Sugden A21 series 1

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richardcooper2k
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Re: Sugden A21 series 1

Post by richardcooper2k » Fri Feb 26, 2016 9:42 am

I guess the other thing to try is put everything back in again, power it up and measure some voltages

Or another to buy a full set of caps and transistors for that channel and replace the lot

Anyway, the next step will have to wait a week, i'm back home next Friday
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Mike H
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Re: Sugden A21 series 1

Post by Mike H » Sat Feb 27, 2016 6:46 pm

richardcooper2k wrote:yep 2 meg resistance range

so connect a resistor from base to collector ?
What sort of value ?
Offhand no idea ~ 100k? 47k? 10k? Try several...
And what am i looking for (send me a link if it's easier - i tried google but didn't find anything yet)
You're looking for whether it conducts when the bias is applied.

There don't seem to be any problems with the diode tests so it should.
 
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richardcooper2k
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Re: Sugden A21 series 1

Post by richardcooper2k » Sat Mar 19, 2016 1:46 am

I seemed to be stalling with the fault investigation and simply replacing all the transistors on the faulty power amp channel has become the more attractive option. So i have ordered them along with replacement electrolytics including the power supply/output coupling ones (ordered 3300uF rather than 2500uF).
I also stumbled across another sugden circuit which seems to have an extra input stage but has the additional components the one i have has, that aren't on the series 2 circuit diagram. i.e. the parallel diode, the extra resistor near the trim pot and the RC network near the output:

http://sound-au.com/tcaas/sugden10w.pdf
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Mike H
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Re: Sugden A21 series 1

Post by Mike H » Sat Mar 19, 2016 4:27 pm

Very interesting!
 
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