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Old 12th Jul 2017, 6:15 pm   #1
Ian - G4JQT
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Default Pen45 pin 7

Is it always ok to use pin 7 as an anchor point on a Pen45 valve? All the data shows it unused, but sometimes this isn't entirely true as 'unused' pins are sometimes used on some valves for internal connections, and shouldn't have anything connected to them.

Thanks.

Ian

PS: Also are pins pins 1, 3, 5 and 7 for a GZ37 rectifier free to use?

Last edited by Ian - G4JQT; 12th Jul 2017 at 6:29 pm.
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Old 12th Jul 2017, 7:01 pm   #2
G6Tanuki
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Default Re: Pen45 pin 7

I always avoid doing this: though your current valves may not have those pins used as "internal connections", who knows what future valves of different manufacture may do?

[The EL41/UL41 being a good example - wiring things to the 'unused' pins 3 and 4 is not a good idea].
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Old 12th Jul 2017, 7:10 pm   #3
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Default Re: Pen45 pin 7

I can understand using an 'unusued' pin on an all-glass valve as an anchor point for some electrode (and therefore not to be wired to externally). But was it common (or indeed, did it ever happen) that, on valves with a separate bakelite base carrying the pins, an extra wire was brought out through the pinch and then terminated to a base pin? I can understand fixing extra supports into the pinch, but not then connected them to a pin.
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Old 12th Jul 2017, 7:22 pm   #4
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Default Re: Pen45 pin 7

I vaguely remember one Octal-based voltage-regulator valve where a couple of pins in the valve-base were linked together inside the valve-base entirely independently of the connections to the anode/cathode of the regulator assembly.

This was used to sense whether there was a regulator-valve fitted [high-end models of receiver being fitted with regulators, poverty-spec models not] and the link was used to short-out an extra dropper resistor accordingly.


Hallicrafters?
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Old 12th Jul 2017, 7:52 pm   #5
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Default Re: Pen45 pin 7

The jumper link in gas discharge regulators is documented in the data sheet. Sometimes it's an independant link, sometimes it's the anode of the stabiliser brought out to 2 separate pins.

The idea was that this link could be wired in series with the regulated output, or with the supply to the regulator valve (e.g. in series with the series resistor) or, in the case of the anode being brought out to 2 pins, the series resistor from the unregulated supply was connected to one pin, and the regulated output taken from the other. Then, if the regulator valve was removed, the output voltage dropped to zero, rather than increasing to the unregulated input voltage. Of course it didn't help if the regulator valve failed but was still in the socket.
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Old 12th Jul 2017, 7:58 pm   #6
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Default Re: Pen45 pin 7

I also once got 'bitten' where a designer had assumed a certain pin on an Octal valve-base was unused and so hooked an IF-stage anode-decoupling resistor/capacitor to it.

The pin was unused on *glass* octals; but was assigned as the outer envelope [should be earthed] on RCA's metal-octals, and so sat at 200+ Volts.

A RCA metal-valve got fitted.

Expletives were uttered.
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Old 12th Jul 2017, 10:51 pm   #7
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Default Re: Pen45 pin 7

Hello,
The Mazda data for the Pen 45 ( https://frank.pocnet.net/sheets/146/p/PEN45.pdf ) gives pin 7 as omitted (ie it is not actually there) so you could not have anything connected to it.
You can "see" the missing pin in the top picture here http://www.r-type.org/exhib/aam0062.htm
The usual problem with this is different manufacturers doing different things, but with a Mazda octal base this is unlikely as most Mazda Octal valves, and almost certainly the 4 volt ones, were only made by Mazda.
The Mullard data for the GZ37 ( https://frank.pocnet.net/sheets/129/g/GZ37.pdf ) shew pin 1 as present but no connection and pins 3, 5 and 7 as not present so you should be OK with pins 3, 5 and 7 with a Mullard valve but possibly not with other makes or equivalents if the pins are present.
Yours, Richard

Last edited by Mr Moose; 12th Jul 2017 at 11:05 pm.
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Old 13th Jul 2017, 8:42 am   #8
Ian - G4JQT
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Default Re: Pen45 pin 7

Thanks for the replies, but thanks particularly to Richard!

What an obvious thing for me to have checked, but one I'd completely overlooked.

You are absolutely right, my four Pen45s don't even have pin 7, and the GZ37 doesn't have the unconnected ones either. (I'll just have to check all makes/equivalents are the same in future.)

Problem solved and I can use those tags on the valve holders.

Thanks again,

Ian
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Old 13th Jul 2017, 11:58 am   #9
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Default Re: Pen45 pin 7

Valve sockets are exposed and get dirty and can breakdown. It's better to use an anchor point that is underneath the chassis.
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Old 13th Jul 2017, 11:21 pm   #10
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Default Re: Pen45 pin 7

Not very exposed if there's a valve plugged in, and the metal bit is under the chassis anyway. Voltages are only same as applied to output valve anyway so not a lot of risk in domestic environment.
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