Pye Black Box mark 2 BBH - UK Vintage Radio Repair and Restoration Discussion Forum

nomad25 · 14th Jul 2017, 8:43 pm

Hi all. I'm in the process of restoring a Pye Black Box, mark 2 BBH. Two speakers and a UA8 auto changer.
I've done a full re-cap and replaced the volume pot. The on/off Tone pot was replaced when I acquired it. Two of the caps were wrong values.
it sounds great with an iPod connected. The only thing is the output seems quite low, iPod and volume cranked up nearly all the way. Is this because of the impedance of the iPod headphone output or is it likely to be the o/p transformer? I'm aware from reading lots of threads on here that they normally have a broken winding somewhere.
Is it worth getting the transformer re-wound, even if it's just for improved reliability and could anyone please give me some advice on how much this costs and who can do it.
I haven't had a chance to test the amp with a record deck connected yet as I'm still working on it.

Ed_Dinning · 14th Jul 2017, 8:49 pm

Hi Nomad, yes the output transformers are not reliable and I've rewound a few in my time.
However, before condemning it do a few checks with a scope to see if it has developed a fault.

Ed

nomad25 · 14th Jul 2017, 8:58 pm

Unfortunately I don't have a scope or the know how ��

Telegraph-Hill · 14th Jul 2017, 9:19 pm

Hi Nomad,
from my experience with a couple of conversions I can confirm the Voltage output of Mobile Phones and Ipods is quite low. To get a reasonable output of e.g. 0.77V you need to push up the volume up to max. Hope this helps.
Cheers,
Oliver

Edward Huggins · 14th Jul 2017, 9:26 pm

Does the player have a good enough volume on records but is only low on the ipod?

nomad25 · 14th Jul 2017, 11:36 pm

Well I hadn't tried it up until tonight. The wiring in the tone arm was completely shot, dead short on all wires, so after putting a new screened cable in I gave it a go. Surprisingly there's loads of power there! The Manky looking X5M cart sounds like it's still going strong.
I've tried a new Chinese made ECC83 in there, wanted to try the Original Mullard in my little guitar amp to give me a slightly lower pre amp gain, and Wow! Does it sound good in there!
Is it possible that the o/p transformer can partly fail and still function?

julie_m · 15th Jul 2017, 7:35 am

Yes. One half of the primary winding can go open-circuit. That then leaves one of the valves doing all the work, and an unbalanced DC in the windings which will cause distortion.

It's easy enough to test the primary winding for continuity, from each anode to the centre tap, with the power off and thevalves cold..

Edward Huggins · 15th Jul 2017, 9:33 am

It may not be the OP transformer at all if it's working that well, but more likely a poor input impedence match between the ipod and the input stage of the amplifier.

Can we assume you've bridged the stereo channels from the ipod to create just a single mono input and that you've connected this input to the volume control?

nomad25 · 15th Jul 2017, 11:53 am

I'm not too concerned about using an iPod with it now I have the deck working. I just want to be sure that my o/p transformer is working well

nomad25 · 15th Jul 2017, 12:40 pm

I have continuity between the primary centre and both anodes, but the readings are quite different. 0.70 one side and 1.01 the other. Does that sound normal?

julie_m · 15th Jul 2017, 5:06 pm

Yes, that's not too unusual. The windings nearer the outside of the transformer will need more metres of wire than the inner ones to make the same number of turns, and the DC resistance varies with the length. (The AC reactance varies with turns squared, and dominates the total impedance.) A ratio of 1.4:1 looks a touch high, but it's conceivable with a small transformer.

I'm presuming the meter was on its 2kΩ range for both measurements?

PJL · 15th Jul 2017, 7:46 pm

Sounds OK. Each half winding will be the same number of turns but the one will be wound over the other which takes more wire so is higher resistance.

nomad25 · 16th Jul 2017, 9:56 am

So all sounds ok then? Maybe mine's not too bad.

14th Jul 2017, 8:43 pm	#1
nomad25 Retired Dormant Member Join Date: Jun 2015 Location: Bournemouth, Dorset, UK. Posts: 42	Pye Black Box mark 2 BBH Hi all. I'm in the process of restoring a Pye Black Box, mark 2 BBH. Two speakers and a UA8 auto changer. I've done a full re-cap and replaced the volume pot. The on/off Tone pot was replaced when I acquired it. Two of the caps were wrong values. it sounds great with an iPod connected. The only thing is the output seems quite low, iPod and volume cranked up nearly all the way. Is this because of the impedance of the iPod headphone output or is it likely to be the o/p transformer? I'm aware from reading lots of threads on here that they normally have a broken winding somewhere. Is it worth getting the transformer re-wound, even if it's just for improved reliability and could anyone please give me some advice on how much this costs and who can do it. I haven't had a chance to test the amp with a record deck connected yet as I'm still working on it.

14th Jul 2017, 8:49 pm	#2
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,194	Re: Pye Black Box mark 2 BBH Hi Nomad, yes the output transformers are not reliable and I've rewound a few in my time. However, before condemning it do a few checks with a scope to see if it has developed a fault. Ed

14th Jul 2017, 8:58 pm	#3
nomad25 Retired Dormant Member Join Date: Jun 2015 Location: Bournemouth, Dorset, UK. Posts: 42	Re: Pye Black Box mark 2 BBH Unfortunately I don't have a scope or the know how ��

14th Jul 2017, 9:19 pm	#4
Telegraph-Hill Triode Join Date: Mar 2017 Location: Totnes, Devon, UK. Posts: 27	Re: Pye Black Box mark 2 BBH Hi Nomad, from my experience with a couple of conversions I can confirm the Voltage output of Mobile Phones and Ipods is quite low. To get a reasonable output of e.g. 0.77V you need to push up the volume up to max. Hope this helps. Cheers, Oliver

14th Jul 2017, 9:26 pm	#5
Edward Huggins Dekatron Join Date: Sep 2015 Location: Southwold, Suffolk, UK. Posts: 8,328	Re: Pye Black Box mark 2 BBH Does the player have a good enough volume on records but is only low on the ipod? __________________ Edward.

14th Jul 2017, 11:36 pm	#6
nomad25 Retired Dormant Member Join Date: Jun 2015 Location: Bournemouth, Dorset, UK. Posts: 42	Re: Pye Black Box mark 2 BBH Well I hadn't tried it up until tonight. The wiring in the tone arm was completely shot, dead short on all wires, so after putting a new screened cable in I gave it a go. Surprisingly there's loads of power there! The Manky looking X5M cart sounds like it's still going strong. I've tried a new Chinese made ECC83 in there, wanted to try the Original Mullard in my little guitar amp to give me a slightly lower pre amp gain, and Wow! Does it sound good in there! Is it possible that the o/p transformer can partly fail and still function?

15th Jul 2017, 7:35 am	#7
julie_m Dekatron Join Date: May 2008 Location: Derby, UK. Posts: 7,735	Re: Pye Black Box mark 2 BBH Yes. One half of the primary winding can go open-circuit. That then leaves one of the valves doing all the work, and an unbalanced DC in the windings which will cause distortion. It's easy enough to test the primary winding for continuity, from each anode to the centre tap, with the power off and thevalves cold.. __________________ If I have seen further than others, it is because I was standing on a pile of failed experiments.

15th Jul 2017, 9:33 am	#8
Edward Huggins Dekatron Join Date: Sep 2015 Location: Southwold, Suffolk, UK. Posts: 8,328	Re: Pye Black Box mark 2 BBH It may not be the OP transformer at all if it's working that well, but more likely a poor input impedence match between the ipod and the input stage of the amplifier. Can we assume you've bridged the stereo channels from the ipod to create just a single mono input and that you've connected this input to the volume control? __________________ Edward.

15th Jul 2017, 11:53 am	#9
nomad25 Retired Dormant Member Join Date: Jun 2015 Location: Bournemouth, Dorset, UK. Posts: 42	Re: Pye Black Box mark 2 BBH I'm not too concerned about using an iPod with it now I have the deck working. I just want to be sure that my o/p transformer is working well

15th Jul 2017, 12:40 pm	#10
nomad25 Retired Dormant Member Join Date: Jun 2015 Location: Bournemouth, Dorset, UK. Posts: 42	Re: Pye Black Box mark 2 BBH I have continuity between the primary centre and both anodes, but the readings are quite different. 0.70 one side and 1.01 the other. Does that sound normal?

15th Jul 2017, 5:06 pm	#11
julie_m Dekatron Join Date: May 2008 Location: Derby, UK. Posts: 7,735	Re: Pye Black Box mark 2 BBH Yes, that's not too unusual. The windings nearer the outside of the transformer will need more metres of wire than the inner ones to make the same number of turns, and the DC resistance varies with the length. (The AC reactance varies with turns squared, and dominates the total impedance.) A ratio of 1.4:1 looks a touch high, but it's conceivable with a small transformer. I'm presuming the meter was on its 2kΩ range for both measurements? __________________ If I have seen further than others, it is because I was standing on a pile of failed experiments.

15th Jul 2017, 7:46 pm	#12
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: Pye Black Box mark 2 BBH Sounds OK. Each half winding will be the same number of turns but the one will be wound over the other which takes more wire so is higher resistance.

16th Jul 2017, 9:56 am	#13
nomad25 Retired Dormant Member Join Date: Jun 2015 Location: Bournemouth, Dorset, UK. Posts: 42	Re: Pye Black Box mark 2 BBH So all sounds ok then? Maybe mine's not too bad.