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Hoffman Amps Forum image Author Topic: 1969 Soundtronics M-A200A bias Wiring  (Read 2577 times)

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Offline plexi50

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1969 Soundtronics M-A200A bias Wiring
« on: February 20, 2018, 05:32:21 pm »
I have a 1969 100 watt M-A200A monster amplifier. I have built the normal fixed bias circuit. The PT has no bias tap that i can find. I found one wire but it only has +14.00 volts DC on it so that's out of the question. I have a 200K resistor tapped from the SS bridge rectifier to one leg of the PT high voltage lead. From there to the bias circuit using a 10K ohm trimmer pot. I can not get any voltage to pass through the 1N4007 diode / DC after the 200K tap resistor.  I remember years ago Steve taught me to use a ,047 or .1 capacitor in place of the resistor but that has no results either. What in the heck am i doing wrong here? The diagram below is what is how i have it wired minus the tube rectifier.

Offline sluckey

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Re: 1969 Soundtronics M-A200A bias Wiring
« Reply #1 on: February 20, 2018, 05:52:47 pm »
As you know, what you have won't work with a bridge rectifier. Look at the bottom of page 5 of this pdf for the solution...

     http://sluckeyamps.com/misc/Amp_Scrapbook.pdf
A schematic, layout, and hi-rez pics are very useful for troubleshooting your amp. Don't wait to be asked. JUST DO IT!

Offline plexi50

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Re: 1969 Soundtronics M-A200A bias Wiring
« Reply #2 on: February 20, 2018, 06:00:21 pm »
Yes thanks Steve. Been a long time since running into this. I cant upload any other pics because they are to large a file size.

Offline plexi50

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Re: 1969 Soundtronics M-A200A bias Wiring
« Reply #3 on: February 20, 2018, 06:45:02 pm »
Got it done and working Steve. Bottom left corner of page 5. Thankyou!

Offline plexi50

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Re: 1969 Soundtronics M-A200A bias Wiring
« Reply #4 on: February 20, 2018, 06:59:04 pm »
Want to post a pic of the work but my file is over 1050 kb. Did Doug change the file upload size?

Offline PRR

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Re: 1969 Soundtronics M-A200A bias Wiring
« Reply #5 on: February 20, 2018, 07:25:37 pm »
No. Probably your camera got bigger.

Image size-How to reduce it

Offline plexi50

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Re: 1969 Soundtronics M-A200A bias Wiring
« Reply #6 on: February 20, 2018, 09:14:25 pm »
I ran into that problem using this new LG K20 plus camera that takes 13 megapixels so I quit using that for pictures but I went back to using my old camera which should be the one I used to use for all my amplifier picture uploads. I'll have to play with it and see.
« Last Edit: February 20, 2018, 09:30:33 pm by plexi50 »

Offline plexi50

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Re: 1969 Soundtronics M-A200A bias Wiring
« Reply #7 on: February 20, 2018, 09:29:03 pm »
I converted the 13 mega pixle camera pic's. I forgot i had to convert them with Free Image Converter. Dah!
« Last Edit: February 21, 2018, 11:49:27 am by plexi50 »

Offline sluckey

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Re: 1969 Soundtronics M-A200A bias Wiring
« Reply #8 on: February 21, 2018, 07:36:53 pm »
Good to see you still kickin'. Is this gonna be a big plexi?   :icon_biggrin:
A schematic, layout, and hi-rez pics are very useful for troubleshooting your amp. Don't wait to be asked. JUST DO IT!

 


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