Need help safely powering old signal generator

[patrick398]

Picked up this beautiful old signal generator last night for £10 but need it has no power lead. The guy i bought it off had Macgyver-ed a power source for it, but being an old two pin device i don't think i'm comfortable doing this. There's a green and yellow cable screwed onto the faceplate so i'm guessing he was using this as some kind of gnd/earth...but that scares me haha.
Does anyone know where i might be able to find a suitable cable? Or suggest a way of making one myself safely?
There's some good information about it here: http://www.electrojumble.org.uk/DATA3/Advance_B4.pdf
Mentions a PL24 mains lead but sadly searching that doesn't yield much info.
Thanks in advance!

[antonis]

I should replace that receptor with any 3-prong one, connecting also ground wire there and maybe adding a line fuse..

Take care of C20 & C21 caps 'cause are close to rust (which never sleeps..) 

[patrick398]

I was hoping to avoid opening the thing up but can do if needs be. Would a standard IEC socket work?
Thanks

[antonis]

Patrick, I ensure you that I'm lazier than you  but not when dealing with mains..

Yes, a standard IEC socket should be more than fine..

Maybe you can find a 2 pole wire plug, like those used for battery/mains ungrounded devices (portable tape recorders, radios, etc.) which could fit on your existing socket (25W draw (roughly) 100mA at 230V - double at 115V, so any cable of 0.8mm/0.032" diameter - 0.5mm²/AWG20 - or greater should be OK..) but I should suggest instrument's internal-mains grounding..

[duck_arse]

 £10 with the boots? that's a good deal.

[antonis]

Maybe we can make a deal with Patrick for £10, Stephen.. 

(you keep the boots and I keep that yam-yam-slourp meter..) 

[patrick398]

Patrick, I ensure you that I'm lazier than you  but not when dealing with mains..

Yes, a standard IEC socket should be more than fine..

Maybe you can find a 2 pole wire plug, like those used for battery/mains ungrounded devices (portable tape recorders, radios, etc.) which could fit on your existing socket (25W draw (roughly) 100mA at 230V - double at 115V, so any cable of 0.8mm/0.032" diameter - 0.5mm²/AWG20 - or greater should be OK..) but I should suggest instrument's internal-mains grounding..

Ok thanks man i'll head your advice, one lazy person to another. Any dangerous capacitors i should be wary of? I'd have usually been told not to mess around with mains stuff and kill myself by now. I'm surprised nobody is intervening...or maybe more than one of you has got their eye on my boots eh? Well good luck prizing them off my cold dead feet when i've fried myself and welded them on 

Could you give me a little more guidance in fitting the IEC? Which disconnected wires go where on the IEC socket and where to attach the ground etc.
Thanks a lot guys

[antonis]

Now you made me afraid, Patrick.. 

Honestly, if you don't know anything about "elementary" mains wiring I would suggest to avoid the project of IEC fitting..

But if you dismandle back plate and loose the existing socket by the 2 slothead screws, post a picture (or more..) and maybe we'll find a solution...

P.S.
Don't desolder/unscrew/release any wire before taking picture..

edit: I've just realize your posted mains receptor is on the front plate.!!
Are you sure it indeed is for mains supply..?? 
(can't see neither ON -OFF switch nor fuse socket..)
Plz, post a pic of back plate..

[R.G.]

All good advice so far. Especially the "take pictures" part.

Here's my cut on it.
1. Do not use the generator in its current condition. The chances are that something about the AC power wiring may have a fault and be dangerous.  It's only rock and roll - and not worth dying for.
2. Do not do AC power wiring on it yourself unless you already know you can do this work properly, and not get electrocuted from doing the work, or build in an electrocution/fire hazard in the work you do. Again, it's not worth dying for. Hiring a tech to do it right may be the best money you ever spent, and cheaper than a funeral.
3. If it were me doing the work, I would find a safety-standards-approved (IEC/TUV/UL, etc.) IEC socket that has a built in fuse holder and switch. These are available for US$5 or so. How much exactly will depend on your country, tariffs, etc.
4. I would replace C20 and C21 with safety rated film capacitors of type Y, same value capacitors. The Y type capacitor is specifically designed for line-to-ground connections >> safely <<.
5. There is a highly specific set of wiring instructions for how to attach safety ground to the chassis of such equipment. You need to know and follow this. You already know if you know this or not.

[thermionix]

70's Twin Reverb?

[PRR]

This is an RF signal generator. It starts at 100KHz (three octaves past musical frequencies) and goes on somewhere beyond the AM broadcast band.(*)

In this, a guitar-pedal chatroom, I don't know why you would want it. I can think of a few odd and unlikely uses. Nothing to justify that big of a box, or the risks of very-very old gear of uncertain condition.

It is not "a potential tube guitar amp". The whole circuit draws under 3mA (and the supply is surely not over-sized), while any little tube amp wants many times more.

I imagine a tea-kettle lead plugs in under that "AF" socket. Maybe not any current UK-legal kettle-lead. And I would not plug it in without looking inside for trouble. Even then, outside on rubber mat with long cord. This ignores the fact that the case really SHOULD be bonded to Protective Earth (your green wire, in the 3-wire cord this thing does not accept).

M1 and X3-6 (plus some resistance) _are_ a half-decent Audio Level Meter, worth salvaging. Those old-skool knobs may be worth a couple bucks each eBay. C2 would be worth something if it was Dual, but it ain't. Steampunk artists might give a buck.

(*)There is a 400Hz source. You can do better, and much safer, with a 9V battery and a TL072.

[Rob Strand]

You should confirm the input is mains and what voltage.
From the front plate it looks like you can configure it.

If it is an Advance B4A5 checkout,  (second has schematic)
https://www.kevinchant.com/advance.html
http://www.kevinchant.com/uploads/7/1/0/8/7108231/advance_signal_generator_type_b4.pdf

[Edit1:  OK from the manual the audio is a fixed 400Hz signal.   From what I can work it it's one of those funky modulators where the whole power supply of the HF oscillator is modulated at 400Hz; (T1, C11, V2).   The 400Hz doesn't come out of the box.
]

[PRR]

> funky modulators where the whole power supply of the HF oscillator is modulated

That's how you make AM. (OK, modulated oscillator isn't the best way.) It appears to be quite clean up to high modulation, limited on the down-swing where the oscillator starts to go lame.

>The 400Hz doesn't come out of the box.

The "AF" jack is the secondary of the transformer. Probably several Volts at many mA. Adjustable (to a point) by varying the B+ to the AF oscillator. If you really want ALL this box for a fixed-frequency (around 400cps but not exact) tone, you could further attenuate down to any level. But again there's smaller safer cheap ways to build an audio tone-box.

[thermionix]

It is not "a potential tube guitar amp".

Not sure if this was in response to my

70's Twin Reverb?

as Patrick didn't mention trying to convert it to an amp.  I was referring to the amp in the background of the first pic.  It looks like a silverface Twin or Pro, but maybe a Vibrolux.

[Rob Strand]

It appears to be quite clean up to high modulation, limited on the down-swing where the oscillator starts to go lame.

That's probably why that configuration was popular.  The variable gain set-ups were asymmetrical; some were pretty bad.

The "AF" jack is the secondary of the transformer.

Ah, now I see it.  It's not marked with T1.

(*)There is a 400Hz source. You can do better, and much safer, with a 9V battery and a TL072.

Quite true.

As much as I like those old oscillators ... maybe turn it into some sort of tube preamp.

[GibsonGM]

Rob is on to something.  Keep the front panel as-is just for a laugh (VERY cool appearance)....use some of the knobs on new pots for gain, vol., tone...make a tube preamp with it by gutting the rest and starting from Scratch with a new power supply.   

Awesome learning experience and will have a SWEET preamp at the end.

[EBK]

In this, a guitar-pedal chatroom...

I keep messing up on that rule so badly.  So much off-topic crap is flung from my keyboard.

[PRR]

> It's not marked with T1.

The switching on that stage wasn't clear, so I stared at it.

(And it is a T, not an L, so it's probably a transformer.)

If mystery winding is on T1 and goes to V2 grid, that closes the loop as a likely oscillator. The tube gain may be >10, so a 10:1 transformer would make it howl. 10:1 ratio from a ~~6K plate would drive <600r, as claimed. C11 *smudge* is likely selected to ring T1 primary near 400Hz. That makes INT work.

In CW, V2b is disconnected, RF is steady.

In EXT, V2b is rigged with an Rk and Rp as a voltage amp, taking signal from the AF connection and banging V2a grid similar to INT, but with other source. (So the AF jack is both In and Out.)

Another objection to "make a preamp" is that the 6V winding appears to be common with the HV 0V. One-side-grounded heat in guitar amps went out in the 1950s- hum was always marginal. It may not really be pinned-out that way.

Anyhow-- the "convert it!" plan runs back to the original question: "...it has no power lead. ... i don't think i'm comfortable doing this." If he's not comfortable, I'm real uncomfy telling him to just stick some wires on. Fire, shock, exploding caps...

Minor tidbit: there was a 110V-250V 40-100cps transformer, which you'd think would cover all cases; AND a 117V 25-60cps model. Yes, the US (and part of Canada?) had 25cps through the 1940s.

[GibsonGM]

Not convert....keep the nice face items, and build an entirely new circuit inside....just getting that on the record, LOL.

There is usually very little in old stuff like that to "convert" or even repair, often, as discussed above in nice detail.  It's so old and without a big background, one would probably not know what was going wrong.     A nice new transformer,  a turret board, 2 or 3 12AU and/or AX7's, pots, caps...EIC connector w/fuse...and a very sweet tube preamp could be had.     But maybe learn about electrical safety first, OK Patrick!???

You gotta start somewhere, a basic transformer-based power supply is one good place, IMO.  Then you go up the ladder from that, to more challenging projects.

[PRR]

This is probably where it was built.


This is "out in the country" a couple miles north of the Dagenham Engine Plant, where millions of Ford cars trucks and tractors were built. One side of the road is still farms, but this cluster of old buildings is the usual run of ugly businesses.