TO 66 PS mod

calman46

AK Subscriber
Subscriber
I am replacing the TO 66 (B5031) with a TIP41C and heat sink on the PS of an MX114. I notice that the flange of this TO 66 is a heat sink only and is grounded to chassis through the board traces. Is this really necessary with the new TO220 heat sink? Heating the ground path does not seem to be a good idea? thanks
 
Case of TO-66 is collector, as well as the tab on the TO-220. It is necessary for electrical connection on the TO-66. The TO-220 can also use the center lead, but if replacing a TO-66, usually the tab is used. (Tab and center lead are electrically the same)
 
Not this one . It looks like a TO66 its a Bendix B5031. The case is a sperate part from the EBC connections and the case is grounded . Mind came apart its just glued together . Do I need to ground the TO220 replacement heatsink ?
 
Peaked at manual. There is no reason I can think of to ground heat sink. If you do so anyway, remember you need more hardware to insulate transistor from heatsink. My guess is they used the ground plane underneath to increase heatsinking area. But that is just a guess….
 
I'm looking into putting the new TO 220 on the top of the board . I don't like heating up the ground plane plus it the heat would dissipate better. I'm good with the TO 220 hardware, thanks
 
I owed an MR73 tuner in 1972 that was drifting during warmup. That's when I noticed that the weird Bendix "pseudo-TO-3" was causing the phenolic circuit board to discolor due to heat. Screwed directly to the board with no heatsink of any kind. My solution was to to have a little aluminum bracket bent that "floated" a LM317 TO-3 adjustable regulator above the board. It was not hard to modify the circuit and determine the resistor ratio. Long story short, I still had to send it to MAC to solve the original problem but the heat problem on the board was gone.
 
Had you been having any issues with your mx114? I have an mx114, and I have a sagging 16v power supply. It is low at initial turn on, like 10-12 volts, and slowly creeps up to 14. This affects the multiplex circuit and I only get mono on fm until I hit 13 volts or so. When the input is switched to aux and the tuner is out of operation I get 16v out from that power supply. I have recapped the unit and all the resistors and diodes on that power supply check out okay, so my main suspect right now is that bendix transistor. Any suggestions or similar behavior observed would be helpful. Thanks!
 
I never notice what you mention .I have now replaced the Bendix with a TIP41C. I have a slight output imbalance that I've been chasing on/off for years .
 
Did you add any heat sink to the tip41c? Was it difficult to mount it on top of the board? I think I will do the same.
 
Yes I did add a TO 220 heat sink with a piece of silicon pad between the heat sink and board. I cut the trace so the TIPc mounting screw could never short the collector to ground. I was concerned even with the screw insulated it was in the middle of the ground trace . I don't like doing this type of mod but in this case I felt it justified . I used the inner screw hole
 
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