 9th Aug 2021, 10:17 pm

Quote:

Originally Posted by IanG3XYV

Silver solder supplied with scopes of that vintage?

Yes. Its important to use it at solderings on the ceramic component holders!
You have to use a low temp-solder type because the ceramics have sensitive silver metalisings as solder pads and they dont withstand for higher temp as usual for typical solders...

TonyDuell · 10th Aug 2021, 4:22 am

I thought that silver-loaded solder had a higher melting point than normal lead/tin solder. In any case there was no recomendation to use a lower temperature iron when working on Tektronix 'scopes.

The problem according to the manual was that the silver plating is soluble in molten solder so if you use the normal stuff you can remove the plating. Having a little silver in the solder already prevents this. It's the same with some modern SMD parts, again you use a silver-loaded solder (I have a reel I bought for SMD use, I also use it in my Tekky 555)

12th Jul 2021, 11:23 am	#1
Tractorfan Dekatron Join Date: Mar 2008 Location: St. Frajou, l'Isle en Dodon, Haute Garonne, France.(Previously: Ellesmere Port, Cheshire, UK.) Posts: 3,183	'The Beast!' Textronix RM502A Hi, A friend of ours travelled down from the Netherlands and presented me with an old oscilloscope that was destined for the scrap. I was very pleased to have it (my mrs. is delighted!), but what I didn't expect was this monster of an instrument! It's a beautifully built Textronix RM502A dual beam 'scope. US in origin and connected for 220 volts with a NEMA 5-15 inlet. I wondered why it had a large fan on the back, and found out when I took the covers off. It sports 39 valves, no less! So, might be a good workshop heater. Not had a chance to power it up yet, but if your street lights go dim, you'll know why. Cheers, Pete. Attached Thumbnails __________________ "Hello?, Yes, I'm on the train, I might lose the signal soon as we're just going into a tunn..."

12th Jul 2021, 12:16 pm	#2
Craig Sawyers Dekatron Join Date: Nov 2010 Location: Oxford, UK. Posts: 4,981	Re: 'The Beast!' Textronix RM502A That is in really nice condition, and well worth saving. The 502A is listed in the 1963 catalogue and was $1050. The RM502A is listed in the 1964 catalogue and was $1150 ($25,000 in today's money). Maximum sensitivity is 100uV/div albeit at 50kHz bandwidth. So think of it primarily as a sensitive and useful audio frequency oscilloscope. The user and service manual can be found easily on line. Craig

12th Jul 2021, 12:32 pm	#3
Craig Sawyers Dekatron Join Date: Nov 2010 Location: Oxford, UK. Posts: 4,981	Re: 'The Beast!' Textronix RM502A Just spotted that this is a true dual beam oscilloscope. The CRT has two guns and vertical deflection systems. There is a single horizontal deflection system and one timebase. So the number of display selections is limited to the vertical amps only. Just as well. The much later 7844 had two entirely independent guns and deflection systems in the same CRT. With two timebases and two vertical amps, there are at least 16 different selectable displays. You really have to keep your wits about you with that one. Craig Last edited by Craig Sawyers; 12th Jul 2021 at 12:38 pm.

12th Jul 2021, 10:27 pm	#4
John_BS Octode Join Date: Dec 2008 Location: Wincanton, Somerset, UK. Posts: 1,780	Re: 'The Beast!' Textronix RM502A Run it up first on a Variac to reform the main HT smoothing caps. Enjoy! John

12th Jul 2021, 11:55 pm	#5
joebog1 Banned Join Date: Jun 2015 Location: Mareeba, North Queensland, Australia Posts: 2,704	Re: 'The Beast!' Textronix RM502A You really have to keep your wits about you with that one. Craig Ill put 100 quid on that comment!! I bet its 50 times easier and simpler to operate than my entry level digital scope Joe

15th Jul 2021, 6:15 am	#6
jamesinnewcastl Heptode Join Date: Jul 2009 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 722	Re: 'The Beast!' Textronix RM502A Hi What a strange position to put the CRT. I know it's rack mount but did they anticipate such a tall rack that the screen would need to be lower? I looked through the Wiki pages for no reason at all and found another of the little characters that Tektronix liked to put on the circuit diagrams. So nice to have a really professional company show that there is a place for humour! Cheers James Attached Thumbnails

15th Jul 2021, 9:26 am	#7
Tractorfan Dekatron Join Date: Mar 2008 Location: St. Frajou, l'Isle en Dodon, Haute Garonne, France.(Previously: Ellesmere Port, Cheshire, UK.) Posts: 3,183	Re: 'The Beast!' Textronix RM502A Hi, I thought it odd too that the tube was low down. When my friend sent me a photo of what to expect when he arrived, I thought he'd posted it upside down! It has swivel brackets on each side which, I presume, allows it to be tilted when it is trolley mounted. And it needs a trolley, it's a heavy lump! Love the little character, but couldn't find him inside the case! Cheers, Pete. __________________ "Hello?, Yes, I'm on the train, I might lose the signal soon as we're just going into a tunn..."

15th Jul 2021, 10:14 am	#9
Craig Sawyers Dekatron Join Date: Nov 2010 Location: Oxford, UK. Posts: 4,981	Re: 'The Beast!' Textronix RM502A That doesn't count the ones that they put on the circuit boards!

15th Jul 2021, 1:08 pm	#10
turretslug Dekatron Join Date: Nov 2011 Location: Surrey, UK. Posts: 4,394	Re: 'The Beast!' Textronix RM502A I have a hunch that "unknown (Pilot Light)" is from the 1481R TV waveform monitor, but wouldn't swear to it.

15th Jul 2021, 1:28 pm	#11
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,868	Re: 'The Beast!' Textronix RM502A There probably was much laughter in Beaverton from the thought that every time someone came across a photo of it, they'd think it was upside down. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

15th Jul 2021, 8:37 pm	#12
MotorBikeLes Nonode Join Date: Dec 2012 Location: Kirk Michael, Isle of Man Posts: 2,350	Re: 'The Beast!' Textronix RM502A Craig, loads of stuff there I have not seen before, but I am sure I recall a spider hanging down off the end of a circuit rail, not in that list. Or was it somewhere else? Les.

15th Jul 2021, 9:11 pm	#13
turretslug Dekatron Join Date: Nov 2011 Location: Surrey, UK. Posts: 4,394	Re: 'The Beast!' Textronix RM502A That rings a bell here too Les, but I'm darned if I can remember which Tek device it was! Colin

15th Jul 2021, 10:58 pm	#15
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,868	Re: 'The Beast!' Textronix RM502A In the manufacturing dyeline master for one board of an HP product (said quietly, the manager of that product may be listening...) I had a 8 bit latch wired as 8 delays of a single bit line, so the schematic looked like a square spiral around the latch. There is a spider hanging off a bit of line from one bottom corner, labelled 'Boris the spider's delay line', of course. Must be 35 years ago. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

9th Aug 2021, 10:07 am	#16
Tractorfan Dekatron Join Date: Mar 2008 Location: St. Frajou, l'Isle en Dodon, Haute Garonne, France.(Previously: Ellesmere Port, Cheshire, UK.) Posts: 3,183	Re: 'The Beast!' Textronix RM502A Hi, Well, I had a bit of time spare over the weekend (quelle surprise!) so I thought I'd fire up the 'Beast'. I couldn't resist taking a couple of photos of the myriad valves glowing merrily within. (I didn't get a shot of the electric meter spinning like a top, alas.) One small round white component was puzzling me, and I thought that maybe it was some sort of inductor. I finally realised what it was. Can you? One little thing that surprised me was that, considering it's built like the proverbial masonry outhouse, there are no valve retaining clips fitted. Maybe they're not needed due to the high quality valve holders. Cheers, Pete. Attached Thumbnails __________________ "Hello?, Yes, I'm on the train, I might lose the signal soon as we're just going into a tunn..."

9th Aug 2021, 10:16 am	#17
IanG3XYV Pentode Join Date: Sep 2014 Location: Bedford, Bedfordshire, UK. Posts: 174	Re: 'The Beast!' Textronix RM502A Silver solder supplied with scopes of that vintage?

9th Aug 2021, 10:32 am	#18
IanG3XYV Pentode Join Date: Sep 2014 Location: Bedford, Bedfordshire, UK. Posts: 174	Re: 'The Beast!' Textronix RM502A Great looking trace by the way.

10th Aug 2021, 4:22 am	#20
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,208	Re: 'The Beast!' Textronix RM502A I thought that silver-loaded solder had a higher melting point than normal lead/tin solder. In any case there was no recomendation to use a lower temperature iron when working on Tektronix 'scopes. The problem according to the manual was that the silver plating is soluble in molten solder so if you use the normal stuff you can remove the plating. Having a little silver in the solder already prevents this. It's the same with some modern SMD parts, again you use a silver-loaded solder (I have a reel I bought for SMD use, I also use it in my Tekky 555)