i need info on an old rf punch 150

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defboy456

Member - Posts: 7

Joined: October 30, 2005

Location: United States

Posted: August 20, 2009 at 8:33 PM / IP Logged

Hi everybody.I have an old school punch 150 that i'm currently restoreing and fixing.The previous owner put tin foil over the already blown fuses inside the amp and now it has a bad output section.When I first powered up the amp to test it,I was adjusting the gains and was a little tired(burning the midnight oil) and I wound up turning the idle pots for the rail because the gains are inside the amp also.I realized then that I had no clue what the pots were supposed to be set at and now i'm in limbo with my resto.So here are my questions:Does anybody have any info on the pot settings I so stupidly turned?Does anyone have a clear pic of the board?The amp has several bad resistors(dead,high reading,low reading,burned) and I'm getting bad readings from a couple of them that are completely burned up with no stripes left.I already tried to read them,they are open(no reading).Any help would be greatly appreciated. http://s186.photobucket.com/albums/x277/defboy456/?action=view&current=punch15012v.jpg

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i am an idiot

Platinum - Posts: 13,671

This member consistently provides reliable information

Joined: September 21, 2006

Location: Louisiana, United States

Posted: August 20, 2009 at 8:41 PM / IP Logged

Turn both of them counterclockwise. All the way counterclockwise. These are the bias adjustments. If you have an Amp Meter at your disposal, I can tell you how to reset them. Either a multimeter with a 10 amp capable amp meter, or a meter on your power supply. Either one will do. Let me know if you have an amp meter.

If these pots are turned full clockwise, they will cause damage. Full CCW will introduce crossover distortion, but will not damage anything.

The 2 watt resistors are (.)1 ohm. There are some 68 Ohm 1/4 watt and 475 Ohm 1/4 watt resistors that fail. The other channel is an exact mirror image of the other. Also the Positive side of the channel is laid out just like the negative half of it. You should be able to look at the other channel or the other half of that channel to identify the resistors. I just zoomed in on your picture and noticed the arrows. The resistors are the 68 and the 475 ohm resistors I was referring to. It has been a while, I do not remember which one went to which transistor. One connects to the Output 2N6487 or 2N6490. The other connects to the driver D40D8 or D41D8. Check the other channel and see which connects to which. Replace with appropriate. A 470 ohm resistor will be much easier to find than the 475.

Let's Go Brandon Brown. Congratulations on your first Xfinity Series Win. LGBFJB

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i need info on an old rf punch 150

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