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by richardcooper2k
Sat Mar 19, 2016 1:46 am
Forum: Solid State
Topic: Sugden A21 series 1
Replies: 33
Views: 6220

Re: Sugden A21 series 1

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...
by richardcooper2k
Fri Feb 26, 2016 9:42 am
Forum: Solid State
Topic: Sugden A21 series 1
Replies: 33
Views: 6220

Re: Sugden A21 series 1

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
by richardcooper2k
Fri Feb 26, 2016 12:23 am
Forum: Solid State
Topic: Sugden A21 series 1
Replies: 33
Views: 6220

Re: Sugden A21 series 1

yep 2 meg resistance range

so connect a resistor from base to collector ?
What sort of value ?
And what am i looking for (send me a link if it's easier - i tried google but didn't find anything yet)
by richardcooper2k
Fri Feb 26, 2016 12:09 am
Forum: Solid State
Topic: Sugden A21 series 1
Replies: 33
Views: 6220

Re: Sugden A21 series 1

Tried all 4 both ways collector-emitter on 2M resistance scale - all OL
I tried dabbing my finger across the base and collector while i was doing it but it didn't seem to have any effect (on all 4)
by richardcooper2k
Thu Feb 25, 2016 11:52 pm
Forum: Solid State
Topic: Sugden A21 series 1
Replies: 33
Views: 6220

Re: Sugden A21 series 1

And yeah by tested OK i meant i i got "OL" on tester (over limit)
Unless it was in a direction it was supposed to behave like a diode
by richardcooper2k
Thu Feb 25, 2016 11:49 pm
Forum: Solid State
Topic: Sugden A21 series 1
Replies: 33
Views: 6220

Re: Sugden A21 series 1

Same again with the other driver VT5
Seems OK
by richardcooper2k
Thu Feb 25, 2016 11:20 pm
Forum: Solid State
Topic: Sugden A21 series 1
Replies: 33
Views: 6220

Re: Sugden A21 series 1

Tried same thing with one of the drivers VT3.
As i was removing it i noticed it was 2N3440 instead of BDY52 like the other 3 drivers. So looks like it has previously been replaced
Tested it in the same way and it seemed fine
by richardcooper2k
Thu Feb 25, 2016 8:52 pm
Forum: Solid State
Topic: Sugden A21 series 1
Replies: 33
Views: 6220

Re: Sugden A21 series 1

Hmm. So i disconnected the output transistors on the failed channel. I used the diode tester on my multimeter. Both tested ok from base to emitter and base to collector both directions Both tested ok from emitter to collector both directions So either the problem only shows up under load or it is el...
by richardcooper2k
Tue Feb 23, 2016 7:07 pm
Forum: Solid State
Topic: Sugden A21 series 1
Replies: 33
Views: 6220

Re: Sugden A21 series 1

I think the fitted BDY20 s are very similar to the BDY38 s in the schematic. They just have a higher voltage rating so i think they should be fine. BDY20 s are £3.60 from Cricklewood so i'll probably stick with those as i think they are probably the origionals If it is possible to sim the circuit it...
by richardcooper2k
Tue Feb 23, 2016 11:04 am
Forum: Solid State
Topic: Sugden A21 series 1
Replies: 33
Views: 6220

Re: Sugden A21 series 1

VT6 is the one that has been replaced previously (it's now 2N3773 rather than BDY20). I wonder if C12 has gone short circuit. But you would pick that up when setting the quiescent current as you are looking for 0.8 colts across R19 which is parallel to it. Could be intermittent.
by richardcooper2k
Tue Feb 23, 2016 10:46 am
Forum: Solid State
Topic: Sugden A21 series 1
Replies: 33
Views: 6220

Re: Sugden A21 series 1

Ah, yes. That would make sense to me now. VT6 is open circuit - low resistance - so not much heat generated at that point
by richardcooper2k
Mon Feb 22, 2016 11:51 pm
Forum: Solid State
Topic: Sugden A21 series 1
Replies: 33
Views: 6220

Re: Sugden A21 series 1

Ok, so i have traced the circuit and it is most similar to the one Mike linked to for the A21 series 2: http://www.audiomisc.co.uk/JES/A21series2/circuit.html I will list the differences: R5 is 4k7 instead of 1k2 R12 is 5k6 instead of 56k R16 is 100 instead of 200 R20 is 0.7 instead of 0.6 The repla...
by richardcooper2k
Sun Feb 21, 2016 11:45 pm
Forum: Solid State
Topic: Sugden A21 series 1
Replies: 33
Views: 6220

Re: Sugden A21 series 1

I've been having a look and it seems it is a hybrid of the 2 circuits. Whether it was made on the cusp of change from the series 1 to the series 2 or maybe Pete Hartley modded it when he was doing repairs. I am going to try and sketch out the schematic so i can see it myself and post it here. My fri...
by richardcooper2k
Sat Feb 20, 2016 11:34 am
Forum: Solid State
Topic: Sugden A21 series 1
Replies: 33
Views: 6220

Re: Sugden A21 series 1

So i managed to get the thing apart to gain some sort of access to the power board. Initial investigations revealed to things on the failed channel. 1) an electrolytic capacitor with a dry joint at one end (it just pulled straight out) 2) what i think is a diode which was only attached at one end. T...
by richardcooper2k
Fri Feb 19, 2016 7:10 pm
Forum: Solid State
Topic: Sugden A21 series 1
Replies: 33
Views: 6220

Re: Sugden A21 series 1

Thanks for the responses. Much appreciated I forgot to mention the owner said the signal (music) faded away gradually over time rather than stopping all of a sudden. I wondered if that would be more indicative of a capacitor ? Anyhow, if i can figure out how to get the darn thing apart i had figured...