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Sugden P28
Sugden P28
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Old 5th December 2014, 05:56 AM   #191
iamjbj is offline iamjbj  Philippines
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Join Date: Dec 2014
Quote:
Originally Posted by Michel View Post
Bonjour Philippe,
Are the heat sinks on each side or at the back of the amplifier ?
Send me your email address so I can send the schematics.
Salutations,
Michel
Hi Michael, I own 2 P28s with heatsinks at the back. Can you spare a copy of the schematics for me at iamjj11@me.com? I also have the C28 preamplifier but no schematicz. Can anyone else help? Thank you from a novice Sugden owner.
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Old 2nd January 2015, 06:40 AM   #192
DennyG is offline DennyG  Australia
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Join Date: Feb 2010
Location: Sydney
Default A28 volume control knob freewheels on shaft

Quote:
Originally Posted by Michel View Post
(Edited)
You probably do not need to replace the volume potentiometer as a cleaning usually corrects the problem.
For this cleaning to be effective you need to use a quality product like DeoxIT®, #D5S-6 from Caig.
If your potentiometer is an Alps Black Velvet you need to lift the film pressed over the connections to be able to reach the slots and gain access.
If it is soldered to the main pcb I think you will have to unsolder it to be able to clean it.
Michel
I've had a scratchy pot in my A28 and took Michel's advice above. I had to remove the ALPS pot because it was soldered to the board. There was extreme difficulty removing to knob but I was able to lever the knob off without doing any damage. I assumed the fit was an interference fit and age had effectively 'glued' the parts together.

However, after putting the pot back the knob is now a free fit on the shaft and with the short shaft there is no way I can use a different knob with a screw to hold it in position. Does anyone have a solution to this problem that I can try?
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Old 2nd January 2015, 02:58 PM   #193
AndrewT is offline AndrewT  Scotland
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Join Date: Jul 2004
Location: Scottish Borders
A gap filling adhesive might take up the excess clearance.
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regards Andrew T.
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Old 3rd January 2015, 06:26 AM   #194
DennyG is offline DennyG  Australia
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Join Date: Feb 2010
Location: Sydney
Default A28 bias voltage dropping over time

Quote:
Originally Posted by AndrewT View Post
A gap filling adhesive might take up the excess clearance.
Thanks Andrew. I'll try that first.

Just checked the bias current on the A28 after an extensive warm up and it's dropped below 200mA on both channels from the nominal 300mA I set it at two and a half years ago. Is this normal?
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Old 6th March 2015, 04:04 AM   #195
iamjbj is offline iamjbj  Philippines
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Join Date: Dec 2014
Quote:
Originally Posted by Michel View Post
Bonjour Philippe,
Are the heat sinks on each side or at the back of the amplifier ?
Send me your email address so I can send the schematics.
Salutations,
Michel
Hi Michel! I read this and maybe you can help me coz I need the Sugden P28 schematics real bad. Something went wrong with my amp and my tech needs to work on it. My email address is jborama@gmail.com. I will appreciate it very much! Thanks!
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Old 11th January 2017, 04:50 PM   #196
dundo is offline dundo
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Join Date: Mar 2011
Hi Michael,
I am about to get my hands on a Sugden P28 b , power amp with coolers on sides. Please be kind and send me a service manual if you have one. I have an intention of "refreshing" it and without original data there no sence starting... My e-mail is darko960@gmail.com
I will post pictures of it after I get in my hands.
rgds from Split, Croatia - Darko
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Old 27th February 2017, 08:02 PM   #197
thanatos78 is offline thanatos78
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Join Date: Nov 2011
I'm working on a A28 MKII with a blown output. I need to find substitutes for 2SD896 / 2SB776

Does anyone have suggestions for good matching modern equivalents ?
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