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Old 10th May 2006, 08:42 PM   #1
shimp is offline shimp  United States
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Default Looking for Part for old Punch 45 TP3055A

Local stereo shop sent me an old Punch 45 amp to fix, I believe this is the really old 1986 model punch 45. It has "The Punch" "Rockford Fosgate" in gothic script on the bottom cover, says it's a mosfet 45.

It has a blown mosfet. It's a motorola part, labeled TP3055A

I cannot for the life of me find a replacement. Closest thing I may have found is made by Fairchild MTP3055VL.

Will that part work? If not does anyone know of another substitute without having to change out any other parts to make it work in the circuit? I'd rather replace it with an original part if I could find one.

Thanks!
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Old 10th May 2006, 09:16 PM   #2
Netlist is offline Netlist  Belgium
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shimp,
Good chance it's a MTP3055A: V-MOS, 60V, 12A, 40W, <0,15ohm(6A)
It can be replaced (technically) with
BUZ 20, IRF 530..533, 2SK919, 2SK1427...

MTP3055VL: FREDFET, LogL, 60V, 12A, 48W, <0,18ohm

Good luck in your search, maybe someone over here has a few of these old devices lying around.

/Hugo
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Old 10th May 2006, 09:26 PM   #3
anatech is offline anatech  Canada
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Hi shimp,
What Hugo is telling you about the replacements is correct.

Now you can fix the amp.

-Chris
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Old 10th May 2006, 09:33 PM   #4
Netlist is offline Netlist  Belgium
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Note, as I have no idea what a FREDFET is, that I wouldn't recommend it as a replacement...unless someone confirms it can be used.

/Hugo
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Old 10th May 2006, 10:04 PM   #5
anatech is offline anatech  Canada
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Hi Hugo,
I was referring to the other suggestions listed.

The Fairchild MTP3055VL seems to be optimized for logic level control (read: switching applications). You want to have a plain jane mosfet in there.

The Fairchild part might work. Don't know.

If these are for the supply, change them all so they behave in a similar way. Otherwise the amp may come back.

-Chris
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Old 11th May 2006, 02:44 PM   #6
shimp is offline shimp  United States
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Thanks for the quick replies. I know most of the newer RF amps use IRF540 and IRF9540. I have lots of these in stock, is there a chance I could use these, without having to make any changes?

The TP3055A in question is for the audio output, not the power supply.

Again, thanks,

Chris
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Old 11th May 2006, 03:05 PM   #7
anatech is offline anatech  Canada
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Hi Chris,
Stick a pair in and set the bias. Watch how stable the bias is after running the amp.

Probably will work fine. These are rated higher so I can't see any problems.

-Chris
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Old 12th May 2006, 06:28 AM   #8
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Since this is an audio output stage, might it be a plain old NPN 2N3055? I'm unfamiliar with the insides of old RF car amps, so I may be way off.
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Old 12th May 2006, 06:50 AM   #9
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Quote:
Originally posted by Brian Donaldson
Since this is an audio output stage, might it be a plain old NPN 2N3055? I'm unfamiliar with the insides of old RF car amps, so I may be way off.

No, when Motorola (as was) brought out P and N-channel general purpose 60V power fets, they had the bright (?) idea of calling them MTP2955 and MTP3055, showing that they were intended for the same sort of role as the old bipolar workhorse 2955 and 3055s. (Whether it caused more confusion than anything else is arguable!)
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Old 12th May 2006, 01:13 PM   #10
anatech is offline anatech  Canada
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Hi Ouroboros,
Quote:
(Whether it caused more confusion than anything else is arguable!)
It sure did! Many shops had techs that don't know a fet from a bipolar. They used the ECG book back then, some even would cross ref in and then out again! I have talked to some that would only match case style and knew the parts as "output transistor" only. "It's what I use for output transistors, it's the same as ECGxxx".

Those guys didn't stand a chance. I got a lot of botched service jobs in.

-Chris
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