Good afternoon to you
Now I might be being a dick here. But this amp is causing me pain
It came in to me with a intermittent noise issue.
I found the fault ir9 was soldered in but leg cut short it wasn't really soldered. Replaced it.
Out the job went ok
1 month later it came back distortion after a while.
I found by heating and freezing the area around iq5 it would go away. In the end I replaced all the transistors in that area iq 1to 7 and 14. As all very close together.
All changed like for like.
Tested the amp heat and freezer it all seemed OK.
Then it went to about 1/2 volume without touching it I wasn't heating or freezing at that time was on for 20 mins before it went
When I tested it I can see its working perfectly without distortion but low output
On checking using scope and signal gen I can see the signal in and out of pre amp is OK and higher level leaving the pre amp than the input.
I'm I being a dick question
But the signal entering the power amp is at same level as the output.!!!!
Is this possible?
Check all voltages 54'v +/- and 15v +/-
Checked all the transistor /diodes
Made sure the transistors I changed are good and correct ones
At output have around 3v ac with gain /vol max
I'm not an experienced tech. Just play for fun
Any assistance would be grateful thanks in advance
Schematic to follow
So set it up again so you have 3VAC going in to the power amp.
Measure the AC voltage at the following points and post your results:
IQ1 base and collector
IQ6 b & c
IQ10 b & c
"Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey
OK as follows using dmm on ac range. Between chassis and transistors
Iq1 base 3v collector 0v emitter 3v
Iq6 base 0v collector 3v
Iq10 base 3 .5v collector 0v emitter 3v
I hope this helps. Many thanks for the help.
I feared no one would help
Is there anyone that can help or shed some light on this.
Too me it makes no senses.
But believe me with a scope probes on input and output both on same setting per div etc.
Do you have both rails- +VCC and -VCC?
“Yeah, well, you know, that’s just, like, your opinion, man.”
Hi. Yes I did. 54v +/— it's OK I have sorted it now.
Resoldered the area again. And cleaned it.
Worked for 4 days 6 hours a day. Been collected to sit about in storage till this shit is over
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