Sugden A21 series 1
- Mike H
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#16 Re: Sugden A21 series 1
At this point I would unsolder all the o/p trannies and test them.
If the drivers are OK the circuit might even start working and stabilize at half supply Volts.
I've saved off the schematic and I was going to put the component values on it including what Richard posted but not had time yet.
Might be able to sim in LTspice.
If the drivers are OK the circuit might even start working and stabilize at half supply Volts.
I've saved off the schematic and I was going to put the component values on it including what Richard posted but not had time yet.
Might be able to sim in LTspice.
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
- Mike H
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#17 Re: Sugden A21 series 1
A quick Google suggests 2N3055 is a better match to BDY20.richardcooper2k wrote:VT6 is the one that has been replaced previously (it's now 2N3773 rather than BDY20).
But obviously someone's been having a go at trying to repair in here.
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
- pre65
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#18 Re: Sugden A21 series 1
If the power transistors are different now, would it not pay to change them all ?
The only thing necessary for the triumph of evil is for good men to do nothing.
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
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- Old Hand
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#19 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 would be interesting to see what difference the differences from the series 2 circuit make
If it is possible to sim the circuit it would be interesting to see what difference the differences from the series 2 circuit make
Thoughts are just little stories that our brains tell us !
- Mike H
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#20 Re: Sugden A21 series 1
Good old Cricklewood to the rescue again.
There ya go then.
There ya go then.
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
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#21 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 elsewhere
What to check next ?
I am going on holiday for a week tomorrow (Friday), back the following Friday
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 elsewhere
What to check next ?
I am going on holiday for a week tomorrow (Friday), back the following Friday
Thoughts are just little stories that our brains tell us !
#22 Re: Sugden A21 series 1
The driver maybe?
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
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- Old Hand
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#23 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
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
Thoughts are just little stories that our brains tell us !
- Mike H
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#24 Re: Sugden A21 series 1
What was this exactly? Should be high resistance in both directions. Only exception being if some bias is put through base to emitter. But diode test is not the best for that.richardcooper2k wrote: Both tested ok from emitter to collector both directions
Diode test base to emitter and base to collector, OK, where positive is on the base (NPN device). In reverse, should be infinite resistance.
To test collector to emitter, best done using Ohms range WITH some bias current applied to the base (I often use fingers placed between collector and base), works best with an analogue moving needle type multimeter on a high resistance range.
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
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#25 Re: Sugden A21 series 1
Same again with the other driver VT5
Seems OK
Seems OK
Thoughts are just little stories that our brains tell us !
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- Old Hand
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#26 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
Unless it was in a direction it was supposed to behave like a diode
Thoughts are just little stories that our brains tell us !
- Mike H
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#27 Re: Sugden A21 series 1
OK then!
Altho 'OL' could also mean the transistor is 'blown' open circuit, so a biased test will prove it's still working.
Altho 'OL' could also mean the transistor is 'blown' open circuit, so a biased test will prove it's still working.
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
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- Old Hand
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#28 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)
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)
Thoughts are just little stories that our brains tell us !
- Mike H
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#29 Re: Sugden A21 series 1
You are using the resistance range aren't you? Won't work in diode test.
Also these trannies wil be low gain so fingers might not be enough, may need a bias resistor.
Also these trannies wil be low gain so fingers might not be enough, may need a bias resistor.
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
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- Old Hand
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#30 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)
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)
Thoughts are just little stories that our brains tell us !