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Old 5th Jan 2012, 1:46 pm   #41
Pepelephew
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Default Re: Bush AC34, no sound.

thanks Graham,
I am in work at the moment,I will check the wiring this evening and let you know.
Bill
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Old 5th Jan 2012, 9:36 pm   #42
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Default Re: Bush AC34, no sound.

Graham,
There is a blue wire from the first pin to the plug and socket and in turn to the transformer on the speaker. My meter is subdivided and in the ohms section it is graded 2m,200k,20k,2k and 200. I think I may be measuring using the wrong grade.I will go over this again.
I measured some of the resistors,some matched the colour codes near enough others were
Off somewhat.
I will try and get voltage measuremeents on the valves this weekend
Thanks for your patience
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Old 5th Jan 2012, 9:38 pm   #43
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Default Re: Bush AC34, no sound.

Hi Pete ,
I will follow your lead and see what I come up with
Thanks
Bill
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Old 5th Jan 2012, 9:42 pm   #44
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Default Re: Bush AC34, no sound.

When using your meter to measure resistance start on the highest range, 2Mohm in your case, and work down the ranges until you get a sensible reading. If the resistance is too high for the range eg trying to measure 500 ohms on the 200 ohms range, you should see some kind of over range indication on the display.
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Old 10th Jan 2012, 10:53 pm   #45
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Default Re: Bush AC34, no sound.

Hi all,
I have taken readings of the voltages on the valves. I have indicated on the diagram the wire colour and the voltage. I have also checked the resistors and have found as far as I can see all are within tolerance. Hope you can make out my drawings.
thanks
bill
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Old 10th Jan 2012, 11:05 pm   #46
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Default Re: Bush AC34, no sound.

OK transcribing readings.

V5 UY41 Rectifier
Pin 1 168 VAC (Heater)
Pin 2 27 0VAC (Anode)
Pin 7 18.6 VDC (Cathode)
Pin 8 168 VAC (Heater)

If these readings are correct there is no voltage across the heater. The readings of pins 1 and 8 should differ by about 31 Volts. First question, is the valve lit? Second question, can you measure the voltage between pins 1 and 8 which will be either side of the gap in the pins. You should see about 31 VAC.

If the reading on pin 7 is indeed 18.6V rather than 186V the HT is very low, but that would be hardly surprising if the heater isn't lit.

You show on your drawing a UCL41. As far as I know there is no such valve, so perhaps it's a UL41? I can't make head or tail of the readings except to note that there are no AC voltages on this valve. This makes me think the heater chain is broken somewhere. You could try removing each valve in turn and checking for continuity between pins 1 and 8 which are connected to the heaters.
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Old 10th Jan 2012, 11:54 pm   #47
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Default Re: Bush AC34, no sound.

Final thought for tonight. The heaters appear to be wired in brown wire. Is it possible that the voltages on pins 1 and 8 of the UL41 are in fact AC rather than DC?

Assuming that the heaters are wired as shown for the AC34, then everything points to a break in the heater chain between V4 and V5. This is unlikely though so check the heater continutiy of all valves as suggested.
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Old 11th Jan 2012, 10:03 pm   #48
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Default Re: Bush AC34, no sound.

Hi Graham,
Checked the readings again and found both brown wired pins are reading the same 169.2v ac each. The red wired pin (7) is reading 22.0 v dc. The other valve is indeed UL41 and mr error again both brown wired pins are reading 168.2 v ac.
On the green wired pin on this valve I get a strange reading of -53.0 v dc??
Not sure how to get a reading between pins 1 and 8 on UY41 using my probes.
When I first powered up there was a very bright glow from valves Uy41 and UCH42 which then subsided just as quick to a steady glow.
Although UL41 is getting warm it does not appear to be lighting up.The faint glow I can see is I believe a reflection from UY41
Thanks
Bill
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Old 11th Jan 2012, 10:30 pm   #49
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Default Re: Bush AC34, no sound.

Bill.

There's something strange going on here. The valves in this set have their heaters wired in series. This means that any break in the heater chain should cause all the valves to go out.

The fact you're measuring the SAME AC voltage on both pins of each valve indicates that the heaters are drawing no current, yet they're lighting up. That's impossible.

Let's try another approach. Switch off the set and set your meter to AC volts. Clip either lead of your meter to one of the brown wires leading from the mains transformer to the heater chain. Now switch on the set and probe the other brown wire on the mains transformer. You should see a high voltage.

Now follow the heater chain which starts at the brown wire your meter lead is clipped to. It will go to pin 1 or 8 of a valve, then leave on the other pin and go to the next valve pin 1 or 8 and so on until it returns to the mains transformer.

Probe each valve pin as you come to it and post the readings (12 in all) here.
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Old 11th Jan 2012, 10:49 pm   #50
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Default Re: Bush AC34, no sound.

Heater pin readings with respect to chassis as transcribed from Bill's drawing and updates.

UL41 168.2 VAC both pins.
UY41 168 VAC both pins.
UF41 (A) 15.9 VAC both pins.
UF41 (B) 15.9VAC and 15.8 VAC
UBC41 10.5 VAC and 10.3 VAC
UCH42 10.2 VAC both pins.
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Old 12th Jan 2012, 12:14 am   #51
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Default Re: Bush AC34, no sound.

Looks like this radio has a magic eye that, probably, can be disconnected when removing the chassis. Is it reconnected when the voltage readings are taken?

David
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Old 12th Jan 2012, 12:26 am   #52
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Default Re: Bush AC34, no sound.

The picture indicates the heater chain is in the following order UCH42 UBC41 -UM34- UF41 UF41 UL41 UY41.

The heater voltages are obviously wildly wrong but they are never going to be that accurate as there will be some DC component due to the half wave rectification.

A heater cathode short might create a few problems so it might be an idea to disconnect both ends of the heater chain from the mains transformer and do some resistance checks along the heater chain and to chassis.
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Old 12th Jan 2012, 12:58 am   #53
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Default Re: Bush AC34, no sound.

Here's what each heater voltage is, in order based on PJL's list.

UY41 - 31 Volts
UL41 - 45 Volts
UF41 - 12.6 Volts
UF41 - 12,6 Volts.
UM34 - 12.6 Volts.
UBC41 - 14 Volts.
UCH42 - 14 Volts.

All take 0.1 Amp.

If all the valves are lit - check! - then the total voltage drop across the valves should be 141.8 Volts.

Looking at the readings you have, I would take each valve out, one at a time please, clean the pins and spray some switch cleaner into the sockets. If you have a meter, switch to Ohms and connect the meter between pins 1 and 8 of the valves, making sure you get a reading. If you don't, clean the pins and check again. The UM34 is different as the heater is between pins 2 and 7. There's a diagram here:

http://www.radiomuseum.org/tubes/tube_um34.html

They are the pins 2 up from the pin on the centre spigot, all else is the same.

(I'm a bit surprised that a set with a mains transformer uses these valves, but it does happen. A Pilot set here does actually. Pilot Jack I think.)

If the valves are lit, the heater chain is OK. If some are lit but not others, switch off quick. If they are all out, check the heaters, sockets, wiring and the series resistor.

All LT voltages will be AC. HT voltages will be DC.

If they are all lit, pay attention to the HT line. The UL41 should have HT on 2 pins. One goes through the primary of the Output Transformer. If they are both dead, go back to the rectifier. If one is dead, the UL41 is probably knackered and so is either the wiring to or the O/P transformer primary. Another check - is the UM34 lit up. It might be very dim though - again check closely.

That's enough for now - Check and come back.

Cheers,

Steve P.
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Old 13th Jan 2012, 10:52 pm   #54
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Default Re: Bush AC34, no sound.

Thanks everyone for your help, I will work through your suggestions and report back...as regards Radio Dave I remove the chassis from the cabinet and disconnect magic eye,dial bulbs and speaker transformer . They are not connected while I am checking voltages??

Bill
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Old 13th Jan 2012, 10:58 pm   #55
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Default Re: Bush AC34, no sound.

Well, that will explain why it's not working then! You must have ALL these items connected when you measure voltages. Without the magic eye the heater chain is broken.

The only odd thing is you were reporting the UY41 was glowing even with the magic eye disconnected. If this was the case you definitely have a heater cathode short.
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Old 14th Jan 2012, 3:14 pm   #56
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Default Re: Bush AC34, no sound.

Thanks PJL
The reason I disconnected from the cabinet was to give me much easier access to the underneath of the chassis not realising it would give me wrong readings. I am not fully sure that UL41 is glowing....it is very faint and could be a reflection.I will measure voltages again
Thanks
Bill
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Old 14th Jan 2012, 9:09 pm   #57
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Default Re: Bush AC34, no sound.

Don't worry, it's the sort of thing we all do. I've lost count of how many times I've wondered why a set isn't working only to find I haven't put the valves back. You learn more from your mistakes than when you get it right first time.

- Joe
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Old 14th Jan 2012, 10:15 pm   #58
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Default Re: Bush AC34, no sound.

Just to make it clear. If the UY41 (or any of the valves) was lit without the magic eye connected then you have a serious problem and should not power the set up.

Either the UY41 or UL41 will have a heater cathode short and will need replacing.
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Old 15th Jan 2012, 8:11 pm   #59
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Default Re: Bush AC34, no sound.

Hi Lads,
I have rechecked the valve voltages,this time with everything connected.
Drawing attached. I hope they make some sense this time.
All the valves appear to be glowing but I am not convinced about UL41, it is very faint and could be a reflection from the valves either side.
Thanks Lads
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Old 15th Jan 2012, 8:35 pm   #60
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Default Re: Bush AC34, no sound.

You need to answer these questions:
1) Switch it OFF!
2) Did ANY of the valves light up when you had the magic eye disconnected?
3) Please confirm the valve in the socket 2nd along from the mains transformer is a UL41
4) Measure the resistance from the UL41 pin 7 to chassis
5) Measure the resistance from UL41 pin 2 to the terminal of the big electrolytic capacitor with the red lead (goes to the UY41) but no resistor
6) Confirm you have replaced the wires to the output transformer

I am still looking at the other voltages but you have quite a few problems so don't power it up again until we have checked the wiring.
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