I came across this strange thing yesterday! - UK Vintage Radio Repair and Restoration Discussion Forum

vinrads · 20th Apr 2021, 9:15 am

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.

kalee20 · 20th Apr 2021, 12:14 pm

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!

vinrads · 20th Apr 2021, 2:00 pm

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.

Hartley118 · 20th Apr 2021, 3:47 pm

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

vidjoman · 20th Apr 2021, 4:50 pm

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.

vidjoman · 20th Apr 2021, 5:14 pm

Found the diagram of the mains input. Probably clearer to see than my description.

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Lucien Nunes · 20th Apr 2021, 6:30 pm

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.

vinrads · 20th Apr 2021, 9:19 pm

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.

vidjoman · 20th Apr 2021, 10:11 pm

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.

vinrads · 21st Apr 2021, 8:47 am

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.

vidjoman · 21st Apr 2021, 10:55 am

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.

vinrads · 21st Apr 2021, 12:36 pm

The wires to the multi socket all original. I have been informed that this may have been a prototype, don't know.

Mick.

20th Apr 2021, 9:15 am	#1
vinrads Dekatron Join Date: Feb 2009 Location: Chesterfield, Derbyshire, UK. Posts: 3,762	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
kalee20 Dekatron Join Date: Feb 2007 Location: Lynton, N. Devon, UK. Posts: 7,081	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
vinrads Dekatron Join Date: Feb 2009 Location: Chesterfield, Derbyshire, UK. Posts: 3,762	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
Hartley118 Nonode Join Date: Aug 2015 Location: Cambridge, Cambs. UK. Posts: 2,198	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 __________________ BVWS Member

20th Apr 2021, 4:50 pm	#5
vidjoman Dekatron Join Date: Jun 2013 Location: East Sussex, UK. Posts: 3,326	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
vidjoman Dekatron Join Date: Jun 2013 Location: East Sussex, UK. Posts: 3,326	Re: I came across this strange thing yesterday! Found the diagram of the mains input. Probably clearer to see than my description.

20th Apr 2021, 6:30 pm	#7
Lucien Nunes Rest in Peace Join Date: Apr 2008 Location: London, UK. Posts: 2,508	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.

20th Apr 2021, 9:19 pm	#8
vinrads Dekatron Join Date: Feb 2009 Location: Chesterfield, Derbyshire, UK. Posts: 3,762	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.

20th Apr 2021, 10:11 pm	#9
vidjoman Dekatron Join Date: Jun 2013 Location: East Sussex, UK. Posts: 3,326	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.

21st Apr 2021, 8:47 am	#10
vinrads Dekatron Join Date: Feb 2009 Location: Chesterfield, Derbyshire, UK. Posts: 3,762	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
vidjoman Dekatron Join Date: Jun 2013 Location: East Sussex, UK. Posts: 3,326	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
vinrads Dekatron Join Date: Feb 2009 Location: Chesterfield, Derbyshire, UK. Posts: 3,762	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.