Pye 1004 (Transistor Black Box) amp faults, help wanted please - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

Nickthedentist · 20th Sep 2019, 2:38 pm

Hello again Edward,

It has the two, round, 6½" R&A speakers.

Nick.

Edward Huggins · 20th Sep 2019, 4:17 pm

This dates it to quite late in 1963 or maybe early 1964. It will have NKT Germaniums throughout unless it's been got at.

AC/HL · 20th Sep 2019, 4:52 pm

Did the later ones have alternative transistor types fitted?

Edward Huggins · 20th Sep 2019, 5:18 pm

Philips were eyeing up Pye at this time and there were some experiments with Mullard OC and AD type transistors, but I seem to remember NKT were used through the whole (rather short) production life.

Nickthedentist · 20th Sep 2019, 8:24 pm

Quote:

Originally Posted by Edward Huggins

This dates it to quite late in 1963 or maybe early 1964. It will have NKT Germaniums throughout unless it's been got at.

That's fascinating, as there are no dates on the cabinet floor or big caps that I can see.

All utterly original and untouched c/w Ronette cartridge which seems to have some output (though I appreciate it's not stereo compatible).

Line-up in this example is NKT226 (VT1), 3 x NKT224 (VT2, 3 & 5), NKT773 (VT4) and 2 x NKT452 (VT6 & VT7).

So, it's as described in the Pye service sheet except that VT4 is listed as NKT751.

The only obvious Philips influence are the "mustard" caps and the Mullard OA5 diode.

P.S. Sorry for the typo in post 16, VT4 is NKT773 (not ...733)!.

OldTechFan96 · 20th Sep 2019, 9:19 pm

I recently worked on a Dynatron radio with distorted audio. I pulled the output pair and one of the transistors had a hfe of 1 with no open/shorted junctions . Once the transistor was replaced the amplifier worked correctly.

I hope this helps!

Nickthedentist · 20th Sep 2019, 10:03 pm

Thanks, that gives me hope

Edward Huggins · 21st Sep 2019, 7:35 am

Quote:

Originally Posted by Nickthedentist

Quote:

Originally Posted by Edward Huggins

This dates it to quite late in 1963 or maybe early 1964. It will have NKT Germaniums throughout unless it's been got at.

That's fascinating, as there are no dates on the cabinet floor or big caps that I can see.

An easy way to date this is the use of the, then new, BSR UA15 autochanger launched early/mid 1963 which was used through the production life of the Pye 1004 during 1964. Soon after that came the 1005 Achoic. My dating comes from me "being there".

Nickthedentist · 30th Sep 2019, 7:59 am

I had half an hour to myself when everyone was in bed last night...

I replaced VT4 (NKT733) and VT6 & VT7 (NKT452) all with original Newmarket components from reputable sources (at some expense!). I then set-up R13 according to the manual, and powered it from a bench supply, limited to 100mA. But all's not well.

At 5V, it drew 5mA. At 10V, 30mA. And at 15V, 80mA. You get the picture! I daren't power it from the specified 25V yet. The manual states that quiescent current at 25V should be 15-30mA.

The only good news is that it does actually amplify now.

Any suggestions as to what I should do next, please?

All the other transistors tested fine and I've replaced all the electrolytic caps, many of which were electrically leaky. I also dismantled and cleaned R13 which was intermittent.

Nick.

dave cox · 30th Sep 2019, 11:37 am

Take a look at the waveform on the output with at least a 10MHz scope, with and without a signal. Any 'blurry' portions are indicatative of oscillation.

dc

Nickthedentist · 30th Sep 2019, 2:00 pm

What a good idea, Dave, I hadn't thought of that. Will report back.

I find DC-coupled amps hard to work with. I can't really take meaningful voltage readings because the supply voltage sags because of the overcurrent protection in my bench supply (as mentioned in post 29), and anyhow, the DC conditions are determined by R13 (at the start of the DC-coupled bit) which I have set to get the correct mid-point at the output pair. Furthermore, there is DC feedback via R27 (collector of VT7 to emitter of VT2). Too many chickens and eggs which all goes to make my head hurt!

Nick.

dave cox · 30th Sep 2019, 2:46 pm

Assuming I have the same schematic, R13 adjusts the DC operating point of the output stage. The voltage at VT2 base ( ratio of R12/R13, relative to the voltage at the top of R12 which is somewhat difficult to work out

) is 'compared' with the output voltage via R27 into VT2's emitter.

Note this schematic reverses the normal trend of putting + at the top so apologies if I get the next bit wrong ...

If the output voltage then goes more -ve (a disturbance) it will pull VT2's emitter -ve and the transistor will start to turn off, VT3 will turn on (more) and the output stage will then try to pull the oposite way to the disturbance.

There is no adjustment for the bias current.

dc

Nickthedentist · 30th Sep 2019, 3:14 pm

Thank you for the very understandable explanation.

That "upside down" style of circuit diagram seems to be not too uncommon for early transistor gear with +ve chassis and germanium, mainly PNP devices.

Nick.

dave cox · 30th Sep 2019, 3:32 pm

I posted an example of a 'hooting' output stage previously, here so you know what to look for. That one popped the fuses and most of the transistors

dc

Station X · 22nd Jun 2020, 10:40 am

Thread reopened at OP's request.

Nickthedentist · 22nd Jun 2020, 11:08 am

Hello everyone,

It's been a while, I know.

After messing around fruitlessly with this for a while, and not having spare cash to spend on a complete set of replacement Ge transistors of unknown provenance, I'm beginning to think that Paul's idea of fitting a replacement IC power amp might be the way to go. Obviously, I'd do this completely reversibly, so that it could be easily returned to original at a later date if desired. Two questsions arise:

(1) Does it sound sensible to leave VT1 and VT2 doing their job, and take-off an audio signal to feed the new power amp from the collector of VT2, via a suitable DC-blocking coupling cap of course?

(2) Obviously, the original amp uses a supply of minus 25V with respect to chassis. If I used a modern IC power amplifier module, would it be simplest to provide it with its own separate positive power supply? Or can things like the TDA2030 be configured for single-rail, negative supply working?

Many thanks,

Nick

paulsherwin · 22nd Jun 2020, 11:20 am

Yes, a TDA2030 should be OK, e.g. https://www.ebay.co.uk/itm/Power-Sup...e/323356814386. If you just want to buy the chip and build your own module: https://www.ebay.co.uk/itm/5PCS-TDA2...N/352976322636. Datasheet and circuits: http://pdf.datasheetcatalog.com/data...onics/1459.pdf

You will probably need to experiment a bit.

Remember that the +ve and -ve rails are decoupled, so are essentially the same 'ground' for AC. You just need an output electrolytic for single rail operation.

Michael Maurice · 22nd Jun 2020, 2:01 pm

Be careful, I tried that once and got loads of hf oscillation. Can't tell you why.

paulsherwin · 22nd Jun 2020, 2:31 pm

Easy enough to lash something up and try it out though, it'll only cost a couple of quid. Don't be tempted to omit the Zobel network on the output though, it's there precisely to suppress any tendency to HF oscillation.

Edward Huggins · 22nd Jun 2020, 4:16 pm

If I were you I'd completely by-pass the original amplifier. Hopefully you may be able to still use the Volume control to get the correct input loading for the Ronette crystal cartridge. If you take off from a point on the original amp's AF stages, you'll only continue to inherit and amplify its foibles. You can series wire the 2 internal speakers to match the new amp's output loading if needed. This way, it's all reversible as hopefully you can return to this later.

20th Sep 2019, 2:38 pm	#21
Nickthedentist Dekatron Join Date: Jan 2005 Location: Oxford, UK. Posts: 17,843	Re: Pye 1004 (Transistor Black Box) amp faults, help wanted please Hello again Edward, It has the two, round, 6½" R&A speakers. Nick.

20th Sep 2019, 4:17 pm	#22
Edward Huggins Dekatron Join Date: Sep 2015 Location: Southwold, Suffolk, UK. Posts: 8,327	Re: Pye 1004 (Transistor Black Box) amp faults, help wanted please This dates it to quite late in 1963 or maybe early 1964. It will have NKT Germaniums throughout unless it's been got at. __________________ Edward.

20th Sep 2019, 4:52 pm	#23
AC/HL Dekatron Join Date: Nov 2003 Location: Heckmondwike, West Yorkshire, UK. Posts: 9,642	Re: Pye 1004 (Transistor Black Box) amp faults, help wanted please Did the later ones have alternative transistor types fitted?

20th Sep 2019, 5:18 pm	#24
Edward Huggins Dekatron Join Date: Sep 2015 Location: Southwold, Suffolk, UK. Posts: 8,327	Re: Pye 1004 (Transistor Black Box) amp faults, help wanted please Philips were eyeing up Pye at this time and there were some experiments with Mullard OC and AD type transistors, but I seem to remember NKT were used through the whole (rather short) production life. __________________ Edward.

20th Sep 2019, 9:19 pm	#26
OldTechFan96 Octode Join Date: Jul 2017 Location: Newcastle Upon Tyne, Tyne & Wear, UK. Posts: 1,178	Re: Pye 1004 (Transistor Black Box) amp faults, help wanted please I recently worked on a Dynatron radio with distorted audio. I pulled the output pair and one of the transistors had a hfe of 1 with no open/shorted junctions . Once the transistor was replaced the amplifier worked correctly. I hope this helps!

20th Sep 2019, 10:03 pm	#27
Nickthedentist Dekatron Join Date: Jan 2005 Location: Oxford, UK. Posts: 17,843	Re: Pye 1004 (Transistor Black Box) amp faults, help wanted please Thanks, that gives me hope

30th Sep 2019, 7:59 am	#29
Nickthedentist Dekatron Join Date: Jan 2005 Location: Oxford, UK. Posts: 17,843	Re: Pye 1004 (Transistor Black Box) amp faults, help wanted please I had half an hour to myself when everyone was in bed last night... I replaced VT4 (NKT733) and VT6 & VT7 (NKT452) all with original Newmarket components from reputable sources (at some expense!). I then set-up R13 according to the manual, and powered it from a bench supply, limited to 100mA. But all's not well. At 5V, it drew 5mA. At 10V, 30mA. And at 15V, 80mA. You get the picture! I daren't power it from the specified 25V yet. The manual states that quiescent current at 25V should be 15-30mA. The only good news is that it does actually amplify now. Any suggestions as to what I should do next, please? All the other transistors tested fine and I've replaced all the electrolytic caps, many of which were electrically leaky. I also dismantled and cleaned R13 which was intermittent. Nick.

30th Sep 2019, 11:37 am	#30
dave cox Nonode Join Date: Jan 2009 Location: Bristol, UK. Posts: 2,061	Re: Pye 1004 (Transistor Black Box) amp faults, help wanted please Take a look at the waveform on the output with at least a 10MHz scope, with and without a signal. Any 'blurry' portions are indicatative of oscillation. dc

30th Sep 2019, 2:00 pm	#31
Nickthedentist Dekatron Join Date: Jan 2005 Location: Oxford, UK. Posts: 17,843	Re: Pye 1004 (Transistor Black Box) amp faults, help wanted please What a good idea, Dave, I hadn't thought of that. Will report back. I find DC-coupled amps hard to work with. I can't really take meaningful voltage readings because the supply voltage sags because of the overcurrent protection in my bench supply (as mentioned in post 29), and anyhow, the DC conditions are determined by R13 (at the start of the DC-coupled bit) which I have set to get the correct mid-point at the output pair. Furthermore, there is DC feedback via R27 (collector of VT7 to emitter of VT2). Too many chickens and eggs which all goes to make my head hurt! Nick. Last edited by Nickthedentist; 30th Sep 2019 at 2:15 pm.

30th Sep 2019, 2:46 pm	#32
dave cox Nonode Join Date: Jan 2009 Location: Bristol, UK. Posts: 2,061	Re: Pye 1004 (Transistor Black Box) amp faults, help wanted please Assuming I have the same schematic, R13 adjusts the DC operating point of the output stage. The voltage at VT2 base ( ratio of R12/R13, relative to the voltage at the top of R12 which is somewhat difficult to work out ) is 'compared' with the output voltage via R27 into VT2's emitter. Note this schematic reverses the normal trend of putting + at the top so apologies if I get the next bit wrong ... If the output voltage then goes more -ve (a disturbance) it will pull VT2's emitter -ve and the transistor will start to turn off, VT3 will turn on (more) and the output stage will then try to pull the oposite way to the disturbance. There is no adjustment for the bias current. dc

30th Sep 2019, 3:14 pm	#33
Nickthedentist Dekatron Join Date: Jan 2005 Location: Oxford, UK. Posts: 17,843	Re: Pye 1004 (Transistor Black Box) amp faults, help wanted please Thank you for the very understandable explanation. That "upside down" style of circuit diagram seems to be not too uncommon for early transistor gear with +ve chassis and germanium, mainly PNP devices. Nick.

30th Sep 2019, 3:32 pm	#34
dave cox Nonode Join Date: Jan 2009 Location: Bristol, UK. Posts: 2,061	Re: Pye 1004 (Transistor Black Box) amp faults, help wanted please I posted an example of a 'hooting' output stage previously, here so you know what to look for. That one popped the fuses and most of the transistors dc

22nd Jun 2020, 10:40 am	#35
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: Pye 1004 (Transistor Black Box) amp faults, help wanted please Thread reopened at OP's request. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

22nd Jun 2020, 11:08 am	#36
Nickthedentist Dekatron Join Date: Jan 2005 Location: Oxford, UK. Posts: 17,843	Re: Pye 1004 (Transistor Black Box) amp faults, help wanted please Hello everyone, It's been a while, I know. After messing around fruitlessly with this for a while, and not having spare cash to spend on a complete set of replacement Ge transistors of unknown provenance, I'm beginning to think that Paul's idea of fitting a replacement IC power amp might be the way to go. Obviously, I'd do this completely reversibly, so that it could be easily returned to original at a later date if desired. Two questsions arise: (1) Does it sound sensible to leave VT1 and VT2 doing their job, and take-off an audio signal to feed the new power amp from the collector of VT2, via a suitable DC-blocking coupling cap of course? (2) Obviously, the original amp uses a supply of minus 25V with respect to chassis. If I used a modern IC power amplifier module, would it be simplest to provide it with its own separate positive power supply? Or can things like the TDA2030 be configured for single-rail, negative supply working? Many thanks, Nick

22nd Jun 2020, 11:20 am	#37
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,940	Re: Pye 1004 (Transistor Black Box) amp faults, help wanted please Yes, a TDA2030 should be OK, e.g. https://www.ebay.co.uk/itm/Power-Sup...e/323356814386. If you just want to buy the chip and build your own module: https://www.ebay.co.uk/itm/5PCS-TDA2...N/352976322636. Datasheet and circuits: http://pdf.datasheetcatalog.com/data...onics/1459.pdf You will probably need to experiment a bit. Remember that the +ve and -ve rails are decoupled, so are essentially the same 'ground' for AC. You just need an output electrolytic for single rail operation.

22nd Jun 2020, 2:01 pm	#38
Michael Maurice Moderator Join Date: Feb 2006 Location: Wembley, Middlesex Posts: 7,223	Re: Pye 1004 (Transistor Black Box) amp faults, help wanted please Be careful, I tried that once and got loads of hf oscillation. Can't tell you why. __________________ Forum Moderator http://www.michaelmauricerepairs.co.uk/

22nd Jun 2020, 2:31 pm	#39
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,940	Re: Pye 1004 (Transistor Black Box) amp faults, help wanted please Easy enough to lash something up and try it out though, it'll only cost a couple of quid. Don't be tempted to omit the Zobel network on the output though, it's there precisely to suppress any tendency to HF oscillation.

22nd Jun 2020, 4:16 pm	#40
Edward Huggins Dekatron Join Date: Sep 2015 Location: Southwold, Suffolk, UK. Posts: 8,327	Re: Pye 1004 (Transistor Black Box) amp faults, help wanted please If I were you I'd completely by-pass the original amplifier. Hopefully you may be able to still use the Volume control to get the correct input loading for the Ronette crystal cartridge. If you take off from a point on the original amp's AF stages, you'll only continue to inherit and amplify its foibles. You can series wire the 2 internal speakers to match the new amp's output loading if needed. This way, it's all reversible as hopefully you can return to this later. __________________ Edward.