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Old 22nd Jan 2014, 11:31 pm   #181
kevinski
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Default Re: Pye Black Box

Which is the reserve capacitor? Is that the big can? Also how would you measure the capacitor?

Kevin

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Old 23rd Jan 2014, 10:48 am   #182
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Default Re: Pye Black Box

The reservoir and smoothing capacitors are housed within the can. Measure the DC voltage between chassis and each tag of the can. If the can is grounded by a tag, expect this tag to read 0V.
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Old 23rd Jan 2014, 2:35 pm   #183
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Default Re: Pye Black Box

Getting only 1Vdc on all three tags when measuring black lead from meter to chassis and red lead to each tag in turn

Kevin

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Old 23rd Jan 2014, 2:49 pm   #184
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Default Re: Pye Black Box

Which version of the Black Box do you have Kevin? I can't seem to find a version with a diagram like that in post #173.

Could be a rectifier problem. Assuming it's a thermionic type, Is it lit? Are any valves lit?
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Old 23rd Jan 2014, 3:15 pm   #185
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Default Re: Pye Black Box

Just checked my rectifier which I changed to a modern one with a 220Ω 7w resistor and I'm only getting 50Vdc from it (now gone up to 89Vdc?). The type of black box is BB/A according to the radio museum
http://www.radiomuseum.org/r/pye_black_box_bba.html.
The rectifier is a metal rectifier not a thermionic rectifier. All the valves are lit the way you would expect.

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Old 23rd Jan 2014, 4:57 pm   #186
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Default Re: Pye Black Box

Unfortunately I don't have the circuit fro the BBA version. Perhaps you or another forum member could post the Power Supply part of the circuit here?

I would suggest the first thing to do is check the 220R resistor to make sure it hasn't gone high resistance. This is very unlikely if it's a wire wound type..

If that's OK, disconnect the rectifier from the mains transformer and measure the AC voltage on the secondary winding or windings feeding the rectifier.
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Old 23rd Jan 2014, 5:11 pm   #187
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Default Re: Pye Black Box

Here's an extract.

The smoothing and reservoir caps are on anther part of the diagram in a classic C-R-C arrangement.
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Old 23rd Jan 2014, 6:58 pm   #188
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Default Re: Pye Black Box

Explicitly (with non PSU bits removed) see attached:
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....__________
....|____||__|__\_____
.=.| _---\__|__|_---_|.
.........O..Chris....O
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Old 23rd Jan 2014, 11:13 pm   #189
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Default Re: Pye Black Box

In both Graham's and Chis's diagrams, MR1 has according to you been replaced by a modern silicon rectifier with a 220R resistor connected in series with one leg from the mains transformer.

Measure the resistance of that resistor it should read 220R if this is OK then next switch your meter to AC range and measure the voltage accross the ~ terminals of the rectifier. You should get around 250V AC.

Let us know what the results are.
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Old 24th Jan 2014, 6:15 pm   #190
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Default Re: Pye Black Box

The resistor still reads 220Ω but I'm not getting any volts across the rectifier. With the resistor removed I measured the blue wire and the black wire separately with the black lead from the meter attached to the neutral tag on the mains switch I get 10Vac on the blue and 206Vac on the black.

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Old 24th Jan 2014, 6:32 pm   #191
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Default Re: Pye Black Box

Hi Kevin,

With the mains disconnected measure the resistance between the body of the smoothing capacitor and the chassis, it should be zero. I've had problems with two of my black boxes because this capacitor had a poor connection to the chassis.

I think it also might be useful if you posted some pictures of how you swapped out the original rectifier and added the series resistor.

David
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Old 24th Jan 2014, 11:38 pm   #192
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Default Re: Pye Black Box

Quote:
Originally Posted by kevinski View Post
I measured the blue wire and the black wire separately with the black lead from the meter attached to the neutral tag on the mains switch I get 10Vac on the blue and 206Vac on the black.
There is no physical connection between mains neutral and the rectifier.

You need to measure the voltage between the two AC tags on the bridge rectifier. These may be marked ~ .
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Old 25th Jan 2014, 12:14 am   #193
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Station X.
Quote:
Originally Posted by kevinski View Post
The resistor still reads 220Ω but I'm not getting any volts across the rectifier.
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Old 25th Jan 2014, 1:07 am   #194
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Default Re: Pye Black Box

That isn't consistent with post #185 where you say you're getting 50V to 89V. I assume that's on the DC side of the rectifier?

If it's on the DC side of the rectifier you should get the same voltage across the reservoir capacitor, as these points are wired together.
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Old 25th Jan 2014, 10:45 am   #195
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Default Re: Pye Black Box

Radio Dave - Picture of how rectifier + resistor has been fitted.

Station X - The inconsistency of measurements is THE main problem with this project. One time it measures ok next it's something completely different.

Kevin
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Old 25th Jan 2014, 11:50 am   #196
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Default Re: Pye Black Box

Looks like the resistor has been wired in on the AC side of the rectifier.

What AC voltage do you get on the Blue and Black wires at the transformer? ie with one meter lead connected to each transformer tag.

What AC voltage do you get with one meter lead connected to each side of the resistor?

Finally what's the AC voltage with one lead connected to the rectifier end of the resistor and the other to the diagonally opposite tag on the rectifier?
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Old 25th Jan 2014, 11:58 am   #197
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Default Re: Pye Black Box

Kevin, You were advised to change that rectifier in post #15. Did you never change it?

David
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Old 25th Jan 2014, 12:10 pm   #198
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Default Re: Pye Black Box

According to post #158 a new rectifier was tried. The one in the picture doesn't look new to me though. Taking a few voltage measurements will do no harm.
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Old 25th Jan 2014, 12:15 pm   #199
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Default Re: Pye Black Box

Radio Dave - Yes I did change it using this

http://cpc.farnell.com/jsp/search/pr...sp?SKU=SC11465

Station X - I get 0Vac when I measure at any of those locations

Kevin
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Old 25th Jan 2014, 12:18 pm   #200
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Default Re: Pye Black Box

Station X - the one in the picture is new but has been put into the original metal block and sealed using Epoxy putty (as recommended by Michael in an earlier post)
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