Sugden P28 and P128
Hi daveC,
I think I do have the schematics for both amplifiers.
Let me know if you are interested and I will look for them.
What is wrong with your P28 anyway?
The first things that go wrong after awhile in most of the Sugden products are the capacitors in the power amplifier section.
Sugden has always had the extremely bad habit of using capacitors that are too close to the working voltage. They do tend too to put resistors , transistors or zener diodes that radiates heat close to them. When replacing them always use 105° C long life capacitors. The other things that go wrong after the capacitors are the BC639 and BC640 drivers which have a little too much on their plate.
They usually do not die but instead develop a fuzzy sound. When I have this problem I find it more efficient to replace all 4 driver and both bias transistors. Another thing you have to look for is the 2SB776 and 2SB896 power transistor insulators, if they look like real mica they are fine but if they look on the thin side and have a milky color replace them as soon as you can because they do tend with time to cause a short circuit. The high value preset is to adjust the voltage at mid point and the low value is to adjust the bias which should be set at around 300 mA measured through the supply fuse. Let it sit and readjust periodically for at least an hour.
If after that you do not find the problem let me know and I will try to give you a hand.
Regards,
Hi daveC,
I think I do have the schematics for both amplifiers.
Let me know if you are interested and I will look for them.
What is wrong with your P28 anyway?
The first things that go wrong after awhile in most of the Sugden products are the capacitors in the power amplifier section.
Sugden has always had the extremely bad habit of using capacitors that are too close to the working voltage. They do tend too to put resistors , transistors or zener diodes that radiates heat close to them. When replacing them always use 105° C long life capacitors. The other things that go wrong after the capacitors are the BC639 and BC640 drivers which have a little too much on their plate.
They usually do not die but instead develop a fuzzy sound. When I have this problem I find it more efficient to replace all 4 driver and both bias transistors. Another thing you have to look for is the 2SB776 and 2SB896 power transistor insulators, if they look like real mica they are fine but if they look on the thin side and have a milky color replace them as soon as you can because they do tend with time to cause a short circuit. The high value preset is to adjust the voltage at mid point and the low value is to adjust the bias which should be set at around 300 mA measured through the supply fuse. Let it sit and readjust periodically for at least an hour.
If after that you do not find the problem let me know and I will try to give you a hand.
Regards,
sugden P28
Hi Michel,
i'll write in English so our readers understand(anyway,i'm not too used to writing French canadian,tabernacle!).
i've been reading your post with great interest since i'm the proud owner of one of these machines,which has turned me down.i have repaired it, but not plugged it in yet(i will let you know in my next post).
To make a long story short,could you send me a pdf version of the circuit diagram?
Many thanks,
philippe.
Hi Michel,
i'll write in English so our readers understand(anyway,i'm not too used to writing French canadian,tabernacle!).
i've been reading your post with great interest since i'm the proud owner of one of these machines,which has turned me down.i have repaired it, but not plugged it in yet(i will let you know in my next post).
To make a long story short,could you send me a pdf version of the circuit diagram?
Many thanks,
philippe.
Hello King,
There are not many things that can do this kind of problem in a P28.
If my memory is good there is not even a speaker relay in there which could be the cause.
The only things I can see is a dirty rca connector or the mono/stereo toggle switch that is inside.
A good cleaning with a quality product such as DeoxIT should cure hesitations.
One other thing, sometimes the fuse holders tabs get loose when they have had frequent careless fuse replacements.
I am not even sure it can happen with a P28 but if it is the case, all you have to do is remove the fuse
and press the tabs between your fingers until they nearly touch each other and put the fuse back.
I have seen that fuse holder tabs problem numerous times, especially with the ones that have the beige base.
The best way to avoid excessive stress to the tabs when replacing a fuse is to use a fuse puller.
The only one I recommend for that is the Ideal Industries 34-015.
Good luck!
Regards,
Michel
There are not many things that can do this kind of problem in a P28.
If my memory is good there is not even a speaker relay in there which could be the cause.
The only things I can see is a dirty rca connector or the mono/stereo toggle switch that is inside.
A good cleaning with a quality product such as DeoxIT should cure hesitations.
One other thing, sometimes the fuse holders tabs get loose when they have had frequent careless fuse replacements.
I am not even sure it can happen with a P28 but if it is the case, all you have to do is remove the fuse
and press the tabs between your fingers until they nearly touch each other and put the fuse back.
I have seen that fuse holder tabs problem numerous times, especially with the ones that have the beige base.
The best way to avoid excessive stress to the tabs when replacing a fuse is to use a fuse puller.
The only one I recommend for that is the Ideal Industries 34-015.
Good luck!
Regards,
Michel
Hi Michel and others, I open up the P28 last night, cleaned the
toggle switch with contact cleaner; and also discovered that indeed one of the 2A fuse holder was loose, so I squeeze the fuse holder with my fingers put the fuse back and now is fuse is tightly seating in place.
Since it was pretty late so I listen to it for may be 20 minutes, and so far no cutting in and out; hope it really resolved that problem.
I also got a reply from Sugden from England; they send me the A28II spec., they said the P28 use the same spec. only it's a power amp.
Stereo: 44 Watts/ch
Bridged: 95 watts
Question: How do you bridge the P28 to 95 watts mono?
Thanks again Michel, really appreciated your input.
Regards,
King
Toronto, Ontario, Canada
toggle switch with contact cleaner; and also discovered that indeed one of the 2A fuse holder was loose, so I squeeze the fuse holder with my fingers put the fuse back and now is fuse is tightly seating in place.
Since it was pretty late so I listen to it for may be 20 minutes, and so far no cutting in and out; hope it really resolved that problem.
I also got a reply from Sugden from England; they send me the A28II spec., they said the P28 use the same spec. only it's a power amp.
Stereo: 44 Watts/ch
Bridged: 95 watts
Question: How do you bridge the P28 to 95 watts mono?
Thanks again Michel, really appreciated your input.
Regards,
King
Toronto, Ontario, Canada
Michel,
Would you please send me the P28 schematic?
My P28 (heatsink on the side) went down and appears the fuzzy sound exactly the same as you mentioned in the thread. The fuzzy sound could last fuzzy sound 5 minutes and worked well initially. Now it comes fuzzy sound only without stop.
My technician (he is good at analog but I am more a digital guy) needs a schematic to examine not only capcitors also power transistors to close the two months mightmire on blindly check those components.
AAfter I read your post, we'd like to follow your suggestion to start over the examination of my P28 (capcitors and BC639/640 drivers) to avoid meassurement in the dark.
Thanks
Would you please send me the P28 schematic?
My P28 (heatsink on the side) went down and appears the fuzzy sound exactly the same as you mentioned in the thread. The fuzzy sound could last fuzzy sound 5 minutes and worked well initially. Now it comes fuzzy sound only without stop.
My technician (he is good at analog but I am more a digital guy) needs a schematic to examine not only capcitors also power transistors to close the two months mightmire on blindly check those components.
AAfter I read your post, we'd like to follow your suggestion to start over the examination of my P28 (capcitors and BC639/640 drivers) to avoid meassurement in the dark.
Thanks
Hi Julian,
To fix a P28 with heatsinks on each side you need the A28B schematic.
Give me your email address and I will send it to you.
There are 5 parts marked by an asterisk on the parts overlay, make sure they are the value shown.
Do not hesitate to contact me if you need more help.
Regards,
Michel
To fix a P28 with heatsinks on each side you need the A28B schematic.
Give me your email address and I will send it to you.
There are 5 parts marked by an asterisk on the parts overlay, make sure they are the value shown.
Do not hesitate to contact me if you need more help.
Regards,
Michel
Michel,
Much appreciated...please send me the schematic to juliansk@ms2.hinet.net and julian.fann@intel.com these two email addresses.
I do love the sound of Sugden so that my concern is those capacitors. I am not sure how much sound quality those capacitors can impact.
My technican (an anlog guy) do concern sound quality by replacing those drivers.
We are guessing if brand of those capacitors and drivers matter on sound quality. How do you think?
I hope my bad English is readable...apology if this makes you confused. I can try to rephrase.
Best regards
Much appreciated...please send me the schematic to juliansk@ms2.hinet.net and julian.fann@intel.com these two email addresses.
I do love the sound of Sugden so that my concern is those capacitors. I am not sure how much sound quality those capacitors can impact.
My technican (an anlog guy) do concern sound quality by replacing those drivers.
We are guessing if brand of those capacitors and drivers matter on sound quality. How do you think?
I hope my bad English is readable...apology if this makes you confused. I can try to rephrase.
Best regards