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Old 15th Jan 2012, 9:03 pm   #61
PJL
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Default Re: Bush AC34, no sound.

I have looked at the voltages and I will try to explain the problem ones:

1) UL41 pin 1 and pin 8 are the heater. They are showing a heater voltage of 18V and not the 45V it is supposed to be. As a consequence all the other heater voltages are high. It could be:-

a) the valve had not warmed up b) the valve is the wrong type c) The valve has a heater short

2) UL41 pin 2 is showing as 0.9V. This is the anode and it should connect to the output transformer and read roughly 250V. This means the output transformer is a) not connected b) open circuit

3) UL41 pin 4 has a green wire attached showing as 257V. Pin 4 is not used so it is being used as a tag to hold a component which appears to go to pin 6 grid? The component looks like a resistor so the grid is at 257V and it should be 0V.
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Old 15th Jan 2012, 9:49 pm   #62
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Default Re: Bush AC34, no sound.

First, make sure that the valves are in the right sockets. Starting at the mains socket at the right and facing towards you...

The first two are the UY41 and the UL41. The UY41 is Behind the UL41 with the mains socket towards you.
The next one is the UBC41.
Then a UF41.
Then, Behind the first IFT is the UCF42.

If there are no volts on the Anode of the UL41 - Pin 2. - then either the wiring is faulty, the transformer is faulty (and now possibly the UL41 too!) or there are no volts coming from the rectifier. If there are volts on Pin 5 and not Pin 2, then you may well have a problem.

Cheers,

Steve P.
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Old 15th Jan 2012, 9:54 pm   #63
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Default Re: Bush AC34, no sound.

Nothing wrong with the rectifier, as there's 178 VDC on pin 5 (Screen Grid) of the UL41.
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Old 15th Jan 2012, 10:06 pm   #64
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Default Re: Bush AC34, no sound.

Going back to the original post would it be worth putting all the old valves back to see if this fault has been introduced with the new? valves?

Stephen
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Old 15th Jan 2012, 10:33 pm   #65
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Default Re: Bush AC34, no sound.

Hi PJL
Yes,the valve in the second socket from the transformer is UL41
All The valves did light up when the magic eye was disconnected
I have not replaced the original wires on the output transformer but I have reconnected them.
How are the pins numbered? I am only identifying them by coloured wire.
Thanks
Bill
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Old 15th Jan 2012, 10:42 pm   #66
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Default Re: Bush AC34, no sound.

Get the valve facing toward you, pins toward you. There is a pip in the glass. From the pin, go clockwise...

The pin immediately after the pip is Pin 1, etc.

If the valves lit up when the wires to the Magic Eye are disconnected, then either it's wired separately or there's a problem here.

If you have had the wires off the O/P transformer and ran the set, then oh dear... Did you connect them right and have you checked the wires on a meter?

Cheers,

Steve P.
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Old 15th Jan 2012, 10:44 pm   #67
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Default Re: Bush AC34, no sound.

This set has a plug which connects the ouput transformer primary and the dial lamps to the chassis.
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Old 15th Jan 2012, 11:16 pm   #68
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Default Re: Bush AC34, no sound.

Thanks for the pin info,
Any wires I disconnected I carefully labelled them to ensure they were reconnected correctly. There is a plug on the side of the chassis which is intact,and is connecting the dial bulbs and speaker transformer
Thanks lads
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Old 15th Jan 2012, 11:42 pm   #69
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Default Re: Bush AC34, no sound.

We need you to answer each of the questions in my post #60. You have still not answered question 2) properly. Did you disconnect the magic eye?
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Old 16th Jan 2012, 9:34 am   #70
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Default Re: Bush AC34, no sound.

I've just read through all the posts in this now extremely long thread.

To summarize, the set is an export model, probably electrically similar to an AC34, but with a magic eye. It has a mains transformer, but uses 'U' series valves with the heaters in series.

Work done on the set is changing the waxies and electrolytic capacitors plus the renewal of some wiring. All valves have been changed except the UL41.

Problem is no sound.

Valves apparently light up even when the plug which connects the magic eye heater into the chain is disconnected. This indicates a fault somewhere in the heater chain or possibly a heater short or heater to cathode short in a valve.

HT is present on the screen grid of the UL34, but not on the anode. This indicates a fault in the output transformer winding or the wiring to it. In an earlier post the resistance of the primary winding was said to be 85 ohms. This is low, but wouldn't prevent HT appearing on the anode of the UL34.
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Old 16th Jan 2012, 9:42 am   #71
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Default Re: Bush AC34, no sound.

Bill. The output transformer and its wiring is easy to check without the need to connect the set to the mains. Unplug the plug which connects to the loudspeaker wiring and the dial lamps.

Meter on ohms range, one lead to each of the output transformer tags which doesn't go to the speaker. What is the reading? If it's infinite the transformer is open circuit.

Assuming you get a reading, trace the wires from the output transformer back to the plug. Measure the resistance between the two plug pins the wires go to. You should get a similar reading. If the reading is infinite there's a problem with the wiring to the plug.
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Old 16th Jan 2012, 4:00 pm   #72
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Default Re: Bush AC34, no sound.

Hi PJL,

In response to post 60, resistance from pin 7, cathode, yellow wire, to chassis. 266.2ohms.
Resistance from pin 2, anode, blue wire to capacitor terminal 11.37 mohms.

Post 61.
The radio was switched on for some time so the valve should be warm enough, it is marked UL41.
Pin 2, anode, blue wire is connected to speaker transformer through the small plug on the side of the chassis. There is also a spur to the tone control from the plug.
Pin 4, internal connection, green wire, is linked to pin 6, control grid, via resistor, also connected to card.

Looking from the back of the chassis the valve line up is as follows
From the right next to the mains trans
UY41
UL41
UBC41
UF41
UF41
UCH42 to the front of chassis

Having disconnected the small plug the reading between the 2 speaker transformer tags is 0.78 kohms steady. Tracing back the wires the reading is 0.77 kohms

Bill

Last edited by Station X; 16th Jan 2012 at 4:21 pm. Reason: Electrode names added.
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Old 16th Jan 2012, 4:11 pm   #73
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Default Re: Bush AC34, no sound.

The reading on ouput transformer tags and at the end of the leads looks reasonable. Plug it into the socket and follow the wires from the socket pins. One should go to pin 2 of the UL41 and other to one of the smoothing capacitors (the ones in the big can), possibly via a 10K resistor. Check that you also see 0.78K, or maybe 10.78K between these points.

I'll leave PJL to respond to your other readings.
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Old 16th Jan 2012, 7:21 pm   #74
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Default Re: Bush AC34, no sound.

1) There are two red wires, one from the speaker socket and one from the electrolytic. I would expect these to be connected together.
2) When you measured the voltage on pin 4 of the UL41 (green wire) it read 257V which is very very wrong. It is even higher than the screen grid pin 5.

a) Can you let us know if you have unsoldered any of these wires?
b) Can you measure the resistance between the two red wires because it should read zero

As we can not rely on the circuit diagram, we need you to draw out the wires to the tag board and any links on the board so we can work out what is going on. We only need from the transformer end to the gap at this stage. You might be able to do this with pictures from the side.

You should not power the set up again until we have everything sorted. I am fairly sure you will need a new UL41.
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Old 16th Jan 2012, 8:41 pm   #75
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Default Re: Bush AC34, no sound.

I'm fairly certain I have a working UL41 which I could send to Bill FOC. I'll dig it out and test it. I really want to hear that this set is working soon!

Apart from that I'll leave sorting the radio in PJL's capable hands.
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Old 16th Jan 2012, 11:37 pm   #76
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Default Re: Bush AC34, no sound.

Hi PJL,

Attached is a photo following Graham's info.
The red wire from the speaker is connected to a 50nF capacitor. I did replace the wax capacitor at this point but I am sure I put everything back as I found it. I only did one piece of soldering at a time. It does not appear to be connected to anything else from this point. There is a reading of 8.33 mohms between the two red wires.
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Old 16th Jan 2012, 11:53 pm   #77
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Default Re: Bush AC34, no sound.

I am fairly sure you have accidentaly removed a link between the two red wires.

We will need the drawing or photo of the tag board showing all the connections around this area as there is also something wrong with the wiring for the green wire.

Alternatively you can check it against the AC34 schematic that Graham has put in post 34. The .05 would suggest it is C34 and next to it is R20 which should be 10K.
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Old 17th Jan 2012, 12:32 am   #78
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Default Re: Bush AC34, no sound.

The resistor is almost certainly R20 which is rated at 2W. However the tag strip layout drawing for the AC34 shows that the adjacent capacitor is C29 which is 50nF.

The resistor connected between pins 4 and 6 of the UL41 will be the grid stopper R17 47K. If the green wire is on the right tag it should go to R16 and C33 at the other end of the tag strip.
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Old 17th Jan 2012, 9:34 am   #79
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Default Re: Bush AC34, no sound.

Hi Graham, I only have trader 1147 and the tag strip layout is very different so I'll leave it to you to check for circuit errors.

The UL41 has almost certainly suffered melt down and the heater has shorted. I looked at the other voltages and one of the UF41 had no anode voltage but it is possible this is the RF amp and switched on SW. No sign of local oscillation as the triode grid is zero.
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Old 17th Jan 2012, 11:09 am   #80
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Default Re: Bush AC34, no sound.

PJL. I've emailed you.

Manufacturer's Sheet:-
R20 Smoothing resistor 10K 2W. C29 0.05uF negative feedback.

Trader Sheet:-
R24 Smoothing resistor 10K 2W. C28 0.05uF negative feedback.
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