The fisher 250TX with a power supply overheating transistor

Fred and Larry
Thank you for your help in repairing the 250tx.
I am using it enough.
It has 2 non-original output transistors (channel R)
I have here one fisher TX 50. I believe that the output transistors of this TX50 are the same 250TX. Can I remove the TX50 output transistors and use in output of 250TX?
Thank you
 
MAYBE! I ran the output #'s thru the NTE xref and got the same #'s. The problem with NTE is that they x-ref a whole range of parts with one. AndNTE just rebadges their parts so you have no idea what you areactually getting and who actually made it. Chances are that they are Chinese fakes is high. With FISHER using proprietary part numbers on their transistors it's very hard to find the actual specs for each part #. At least I haven't found one.

The problem is that the TX-50 is rated for 16watts and the 250-TX is rated for approx 30-32 watts. So it's highly probable that you can swap the 250TX transistors into the TX-50 and they will work and loaf along. Going the other way, TX50 to 250TX the transistors would possibly be overloaded.


TX-50
TR1036-1 (pnp) NTE # 183
TR1037-1 (npn) NTE # 182

250tx
TR02058-5 (pnp) NTE # 183
TR01058-5 (npn) NTE # 182

For Either unit. NPN use KSC2690AYS ($0.50ea @ mouser ) and for PNP KSA1220AYS ($0.45ea @ mouser) These are heavier duty than the NTE's and are made by FAIRCHILD. Let me check my stash and see if I have some to spare.
 
.....
Insulate the + POS Probe with tape or heatshrink tube to the very end. You just want the tip of the probe to be exposed.
.....

Alternately, use an insulated clip lead and connect it to the point to be checked. Now, you can look at the meter without being distracted by having to keep looking at the probe and the possibility that the probe will move when you look back at the meter.
 
For Either unit. NPN use KSC2690AYS ($0.50ea @ mouser ) and for PNP KSA1220AYS ($0.45ea @ mouser) These are heavier duty than the NTE's and are made by FAIRCHILD. Let me check my stash and see if I have some to spare

Larry
So, Can i replace the power output transistor from my Fisher 250TX (npn TR01058 & pnp TR02058) by:
npn KSC2690A-Y from Fairchild
pnp KSC1220A-Y from Fairchild;

or
npn MJE3055 from Motorola
pnp MJE2955 from Motorola;

You agree?
Regards
 
For Either unit. NPN use KSC2690AYS ($0.50ea @ mouser ) and for PNP KSA1220AYS ($0.45ea @ mouser) These are heavier duty than the NTE's and are made by FAIRCHILD. Let me check my stash and see if I have some to spare

Can i use a motorola MJE 15032 and MJE15033 as output transistor equivalent too? replacing 01058 and 02058?
Regards
 
I would say probably ok. Compare the specs of the Fairchilds and the Motorola's.
 
Thanks larry and fred
Is hard to find some good transistors here.
I have replaced one pair of the output transistors 01058 and 02058 (TO127) by ST brand TIP3055 and TIP2955. I think that is a low quality transistor.

I found here a C2690A-Y from fairchild. Maybe can i find a C1220A-Y from fairchild too. this pair can be a good substitutes to originals 01058 and 02058?

MJExxxxx are usually drivers, not outputs. Outputs would be MJ(no E)xxxxx.
I just can find a MJExxxx series.

is there any other couple of good transistors that I can use as substitutes for 01058 and 02058? My 250TX have one pair original, and other TIPs ST brand.
Regards, and thanks
 
TIP2955 and TIP3055 are rated at 60 volts. You have 64 volts rail to rail and with high line voltage, that could be higher. These transistors will work but you will not be able to drive the amplifier to maximum power where the output rail peaks close to the supply voltage.
 
Hi fred and larry
Finally, i found a 2SA 1220A PNP transistor.
Yesterday, i installed a 2SC2690A (fairchild) and a 2SA1220A (Nec) ou R side of output from my 250TX.
Great results. Great sound. I drank some beers to listen better. The side with new transistores are fine, OK.
In another channel, that have the original output transistors, i can listen some plocs,
Maybe i will replace the transistores from another side too, with new C2690 and A1220 transistores.
Thanks for your help.
Regards.
 
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Hi guys. I Have one fisher 250 TX, in excellent condition. I replaced all electrolytic caps from power supply. I replaced too one diode and one resistor. Now, the receiver power on. Phono and aux inputs is normal. FM and Am inputs isn't function perfectly, with a noise. The tune - o - matic function perfectly. When TURN ON (aux, phono or tuner) the receiver, 5 seconds after this, the transistor (TR1001- with circular heatsink) from power supply over heating... too much hot.... Thank you a lot if you can help me.
Hello, a little late to this discussion but how did you leave the hot power supply (Fisher 250TX 2040-1 board Q951 TR1001) transistor over heating issue. I have the exact same problem, the unit had operated intermittently due to this. Replaced the transistor, it works but still runs hot, it's hard to believe this is normal for this power supply design.
Please advise, thank you!
 
hi googleplex
well. I had this same feeling, but larryderoin insisted that it was normal, i just left it alone.
since then, despite only using the fisher 250tx sporadically, it has never had problems with the power supply.
i think was he right.
be sure to replace the power supply electrolytics too
regards.
 
@googleplex. Q951 drops B+ from 60V down to 15v and 12v. It generates a lot of heat, hense the heatsink. See posts 9, 10, 12 and 14. Fred suggests changing R854 to 250Ω 5W to halve the dissipation from the transistor and put it on the resistor. Resistor is better able to handle heat loading. See freds post #14. That transistor will run hot no matter what you do. You can drop it some with resistor change, but it will still run hot. The factory was still getting a handle on how to drop voltages and keep them reasonably cool as they were still transistioning to Solid state from tube.

What exactly did you replace it with. And did you add heatsinking to it?? If a KSA1220A or AYS get some TO-126 /TO-220 type heatsink's and fit them to the KSA1220. If you can sandwich the transistor, even better. Use heatsink grease btwn the sinks and the transistor.
 
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Many thanks to all, havols, larryderouin most recently, for the comments on this old thread! Yes, seems true, this power supply design was not Fisher's finest moment and it will run like this, mine did for 30 of the last 50 years.

But I've resolved my problem with it to my satisfaction... Q951,a 0.8W max power dissipation part was dissipating 1.8W according to my measurements and calculations so I too limited collector and emitter currents by changing R954 to 135ohm/4W and R953 to 235ohm/4W resistors, they had been running hot too. Also, to address the 19.1V reading on the 15V supply going off the board at pin 9E, I replaced zener diode CR952, pin 9E is now at 15.6V. I can't be sure it was bad, the overdriven Q951 may have pushed the diode reverse current along it's V-I curve to 19.1V - the diode is a 5W unit, might be able to take it (it did out-of-circuit bench test fine, 15.2V at 75mA).

To cool Q951, the puny heat sink is replaced by two finned back to back Thermalloy units staked to the PCB, each with twice the thermal conductivity of the original. The board was browned and the transistor solder joints compromised to the point of intermittent operation.

Bottom line - only wanted to reassemble once, did so with these changes - Q951, R954 and R953 run noticeably cooler now and the sections that had been running on 15V supply at 19.1V should be happier. My signal strength meter that had been pegged out when any station of reasonably good power was tuned in is usable again, back to a 4.5 reading max.

New parts:

Q951 = NTE128 TO-39 NPN
CR952 = NTE5130A
heat sinks (2) = MarVac Electronics www.ebay/str/marvacelectronics HS-14 snap-on HS T0-39 Item ID:25587573538

I don't know if my Flir camera thermal images will embed here below, was trying to show these temps, recorded after only the new Q951 heat sinks were added:

Q951 30.2 deg C
Q951 HS 72.7 deg C
R953 84.6 deg C
R954 76.9 deg C

P0bbRQF
 
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