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Old 19th Jun 2017, 11:05 pm   #141
DonaldStott
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Default Re: Bush A.C.91

Using a 60W bulb in the lamp limiter.

Quote:
Originally Posted by Station X View Post
This set uses an auto-transformer. Check the total DC resistance of the windings. It should be around 210 ohms.

Does the lamp in the lamp limiter still glow brightly if you remove a valve?
Measuring from the 250v tap to 0v (ground) I'm only getting 172 ohms?

Which valve should I remove to test this?
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Old 20th Jun 2017, 9:30 am   #142
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Default Re: Bush A.C.91

To get a realistic resistance reading you will have to remove one of the valves, any valve will do.

EDIT: Last time you checked the transformer the resistance reading appeared to be ok, posts 45 to 48:

http://www.vintage-radio.net/forum/s...=132722&page=3

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Last edited by ms660; 20th Jun 2017 at 9:42 am.
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Old 20th Jun 2017, 9:48 pm   #143
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Default Re: Bush A.C.91

Some preliminary readings after a hard day at work and other challenges!

Valves removed.

Auto-transformer 250v tap to ground : 203 ohms

Output-transformer with speaker wires disconnected.

Primary : 549 ohms

Secondary : can't get a reading!

Surely this hasn't gone open circuit as well - what could have caused that?

Before disconnecting the speaker wires when I measured the Primary the speaker did crackle a bit. The speaker itself is measuring 3.3 ohms.
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Old 20th Jun 2017, 10:08 pm   #144
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Default Re: Bush A.C.91

Auto-transformer looks OK.

Output transformer primary looks OK. They generally fail short-circuit rather than high resistance. If the secondary is open-circuit the set won't work.

However an open circuit output transformer doesn't explain why the test lamp glows brightly. Does it still glow brightly with the valves removed?
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Old 20th Jun 2017, 10:15 pm   #145
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Default Re: Bush A.C.91

Output transformer secondary will be almost zero ohms, if the speaker crackles when you test the primary it must be OK on the secondary and the speaker.
Your quote "can't get a reading" is ambiguous, a short circuit is zero ohms, no reading, an open circuit is high infinitely so no reading again. Better to say a very low ohms or a infinite resistance reading then its clear.

Those resistance readings seem OK, if you suspect the mains transformer has shorted turns I would run it for a time on full power with no loads on the secondaries to see if it overheats.
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Old 21st Jun 2017, 7:22 pm   #146
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Default Re: Bush A.C.91

Firstly an apology - what I meant by "can't get a reading" was that I couldn't get the meter probes properly onto the Secondary tags as they are located behind the metal strut/support for the scale lamp. Removed this strut to gain access and gave the solder on the tags a qucik dab with liquid flux to remove the oxidation. Result, I'm getting a reading of 0.8 ohms on the Output Transformer Secondary - seems good to me?

Secondly is where the mystery (for me) really starts. Reconnected back up to my lamp limiter and got the same result with the bulb glowing quite brightly and the scale !amp barely lit - a dull orange glow. Removed one of the valves (CY 31) at this point and the bulb in the lamp limiter got brighter as did the scale lamp!

I have no idea what is going on...?
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Old 21st Jun 2017, 8:30 pm   #147
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Default Re: Bush A.C.91

Have you changed or removed C30 which is connected directly across the incoming mains supply?

Does the test lamp still glow if you turn the set off?

Try disconnecting points A, B and C from the mains transformer to remove all possibilities of it being loaded.
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Old 21st Jun 2017, 8:51 pm   #148
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Default Re: Bush A.C.91

I assume you don't have anything earthed connected to this set?
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Old 21st Jun 2017, 8:54 pm   #149
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Default Re: Bush A.C.91

C30 has been replaced with an X2 capacitor - see attached picture.

Bulb in lamp limiter glows very faintly when set is turned off.

Need to wait until tomorrow to disconnect points A, B and C.
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Old 21st Jun 2017, 9:03 pm   #150
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Default Re: Bush A.C.91

For the lamp limiter to glow at all it must be passing current. With S3 (I assume that's the on/off switch) open, the current can't be flowing back down the neutral wire. So check that S3 really is opening.

Otherwise, that current must be flowing through something else. If the lamp limiter is in series with the upper wire on the circuit posted a few message back, that is, not the wire going through S3 to chassis, then a leak to earth at some point could do it.
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Old 21st Jun 2017, 10:23 pm   #151
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Default Re: Bush A.C.91

At the start of this Thread I highlighted that this set had "been got at" before I acquired it. Some capacitors and links were removed by myself from around the mains socket which had been replaced at some point by an IDE socket.

I'm open to the possibility that I may have wired up something incorrectly in this locality as a consequence of undoing previous "fixes".

Any Bush AC91 experts out there that could advise on how the on-off switch/volume control should be wired up, including connections to the mains Live and Neutral tags. There is nothing connected to the IDE earth tag.
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Old 21st Jun 2017, 10:40 pm   #152
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Default Re: Bush A.C.91

As per the diagram in post #147 and the under chassis drawing in the service sheet I should think.

Call C30's leads Y and Z.

One side of the mains connector would have C30 lead Y and the voltage selector lead connected to it.

The other side of the mains connector would be wired to S3.

The other side of S3 would have C30 lead Z, Wire D and tag E connected to it.
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Old 22nd Jun 2017, 11:49 am   #153
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Default Re: Bush A.C.91

Looking at your picture in post #149, the Rifa capacitor C30 is connected from one side of the mains connector to S3, which is correct. However on the same pin of the mains connector is a reddish/brownish wire which appears to go to V4, Unless a spare pin on V4 is being used as a termination point this is incorrect. The wire should in fact go to the voltage selector.

The other side of the mains connector is connected directly to S3 which is correct.

I would suggest reverse engineering this part of the circuit.
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Old 22nd Jun 2017, 12:31 pm   #154
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Default Re: Bush A.C.91

I think the brown wire going to V4 is connected to V4's screen, I'm not sure if the other end is connected to the IEC socket? There's an overall view in this pic of the underneath as the radio was received although it's not conclusive:

http://www.vintage-radio.net/forum/a...7&d=1483799563

Lawrence.
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Old 22nd Jun 2017, 12:46 pm   #155
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Default Re: Bush A.C.91

Checking for wiring faults using pictures is never easy.

We'll have to wait for the OP to trace out the circuit.
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Old 22nd Jun 2017, 12:48 pm   #156
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Default Re: Bush A.C.91

Thanks guys for your time and effort in trying to resolve this puzzle.

The overall picture here shows the complications I encountered with the two yellow tubular capacitors which were not in the Circuit Diagram: -

http://www.vintage-radio.net/forum/a...7&d=1483799563

See also my Post #49 here (and Lawrence's correction in #50): -

http://www.vintage-radio.net/forum/s...=132722&page=3

Will do some more detailed circuit tracing tonight.
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Last edited by DonaldStott; 22nd Jun 2017 at 12:49 pm. Reason: Miissed last point
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Old 22nd Jun 2017, 7:32 pm   #157
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Default Re: Bush A.C.91

Some pictures , that might be of help , regards, Tim.
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Old 22nd Jun 2017, 9:01 pm   #158
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Default Re: Bush A.C.91

Thanks Tim for some fabulous pictures and your ongoing support.

Am I allowed to use the word flummoxed on this Forum - this is where I am now as I compare and contrast with what has been done on my set!
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Old 22nd Jun 2017, 10:55 pm   #159
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Default Re: Bush A.C.91

A couple more pics Alistair , might be of help.
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Old 23rd Jun 2017, 10:20 am   #160
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Default Re: Bush A.C.91

Quote:
Originally Posted by tim.norris View Post
A couple more pics Alistair , might be of help.
Thanks again Tim - definitely a Senior moment on my part - roll on Retirement!

A case of not being able to see the wood for the trees or the connections for the cables.

Using Tim's pictures and tracing the Circuit Diagram I now have a far better understanding of how to rewire it correctly (hopefully!).
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