Pye black box no sound - Page 3 - UK Vintage Radio Repair and Restoration Discussion Forum

Minster97 · 25th Feb 2021, 6:12 pm

Resistor numberings may be different to mine.I have had a guess that the anode resistors are those that run through the anode leads to the respective pins.
Pin 1 56K
Pin 6 224K
What I think may be resistor 13 is 21K,very strange as sometimes read negative resistance.

Station X · 25th Feb 2021, 7:10 pm

Correct values are 47k, 220k and 27k. Check the colour codes.

Negative resistance reading suggests residual voltage in the circuit as a result of undischarged smoothing capacitors.

ms660 · 25th Feb 2021, 7:40 pm

V1b's anode (pin 1) resistor is 57k in the photo.

Lawrence.

barretter · 25th Feb 2021, 10:09 pm

The leaflet you can find online for the Pye Black Box gives 57K as the value for the resistor on V1b's anode but a footnote says it can be anything from 47k to 68K.
Is it possible that the capacitor coupling the two halves of thr ECC83 is not coupling?

Half a Mullard · 25th Feb 2021, 10:20 pm

I'm happy to be corrected here but I think there should be 2 high stability resistors marked on the service sheet. I don't think the actual value is critical but they both should be (very near) the same value.

barretter · 26th Feb 2021, 1:16 am

Yes, there is another 57K resistorin the cathode circuit of V1b which is subject to the same footnote as the one in the anode circuit and, yes, it does say "high stability" .

Station X · 26th Feb 2021, 9:45 am

I've obviously been looking at the wrong diagram, but I think it is only component values which differ. I agree that there are a pair of precision resistors in the phase splitter circuit, presumably to keep it "balanced"? However even if these resistors had drifted in value I'd still expect a buzz test to yield some output.

The grid voltages are strange too. There should be zero volts on the grid of the preamp stage and I'd have expected the grid voltage of the phase splitter stage to be closer to its cathode voltage.

A coupling capacitor might not be coupling, but I fear a lot of components could be changed and the player still wouldn't work. Perhaps something has been overlooked?

Edward Huggins · 26th Feb 2021, 10:15 am

Howard's point in Post#45 is correct. As mentioned before, I cannot emphasise enough the importance of the value and tolerance of the resistors in this this circuit. However, there appears to be no amplification at all as yet. Taking all these voltage readings may be of little point if some components have failed or are off value. It might be worthwhile for the OP to consider removing the amp (easy) and Posting this off to a Member familiar with this circuit and it's idiosyncracies?

Station X · 26th Feb 2021, 10:30 am

Quote:

Originally Posted by Edward Huggins

Taking all these voltage readings may be of little point if some components have failed or are off value.

I have to disagree. The point of taking voltage readings is to find out which components have failed or are off value. If that were not the case the manufacturer wouldn't have bothered putting typical voltage readings in the service sheet. You have to be able to trust the reading you're given though in order to interpret them.

As far as resistors go these are best checked in circuit by measuring their resistance, allowing for any shunting.

ms660 · 26th Feb 2021, 11:33 am

What's the voltage drop across V1b's cathode bias resistor (4.7k)?

Lawrence.

Edward Huggins · 26th Feb 2021, 12:26 pm

Graham is absolutely correct in his Post#49, but I perversely made this point because so many readings have been taken thus far that are way off from where they should be.
A more experienced restorer may be able to establish the electronic/physical issues by observation and thorough measurement.

Minster97 · 27th Feb 2021, 7:24 am

Dear All,A number of you have mentioned a more experienced restorer ( this is my first restoration)If there is anyone available I would like to send it Any suggestions please?
Gary

Minster97 · 27th Feb 2021, 7:26 am

Forgot to mention this tenth tag under the valve holder at right angles to the others which is not connected.Don’t know what this is

snowman_al · 27th Feb 2021, 7:58 am

A picture would help...
Alan

Sideband · 27th Feb 2021, 12:56 pm

Quote:

Originally Posted by Minster97

Dear All,A number of you have mentioned a more experienced restorer ( this is my first restoration)If there is anyone available I would like to send it Any suggestions please?
Gary

Gary you have a PM

Minster97 · 28th Feb 2021, 8:23 pm

Thank you All. I am sending it one of you who has kindly agreed to look at it for me .It would have been nice if I could have got it going but it is my first attempt and I have learned a great deal from you all. I hope my next attempt will be better

Edward Huggins · 1st Mar 2021, 9:10 am

Don't feel bad about it. As a first project, this was definately not easiest amplifier to start out on. Many experienced restorers struggle with this particular generation of Pye amplifiers!

Station X · 1st Mar 2021, 2:40 pm

We look forward to seeing a full report from the repairer.

Sideband · 1st Mar 2021, 4:09 pm

Depending on what I find wrong, I'll do a write-up of my findings and return any faulty components with the amplifier. What I could do is do a success story (assuming it IS a success)!! with details of the repair as I go. That way it's kept for reference.

These are not the easiest of amps to work on for a beginner. In their day they probably didn't give a lot of trouble but of course they are now well past their intended service life and they do suffer from a lot of problems, particularly the valveholders although why that is, I don't know since the same valveholders are (were) used in many other products at the time and still function well. I'm keeping my fingers crossed that the output transformer is OK

Sideband · 26th Mar 2021, 4:46 pm

Update:

I have now repaired the amplifier and it's on its way back to Gary.

I'll do a proper write-up as time permits but probably sufficient to give a brief summary for now, circuit refs taken from Pye manual:

R8 2.2M grid leak to ECC83 (pin 2) disconnected...difficult to see without moving other components....resoldered.

R10 4.7K cathode of ECC83 gone high to 7.7K replaced.

ECC83 low gain about half what it should be.

EL42 very low....less than half what it should be.

EL42 Low....about half what it should be

EZ41 Emission ok but shows leak between cathode and heater.

(valves checked with Avo two-panel tester)

Heater contact in EL42 holder intermittent....replaced.

Anode contact in EL42 valveholder broken, replaced.

Heater pins in EZ41 valveholder intermittent, replaced.

ECC83 valveholder showed leakage from anode to grid pin (causing low anode volts....there was about 1.75V positive on the grid). Replaced.

Volume and tone controls cleaned.

With a new set of valves, there is plenty of volume using my test signal source (Jason tuner) and it sounds very good through one of my bookshelf bass reflex test speakers.

25th Feb 2021, 6:12 pm	#41
Minster97 Pentode Join Date: Nov 2013 Location: Essex, UK. Posts: 103	Re: Pye black box no sound Resistor numberings may be different to mine.I have had a guess that the anode resistors are those that run through the anode leads to the respective pins. Pin 1 56K Pin 6 224K What I think may be resistor 13 is 21K,very strange as sometimes read negative resistance.

25th Feb 2021, 7:10 pm	#42
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: Pye black box no sound Correct values are 47k, 220k and 27k. Check the colour codes. Negative resistance reading suggests residual voltage in the circuit as a result of undischarged smoothing capacitors. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

25th Feb 2021, 7:40 pm	#43
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Pye black box no sound V1b's anode (pin 1) resistor is 57k in the photo. Lawrence.

25th Feb 2021, 10:09 pm	#44
barretter Heptode Join Date: Jan 2006 Location: Todmorden, West Yorkshire, UK. Posts: 870	Re: Pye black box no sound The leaflet you can find online for the Pye Black Box gives 57K as the value for the resistor on V1b's anode but a footnote says it can be anything from 47k to 68K. Is it possible that the capacitor coupling the two halves of thr ECC83 is not coupling?

26th Feb 2021, 1:16 am	#46
barretter Heptode Join Date: Jan 2006 Location: Todmorden, West Yorkshire, UK. Posts: 870	Re: Pye black box no sound Yes, there is another 57K resistorin the cathode circuit of V1b which is subject to the same footnote as the one in the anode circuit and, yes, it does say "high stability" .

25th Feb 2021, 10:20 pm	#45
Half a Mullard Hexode Join Date: Mar 2012 Location: East Yorkshire, UK. Posts: 354	Re: Pye black box no sound I'm happy to be corrected here but I think there should be 2 high stability resistors marked on the service sheet. I don't think the actual value is critical but they both should be (very near) the same value. __________________ Howard

26th Feb 2021, 9:45 am	#47
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: Pye black box no sound I've obviously been looking at the wrong diagram, but I think it is only component values which differ. I agree that there are a pair of precision resistors in the phase splitter circuit, presumably to keep it "balanced"? However even if these resistors had drifted in value I'd still expect a buzz test to yield some output. The grid voltages are strange too. There should be zero volts on the grid of the preamp stage and I'd have expected the grid voltage of the phase splitter stage to be closer to its cathode voltage. A coupling capacitor might not be coupling, but I fear a lot of components could be changed and the player still wouldn't work. Perhaps something has been overlooked? __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

26th Feb 2021, 10:15 am	#48
Edward Huggins Dekatron Join Date: Sep 2015 Location: Southwold, Suffolk, UK. Posts: 8,328	Re: Pye black box no sound Howard's point in Post#45 is correct. As mentioned before, I cannot emphasise enough the importance of the value and tolerance of the resistors in this this circuit. However, there appears to be no amplification at all as yet. Taking all these voltage readings may be of little point if some components have failed or are off value. It might be worthwhile for the OP to consider removing the amp (easy) and Posting this off to a Member familiar with this circuit and it's idiosyncracies? __________________ Edward.

26th Feb 2021, 11:33 am	#50
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Pye black box no sound What's the voltage drop across V1b's cathode bias resistor (4.7k)? Lawrence.

26th Feb 2021, 12:26 pm	#51
Edward Huggins Dekatron Join Date: Sep 2015 Location: Southwold, Suffolk, UK. Posts: 8,328	Re: Pye black box no sound Graham is absolutely correct in his Post#49, but I perversely made this point because so many readings have been taken thus far that are way off from where they should be. A more experienced restorer may be able to establish the electronic/physical issues by observation and thorough measurement. __________________ Edward.

27th Feb 2021, 7:24 am	#52
Minster97 Pentode Join Date: Nov 2013 Location: Essex, UK. Posts: 103	Re: Pye black box no sound Dear All,A number of you have mentioned a more experienced restorer ( this is my first restoration)If there is anyone available I would like to send it Any suggestions please? Gary

27th Feb 2021, 7:26 am	#53
Minster97 Pentode Join Date: Nov 2013 Location: Essex, UK. Posts: 103	Re: Pye black box no sound Forgot to mention this tenth tag under the valve holder at right angles to the others which is not connected.Don’t know what this is

27th Feb 2021, 7:58 am	#54
snowman_al Octode Join Date: Dec 2018 Location: Llandeilo, West Wales, UK. Posts: 1,092	Re: Pye black box no sound A picture would help... Alan __________________ Never Leave Well Enough Alone...

28th Feb 2021, 8:23 pm	#56
Minster97 Pentode Join Date: Nov 2013 Location: Essex, UK. Posts: 103	Re: Pye black box no sound Thank you All. I am sending it one of you who has kindly agreed to look at it for me .It would have been nice if I could have got it going but it is my first attempt and I have learned a great deal from you all. I hope my next attempt will be better

1st Mar 2021, 9:10 am	#57
Edward Huggins Dekatron Join Date: Sep 2015 Location: Southwold, Suffolk, UK. Posts: 8,328	Re: Pye black box no sound Don't feel bad about it. As a first project, this was definately not easiest amplifier to start out on. Many experienced restorers struggle with this particular generation of Pye amplifiers! __________________ Edward.

1st Mar 2021, 2:40 pm	#58
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: Pye black box no sound We look forward to seeing a full report from the repairer. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

1st Mar 2021, 4:09 pm	#59
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,572	Re: Pye black box no sound Depending on what I find wrong, I'll do a write-up of my findings and return any faulty components with the amplifier. What I could do is do a success story (assuming it IS a success)!! with details of the repair as I go. That way it's kept for reference. These are not the easiest of amps to work on for a beginner. In their day they probably didn't give a lot of trouble but of course they are now well past their intended service life and they do suffer from a lot of problems, particularly the valveholders although why that is, I don't know since the same valveholders are (were) used in many other products at the time and still function well. I'm keeping my fingers crossed that the output transformer is OK __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman..... Last edited by Sideband; 1st Mar 2021 at 4:19 pm.

26th Mar 2021, 4:46 pm	#60
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,572	Re: Pye black box no sound Update: I have now repaired the amplifier and it's on its way back to Gary. I'll do a proper write-up as time permits but probably sufficient to give a brief summary for now, circuit refs taken from Pye manual: R8 2.2M grid leak to ECC83 (pin 2) disconnected...difficult to see without moving other components....resoldered. R10 4.7K cathode of ECC83 gone high to 7.7K replaced. ECC83 low gain about half what it should be. EL42 very low....less than half what it should be. EL42 Low....about half what it should be EZ41 Emission ok but shows leak between cathode and heater. (valves checked with Avo two-panel tester) Heater contact in EL42 holder intermittent....replaced. Anode contact in EL42 valveholder broken, replaced. Heater pins in EZ41 valveholder intermittent, replaced. ECC83 valveholder showed leakage from anode to grid pin (causing low anode volts....there was about 1.75V positive on the grid). Replaced. Volume and tone controls cleaned. With a new set of valves, there is plenty of volume using my test signal source (Jason tuner) and it sounds very good through one of my bookshelf bass reflex test speakers. __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman.....