the first run of punch 150's

bogart · Post by **bogart** » Sat Aug 22, 2009 10:51 am

this was brought to me for repair...it is a mess...missing fets and a few missing tracers...but it'll be fun to see if I can get her going.

I remember these amps quite well from back in the day...quite fondly!!!! Anyhow I thought I'd post pics and share the rework on this one as it should be pretty easy!!!!!

Post by **Eric D** » Sat Aug 22, 2009 12:27 pm

I highly doubt you will be able to fix it. Maybe you will see it as a challenge, but you will probably loose.

I have a pair of the Punch 45 version of this amp. I have spent time over the years working on them and never got them going.

They don't have PWM (pulse width modulation) power supplies. Instead they rely on an osculation method. Well, I am not an expert, but my best guess is modern transistors are built too good and are too fast. They don't oscillate like those originally did in these amps. Every time I try new FETs they just burn up.

But, your luck may be different. And if you do figure out what it takes to get these working, please let me know. I would love to have these 45s functional.

bogart · Post by **bogart** » Sat Aug 22, 2009 1:20 pm

oh man, that sucks Eric...it makes since though. I will play with it and see...maybe find some old stock fets somewhere...so is the oscillation off of an ic....

There are funny chips and in abundance....

Thanks Eric....I will play with it and see if I can round up the schematic on it...and those 45...I may have a source...will let you know for sure....

Post by **Eric D** » Sat Aug 22, 2009 2:38 pm

Well, if I remember right the amp is setup so when a FET turns on, it forces the other one off, but when off another smaller transistor forces the first one back on. The opposite occurs for the other side of the power supply. This keeps happening back and forth and generates the needed AC oscillation for the power supply transformer.

But, old FETs were slower, and my guess is the design of the transformer is actually "tuned" to the speed of the older FETs. Modern ones are significantly faster. All I can think is with modern FETs in the supply it switches so fast something breaks down. Either the transformer saturates or the FETs end up fighting each other or something. Either way, the FETs burn up. Now I don't have a deep understanding of this, so I could be way off, but all I know is I have had no luck fixing one of these and I have replaced every single transistor in the power supply trying to solve the problem.

bogart · Post by **bogart** » Sat Aug 22, 2009 2:50 pm

wow....that is crazy. Let me run it by a guy I know who may have an understanding of these amps....may be some info available somewhere as well. I am going to see if I can round up the schematics for these amps...if I can find just one It'll tell us a great deal about the overall design plan on these as I'd bet they are all similar. This amp has more issues then I can list just looking at it....burns...tracers....a handfull of resistors are obviously toast. cap need to go just being what they are....and where to find the ancient equipment to repair it....

I told the owner that this was a long shot and he is of the state of mind that it can't really be more dead either way and to play with it if I want....so I'll look into it but I doubt I can do much with it but burn up money to see it burn back up in turn....it is cool though....these were out when I was in high school and I am 37....haha....a little piece of audio history really

Misfire · Post by **Misfire** » Sat Aug 22, 2009 5:25 pm

I loved those old Punch amps! They where hot back in the day. Good luck with the repair!

bogart · Post by **bogart** » Sat Aug 22, 2009 5:30 pm

found the schematic for the 45's and some good repair notes...maybe just maybe...but after pulling the board there are so many fucked up parts that I am sure more is wrong with it then right but I am trying to learn to read and understand schematics so this is an exercise in patience and I am learning either way....

Eric....sent you the schematics for the 45's and I've got some other stuff you may be interested in....may as well be in chinese for me....

marko · Post by **marko** » Sat Aug 22, 2009 10:06 pm

i got a punch 75 in the same style, i lovingly restored it and fitted new bass/treble pots (thanks eric!!), then i sold it some time later and the buyer siad it didn't work so sent it back and guess what... bothe bass/treble pots smashed up again

(thanks royal fail

)

so i have one for restoration too but those pots are hard to find now..