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!
(https://s14.postimg.org/4tmrzi5f1/28035269_2051011075176217_1573247233_o.jpg) (https://postimg.org/image/4tmrzi5f1/)
(https://s14.postimg.org/5kfi4t2i5/28034865_2051010571842934_938686363_o.jpg) (https://postimg.org/image/5kfi4t2i5/)
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..) :icon_wink:
I was hoping to avoid opening the thing up but can do if needs be. Would a standard IEC socket work?
Thanks
Patrick, I ensure you that I'm lazier than you :icon_wink: 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..
£10 with the boots? that's a good deal.
Maybe we can make a deal with Patrick for £10, Stephen.. :icon_wink:
(you keep the boots and I keep that yam-yam-slourp meter..) :icon_redface:
Quote from: antonis on February 13, 2018, 08:36:01 AM
Patrick, I ensure you that I'm lazier than you :icon_wink: 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 :icon_lol:
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
Now you made me afraid, Patrick.. :icon_redface:
Honestly, if you don't know anything about "elementary" mains wiring I would suggest to avoid the project of IEC fitting.. :icon_mrgreen:
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..?? :icon_wink:
(can't see neither ON -OFF switch nor fuse socket..)
Plz, post a pic of back plate..
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.
70's Twin Reverb?
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.
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.
]
> 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.
Quote from: PRR on February 13, 2018, 04:38:48 PM
It is not "a potential tube guitar amp".
Not sure if this was in response to my
Quote70'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.
QuoteIt 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.
QuoteThe "AF" jack is the secondary of the transformer.
Ah, now I see it. It's not marked with T1.
Quote(*)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.
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.
Quote from: PRR on February 13, 2018, 04:38:48 PM
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. :icon_frown:
> 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.
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.
This is probably where it was built.
(https://s18.postimg.org/efgzlc6yd/Roebuck_Road.jpg) (https://postimg.org/image/efgzlc6yd/)
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.
Quote from: R.G. on February 13, 2018, 01:48:39 PM
Hiring a tech to do it right may be the best money you ever spent, and cheaper than a funeral.
Not in case of public expenditure funeral.. :icon_wink:
Seriously Patric, mains wiring looks pretty simple job - with many (potentially lethal) hidden details..
(especially in case of old/rusty/(possibly) internaly violated/modified instrument..)
Was away from my computer for a while so only just seen all these replies, thanks so much!
Part of the reason i went and picked this up was because i think it's beautiful, i really love the look of old gear so for me it was a bonus if i could get it working or if it was actually useful for my needs. I did think i could potentially use it for pedal building, as a signal generator but from what some of you have said it's not really much use to me.
But that's fine because i did also have thoughts of gutting it and turn it into something else. My first thought was to house a few effects in there but i am starting to really like the idea of making a preamp out of it. Once i've got a few other projects cleared out the way i'll start looking into that properly.
It ways a ton as it is so hopefully i can shed a few pounds from it and potentially take it out on the road.
It is a 78 pro reverb you see in the background, i have beautiful fender clean tones, and a completely broken spine.
Any preamp schems specifically you recommend i take a look? Or other ideas for what to do with it?
Thanks, you guys are d'best!
Quote from: patrick398 on February 15, 2018, 12:22:16 PM
It is a 78 pro reverb you see in the background, i have beautiful fender clean tones, and a completely broken spine.
Not completely broken, you need a Twin for that. My amp is basically a Pro Reverb, but only the "party" channel, and a mid control.
:icon_lol: Which is the party channel?
Reverb/trem.
Ah makes sense, thought maybe there was some secret party channel going out behind my back...story of my life
Mains input filter capacitors C20 & C21 should be replaced with modern Y class capacitors. Alternatively, if you decide to fit an IEC inlet, you can buy ones with inbuilt filters, fuse and switch (maybe not all three) but they do take up a bit of space.
https://www.allaboutcircuits.com/technical-articles/safety-capacitor-class-x-and-class-y-capacitors/
I have an Advance AF signal generator, which I still use sometimes in my day job. It originally had an inlet connector like yours, but I replaced it with a cable gland and flexible cord.
Just want to throw this question in here:
How do you know what type (rating, fast/slow) of fuse you need?
QuoteThis is probably where it was built.
The closer I look at it the more I'd have to agree.
(https://s13.postimg.org/qvdaj0b5v/image.jpg) (https://postimg.org/image/qvdaj0b5v/)
Quoteust want to throw this question in here:
How do you know what type (rating, fast/slow) of fuse you need?
Working out fuses properly is a real pain in the butt.
There was a thread on it some time back and RG and I too'd and fro'ed a few things.
The manual states 25W. That usually amounts to a 250mA to 500mA.
[Edit:
Actually this is fairly good account of the issues fusing small transformers.
Small being less than say 20VA to 30VA, where the winding resistance becomes significant and limits the fault current:
http://sound.whsites.net/articles/fusing.htm
]
Very nice article at that link. Frightening though.... The short version (no pun intended) appears to be that you specify a fuse by guessing (but not haphazardly) and hope for the best. :icon_eek:
Quote from: EBK on February 16, 2018, 05:27:45 AM
Very nice article at that link. Frightening though.... The short version (no pun intended) appears to be that you specify a fuse by guessing (but not haphazardly) and hope for the best. :icon_eek:
... and if it keeps blowing try a slo-blo
(https://i.imgur.com/TtFotWu.jpg)
QuoteFrightening though.... The short version (no pun intended) appears to be that you specify a fuse by guessing (but not haphazardly) and hope for the best
The article does say that but it's not as bad as he phrases it. You need to choose a fuse large enough so it won't blow under normal use. The first guess is the operating current but it is likely that will blow at some point. So then he suggests a safety factor of 2 to stop that happening. So you have narrowed down the choice of the fuse current to within a factor of two.
There are well known ways to come-up with a better estimate but they are quite complicated and require a lot of measurements and also require data about the specific fuse you intend to use. Sometimes this info isn't available. Going down this path can be a bit painful and a job for the "professional".
The second important point is the relative size of the fault current compared to the operating current. If the fault current is much larger than the operating current then even of your estimate of the minimum fuse current was off the fuse is likely blow under most faults. However, if the transformer is small the fault current isn't much different to the running current. This is where is becomes a problem. It also means you need to have good estimate of the minimum fuse size and a good estimate of the fault current. If those are too close together the choice of a suitable is very narrow and if you use that fuse it might blow in use and/or not blow when you have a fault. You hit this problem when a transformer is below about 20VA. The modern solution for small stuff is to give up using a fuse. You use thermal thermal fuses instead which measure the transformer temperature, this is actually a better indication of a fault and of a dangerous situation. These type of fuses trip and reset or fail permanently.
@ EBK
Some of my friends were quite fond of the 250A model and they did manage to cook some wiring (only 12V though).
Good luck finding a 7.62x51mm fuse holder these days.
(The multi-dispensers are still quite common though)
If i can get another project finished up i might well end up gutting this thing tonight. But first, what's going to fry me? Big capacitors i'm guessing. Discharge them first with a screwdriver or something right? What about the transformer? I don't want to go digging around in there with wire cutters unless i know it's not going to roast my chestnuts
Quote. But first, what's going to fry me? Big capacitors i'm guessing. Discharge them first with a screwdriver or something right? What about the transformer? I don't want to go digging around in there with wire cutters unless i know it's not going to roast my chestnuts
No offense meant but you shouldn't take on such a job without at least being able to identify those issues yourself. A few posts will put you on the right track but if you can't work out one of the 20 items not covered you can get into serious trouble.
Here's some areas:
- Mains wiring
http://sound.whsites.net/earthing.htm
Note the cable must be correctly rated.
There are correctly rated fuse holders. Modern ones are designed to reduce risk of shock.
- High voltage on the secondary side. AC, DC.
Yes discharge the caps with a 100R to 1k 1W resistor. But you have to wire it up so you can't slip and touch the wires. Don't forget one.
- Check your work before you turn it on.
- Be aware of things that will catch fire if you have a fault. No paper.
- Work practices:
- Remove the plug completely from the wall when working on it.
Don't just turn it off at the switch. And definitely don't rely on the equipment switch.
- No children or animals in the vicinity. Close the doors.
- Tell someone what you are doing
- No drinks or liquids on the same table.
- Don't leave it plugged in if you aren't there.
- If you have unfinished work don't leave it in a state where it is dangerous for someone else to plug in.
If you are just talking about gutting it, then you should be right as long as it hasn't been on recently. Capacitors do hold a charge, and power supply caps can have charge for a while. They are probably OK but it is always good to discharge then as a matter of course just in case. If all you are doing is disassembly then you will be fine with that.
Yeah just gutting it, i won't be building anything with high voltages until i feel comfortable and safe about it. More reading to be done for sure. I just wanted to make sure there wasn't anything specific i should bare in mind when taking it apart, Thanks