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Old 3rd Aug 2011, 7:08 am   #1
SteveSmit
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Default Acquired a Mazda tuning indicator valve. Advice?

Greetings,

A gent at work has given me an old tuning indicator valve, a Mazda 6M1. It looks to be in reasonable condition and (excrutiatingly) he said it was working before he dismantled the radio it was in ("glowed a lovely blue green"). He is into building things out of pieces of 'scrap' and no doubt the horde of electromechanical items in the old radio in question were more than he could resist.

Still, no use crying over spilt milk, and I have this valve at least, so down to the question.

Is there any way I can power this little thing up, and or use it for anything? I gather from my brief searching on the 'net that it's a tuning indicator valve, so I'm guessing its scope is reasonably limited but still it'd be nice to see if I can get it to light up.

I'm afraid my knowledge of valves is very limited, in fact this is the first time I've actually seen one at close quarters, so I'm not entirely sure where to begin with it.

It's plugged into a valve socket, with the solder points (plus a few strands of rubber-sheathed wire hanging off it) intact. Bridging one pair of solder points is a 350VDC 0.05 MFD capacitor (although it must mean mF) , and bridging another pair is a fairly meaty looking resistor, that I've measured to 2.9 Mohm. Although the bands themslves don't seem to say that (Brown band, black band, green band, no fourth)

Any tips or advice? It's an awful shame the rest of the radio has disappeared, it'd be nice to be able to use at least this for something. Even if it's just a nice ornament.
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Old 3rd Aug 2011, 9:11 am   #2
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Default Re: Acquired a Mazda tuning indicator valve. Advice?

Lots of information here including pin-outs and simple projects, might have a go myself.

http://www.magiceyetubes.com/

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Old 3rd Aug 2011, 5:01 pm   #3
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Default Re: Acquired a Mazda tuning indicator valve. Advice?

Thanks very much for that, I'll have a gander.
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Old 3rd Aug 2011, 11:05 pm   #4
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Default Re: Acquired a Mazda tuning indicator valve. Advice?

Quote:
Originally Posted by SteveSmit View Post
.... bridging another pair is a fairly meaty looking resistor, that I've measured to 2.9 Mohm. Although the bands themslves don't seem to say that (Brown band, black band, green band, no fourth)
Sounds like a 1Megohm 20% carbon resistor doing the usual going high trick.
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Old 4th Aug 2011, 9:11 am   #5
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Default Re: Acquired a Mazda tuning indicator valve. Advice?

See this

http://www.g1jbg.co.uk/pdf/Tay110C.pdf

I used one of these in my chemistry studies in the 1950s connected to a conductivity sensor of two blades immersed in the test solution.
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Old 4th Aug 2011, 10:54 am   #6
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Default Re: Acquired a Mazda tuning indicator valve. Advice?

Treasure it, these are getting particularly rare(and consequently expensive) for a good example, particularly the "less used" types. The Mazda 6M1 as far as I am aware has no equivalent.
Murphy used these in a few sets such as the A242.
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Old 5th Aug 2011, 4:50 pm   #7
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Default Re: Acquired a Mazda tuning indicator valve. Advice?

Thanks for all the responses folks. For anybody who may be interested, here is a photograph of the valve in question. Whether or not that's a good example, I couldn't tell you! I can see the glass is a little discoloured around the base, but whether that's usual or not, I've no idea. As I say though, the guy said it worked before he took it out.
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Old 5th Aug 2011, 4:55 pm   #8
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Default Re: Acquired a Mazda tuning indicator valve. Advice?

As Tim says, these are relatively rare valves so you might want to consider passing it on to someone who can use it in a radio restoration, especially if it's in good working condition.
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Old 5th Aug 2011, 7:11 pm   #9
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Default Re: Acquired a Mazda tuning indicator valve. Advice?

I sold one of these quite recently. Mainly because i never found a use for it. They are a different size to the average eye and wont fit a lot of radios. I was always led to believe that these were equivalent to the Y63, 6U5/6G5 etc. Very common i thought. Colin.
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Old 5th Aug 2011, 8:17 pm   #10
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Default Re: Acquired a Mazda tuning indicator valve. Advice?

The discolouration around the base looks more like just the usual getter deposit.

I'd certainly hang onto, and treasure, this valve. A look on eBay will indicate prices for magic eyes / tuning indicators. And, as a finite and diminishing resource, prices can only go up!

Conversely, if you want to play with one, there are many dim ones around - Forum members will be able to oblige I'm sure.
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Old 7th Aug 2011, 1:02 pm   #11
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Default Re: Acquired a Mazda tuning indicator valve. Advice?

I'll do that. It's a lovely looking thing even if it doesn't end up being used. Thanks for the responses
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Old 8th Aug 2014, 4:25 pm   #12
Anthony D
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Default Re: Acquired a Mazda tuning indicator valve. Advice?

Hi Steve
I have a Murphy Radio model A188C, still working.
No serial no.(lost) but I learn these were built in 1951.
But it has a 6M1 tuner valve which is not working. Could be the circuitry of course but I suspect the valve is defunct. So an excellent use for your valve would be to sell it to me and enable a marvellous old set to keep going to full spec.
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Old 17th Dec 2014, 10:02 pm   #13
SteveSmit
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Default Re: Acquired a Mazda tuning indicator valve. Advice?

Firstly apologies for the huge wait with this, I must've missed the response to the topic.

I'll have a dig for the valve.

I've recently moved house, so I'm not sure off the top of my head immediately where it is, but I'll find it. I know I've kept it safe wherever it is.

As may be inferred from the original conversation, I've never actually seen it powered up, so I'm not at all sure of its operating condition, or even, to be totally honest whether it works properly at all.

But assuming this isn't far too late and you're happy to cover the postage, you're welcome to it. It'd be nice to know it's being used!

Steve
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Old 18th Dec 2014, 3:57 pm   #14
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Default Re: Acquired a Mazda tuning indicator valve. Advice?

Blimey, that is a long wait. TWO of the contributors to the thread have passed away since we last heard from you!
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Old 18th Dec 2014, 5:44 pm   #15
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Default Re: Acquired a Mazda tuning indicator valve. Advice?

Be interesting to see if Anthony D of the one post ever and that about this indicator notices in less time
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Old 18th Dec 2014, 6:05 pm   #16
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Default Re: Acquired a Mazda tuning indicator valve. Advice?

If you could pick up some Voltage from a working set (or PSU), it's not too difficult to test the eye to see if it has any life left in it.

You'd need about 260 - 275V DC for the HT on Pin 4, then a 1 M Ohm resistor from pin 3 to pin 4. Then 6.3V AC for the heater on pins 2 & 7, and a means of applying a negative voltage of a few volts on the input grid (pin 3). (Connect the Cathode to ground via a 1k resistor). To check that the eye opens and closes in sympathy with the signal strength (the stronger the signal, the more the AGC voltage on the grid will go negative), if you don't have a variable low voltage DC supply, you could used say three low voltage batteries - for example, a 1.5V cell, 2 x 1.5V, and a 9V PP3 with the negative to pin 3 and the positive to ground. That would simulate the section of the circuit of the Murphy A188, which uses a 6MI (same base as a Y63). The magic eye should open and close when different levels of negative Voltages are applied to the grid on pin 3, starting with no Voltage at all on that pin, and observing the different patterns. Of course, if it doesn't glow at all, or only dimly, it's off along that well trodden path which is the ultimate destiny of all magic eyes, to landfill.

I've attached the relevant part of the A188 circuit to give you an idea.

When restoring a Pye Fenman1 a while ago I made a little tester to test EM80 magic eyes to check whether they were faulty or whether the set was faulty. (It worked well except for the lazy eye). I've attached a few pics. of the tester I knocked up. The little container inside the box is just a 1.5V cell to switch in an out to apply -1.5V to the grid to see if the eye opened and closed. The end result was that the eyes I had weren't faulty, and neither was the set. The problem was that without an external aerial there wasn't enough variation in AGC Voltage for the eye to function properly when stations were tuned in. Plugged in a decent outdoor aerial and the 'angels wings' of the EM80 eye were wafting back and forth as stations were tuned in an out. Oh well, there's no fool like an old fool!

(As has been said, the 6MI is the same basing as the Y63 - a more common magic eye).
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Old 18th Dec 2014, 11:57 pm   #17
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Default Re: Acquired a Mazda tuning indicator valve. Advice?

Hehe, being fair, Anthony D's post was only a few months back! I'd thought this thread was long dead by now.
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