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Old 22nd November 2012, 04:33 PM   #11
Mooly is offline Mooly  United Kingdom
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Very nice

(The output transistors are bjt by the way... just with you mentioning FET's earlier... but it doesn't matter, its a nice amp)
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Old 22nd November 2012, 04:40 PM   #12
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well, is anybody know a detail information of bjt transistors?
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Old 22nd November 2012, 04:44 PM   #13
Mooly is offline Mooly  United Kingdom
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Quote:
Originally Posted by aras84 View Post
well, is anybody know a detail information of bjt transistors?
Whaddya wanna know

They are "normal" output transistors (bjt is bipolar junction transistor). Most transistors big and small are bjt and are used in most designs unless it happens to be a FET device

Bipolar junction transistor - Wikipedia, the free encyclopedia
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Old 22nd November 2012, 04:49 PM   #14
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Thx, I check out wiki...
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Old 22nd November 2012, 04:55 PM   #15
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By the way, is a huge auido difference between bjt with mosfet and v-fet? Correct me pls, I know v-fets are the closest sound quality to tube amplifiers...
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Old 22nd November 2012, 08:33 PM   #16
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Originally Posted by jneutron View Post
I used the plastic insulating pads for high power transistors...every decade or so I make sure the screws holding them down are tight.

j
Along that line I was restoring a 1978 Ampex AVR-3 2" broadcast VTR. I removed all the power transistors (and there are LOT in there) and found the heatsink grease no longer grease, just the zinc oxide powder. I cleaned the residue, checked each transistor on a curve tracer and if it was good (all but 1) re-greased and re-installed. I guess the greased mica could have been replaced with silpads

TO-3 Transistor Silicon Insulator,Insulation sheet,x 50 on sale - electronic parts and components supply store

G
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Old 22nd November 2012, 08:55 PM   #17
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It might look worse than it is, but the pnp driver on the right side in the big open bottom photo seems to barely have a base leg in the solder.

Last edited by Andrew Eckhardt; 22nd November 2012 at 09:00 PM.
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Old 23rd November 2012, 06:39 AM   #18
Mooly is offline Mooly  United Kingdom
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Quote:
Originally Posted by aras84 View Post
By the way, is a huge auido difference between bjt with mosfet and v-fet? Correct me pls, I know v-fets are the closest sound quality to tube amplifiers...
The old original unobtainable depletion mode V-FET's and todays Lateral FET's are claimed by many to have valve like characteristics but as with most things there is a lot more to it than that. Good amps (that sound valve like if thats what you want) can be made with all device types including bjt.


Quote:
Originally Posted by Andrew Eckhardt View Post
It might look worse than it is, but the pnp driver on the right side in the big open bottom photo seems to barely have a base leg in the solder.
Its the latest point contact protection device... as the leg warms it parts contact with the PCB thus opening the circuit

(Very well spotted, maybe its an effect of the lens/light but it does look highly suspect... check it out aras84)
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Old 23rd November 2012, 10:29 AM   #19
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Originally Posted by Andrew Eckhardt View Post
It might look worse than it is, but the pnp driver on the right side in the big open bottom photo seems to barely have a base leg in the solder.
thank you so much i will try to fix it
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Old 23rd November 2012, 12:46 PM   #20
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Originally Posted by aras84 View Post
I really wondered, do you have a before and after picture of it
I never took pictures of it because I never think of doing so because I have cleaned up so many (I am sucker for a bargain). After that experience (and having kids) I may have gotten a little snobbish as I will pass up on what I considered, "okay integrated amps but dirty as all heck however Windex and some time will so some wonders".

It had better be something special (like a SPEC-2, a KRELL KSA-50, an ST-70, or an inch of grime covered Marantz 8b) before I get back up to my elbows in suds and stink up my garage while using my shopvac again.
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