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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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20th Apr 2021, 9:15 am | #1 |
Dekatron
Join Date: Feb 2009
Location: Chesterfield, Derbyshire, UK.
Posts: 3,767
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I came across this strange thing yesterday!
An amplifier arrived on the bench complaining of a hum. It was a German Wurlitzer using four ECL86's, as normal with Juke Box amps the mains goes to the mech and is switched from there. As there was a two pin socket on the chassis I assumed that this was where the switching was done so I linked the socket out. There was a 13 amp plug on the lead so I plugged it in and pop it blew a 6 amp fuse. The primary read low ohms, decided to connect to the Variac and monitor the 6.3 volt heaters. To my amazement it only needed about 20 volts at 3.5 amps, all HT voltages OK. Apparently the mains goes via a lighting choke, anyway having replaced the smoothing capacitors and given a service all was OK. Now working back in the juke box, very strange!
Mick. |
20th Apr 2021, 12:14 pm | #2 |
Dekatron
Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 7,088
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Re: I came across this strange thing yesterday!
So you're saying the amplifier works from 20V AC?
Really odd! And would be a fairly chunky choke, dropping best part of 240V at 3.5A! |
20th Apr 2021, 2:00 pm | #3 |
Dekatron
Join Date: Feb 2009
Location: Chesterfield, Derbyshire, UK.
Posts: 3,767
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Re: I came across this strange thing yesterday!
Yep seems that way, that was my thoughts regarding the choke, unless there is something else, but the owner assures me that the two pin plug just goes to the lighting ballast /choke.
Mick. |
20th Apr 2021, 3:47 pm | #4 |
Nonode
Join Date: Aug 2015
Location: Cambridge, Cambs. UK.
Posts: 2,198
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Re: I came across this strange thing yesterday!
I agree that a 'lighting choke' would be a strangely inappropriate bit of design.
Perhaps the owner was under a misapprehension Maybe it's actually a step-down lighting transformer like the type designed to feed halogen lamps. They can look rather like fluorescent chokes, being long and narrow to fit through a downlighter ceiling hole. Martin
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20th Apr 2021, 4:50 pm | #5 |
Dekatron
Join Date: Jun 2013
Location: East Sussex, UK.
Posts: 3,327
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Re: I came across this strange thing yesterday!
Afraid you got it wrong. The 2 pin socket on the top of the chassis is a 220 volt feed for the lighting taken from the tap on the transformer. The mains transformer primary, when set for 240 volts, will have one side of the mains connected to 0 volts and the other to 240 volts input which comes via the on/off switch on the chassis.
By shorting out the lighting socket you put the 220 volt transformer tap to the 0 volts input, shorting out most of the primary winding, and the normal mains live to the 240 volt transformer tap. That is why you only needed 20 volts input. I’m surprised the transformer didn’t give up as the primary windings are not built for 3.5 amps. Clearly you didn’t have a circuit diagram as it’s clearly shown, although in German. |
20th Apr 2021, 5:14 pm | #6 |
Dekatron
Join Date: Jun 2013
Location: East Sussex, UK.
Posts: 3,327
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Re: I came across this strange thing yesterday!
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20th Apr 2021, 6:30 pm | #7 |
Rest in Peace
Join Date: Apr 2008
Location: London, UK.
Posts: 2,508
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Re: I came across this strange thing yesterday!
I can just about imagine the transformer being able to operate the amplifier when fed 20V between the 220V and 240V taps, albeit with that section of the primary running dangerously hot. But surely not with 0-220V section shorted out? However, for it not to be shorted, the neutral end of the winding would have to be O/C, in which case it wouldn't work on 240V. Curious.
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20th Apr 2021, 9:19 pm | #8 |
Dekatron
Join Date: Feb 2009
Location: Chesterfield, Derbyshire, UK.
Posts: 3,767
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Re: I came across this strange thing yesterday!
Thanks for that Vidjoman , I knew there was some thing strange , the amp had been worked on prior to me working on it ,as it is the neutral goes via the two pin socket, I have just contacted the owner asked him not to use it ,it needs another look at , all the wires to the mains tx look original we will see , Mick.
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20th Apr 2021, 10:11 pm | #9 |
Dekatron
Join Date: Jun 2013
Location: East Sussex, UK.
Posts: 3,327
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Re: I came across this strange thing yesterday!
Often a problem with Jukebox amps is that 'someone' has had a go who doesn't understand how they are configured. The neutral does go to the 2 pin socket, as you can see in the diagram, and the 2nd pin is from the 220 volt tap on the transformer. Unfortunately the German Wurlitzer amps are not the best build quality and as they are fitted to a 'budget' jukebox they are often abused, i.e. bodged. The relay needs to be energised or the contacts shorted to get the HT operational. I've seen them with the relay missing and just shorted out so the HT is on all the time the box is on and that shortens the life of the valves.
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21st Apr 2021, 8:47 am | #10 |
Dekatron
Join Date: Feb 2009
Location: Chesterfield, Derbyshire, UK.
Posts: 3,767
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Re: I came across this strange thing yesterday!
Update on the amp. Asked the customer to unplug the light feed the two pin plug, to see if the amp still worked, it does. That circuit is not the one for this amp as the mains neutral goes to the mechanism via a long multi plug then it must come back again to the transformer. I did wedge the relay closed to work on it originally. Anyway he is happy it's working OK.
Thanks for the replies, Mick. |
21st Apr 2021, 10:55 am | #11 |
Dekatron
Join Date: Jun 2013
Location: East Sussex, UK.
Posts: 3,327
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Re: I came across this strange thing yesterday!
Looked at all the Lyric circuits I have, valve and transistor, and they all have mains input going direct to the master switch on the amplifier chassis. All show the lighting socket connected to 220 volt transformer tap. The mechanism runs off the 30 volt secondary with other secondary windings feeding valve or transistor supplies.
If there is a loop out and back on the neutral line then it is a non-standard mod. Perhaps someone has added these for a ‘remote’ on/off switch. |
21st Apr 2021, 12:36 pm | #12 |
Dekatron
Join Date: Feb 2009
Location: Chesterfield, Derbyshire, UK.
Posts: 3,767
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Re: I came across this strange thing yesterday!
The wires to the multi socket all original. I have been informed that this may have been a prototype, don't know.
Mick. |