|
|
|
|
|||||||
| Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment. |
 |
|
|
Thread Tools |
12th Nov 2018, 8:15 pm
|
#1 |
|
Moderator
Join Date: Feb 2006
Location: Wembley, Middlesex
Posts: 7,224
|
Pye Black Box PCL83 version
I’m currently restoring a Pye Black box fitted with PCL83’s.
I’ve checked the O/P transformer and I’m concerned it may have shorted turns. The readings from the centre tap (HT) are 104 ohms and 97 ohms to each anode and around 26 ohms and 18 ohms between the centre tap and each screen. This seems to low Can someone confirm please? |
|
|
12th Nov 2018, 10:25 pm
|
#2 |
|
Dekatron
Join Date: Jan 2005
Location: Oxford, UK.
Posts: 17,846
|
Re: Pye Black Box PCL83 version
The manufacturer's data states primary start to finish 200 ohms which is pretty damn close to your 104 + 97.
|
|
|
13th Nov 2018, 12:29 pm
|
#3 |
|
Octode
Join Date: Apr 2007
Location: Hampshire, UK.
Posts: 1,577
|
Re: Pye Black Box PCL83 version
You won't detect shorted turns with a simple resistance check. The chances are that any short will be between adjacent turns or layers, so the loss of wire length is negligible. The real effect will be a drastic loss of measured inductance, which can only be determined under dynamic conditions.
|
|
|
|
13th Nov 2018, 12:58 pm
|
#4 |
|
Dekatron
Join Date: Jan 2005
Location: Oxford, UK.
Posts: 17,846
|
Re: Pye Black Box PCL83 version
Good point, Tim
 What kind of inductance would a typical audio output transformer have? Would this be measurable with one of those Chinese testers or a Peak Atlas LCR, for example? |
|
|
|
13th Nov 2018, 4:05 pm
|
#5 |
|
Banned
Join Date: Dec 2013
Location: Middlewich, Cheshire, UK. & Winter in the Philippines.
Posts: 3,897
|
Re: Pye Black Box PCL83 version
Yes, the CCT (Cheap Chinese Tester ) will but I can't interpret the readings.
Best way to see if there are shorted turns is to bung say 50v AC through the primary for a while and watch for smoke. Sam. |
|
|
|
13th Nov 2018, 5:12 pm
|
#6 |
|
Nonode
Join Date: Nov 2016
Location: Aberaeron, Ceredigion, Wales, UK.
Posts: 2,884
|
Re: Pye Black Box PCL83 version
If you have a scope you can always ring it, it’s donkey's years since I did that, but if you have two identical transformers you can compare them and measure the decay.
Cheers John |
|
|
|
13th Nov 2018, 6:22 pm
|
#7 |
|
Nonode
Join Date: Oct 2017
Location: Bristol, UK.
Posts: 2,384
|
Re: Pye Black Box PCL83 version
What are the symptoms that make you think the OPT might have shorted turns? Does the thing work at all? Cheers, Jerry
|
|
|
|
13th Nov 2018, 6:47 pm
|
#8 |
|
Rest in Peace
Join Date: Mar 2006
Location: N.W. Oxfordshire(Chipping Norton)
Posts: 7,306
|
Re: Pye Black Box PCL83 version
On the subject of Shorted turns, somewhere I have a diagram of a Shorted Turns tester. This simply a neon with series resistor in parallel with a 9v battery, the + 7- leads from this are clipped across a suspect winding - if a shorted turn is present, the neon will either not light at all or glow very dimly.
|
|
|
|
13th Nov 2018, 7:43 pm
|
#9 |
|
Nonode
Join Date: Nov 2016
Location: Aberaeron, Ceredigion, Wales, UK.
Posts: 2,884
|
Re: Pye Black Box PCL83 version
When we were testing EHT transformers, for possible faults, we used to use a small battery and just flick it onto one winding and look for sparks out of the other, if you did enough you could soon detect a faulty transformer.
Cheers John |
|
|
|
14th Nov 2018, 12:29 am
|
#10 |
|
Moderator
Join Date: Feb 2006
Location: Wembley, Middlesex
Posts: 7,224
|
Re: Pye Black Box PCL83 version
Transformer checked out OK and amplifier is now working, has been on a long soak test.
Incidentally I found one resistor that had never been soldered to the tag and the cathode bypass capacitor was fitted the wrong way round at the factory. |
|
|
