Hi, Gang,
I'm making a new PC-43 with Eagle and do not have an original board. I'm incorporating all of the Boak-Jung mods from AA plus a few other tweaks of my own.
I know that Q6 has to thermally track Q10 & Q11 by mounting on the same heat sink and have laid out the board for that.
Looking at the copy of the board fab in the assembly manual, Q8 and Q9 are adjacent.
Can anyone kindly provide a picture of a populated PC-43 or tell me if Q8 & Q9 should also share their own heatsink?
Also, does anyone know where to get the little TO-92 clamps Dynaco uses to attach Q6 (and other TO-92s) to a heatsink? These are used on the ST-150 and all versions of the ST-4xx, but I'm not finding anything like that in Digi-Key or Mouser.
Thank you!
Cheers,
Frank
I'm making a new PC-43 with Eagle and do not have an original board. I'm incorporating all of the Boak-Jung mods from AA plus a few other tweaks of my own.
I know that Q6 has to thermally track Q10 & Q11 by mounting on the same heat sink and have laid out the board for that.
Looking at the copy of the board fab in the assembly manual, Q8 and Q9 are adjacent.
Can anyone kindly provide a picture of a populated PC-43 or tell me if Q8 & Q9 should also share their own heatsink?
Also, does anyone know where to get the little TO-92 clamps Dynaco uses to attach Q6 (and other TO-92s) to a heatsink? These are used on the ST-150 and all versions of the ST-4xx, but I'm not finding anything like that in Digi-Key or Mouser.
Thank you!
Cheers,
Frank
You can buy Japanese TO92 transistors on EBAY and extract the metal tab from them. I've successfully used MJF15030's for bias transistors on Phase Linear amps. The device is a TO220 in an isolated case. I cut off the the 3 pin connector cables from computer case fans which fit perfect on the leads of TO 220 transistors. The transistors mounts on the heat sink and the cable easily solders to the board. You can buy the cable assembly from MPJones.
Thanks for the reply, d3imlay, I'm not sure I was clear in what I'm describing.
The clip I am referring to is the one in the middle. This is from an ST-400 and the concept is the same - thermally coupling a bias transistor to drivers. Of course I could make a few, I'm just wondering if anyone has some.
The clip I am referring to is the one in the middle. This is from an ST-400 and the concept is the same - thermally coupling a bias transistor to drivers. Of course I could make a few, I'm just wondering if anyone has some.
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Dynaco used a TO-92 becaused it saved them 20 cents when that would buy a cup of coffee. TO-202 has better thermal coupling to the heat sink, and would be a better part, but costs 40 cents. Dynaco was huge in part because they were a price leader. The function is less than one tenth hertz temperature pickup, so capacitance of the junction of a bigger part doesn't matter. Main thing wrong with BC139/140 or MJE340/350 is that they are BCE instead of EBC. But you are laying out a new board, there is no reason you should force yourself to use an obsolete unavailable part. Yes, you can get TO-92 EBC. No, you can't buy that clip.
I've never seen a clip like that. I had TO-92 clips on an obsolete board that were folded over strips of 16 ga metal with a hole drilled in the overlapped flange. But the burglar took that board 9/15/20.
In general, drivers on separate heatsink from output transistors has been proven to inhibit thermal runaway. Reason darlington output amps are such boat anchors, they blow up too often. There is no reason for drivers to share a common heat sink. I've got screw on thermalloy or something sinks on TO220 drivers on the AX6 board in my ST-120. Original ST-120 board had TO5 2n5320/22 drivers with separate heat sinks. I haven't been able to buy those since I bought the ST120 in 1986. Yes, NTE has a pin compatible part. No, the Ft is not specified to be 50 mhz. Ft matters in a driver, NTE subs sounded bad and 6 mhz TIP31c/32c sounded bad on top octave solo piano too. One pair of 2n5320/22 survived & sound great driving MJ15003 output transistors.
I've never seen a clip like that. I had TO-92 clips on an obsolete board that were folded over strips of 16 ga metal with a hole drilled in the overlapped flange. But the burglar took that board 9/15/20.
In general, drivers on separate heatsink from output transistors has been proven to inhibit thermal runaway. Reason darlington output amps are such boat anchors, they blow up too often. There is no reason for drivers to share a common heat sink. I've got screw on thermalloy or something sinks on TO220 drivers on the AX6 board in my ST-120. Original ST-120 board had TO5 2n5320/22 drivers with separate heat sinks. I haven't been able to buy those since I bought the ST120 in 1986. Yes, NTE has a pin compatible part. No, the Ft is not specified to be 50 mhz. Ft matters in a driver, NTE subs sounded bad and 6 mhz TIP31c/32c sounded bad on top octave solo piano too. One pair of 2n5320/22 survived & sound great driving MJ15003 output transistors.
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indianjo - of course I'm using modern devices, mainly ONSemi. Good idea changing the bias comp to a TO-220 - that's complete now. To be clear - the Dyna drivers and their outputs are on completely different heatsinks.
Back to the other question - the original layout has Q8 and Q9 adjacent to each other.
Can anyone kindly provide a picture of a populated PC-43 or tell me if Q8 & Q9 should also share their own heatsink?
Back to the other question - the original layout has Q8 and Q9 adjacent to each other.
Can anyone kindly provide a picture of a populated PC-43 or tell me if Q8 & Q9 should also share their own heatsink?
Hi, any updates on your progress with Q8 and Q9 on the PC 43 boards? I have been confused about these for some time now. I can tell you that in all of the PC 43 boards that I have seen, there is no heat sink for Q8 or Q9, they sit free on the board. I cannot reconcile the ECB orientation of the transistors on the board vs. the schematic vs. the data sheets for the transistors, I must be missing something in my interpretation. I have photos of original PC 43 boards (and the similar PC 36 boards) that the transistors face opposite directions, but if you go by the datasheets of the MPSA20's and the BC307-8-9 series, they ought to face the same direction. I have rebuilt one ST-150 with PC36 boards with the transistors facing the same way, in order to match the ECB orientation on the schematic and board, and that amp works great and sounds fantastic. Now I have done the same to a PC 43 based amp that I am working on and the circuit seems to be all screwed up. Unfortunately, I do not have the experience or test equipment to really diagnose what is going on.
I fix them with 1. a DVM 2. an analog voltmeter with a series capacitor on 20 VAC scale 3 a pocket FM radio with earphone plug to dual RCA plug adapter. Also trash speakers from the charity resale shop. Knowledge, you can get here. I did. My first repair the ST120 was putting out 20 w/ch, 40 w total.