This belonged to my Granddad. I did some research on it as I wasnt entirely sure what it was, it turned out its an old PA system.
I have never had it working...
I play in bands and Id love to see if it could be used as or turned into a guitar amp or maybe put vox though it and see how it sounds. I have no idea what sort of wattage it would put out or how to approach getting it working.
I realize that some testing is likely to be needed prior to plugging it into the mains. Then there is the issue of how to plug it into the mains given the weird power socket arrangement with 10 pins (I have never even seen one like it).
Then there are the outputs which I cant make head nor tail of....One of them, rather alarmingly, is labelled "100v".
Anyone got any input? Id really appreciate any ideas.
Thanks 🙂
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
I have never had it working...
I play in bands and Id love to see if it could be used as or turned into a guitar amp or maybe put vox though it and see how it sounds. I have no idea what sort of wattage it would put out or how to approach getting it working.
I realize that some testing is likely to be needed prior to plugging it into the mains. Then there is the issue of how to plug it into the mains given the weird power socket arrangement with 10 pins (I have never even seen one like it).
Then there are the outputs which I cant make head nor tail of....One of them, rather alarmingly, is labelled "100v".
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Anyone got any input? Id really appreciate any ideas.
Thanks 🙂
Here you can see the pics bigger. Cheers.
Postimage.org / gallery - IMG 1075, IMG 1076, IMG 1077, IMG 1078
Postimage.org / gallery - hifiltd staffs amp 1, hifiltd staffs amp 2, hifiltd staffs amp 3
Postimage.org / gallery - IMG 1075, IMG 1076, IMG 1077, IMG 1078
Postimage.org / gallery - hifiltd staffs amp 1, hifiltd staffs amp 2, hifiltd staffs amp 3
Some more of the internals
Postimage.org / gallery - IMG 1079, IMG 1080, IMG 1081, IMG 1082, IMG 1083, IMG 1084, IMG 1085
Postimage.org / gallery - IMG 1079, IMG 1080, IMG 1081, IMG 1082, IMG 1083, IMG 1084, IMG 1085
It looks like a very well built PA amp, and should make a great platform for a guitar amp. The difficult bit is to find or worse trace out the schematic. But for starters, you should make up a list of all the tubes that are used in the amplifier, as well as any information that you can glean from looking at the power and output transformers. Of course, any model number stamped on the chassis would be helpful.
Whilst I am confident to 'have a go' at this sort of things I am a complete amateur!
I'm not sure I understand which the power or output transformer :/
Iv had the valves out though and they read as follows:
4 x Brimar 6BR7
2 x Mullard EL34
2x Tungsram EZ81
I'm not sure I understand which the power or output transformer :/
Iv had the valves out though and they read as follows:
4 x Brimar 6BR7
2 x Mullard EL34
2x Tungsram EZ81
The 100V output is a common feature in PA equipment, just don't use it.
It's for speakers with an internal high impedance step down transformer.
Looks worth the trouble of restoring, but you'll have to replace all the electrolytic capacitors at a minimum.
Sounds liek there might ba a separate power supply chassis that plugs into the 10 pin socket.
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Hi,
The 100V output is typical of a old PA for a building.
Each "Tannoy" has a tapped 100V transformer to adjust level.
The 100V transformer for typical use is not needed.
Gram inputs are old fashioned ceramic, line level.
Do you have the supply with the correct cable ?
I'm wondering what battery it could run off and how.
rgds, sreten.
What are the terminals next to the voltage selector ?
the wired short across them doesn't look a good idea.
The 100V output is typical of a old PA for a building.
Each "Tannoy" has a tapped 100V transformer to adjust level.
The 100V transformer for typical use is not needed.
Gram inputs are old fashioned ceramic, line level.
Do you have the supply with the correct cable ?
I'm wondering what battery it could run off and how.
rgds, sreten.
What are the terminals next to the voltage selector ?
the wired short across them doesn't look a good idea.
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Ok. Unfortunately I do not have the power supply. Could this prove to be the biggest problem?
The terminals next to the voltage selector I assumed to be some sort of re wire able fuse (fuse wire?)
Something else that I just thought of... Did they used to earth amps in the 60's? I'm wondering if this thing is even earthed?
Keep the ideas flowing people 🙂.
Cheers.
The terminals next to the voltage selector I assumed to be some sort of re wire able fuse (fuse wire?)
Something else that I just thought of... Did they used to earth amps in the 60's? I'm wondering if this thing is even earthed?
Keep the ideas flowing people 🙂.
Cheers.
Hi,
The power supply is probably not a problem due to the
voltage selector. However it seems to me its best
stripped for parts and reworked from the ground up.
Which is no trivial matter for a pro, nevermind an amateur.
A lot of gumption is required to understand the parts.
rgds, sreten.
I don't buy the rewirable fuse, they look like speaker terminals.
The power supply is probably not a problem due to the
voltage selector. However it seems to me its best
stripped for parts and reworked from the ground up.
Which is no trivial matter for a pro, nevermind an amateur.
A lot of gumption is required to understand the parts.
rgds, sreten.
I don't buy the rewirable fuse, they look like speaker terminals.
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To be honest that's not really an option. Its either have a bash at getting it working myself or it goes back in the loft. I was hoping to try and make it safe, replace what needs replacing (minimum), find a way to power it, and then just use it as it is.
I suppose one day I could pay a professional to do it but whether id ever justify the costs I couldn't say.
I suppose one day I could pay a professional to do it but whether id ever justify the costs I couldn't say.
Maybe someone from the British Vintage Wireless Society would be happy to help you:
BVWS - British Vintage Wireless Society
Anyway, for your information: electrolytic capacitors that haven't been used for decades have a much increased leakage current. This leakage will disappear when you charge them very slowly to their normal voltage. If you suddenly apply the normal supply voltage, there is a considerable risk that an electrolytic capacitor will explode or a filter resistor in a CRCRC-chain that filters the hum off the supply will burn out. This doesn't apply when you preventively replace all electrolytics, of course (which would be at the expense of the historical value of the amp).
There are various tricks you can use to prevent these problems. If you have a variac, you can turn it up very slowly. If you have a bunch of incandescent lamps of various powers, you can connect a low-power lamp in series, turn the equipment on, wait until the amount of light coming from the lamp stabilises and then switch to a lamp with higher power. My favourite method is to remove all valves except the rectifiers, connect 150 kohm, 1 W resistors in series with the supply electrolytics, turn the equipment on and wait until the caps are fully charged (which may take as long as a few hours).
Old paper capacitors are also notorious for their leakage, especially when some moisture got in somehow. Be especially careful with snubber capacitors (they may get hot when they are faulty) and the DC blocking capacitors between the driver stage and the EL34 end valves (they may blow up the EL34s if their leakage current is too high). Dubious paper capacitors need to be replaced, I don't know of any reliable method to bring them back in their non-leaking state.
By the way, some members of the Dutch vintage radio society (NVHR) have a forum dedicated to restoration of old valve equipment: http://www.gloeidraad.nl/radioforum . It is accessible for people who are not a member of the NVHR and even though most contributions are in Dutch, you usually do get answers to questions in English.
BVWS - British Vintage Wireless Society
Anyway, for your information: electrolytic capacitors that haven't been used for decades have a much increased leakage current. This leakage will disappear when you charge them very slowly to their normal voltage. If you suddenly apply the normal supply voltage, there is a considerable risk that an electrolytic capacitor will explode or a filter resistor in a CRCRC-chain that filters the hum off the supply will burn out. This doesn't apply when you preventively replace all electrolytics, of course (which would be at the expense of the historical value of the amp).
There are various tricks you can use to prevent these problems. If you have a variac, you can turn it up very slowly. If you have a bunch of incandescent lamps of various powers, you can connect a low-power lamp in series, turn the equipment on, wait until the amount of light coming from the lamp stabilises and then switch to a lamp with higher power. My favourite method is to remove all valves except the rectifiers, connect 150 kohm, 1 W resistors in series with the supply electrolytics, turn the equipment on and wait until the caps are fully charged (which may take as long as a few hours).
Old paper capacitors are also notorious for their leakage, especially when some moisture got in somehow. Be especially careful with snubber capacitors (they may get hot when they are faulty) and the DC blocking capacitors between the driver stage and the EL34 end valves (they may blow up the EL34s if their leakage current is too high). Dubious paper capacitors need to be replaced, I don't know of any reliable method to bring them back in their non-leaking state.
By the way, some members of the Dutch vintage radio society (NVHR) have a forum dedicated to restoration of old valve equipment: http://www.gloeidraad.nl/radioforum . It is accessible for people who are not a member of the NVHR and even though most contributions are in Dutch, you usually do get answers to questions in English.
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I'm not too bothered about the historical value. Im happy to replace like for like for modern components where necessary in order to get this thing working. I think it should be used.
This units power supply is a storage battery,the kind you'd find in a car (That means BIG!) The large ,socketed silver can is a vibrator. This 'chops' the dc into ac,which is then stepped up by a transformer to provide the high voltages necessary for the plates. The filaments run off the battery directly.
Although the vibrator is labelled as 12 volt,this may be an incorrect replacement,as all the tubes have 6 volt heaters. You will have to check the heater wiring to be sure,as they could have been run in a series/parallel arrangement. If you have a 6/12 volt battery charger(10 amps minimum) you're on you're way!
Although the vibrator is labelled as 12 volt,this may be an incorrect replacement,as all the tubes have 6 volt heaters. You will have to check the heater wiring to be sure,as they could have been run in a series/parallel arrangement. If you have a 6/12 volt battery charger(10 amps minimum) you're on you're way!
That's interesting. So the original power supply would have used a step down transformer?
I read this about the same model which led me to believe the amp could run off a battery or mains supply.
"The heaters would be wired in series/parallel to operate from 12volts (unless it worked from a six volt battery). The connector would be the same for either mains or battery supply, just different pins wired for each option."
I read this about the same model which led me to believe the amp could run off a battery or mains supply.
"The heaters would be wired in series/parallel to operate from 12volts (unless it worked from a six volt battery). The connector would be the same for either mains or battery supply, just different pins wired for each option."
Before it goes in the loft if that is what happens, pull those tubes, especially the Mullard EL34s. Find a way to test them. Those EL34s could go for $100 if they test good. You could also sell those EZ81s. I also see a Telefunken hiding in image 1083. This could also be valuable. Be careful as the paint comes off very easily from these old tubes.
I don't intend to sell any bits from this. It stays intact, I'm afraid! I want to see it get put back into use. My plan is hopefully still to replace the bare minimum and then try and power it up.
Unless they are dried out and have lost most of their capacitance, there is no real need to replace electrolytics, just as long as you don't power them up abruptly after decades. If there are any paper capacitors at critical places, I would definitely replace those.
Il take a closer look tomorrow. As these were not popular amps there is no schematics etc available. I not 100% sure what I m looking for but Il do some research. Would you be able to take a closer look at the pics of inside the amp and see if you can spot any that are obvious? That would be a great help.
🙂
🙂
Glad to hear that. It's really neat to see some of these old marvels of engineering(for its day) reborn! Just wanted to inform you of the value of the tubes, although somewhere along the line you will want to test them so as to eliminate any possible damage done by defective tubes, especially in the power section,akaEL34. You don't want shorted grids, screen or control, to do damage.
Since there are four 6BR7 pentodes and you have four volume controls, 2 mic and two gram-gramophone,more than likely these serve as the first gain stage for each channel. That Telefunken tube I saw in image 1083 is probably the phase inverter and the Mullard EL34 tubes are the output tubes probably putting out 25 watts or so operating in push-pull. If you can trace where the wires from pin 3 from these go, this will be your output transformer. Back in those days, that was a lot of power. Nowadays, these will put out 50 watts or so.The two Tungsrams are the power supply tubes. One probably was for the power section and the other was for the rest. And yes, it appears it had a 12 volt storage battery maybe for filaments of the tubes.If you can trace where pin 2 and 7 of the EL34s go, this is where the filament power came from.
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Appreciate the input, thank a lot. I think basically what your saying is that the tubes will need testing before the unit it powered up to avoid damage to other parts of the circuit. Im hoping to get in touch with someone who has the means to test velves in order to confirm this.
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