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Old 25th May 2013, 05:22 PM   #161
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Location: Lyon
Hi All

After a long time, finally some pics of my A28 with brand new caps
Many thanks to Nikolay for the 2 blue BC caps 10000uF/40V, and to Patrick for his helping hand with Mouser order. Nice to see concerned DIYer's
I've encountered some troubles due to caps size and "extended" existing holes for them to fit in.
Be carefull when you desolder components, PCB traces are IMHO very "weak".

The amp is sounding fine, but the right channel is much warmer than the left.
Could someone point me to what to check and "howto"
Thanks for your help

Regards

Phil
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Old 25th May 2013, 08:26 PM   #162
jazko is offline jazko  United Kingdom
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Lovely amplifier. Glad I could help.

Regards,
Nikolay
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Old 28th May 2013, 05:35 PM   #163
Michel is offline Michel  Canada
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Location: L'Assomption, QC
Hello Phil,

The temperature difference is due to improper biasing of the output stages. You have to adjust the 4.7 k blue trimmer, for each channel, until you can read approximately 300 mA on your ammeter that should be connected to the fuse holder contacts. Do not forget to remove the fuse for this measurement. Unless you have two ammeters, do one channel at a time. Make sure you let the amp warm-up for at least an hour and readjust until it stabilizes. When this is done measure the voltage between the emitters of each pair of output transistors to confirm it is approximately the same.

Good luck!

Michel
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Old 29th May 2013, 08:52 AM   #164
AndrewT is offline AndrewT  Scotland
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You could fit a 0r5 resistor inside a dead fuse.
Then you can let the amp run with the 0r5 in the supply feed. Intermittently measure the voltage drop across the fuse holder to monitor the current passing.
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Old 30th May 2013, 01:09 PM   #165
Bonsai is online now Bonsai  Taiwan
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Quote:
Originally Posted by jazko View Post
Lovely amplifier. Glad I could help.

Regards,
Nikolay
Class A magic sound .
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Old 30th May 2013, 01:21 PM   #166
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300mA is rich AB, not Class A
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Old 30th May 2013, 03:08 PM   #167
Bonsai is online now Bonsai  Taiwan
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I run my 15Watter at 1.4 amps. It runs HOT
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Old 2nd August 2013, 07:53 PM   #168
Yle160 is offline Yle160  Canada
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Default Question a Michel

Montréal, 2013-08-02

Bonjour Michel,

Je demeure sur la rive sud de Montreal et je suis a la recherche d'information concernant un Sugden P28B. J'ai besoin de faire vérifier l'ampli. Est-ce que tu fait cela ? connais-tu un endroit fiable ? Peux-t-on communiquer ? tu peux m'écrire a mon email y_lefebvre@hotmail.com

Hi Michel, i live in the south shore of Montreal. I search information about a sugden P28B. i would like to bring my amp for a check up. do you do this ? do you know a good place ? can we communicate ? you can send me an email to y_lefebvre@hotmail.com.

Merci pour ton aide.

Yves
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Old 11th August 2013, 02:02 PM   #169
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Default Smokey Mountains

Hello, replying to this thread.

I have bought a pair of sugden p28, both identical rear heatsink gold text on front.
They have been standing for 10 years unused.
Some work has been done to them, a note says that its rewired to go mono.
When connected i got some smoke coming out of one amp, and also no sound.
Evidently some component blew, so i opened and a resistor between the 2 leftside transistors the one furthest in towards the sink was burned.
When i measure the transistors i get 1st 4 volts 2nd 0 volts 3/4rd 0,62 volts.
And over the fusesholders 80ma.

Also when i connected the preamp something broke (in the preamp), feels like an shortcircuit?

So i wonder if some nice soul could send me schematics so i can get some spares for the amp.
And if someone have an idea about what i should look for or even had a similar
problem please tell.

Im going mono.....

my adress:
a r o n @ g r i n d v i k . n u
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Old 23rd September 2013, 09:01 PM   #170
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Hi, I just purchased an A28II. The cost was a resonable €50, as one channel was dead.

The dead channel was because of a blown fuse :-)

But I would wery much like the schematics for the amp, if possible ? Please email to kenneth(at)farlig.dk

Best regards
Kenneth Jensen
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