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- Jan 14, 2011
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- Gillette, Wyo.
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- Halfbiass...Electron Herder and Backass Woof
Good job Gary. You're getting them ferreted out. I am going to send you a complete set of transistors for both sides of the board. Q4 is a TO-92 form factor sitting right beside Q3, I was giving you numbers of what it SHOULD be , obviously it's something different...
Capacitors. There are a number of things you can do to help the factory board out. One of them is changing C6 to a 470uf/25 volt AUDIO GRADE cap, and then to eliminate the "latch up" tendency, add some 1N4148 diodes to the leads on the back of the board, this explains it..http://forums.phxaudiotape.com/show...-latch-up-tendency-in-Phase-Linear-Amplifiers
The rest of the electrolytic caps should be changed also and these will be in the box with the transistors.
The heatsinked RCA 40412V's were actually pretty robust, and the heatsinking adequate so I would suggest leaving them alone. There is a viable sub in the 2N3439 but it also will take a good heatsink, the 2N3439 is a better transistor by far so it will be in the bag with the appropriate heatsink also.
If a 2N1304, or 2N1305 went south then D9, or D10 went also, so there will be a handfull of 1N4148's in with the rest of the stuff.
The changing of C6's value greatly improves the low frequency response of this amplifier. I will also send the rest of the electro's to change out on the board. All diodes can be checked in circuit except D13, which will test at .079 or .080 both ways. One end of D1 or D2 will have to be pulled to test D1 and D2. One end of D4 or D5 will have to be pulled to test D4 and D5. The rest will test in circuit.
The 1N4004 diodes on the backwall are probably ok but with all the shorts you have the end of the left 1N4004 on each back wall will have to removed to test. Take em out anyway, I have had an amp returened because I didn't go with my gut feeling and did NOT replace that 5 cent part. Those will also be in the box I send.
The output transistors should be removed, the white goo cleaned up along with the transistor leads and new silpads put in their place, I will send 25 of those.
I need the values of C3, they can be different depending on which PL 14 variant you have...
Capacitors. There are a number of things you can do to help the factory board out. One of them is changing C6 to a 470uf/25 volt AUDIO GRADE cap, and then to eliminate the "latch up" tendency, add some 1N4148 diodes to the leads on the back of the board, this explains it..http://forums.phxaudiotape.com/show...-latch-up-tendency-in-Phase-Linear-Amplifiers
The rest of the electrolytic caps should be changed also and these will be in the box with the transistors.
The heatsinked RCA 40412V's were actually pretty robust, and the heatsinking adequate so I would suggest leaving them alone. There is a viable sub in the 2N3439 but it also will take a good heatsink, the 2N3439 is a better transistor by far so it will be in the bag with the appropriate heatsink also.
If a 2N1304, or 2N1305 went south then D9, or D10 went also, so there will be a handfull of 1N4148's in with the rest of the stuff.
The changing of C6's value greatly improves the low frequency response of this amplifier. I will also send the rest of the electro's to change out on the board. All diodes can be checked in circuit except D13, which will test at .079 or .080 both ways. One end of D1 or D2 will have to be pulled to test D1 and D2. One end of D4 or D5 will have to be pulled to test D4 and D5. The rest will test in circuit.
The 1N4004 diodes on the backwall are probably ok but with all the shorts you have the end of the left 1N4004 on each back wall will have to removed to test. Take em out anyway, I have had an amp returened because I didn't go with my gut feeling and did NOT replace that 5 cent part. Those will also be in the box I send.
The output transistors should be removed, the white goo cleaned up along with the transistor leads and new silpads put in their place, I will send 25 of those.
I need the values of C3, they can be different depending on which PL 14 variant you have...
