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Old 12th July 2004, 06:20 PM   #1
cowanrg is offline cowanrg  United States
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Default backwards MPSA18? what does it do?

ok, so after my long struggle, i think ive ACTUALLY found out what's wrong. i noticed that i have both MPSA18's and BC546's in my parts bin. the BC546's leads are backwards compared to the MPSA18's. I THINK i have the MPSA18's in backwards! i was looking the other's data sheet for some reason when i installed them. can the amp still work with this in backwards? i dont want to reverse it and blow the amp. ive had oversights before, so it might be right afterall... so, can i hurt anything by reversing it?
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Old 12th July 2004, 06:28 PM   #2
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Why take the risk? Figure out the right pinout, check it, and fix if necessary. If you don't do that and it still doesn't work after reversing, what have you learned? Nothing.

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Old 12th July 2004, 06:38 PM   #3
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hehe, true.

im just being overly worried because ive had so many problems getting this amp working.
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Old 12th July 2004, 06:58 PM   #4
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Exactly. It's time to do it right for a change.. ..don't take it too personal.

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Old 12th July 2004, 07:44 PM   #5
cowanrg is offline cowanrg  United States
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haha, i hear ya. since ive started this, everything ive "fixed" has created a worse problem. im just paranoid.

it seemed to have worked. my test speakers are fried, gonna go see if i can get some new ones! it measures ok i guess...

Quote:
Originally posted by janneman
Exactly. It's time to do it right for a change.. ..don't take it too personal.

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Old 12th July 2004, 08:42 PM   #6
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I've had the same problem (reversed transistors, in my case BC550C).

The effect; the current sources didn't function thereby prohibiting the entire amp to function properly.

My advice (just like Janneman's) would be not to fool around, but fix it rightaway. I've been there and I've done that. Works like a charm ......



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Old 12th July 2004, 09:12 PM   #7
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It is amazing how small things can cause big problems. Don't get too frustrated, as you're not the only one to have struggled with troublesome problems. If you want some commiseration, read my troubles getting my headphone amp up and running here where noise in the temporary test PS was causing wierd behaviour. I didn't figure it out until I gave up trying to solve it and built my final PS, at which point the problems dissappeared.
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Old 12th July 2004, 09:22 PM   #8
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Actually, if you reverse Collector for Emitter, it should work,
but the breakdown voltage is low.
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Old 12th July 2004, 10:45 PM   #9
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as in my other post to you...to check q104 and 105, reversing it on your aleph 3 could be the problem and the B-E junction of 0.5V is fed into gates of q106-109. The 1.5V you are getting across r120-123 is the B-C junction voltage instead.
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Old 12th July 2004, 10:51 PM   #10
cowanrg is offline cowanrg  United States
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i think that did it...

it appears to be working fine. i need to measure current draw, it isnt getting horribly hot. BUT, maybe before it was just getting TOO hot.

this was one LONG troubleshooting period!
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