Pye Audio Frequency Oscillator

[Electro Dabbler]

Hi

Hope this is on-topic. From my experience years ago I figured that this group was probably a good place to ask for electrical stuff this old. If not, my apologies. If nothing else hope you enjoy the story.

I recently saved an old PYE signal generator from a bin for a bit of fun. Opened it up: valves test OK (even the one with the loose base), transformers aren't open, electrolytics look OK (though I'll probably end up replacing them just to be on the safe side), replaced a bunch of wax-paper coupling caps in various stages of melted, everything else looks fine.

I've put some pictures of it here: http://s158.photobucket.com/user/iphantoms/library/PYE%20oscillator

After a bit of messing around (cleaning contacts mostly) I got it to work, but erratically. It would warm up, oscillate fine, then the oscillations gradually die out to nothing, come back if I switched ranges, then die, output levels all over the places... so generally annoying symptoms.

So I started testing resistors - all tested good - and traced the circuit out. It's unlike anything I've seen - frequency adjustment is controlled by a rather huge dual 100k variable resistor (which you can see in the pictures). Certainly nothing like the HP-like circuit I'm used to.

Partial circuit here if you'll excuse the bad handwriting (100k frequency controlling resistor in blue, actual measured resistances in brackets): http://i158.photobucket.com/albums/t87/iphantoms/PYE%20oscillator/pyeoscmod_zps63c227d8.jpg

After more nosing around I found that I could generally "tune in" the oscillator by adjusting the feedback pot on the right of the circuit diagram above. But it wasn't reliable, or consistant across the full range, plus the "tune in" point was basically the max feedback point. Set it for one frequency, it would stop working when you moved to the next. Pot tested fine. In fact, too fine: it measured 49k, in circuit, with the "lamp" in parallel, which makes no sense unless the "lamp" was a neon bulb. The lamp is shown on the right of the schematic. Presumably it was included to stabilise the oscillator.

On closer inspection the lamp looks dubious (see photos in album above), so I removed it. Success-ish! Horribly distorted, but consistent output. And after re-tuning the pot and I get nice, clean looking sine waves over the entire range. Output levels are a bit variable, but still infinitely more stable and reliable than before removing the lamp. Almost usable in fact.

But here's the weird thing. The lamp is tiny. About an inch long. I can see filament in the lamp - just - and it looks busted, as confirmed by the multimeter (resistance >10M). And it doesn't look like a neon bulb to me (it has a filament to start with). But the circuit acts radically differently depending on whether the "dead" lamp is included or not.

Sooo, to my questions:

- how on earth can an open-circuit lamp change the operation of the original circuit in the way I observed?
- where might I find a replacement lamp (or something even vaguely similar)?
- if I can't find a replacement, and given that the circuit behaves reasonably well without it anyhow, is it OK to just leave it the lamp out and go with what works?

Any thoughts or suggestions for those who read this far?

[Foxs Mercantile]

On 4/21/2013 12:39 AM, Electro Dabbler wrote:
> Any thoughts or suggestions for those who read this far?

The lamp is part of the feedback circuit. The negative
resistance effect of the lamp is what makes the output
look like a very clean sine wave.

<http://en.wikipedia.org/wiki/Wien_bridge_oscillator>

R1 and R2 are your dual 100K pot. Rb is the light bulb.

Jeff-1.0
wa6fwi

[Electro Dabbler]

Thanks, but I guess my question was more why a lamp which both my eyes and my multimeter agree is open circuit would influence the circuit such that it doesn't actually work properly with the (non-functional) lamp in place? That doesn't make sense to me. Also, can you by replacements for the type of lamp shown in the picture?

[Jim Mueller]

Are you sure it's a lamp? In all of the photos I see a little black dot
above the lead-in wires, where the filament would be. Maybe it's a
thermistor.

As to why connecting it affects operation, perhaps it is intermittent.
Try testing it in different positions, warming and cooling it, tapping on
it, etc. and see if that makes any difference. If you can cause a
condition where you can get a resistance measurement, that would help in
finding a replacement.

--
Jim Mueller wron...@nospam.com

To get my real email address, replace wrongname with dadoheadman.
Then replace nospam with fastmail. Lastly, replace com with us.

[N_Cook]

Electro Dabbler <alsh...@gmail.com> wrote in message
news:914ad94b-35bb-428e...@googlegroups.com...

+++++

My first thought is it would be a bead thermistor but for the >10M and
functionability. Second thought some sort of VDR ? what sort of voltages on
the "lamp". ?
What is the model number if not as in the title ?

[Michael A. Terrell]

Jim Mueller wrote:
>
> Are you sure it's a lamp? In all of the photos I see a little black dot
> above the lead-in wires, where the filament would be. Maybe it's a
> thermistor.

HP and others used a lamp as a thermistor, to level the output and
minimize distortion.

[Michael Black]

On Mon, 22 Apr 2013, Michael A. Terrell wrote:

>
> Jim Mueller wrote:
>>
>> Are you sure it's a lamp? In all of the photos I see a little black dot
>> above the lead-in wires, where the filament would be. Maybe it's a
>> thermistor.
>
>
> HP and others used a lamp as a thermistor, to level the output and
> minimize distortion.
>

Did thermistors exist when that circuit was designed, I thought by HP?

MIchael

[Electro Dabbler]

I think you might be onto something with the thermistor. I've never seen a glass thermistor before in person, but it has the bead you and Jim mentioned and visually matches a quick google image search. It has about 100-130V across it. Actually I'm wondering if the high voltage might be enough to arc over the small break in the filament, which might explain the behaviour I'm seeing.

The oscillator has PYE ser. no. (serial number I assume?) 20.981 Audio Frequency Oscillator written on the front, nothing written on the back or the chassis that I can see.

[Michael A. Terrell]

Michael Black wrote:
>
> On Mon, 22 Apr 2013, Michael A. Terrell wrote:
>
> >
> > Jim Mueller wrote:
> >>
> >> Are you sure it's a lamp? In all of the photos I see a little black dot
> >> above the lead-in wires, where the filament would be. Maybe it's a
> >> thermistor.
> >
> >
> > HP and others used a lamp as a thermistor, to level the output and
> > minimize distortion.
> >
> Did thermistors exist when that circuit was designed, I thought by HP?

The HP200 was based on their thesis, and used a common & cheap auto
lamp. Nothing in the design was an expensive component other than the
power transformer and tuning capacitor. Their professor encouraged them
to manufacture their design.

According to Wikipedia: 'The first NTC thermistor was discovered in 1833
by Michael Faraday.'

[Electro Dabbler]

On Monday, April 22, 2013 10:34:58 AM UTC+10, Jim Mueller wrote:
> Are you sure it's a lamp? In all of the photos I see a little black dot
> above the lead-in wires, where the filament would be. Maybe it's a
> thermistor.
>
> As to why connecting it affects operation, perhaps it is intermittent.
> Try testing it in different positions, warming and cooling it, tapping on
> it, etc. and see if that makes any difference. If you can cause a
> condition where you can get a resistance measurement, that would help in
> finding a replacement.

You might be right about it being a thermistor (see my other reply to N Cook). I'll try different positions etc and see what I can come up with re resistance.

Mind you, I'm tempted to just grab an NTC thermistor (or a few different ones) with a nominal resistance somewhere around 10-100k or so, plug it in and see how it goes. Granted it will probably either vanish in a puff of smoke or do very little, but it's a cheap experiment that should pose little danger to the oscillator, and if it works then I could potentially save myself a lot of messing around.

[oldco...@gmail.com]

The bulb filament's very small thermal mass (and fast time constant) is probably a design criterion. A "button type" thermistor would have a much larger thermal mass and hence slow response to amplitude changes, negating the purpose of the design. Seems like, anyhow.

Bill(oldcoot)

[Adrian Tuddenham]

> - original circuit in the way I observed? where might I find a replacement
> - lamp (or something even vaguely similar)? if I can't find a replacement,
> - and given that the circuit behaves reasonably well without it anyhow, is
> - it OK to just leave it the lamp out and go with what works?

>
> Any thoughts or suggestions for those who read this far?

I have re-drawn the circuit to show the phase shifts:

http://www.poppyrecords.co.uk/other/images/PyeOsc.gif

Although the 180-degree shift is independent of frequency, the two
90-degree shifts will only be 90 degrees at one frequency, so it will
only have 360 degrees feedback at one frequency. There was a
description of an oscillator of this type in Wireless World back in the
1950s, but I don't have the reference to hand.

The "lamp" looks to me awfully like a vacuum-bulb thermistor. It is
heated to a variable degree by the valve anode current, which might seem
a bit odd, because the average anode current will not vary if that stage
is running in undistorted class A.. However, the heating effect will
depend on I squared, so a larger signal will give more heating effect.

My guess is that your thermistor is a relatively high resistance device
compared with what you are used to in transistor circuits. With a
voltage drop of about 100 volts across it, its resistance might be a lot
less than you have measured cold. If it is stopping the circuit from
working, you either don't have enough gain somewhere or you have
excessive anode current in the output valve which makes it go too low
resistance. Is the anode-grid coupling capacitor leaking HT from the
previous stage onto the grid of the output valve? Do you have a
heater-cathode short in the output valve?


-- ~ Adrian Tuddenham ~ (Remove the ".invalid"s and add ".co.uk" to
reply) www.poppyrecords.co.uk

[Electro Dabbler]

On Tuesday, April 23, 2013 5:19:08 AM UTC+10, Adrian Tuddenham wrote:
> I have re-drawn the circuit to show the phase shifts:
>
>
>
> http://www.poppyrecords.co.uk/other/images/PyeOsc.gif
>
>
>
> Although the 180-degree shift is independent of frequency, the two
>
> 90-degree shifts will only be 90 degrees at one frequency, so it will
>
> only have 360 degrees feedback at one frequency. There was a
>
> description of an oscillator of this type in Wireless World back in the
>
> 1950s, but I don't have the reference to hand.
>
>
>
> The "lamp" looks to me awfully like a vacuum-bulb thermistor. It is
>
> heated to a variable degree by the valve anode current, which might seem
>
> a bit odd, because the average anode current will not vary if that stage
>
> is running in undistorted class A.. However, the heating effect will
>
> depend on I squared, so a larger signal will give more heating effect.
>
>
>
> My guess is that your thermistor is a relatively high resistance device
>
> compared with what you are used to in transistor circuits. With a
>
> voltage drop of about 100 volts across it, its resistance might be a lot
>
> less than you have measured cold. If it is stopping the circuit from
>
> working, you either don't have enough gain somewhere or you have
>
> excessive anode current in the output valve which makes it go too low
>
> resistance. Is the anode-grid coupling capacitor leaking HT from the
>
> previous stage onto the grid of the output valve? Do you have a
>
> heater-cathode short in the output valve?
>
>
>
>
>
> -- ~ Adrian Tuddenham ~ (Remove the ".invalid"s and add ".co.uk" to
>
> reply) www.poppyrecords.co.uk

Thanks Adrian: you're redraw of the schematic makes things a lot clearer. Also interesting to get a rough date on the circuit.

I don't think the issue would be the coupling caps as one of the first things I did was replace the lot with 630V greencaps (the originals were wax-paper caps that were in very bad shape). You could be on to something with the valves. The oscillator was salvaged along with some other signal generators and the like from a bin at uni, and most of the gear showed signs of quite heavy use (worn dial markings and general wear and tear).

Anyhow the 6J5 looked OK on my previous quick go/no-go test, but maybe a longer more thorough test is in order. If it is bad then I'm pretty sure I have a VT94 that could be used as a substitute. I'll try to find some time tonight for testing.

[Sofa Slug]

You might try emailing these folks about a schematic. They are, after
all, the Pye Museum :)... <http://www.qsl.net/gm8aob/g8epr.htm>

[Adrian Tuddenham]

The fact that you could get it to oscillate without the thermistor shows
that there is some loop gain, but perhaps not enough. Have you any idea
roughly how far the wiper was along the gain pot when the circuit just
began to oscillate? If it was nearly at the anode end, that suggest
that the gain is low, but if it was near the HT end, it suggests that
the gain is adequate.

If the gain without the thermistor is adequate, it is probable that the
thermistor is shunting too much signal. That could be because it has
gone low resistance, but your 'cold' resistance reading rules that out.
The alternative possibility is that it is being overheated by faulty DC
conditions . If the pot had been open circuit, that would have forced
the full anode current through the thermistor and made it overheat; but
you would then not have been able to make the circuit oscillate without
the thermistor. Try measuring the voltage dropped across the pot, both
with and without the thermistor connected. If it is more than half the
total HT without the thermistor I would suspect the 6J5 of taking too
much current.

If the gain without the thermistor is low, try feeding a 1Kc/s signal
into each stage in turn from a low source impedance signal generator
coupled by a 100nf capacitor onto the grid of each valve. The two
halves of the ECC81 ought to give a voltage gain of 1 at the cathode and
-1 at the anode (they are just used as unity-gain inverters). The 6J5
ought to give a voltage gain of nearly -50.

[dave]

Invented by Bill Hewlett while in college.

[dave]

On 04/23/2013 12:37 AM, Adrian Tuddenham wrote:
> Electro Dabbler <alsh...@gmail.com> wrote:
>
>> On Tuesday, April 23, 2013 5:19:08 AM UTC+10, Adrian Tuddenham wrote:
>>> I have re-drawn the circuit to show the phase shifts:
>>>
>>>
>>>
>>> http://www.poppyrecords.co.uk/other/images/PyeOsc.gif
>>>
>>>

http://www.hp.com/hpinfo/abouthp/histnfacts/museum/earlyinstruments/0007/

Bill Hewlett designed the prototype for what eventually would be called
the Model 200A audio oscillator as a thesis subject while working toward
his electrical engineering degree at Stanford University in 1938. The
Model 200A would become HP's first product.

Bill felt there was a real need for a new type of oscillator that would
combine the stability of the coil-condenser type and the flexibility of
operation of the beat-frequency type, and still be light and portable as
well as simple in construction and adjustment. His was a new type of
oscillator in which the frequency-determining element is a
resistance-capacity network.

What made Bill's oscillator design unique?
In simple terms, Bill's unique contribution to the oscillator design was
to achieve excellent performance at a low cost by adding a small light
bulb to act as a "negative feedback" element in the oscillator circuit.

The small light bulb is set to be partially on. If the oscillator's
signal strength becomes stronger or weaker, the light bulb turns on more
or less to cancel the unwanted variations. This allows the oscillator to
maintain a nearly constant output over its designed operating range.

[Adrian Tuddenham]

dave <rick...@earthlink.net> wrote:

> On 04/23/2013 12:37 AM, Adrian Tuddenham wrote:
> > Electro Dabbler <alsh...@gmail.com> wrote:
> >
> >> On Tuesday, April 23, 2013 5:19:08 AM UTC+10, Adrian Tuddenham wrote:
> >>> I have re-drawn the circuit to show the phase shifts:
> >>>
> >>>
> >>>
> >>> http://www.poppyrecords.co.uk/other/images/PyeOsc.gif
> >>>
> >>>
>
>
> http://www.hp.com/hpinfo/abouthp/histnfacts/museum/earlyinstruments/0007/

[...]

> What made Bill's oscillator design unique?
> In simple terms, Bill's unique contribution to the oscillator design was
> to achieve excellent performance at a low cost by adding a small light
> bulb to act as a "negative feedback" element in the oscillator circuit.

There were many post-war designs based on his work. Some of the BBC
oscillators used a GPO switchboard lamp, but Solartron were using a
thermistor, like the one shown in the Pye oscillator photographs, by the
early or mid 1950s.

[Adrian Tuddenham]

I've had some time to ponder over that circuit and I am beginning to
wonder if it hasn't been re-arranged by some well-meaning person in the
recent past (i.e. just before throwing it away as beyond repair)?

The circuit I have drawn at:

http://www.poppyrecords.co.uk/other/images/PyeOsc2.gif

...would make much more sense, as it removes the DC component from the
thermistor and makes it far less dependent on the chartacteristics of
the 6J5.

Does the wiring shows any signs of having been altered?

[oldco...@gmail.com]

> I've had some time to ponder over that circuit and I am beginning to
> wonder if it hasn't been re-arranged by some well-meaning person in the
> recent past (i.e. just before throwing it away as beyond repair)?
>
> The circuit I have drawn at:
>
> http://www.poppyrecords.co.uk/other/images/PyeOsc2.gif
>
> ...would make much more sense, as it removes the DC component from the
> thermistor and makes it far less dependent on the chartacteristics of
> the 6J5.
>

- show quoted text -
Problem with this configuration (unless I'm missing something) is-- since the bulb is responding to signal amplitude only (no DC component), the result will be posittive amplitude feedback instead of the negative feedback provided by the original configuration.

[Adrian Tuddenham]

It depends whether the temperature coeeficient of the thermistor is
positive or negative - both types are made.

If the resistance falls as the thermistor element heats up, it will
progressively shunt the signal to earth. The very high 'cold' reading
suggests that this one is intended to behave in that way.

If the electrolytic capacitor began to get a bit leaky, that would give
a standing current through the thermistor, which could heat it up to the
point where oscillation could not occur. That would be my first guess
at the initial failure mode which led to the instrument being scrapped..

[oldco...@gmail.com]

> it depends whether the temperature coeeficient of the thermistor is

> positive or negative - both types are made.
>
> If the resistance falls as the thermistor element heats up, it will
> progressively shunt the signal to earth.

Not if it's a bulb with tungsten filament. It'll do the opposite, i.e., resistance increases with temp (positive coef.).

> The very high 'cold' reading
> suggests that this one is intended to behave in that way.

Since the thermistor shown is clearly an incandescent bulb, it would have a low 'cold' reading.

> If the electrolytic capacitor began to get a bit leaky, that would give
> a standing current through the thermistor, which could heat it up to the
> point where oscillation could not occur. That would be my first guess
> at the initial failure mode which led to the instrument being scrapped..

If you think it through based on the bulb having pos. coef., I b'lieve you'll see that the original wiring configuration is correct, and that the failure mode was probably the bulb going open.

As a side note, the earliest bulbs using carbon filaments had neg. coef., pulling exponentially more current with increasing temperature.

Bill(oldcoot)

[Adrian Tuddenham]

<oldco...@gmail.com> wrote:

> > it depends whether the temperature coeeficient of the thermistor is
> > positive or negative - both types are made.
> >
> > If the resistance falls as the thermistor element heats up, it will
> > progressively shunt the signal to earth.
>
> Not if it's a bulb with tungsten filament. It'll do the opposite, i.e.,
> resistance increases with temp (positive coef.).

In which case it will increase the anode load resistance and give more
voltage gain as it heats up - the opposite of what that circuit
requires.

There is an unbypassed cathode resistor, so the valve is acting as a
high impedance current source (unlike a grounded cathode triode) as far
as the signal is concerned. This means that the signal voltage
developed at the anode is almost directly proportional to the anode load
resistor over a reasonable range of values.

> > The very high 'cold' reading suggests that this one is intended to
> > behave in that way.
>
> Since the thermistor shown is clearly an incandescent bulb, it would have
> a low 'cold' reading.

It does not look like an incandascent bulb to me, it looks exactly like
the thermistors used in similar British signal generators of that period
(one of which I still use daily). This device measured high impedance
when cold and behaved as though it went low impedance when it was
connected across the 50k pot and heated up.

>
> > If the electrolytic capacitor began to get a bit leaky, that would give
> > a standing current through the thermistor, which could heat it up to the
> > point where oscillation could not occur. That would be my first guess
> > at the initial failure mode which led to the instrument being scrapped..
>
> If you think it through based on the bulb having pos. coef., I b'lieve
> you'll see that the original wiring configuration is correct, and that the
> failure mode was probably the bulb going open.

When the device (bulb or thermistor) is disconnected, the circuit
oscillates, but it will not oscillate with the device connected. If
that were an open-circuit bulb, it would make no difference whether it
was connected or not.

[Jim Mueller]

Are you sure the output tube is a 6J5? The pin numbers on the schematic
don't match this type. If a 6J5 were plugged into a socket wired like
that, nothing would happen since pins 4 and 6 aren't connected and pin 1
connects to the metal shell.

[Michael A. Terrell]

Invented? The non-linear thermal characteristics of incandescent
lamps were well know before he was born.

[N_Cook]

Adrian Tuddenham <adr...@poppyrecords.invalid.invalid> wrote in message
news:1l1uqnh.rh04an1sgvcimN%adr...@poppyrecords.invalid.invalid...

Non - valve probably 70s, Marconi TF2103 that I use every day contains an
inch long glass-bulbed bead thermistor in the Wien circuit

[Adrian Tuddenham]

N_Cook <div...@tcp.co.uk> wrote:

> Adrian Tuddenham <adr...@poppyrecords.invalid.invalid> wrote in message
> news:1l1uqnh.rh04an1sgvcimN%adr...@poppyrecords.invalid.invalid...

[...]

> > It does not look like an incandascent bulb to me, it looks exactly like
> > the thermistors used in similar British signal generators of that period
> > (one of which I still use daily).

[...]

> Non - valve probably 70s, Marconi TF2103 that I use every day contains an
> inch long glass-bulbed bead thermistor in the Wien circuit

The TF2103 appeares to be a Marconi-badged version of the Venner
transistor audio oscillator. Both of them use the same
thermistor-stabilised circuit; as do a host of other makes and models
from around that time.

On the valve side, a thermistor is used in the Solartron 546 from a few
years earlier (which is still my everyday workhorse). To keep the
thermistor away from the heat of the valves, they mount it on the front
panel behind the tuning dial.

BBC valve designs use lamps in their TS9, PTS10 and PTS12 'tone
sources', but I think they use a thermistor in the TS10. The PTS15 and
PTS 16 use the AGC action of an over-driven valve with a high-value grid
leak, but they are not intended to be accurate measuring instruments.
Valve designs, being high impedance, allow the use of a four-gang
capacitor as the continuously-variable element of the Wien bridge.

The only surprising thing about this Pye oscillator is the use of
phase-shift networks instead of a Wein bridge. I wonder if the
phase-shift arrangement gives bettter gain stability and reduced
'amplitude bounce' from pot-ganging inaccuracies when sweeping rapidly
through the frequency range?

[Adrian Tuddenham]

Electro Dabbler <alsh...@gmail.com> wrote:


> I recently saved an old PYE signal generator from a bin for a bit of fun.

[...]

Any success yet with repairing it?

[N_Cook]

Adrian Tuddenham <adr...@poppyrecords.invalid.invalid> wrote in message

news:1l25s9p.1glsgyrs0mp9yN%adr...@poppyrecords.invalid.invalid...

Did you see Dr Who from 20 April? , about a dozen Solartron , Telequipment
etc scopes with some sort of trace on all of them, no mean feat, plus
Advance sig gen etc

[Adrian Tuddenham]

I don't have a television set, but that sounds really interesting. I
wonder if there is someone in the production team with some knowledge of
engineering at last (or if they hired-in the gear from a knowledgeable
supplier)?

I would be really impressed if they could keep a trace on an old Marconi
'scope that we used to have when I worked for Eddystone's. It took
several minutes for the thermal delay switch to bring in the mercury
rectifier; but, as the MTBF was of a similar magnitude to the delay, it
only worked for a few minutes before we had to shut it down, cool it off
and start again.

[Michael A. Terrell]

Adrian Tuddenham wrote:
>
> I don't have a television set, but that sounds really interesting. I
> wonder if there is someone in the production team with some knowledge of
> engineering at last (or if they hired-in the gear from a knowledgeable
> supplier)?
>
> I would be really impressed if they could keep a trace on an old Marconi
> 'scope that we used to have when I worked for Eddystone's. It took
> several minutes for the thermal delay switch to bring in the mercury
> rectifier; but, as the MTBF was of a similar magnitude to the delay, it
> only worked for a few minutes before we had to shut it down, cool it off
> and start again.

I finally broke down and got a better, but used scope. 350 MHz, four
channel. An old Tek 2465. Now I can see what's wrong with my old(er)
Tek scope. :)

[Doug McDonald]

somebody wrote:
> I finally broke down and got a better, but used scope. 350 MHz, four
> channel. An old Tek 2465. Now I can see what's wrong with my old(er)
> Tek scope. :)
>

Those are wonderful scopes. I have two. I also have a 2 454s, the most
wonderful of all, and both still work perfectly. At home I have a 7904
with a 7L12 spectrum analyzer. The scope works perfectly, but the
plugin has switch issues.

Doug McDonald

[Michael A. Terrell]

I had a 2465A on my bench at Microdyne. The only one outside of
engineering. They made the mistake of taking the 2465 I had at first. It
cost them the 2465A. Then they told me they could take anything they
wanted from production. I reminded them that I got there two hours
before anyone in engineering, and it would be all out war if they
touched it. ;-)


What switches are bad? If I ever get my smaller shop cleaned out, I
think I have all the switches from a junked Tektronix 564 rack mount
storage scope. I saved almost all of it except the HV section and CRT
but I don't know if it's still there.

I have a Sony/Tektronix 324 battery powered scope, as well. I need to
build a new batter pack, and make a power cord. It uses the same
square, fur pin power connector as their early 5" B&W TVs, but they are
wired differently. The DC cable to run the TVs in a car are wired
properly, but those are worth more than the TVs or the scope because
they are so rare.