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Old 17th Jan 2012, 11:32 am   #81
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Default Re: Bush AC34, no sound.

Using TRADER SHEET component designations.

The red wire which terminates on C29 shouldn't be there, as C29 is in an entirely different part of the circuit. It should in fact go to R20.

With any luck the other red wire on R20 goes to C36 and V5 pin 7.

Just checked the picture in post #74. The other wire does indeed go to C36 and V5 pin7.

Where does the green wire on the UL41 pin 4 go to?
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Old 17th Jan 2012, 4:37 pm   #82
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Default Re: Bush AC34, no sound.

Check the following:

UL41 -

1 and 8 - Heater.
3 and 7 - Connected to R21 and then Deck, Also R19. R21 is 220 Ohms, R19 is 1 Kilohm.
Pin 6 - Goes to R18 (47K) then C26 (THAT capacitor.)
Pin 5 goes to HT (C33 - 16uF)
Pin 2 - Goes to the Output Transformer via that plug and socket and then to C32.

C33 and C32 are the smoothing can and these caps are linked together using a 10 k resistor,

If you needt the colour codes from the resistors, then they are here:

http://www.vintage-radio.com/repair-...resistors.html

As the wire we don't know about is Green, maybe it should be on 3 rather than 4. What's on the other end of it? Pin 4 is not used in the UL41, but it is sometimes used as an anchor point (Bush DAC90A!) but if there's only one wire there, then it is wrong.

The component values here are Trader ones.

Cheers,

Steve P.
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Old 17th Jan 2012, 4:53 pm   #83
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Default Re: Bush AC34, no sound.

We need to be careful as the circuit is not for this radio. The volume control is to earth so this set does not have -ve feedback or C29.

Bill, please confirm the following:
1) There is no other connection to the top of the 0.05uF capacitor (just the red wire to the output transformer socket).
2) The bottom of the 0.05uF capacitor is connected to the blue wire going to the tone control
3) Measure the resistance from UL41 pin 4 (green wire) to UY41 pin 7 (red wire)

My thinking at the moment is a) The UL41 pin 4 was really 0.257V as I just can't see where 257V could come from b) The 0.05uF is the tone control capacitor and we are missing the link
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Old 17th Jan 2012, 5:34 pm   #84
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Default Re: Bush AC34, no sound.

Bill.

I've located and tested a used UL41. It ain't the best UL41 I've seen, but it certainly works. Yours FOC should you need it. Best get the other problems sorted first though.
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Old 17th Jan 2012, 6:15 pm   #85
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Default Re: Bush AC34, no sound.

Hi lads,
Here are some photos of the area concerned and a very rough sketch.
I have just read the latest posts and I will check those readings.

Bill
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Old 17th Jan 2012, 6:32 pm   #86
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Default Re: Bush AC34, no sound.

Hi PJL,
There is no other connection from the top of the cap. the bottom is connected by blue wire to tone control.
The resistance between pins is 0.416 m ohms
Should I recheck the voltage on the green wire?

Bill
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Old 17th Jan 2012, 6:40 pm   #87
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Default Re: Bush AC34, no sound.

I have modified the schematic for the AC34 to make it closer to yours.

Let's wait for Graham to check our thinking.

Then:
1) Put a link between the two red wires I have marked before
2) Power up and measure the UL41 pin 4 (green) and UL41 pin 2 (blue) again

PS: The UL41 is faulty and is putting stress on the other valves so we must not apply power for long.
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Old 17th Jan 2012, 6:46 pm   #88
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Default Re: Bush AC34, no sound.

Measure the 'Blue to Plug' on Pin 2 of the UL41 while you're about it. If there's nothing here, then there are no volts on the anode of the UL41.

Cheers,

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Old 17th Jan 2012, 6:59 pm   #89
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Default Re: Bush AC34, no sound.

PJL.

I agree with your thinking re the Red wires. They can be linked.

Green wire comes from the grid stopper resistor and goes to what I assume is the grid leak resistor the other side of which would go to chassis. Common to the chassis point is the cathode bias resistor which goes to the cathode (pin 7) of the UL41. So we need to confirm that this common point is indeed connected to chassis.

Bill. See the two small resistors to the right of the large resistor on your tag strip drawing? Measure the resistance from their common point to chassis. With any luck it'll be very low ie less than an ohm. If higher trace any wire on the common tag to see where it goes to.
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Old 17th Jan 2012, 7:50 pm   #90
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Default Re: Bush AC34, no sound.

Hi Graham,
The 2 small resistors.... Measuring from where they join to chassis. 0.000 ohms
Bill
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Old 17th Jan 2012, 7:55 pm   #91
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Default Re: Bush AC34, no sound.

Quote:
Originally Posted by Pepelephew View Post
Hi PJL,
The resistance between pins is 0.416 m ohms
Bill
Graham, I agree something may still be wrong. There is a 470K to earth but this is measuring less than 470K to HT. Of course the UL41 has been toasted so it's possible there is leakage.

Bill, after you have done Graham's test can you pull out the UL41 and repeat the resistance check between UL41 pin 4 (green) and UY41 pin 7 (red).
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Old 17th Jan 2012, 8:32 pm   #92
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Default Re: Bush AC34, no sound.

Quote:
Originally Posted by Pepelephew
Hi Graham,
The 2 small resistors.... Measuring from where they join to chassis. 0.000 ohms
That's good.

Quote:
Originally Posted by Pepelephew
The resistance between pins is 0.416 m ohms (HT+ to UL41 pin 4)
That's bad. Let's see what result you get with the UL41 pulled out of its socket.
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Old 17th Jan 2012, 8:42 pm   #93
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Default Re: Bush AC34, no sound.

I am getting 395.2 k ohms
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Old 17th Jan 2012, 8:46 pm   #94
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Default Re: Bush AC34, no sound.

OK. Disconnect one end of C26 10NF and measure again.
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Old 17th Jan 2012, 9:30 pm   #95
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Default Re: Bush AC34, no sound.

Hi graham,
I am getting 0.78 m ohms 780K
Bill
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Old 17th Jan 2012, 9:32 pm   #96
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Default Re: Bush AC34, no sound.

C26 needs to be replaced. Have you replaced any capacitors?

PS: We are making good progress even if it doesn't feel like it!
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Old 17th Jan 2012, 10:23 pm   #97
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Default Re: Bush AC34, no sound.

Hi PJL,
Yes
When I started this project I replaced some of the old wax capacitors, this one included. I presume the fault in this set caused damage to even a new capacitor
Bill
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Old 17th Jan 2012, 11:46 pm   #98
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Default Re: Bush AC34, no sound.

What is the voltage range of the capacitor? Do you have another?

I am not too sure what is going on. Measure the resistance from UL41 pin 4 (green) to chassis.
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Old 17th Jan 2012, 11:52 pm   #99
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Default Re: Bush AC34, no sound.

Quote:
Originally Posted by PJL
I am not too sure what is going on. Measure the resistance from UL41 pin 4 (green) to chassis.
Do that with the UL41 unplugged, so any faults with it do not affect the reading.

You can check the health of the UL41 heater by unplugging it and measuring the resistance between pins 1 and 8 which are either side of the pip in the glass. Measure on the valve, not on the holder. Make sure your probes or clips don't touch each other. Expect a reading of about 70 ohms. That's what I measured on a sample.
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Old 18th Jan 2012, 1:25 am   #100
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Default Re: Bush AC34, no sound.

Please answer just one question for me. Are there HT volts on Pin 2 of the UL41.

Cheers,

Steve P.
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