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Old 18th Jan 2012, 9:06 am   #101
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Default Re: Bush AC34, no sound.

That's going to depend on whether Bill has put a link between the two red wires on the tag strip.

I also think it's important to check for faults in the heater chain before powering up. Remember that some of the valves light up even though the magic eye heater is disconnected from the chain.

There's also the problem of the low resistance between HT positive and the UL41 pin 4. It's possible this is down to Bill's meter charging up the smoothing caps.
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Old 18th Jan 2012, 9:24 am   #102
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Default Re: Bush AC34, no sound.

Hi Steve, we are trying to avoid switching it on as there were no volts on the UL41 anode and 257V on the grid. All measurements are resistance.
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Old 18th Jan 2012, 10:46 am   #103
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Default Re: Bush AC34, no sound.

Quote:
Originally Posted by PJL View Post
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.
Don't have another just yet
I.D. on capacitor is 10nf ,1500 vdc

Resistance without valve from green to chassis 383.4 k ohms
I will try Maplin to day for cap.
Bill
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Old 18th Jan 2012, 10:50 am   #104
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Default Re: Bush AC34, no sound.

Quote:
Originally Posted by Station X View Post
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.
Reading on pins 73.4 ohms
Bill
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Old 18th Jan 2012, 11:44 am   #105
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Default Re: Bush AC34, no sound.

Quote:
Originally Posted by Pepelephew
Resistance without valve from green (pin 4) to chassis 383.4 k ohms
That's a lower reading than expected. What do you get if you measure the resistance of R17? It should be 470K. If it's lower disconnect one end and check again.

Quote:
Originally Posted by Peplelephew
Reading on pins 73.4 ohms.
If that's 73.4 ohms between pins 1 and 8, then the reading is a good one.

As an additional check make sure that theres no continuity from pins 1 and 8 to any of the other valve pins.
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Old 18th Jan 2012, 12:38 pm   #106
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Default Re: Bush AC34, no sound.

If there are no volts on the anode, then trace it back. You can do thiswith the set turned off and on Ohms mode!

There is a bigger problem here that needs to be sorted. From Pin 2, go back to the Output Transformer. One pin should be lower than the other on the O/P transformer, by about 500 Ohms. The winding you want is about 500 ohms if you go across it. If this is OK, and there's no link to the valve, then follow it through and find out where it's going astray.

If you can't get a reading on the O/P transformer, then it's looking like the O/P transforner is faulty, which will cause the 'No Sound' symptom and also kill the UL41.

There should, at the end of the day, be about 500 Ohms between Pin 2 of the UL41 and Pin 7 of the UY41.

Remember the system ; Start at the Rectifier and go back towards the aerial, putting right each fault as you find it..

Cheers,

Steve P.
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Old 18th Jan 2012, 1:08 pm   #107
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Default Re: Bush AC34, no sound.

In post #72 the resistance of the output transformer primary was measured as 780 ohms. I have no doubt that if a link was inserted between the two red wires on the tag strip then HT would appear on the anode of the UL41.

However we don't want to power up the set and blow all the heaters because of a possible earth fault in the heater chain.
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Old 18th Jan 2012, 1:36 pm   #108
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Default Re: Bush AC34, no sound.

At the moment I'm trying to get the correct diagram for this set. Not having a lot of luck.

All the valves out and the dial lights out. Measure 1 and 8 on all pins (3 and 4 on the Magic Eye) to earth. One pin (V3) and one pin V5 should give a reading, the rest shouldn't.

Check the readings on all the valves (Ohms) and see what they are. Clean the sockets while you're about it. 1 and 8 should have a reading, no other pin should have a reading between it and Pins 1 and 8. The UL41 might have a reading of several Kiloms though.

The fault in a valve maght not occur until it's warm though.

Was there a link between those two wires before?

Cheers,

Steve P.
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Old 18th Jan 2012, 3:26 pm   #109
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Default Re: Bush AC34, no sound.

Hang on there Steve. Graham is trying to find out why the grid was at 257V before we go applying power to the poor thing!

The resistance checks seem to be showing a problem. The UL41 has probably failed as it has been run with the anode disconnected and possibly a grid current.
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Old 18th Jan 2012, 3:35 pm   #110
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Default Re: Bush AC34, no sound.

Lets summarise these resistance readings:
1) UL41 in, pin 4 to HT = 416K
2) UL41 out, pin 4 to HT = 395K
3) UL41 in, C26 disconnected, pin 4 to HT = 780K
4) UL41 in, pin 4 to chassis = 383K

Is there a problem with leakage in the tag strip? There appears to be some corrosion on the terminals. Is it a problem with the meter? I would be tempted to put the missing link in, turn on, and monitor the UL41 grid voltage and switch off if it starts rising above 2V.
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Old 18th Jan 2012, 5:48 pm   #111
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Default Re: Bush AC34, no sound.

Hi Lads,
I have a new capacitor for c21...10 NF +/-5% 1500 vdc
Should I put that in and should I put in the link between the 2 red wires

Bill
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Old 18th Jan 2012, 6:21 pm   #112
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Default Re: Bush AC34, no sound.

Bill.

I don't know whether you saw Steve P's reply before he deleted it?

Replace C26.

Link the two red wires on the tag board.

Before we apply power I'd like to know the resistance of R17 when one end is disconnected. When connected it read 383K ohms. It should read 470K ohms.
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Old 18th Jan 2012, 6:34 pm   #113
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Default Re: Bush AC34, no sound.

Ok Graham,
I will work on that and report
Bill
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Old 18th Jan 2012, 8:34 pm   #114
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Default Re: Bush AC34, no sound.

Hi Graham,
New cap in place and link placed between 2 red wires.......where do I measure the resistor r17 from please
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Old 18th Jan 2012, 8:42 pm   #115
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Default Re: Bush AC34, no sound.

See the sketch in post #89 and the picture in post #87. Locate R17 on the tag board. Disconnect whichever end's most convenient and put your clips on the resistor leads.
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Old 18th Jan 2012, 9:01 pm   #116
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Default Re: Bush AC34, no sound.

Hi Graham,
Measuring the smaller resistor of the 2 in pic.
Connected 0.647 mohms
Disconnected 0.686 mohms
Bill
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Old 18th Jan 2012, 9:23 pm   #117
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Default Re: Bush AC34, no sound.

If it's R17 it will be colour coded yellow, violet, yellow 470K.

If it's measuring 686K it's gone high in value and could do with replacing. Don't worry about it for the moment though, just reconnect it.

Right leave the speaker and magic eye plugs disconnected for the moment. Switch on and check whether any valves light up. There should be NO valves lit.

If valves are lit switch off and come back here for further advice.

If NO valves are lit, switch off and reconnect the plugs. Meter on DC volts. Negative lead to chassis and positive lead to UL41 pin 6 (Control Grid). Switch on. If reading rises to more than 2V come back here for further advice.

If reading is less than 2V take voltage readings on all pins of UY41 and UL41. Report results here.
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Old 18th Jan 2012, 10:04 pm   #118
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Default Re: Bush AC34, no sound.

Graham,
First test....no valves lit with magic eye,speaker and dial lights disconnected.
Second test,all reconnected...reading of 198.2.mv from pin 6 (resistor between this pin and pin 4 ,green wire).
Bill
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Old 18th Jan 2012, 10:07 pm   #119
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Default Re: Bush AC34, no sound.

Looks good. Let's have some voltage readings for the UY41 and UL41
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Old 18th Jan 2012, 10:24 pm   #120
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Default Re: Bush AC34, no sound.

Graham,
voltage readings, black to chassis, red to pin.

UY41
Pin 1 brown. 158.6 VAC (Heater)
Pin 2 red 257.5 VDC (Anode)
Pin 7.red 318.8 VDC (Cathode)
Pin 8 brown 116.1 VAC (Heater)

UL41
Pin 1 brown 116.2 VAC (Heater)
Pin 2 blue 319.5 VDC (Anode)
Pin 4 green 378.3 mV (Spare pin used to terminate grid stopper resistor)
Pin 5 red 182.7 VDC (Screen Grid)
Pin 6 298.1 mV (Control Grid)
Pin 7 yellow (Cathode)
Pin 8 brown 98.4 VAC (Heater)

Bill

Last edited by Station X; 18th Jan 2012 at 10:32 pm. Reason: Electrode designations added.
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