Re: Re[2]: 2N6259's

Just for information, I'm running a GO8 monitor with the WICO X-Y Pattern
generator on the cross-hatch pattern and after fifteen minutes the 2N6259
transistors are also relatively cool. I can rest my finger on them for a
few seconds - they are not unpleasantly hot (perhaps 100-115F or 40C - I'll
bring my digital thermometer tomorrow). This is AFTER I soldered the Base
and Emitter leads directly to the transistor. I believe that the sockets
might be contributing to the problems as well as contact resistance in the
small boards. To help reduce that I've coated the pins with Dow-Corning #4
Electrical insulating compound. I find it really can reduce the heat of
connections indicating a better electrical connection.

I also experimented with running the monitor with the YOKE unplugged. No
problems! Nice square wave on the output pins (#1 and #4 of the 4 pin yoke
plug). This is a safe way to test your monitor so you won't blow up the
output transistors or fry any resistors, etc. This is simply removing the
load. Hook up a scope and make sure that your signal appears to be roughly
centered across the 0V reference point for each channel.

I found a good book (Audio Power Amplifier Design Handbook - Douglas Self
(published by Newnes) at my local library that covers the theory of this
type of amplifier (treat it like an audio amp, eh?) - it's called a
Complimentary Feedback Pair (CFP) or Sziklai-Pair.

Need to understand this circuit more as I have several sick GO8 monitor
boards to fix...

John :-#)#

At 05:30 PM 07/10/2002 -0400, Mark Jenison wrote:

>Well, chalk up another 8 hours of straight running on MJ15024 transistors.
>And I can still put my finger on them. I'm putting the monitor away now;
>I've seen enough to make my decision.
>
>----- Original Message -----
>From: "Mark Jenison" <jenison@enteract.com>
>To: <vectorlist@synthcom.com>
>Sent: Monday, October 07, 2002 10:06 AM
>Subject: Re: Re[2]: VECTOR: 2N6259's
>
>
> > ----- Original Message -----
> > From: "Mark Jenison" <jenison@enteract.com>
> > To: <vectorlist@synthcom.com>
> > Sent: Thursday, October 03, 2002 11:11 PM
> > Subject: Re: Re[2]: VECTOR: 2N6259's
> >
> > > Someone suggested trying the MJ15024 transistor, so I purchased 4 of
>them
> > > and will be trying them out this weekend. I forget the exact price, but
> > > they were cheap. Will report back the results on Monday.
> >
> > Thanks to Derek Bell for sending me a spare chassis that had a good custom
> > chip on it. I replaced it in my test monitor and it works perfectly
>again.
> >
> > So I installed 4 MJ15024 transistors in a spare heat sink/fan unit, and
> > dropped it into my test monitor this weekend. Has been running fine for
>10
> > hours; transistors are running just slightly cooler than the 2N6259s in
> > another game that I'm running at the same time (2N6259s too hot to keep
> > finger on; MJ15024s just bearable -- there's some accurate measurements
>for
> > ya ;-)).
> >
> > How much testing should be done before giving a "thumbs up" on a
>replacement
> > part?
> >
> > --
> > Mark Jenison
> >
> >
> >
> >
> > --------------------------------------------------------------------------
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Received on Mon Oct 7 18:30:40 2002