Re: Re[2]: 2N6259's

I've just run the GO8 monitor with the original 2N6259's for about four
hours. Temperature on the case is 66C for a cross-hatch pattern that fills
roughly 90% of the screen. A simple "+" pattern runs closer to 40C. Now on
to other GO8 boards & HV cages...I have a pile.

In researching the driver transistors it appears to me that either the
MJ15024 (250Vceo) or the MJ15022 (200Vceo) will sub quite nicely for the
2N6259. They have the same gain, same current rating, same wattage rating
(250W). The only info I don't have for the 2N6259 is the maximum speed when
used in a switching application. For the MJ15022/4 it is 5Mhz.

I do recommend that the ALL the connectors to the output transistors be
carefully examined with the suggestion that small jumpers might be a good
idea, or using the DOW #4 Electrical grease. I also RECOMMEND that the
transistors be soldered to the sockets - I moved the wires from the socket
directly to the Base and Emitter pins and soldered them on. This should
remove contact resistance as a contributing factor to failure on the GO8's

I have been informed that running the monitor without the yoke might not be
such a good idea for the GO8 monitor (it is OK I think for the Wells
Gardner), so I am going to experiment with a simple load - a pair of 11watt
light bulbs (115V) in place of the yoke. These should allow a visual
indication of problems, and yet be self current limiting - the brighter
they get the higher their resistance - this should reduce the risk of
burning out driver transistors during test, yet allow the feedback to work
correctly.

John :-#)#

At 06:03 PM 07/10/2002 -0700, John Robertson wrote:
>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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>>
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Received on Tue Oct 8 11:43:16 2002