Hello all, I wanted to ask this question here as I’ve received great answers here in the past.
So I work on a lot of vintage McIntosh gear, many of my family members run them as well as friends. I’m restoring an amp/preamp combo and gifting them to my father.
Many of the integrated and power amps from the era use the same driver board and use the same pre-drivers. McIntosh recommends upgrading them all to 2N5320 and 2N5322 (McIntosh part numbers cross reference to these parts).
With these TO39 parts being both expensive and likely won’t be around far into the future I’m hoping to find a suitable equivalent. Plus my suggested parts, I have many on hand so I wouldn’t need to place an order and they’re like 1/7th the cost.
The reason McIntosh recommends the upgrade is because they wanted transistors with higher power dissipation. I’m wondering how would the MJE243G and MJE253G with appropriate heatsink do in substitution. They have even higher dissipation, higher Vce, higher Ic, equal elsewhere, but slightly slower Ft.
and a comparison of the PNPs
Is there any reason these TO126 wouldn’t make a good drop in for the much more expensive TO39? I’m looking for long term, if I was just doing this one amp this one time I’d probably just bight the bullet and order maybe 10 of each, but I’d really like to not do that.
Here is this particular circuit that they are in, discussing Q111 and the complementary Q113.
Thoughts?
Dan
So I work on a lot of vintage McIntosh gear, many of my family members run them as well as friends. I’m restoring an amp/preamp combo and gifting them to my father.
Many of the integrated and power amps from the era use the same driver board and use the same pre-drivers. McIntosh recommends upgrading them all to 2N5320 and 2N5322 (McIntosh part numbers cross reference to these parts).
With these TO39 parts being both expensive and likely won’t be around far into the future I’m hoping to find a suitable equivalent. Plus my suggested parts, I have many on hand so I wouldn’t need to place an order and they’re like 1/7th the cost.
The reason McIntosh recommends the upgrade is because they wanted transistors with higher power dissipation. I’m wondering how would the MJE243G and MJE253G with appropriate heatsink do in substitution. They have even higher dissipation, higher Vce, higher Ic, equal elsewhere, but slightly slower Ft.
and a comparison of the PNPs
Is there any reason these TO126 wouldn’t make a good drop in for the much more expensive TO39? I’m looking for long term, if I was just doing this one amp this one time I’d probably just bight the bullet and order maybe 10 of each, but I’d really like to not do that.
Here is this particular circuit that they are in, discussing Q111 and the complementary Q113.
Thoughts?
Dan
2n5320/5322 is EBC pinout. MJE243/253 is BCE pinout. I think the 243/253 pins are fatter than the 5320/5322.
I tried to replace 5320/22 with a NTE49/50 and after 18 months a pin broke off. It didn't like being twisted around. It did have a small heat sink on it. When I tried to replace it again, I lifted the land off the PCB and trashed the board. You may have better luck with the MJE243/253. I'll spend the price for TO39 until a EBC plastic product with this wattage rating is sold. Hasn't been for 2 or 3 decades already.
I tried to replace 5320/22 with a NTE49/50 and after 18 months a pin broke off. It didn't like being twisted around. It did have a small heat sink on it. When I tried to replace it again, I lifted the land off the PCB and trashed the board. You may have better luck with the MJE243/253. I'll spend the price for TO39 until a EBC plastic product with this wattage rating is sold. Hasn't been for 2 or 3 decades already.
I definitely get your point about the thicker legs. I have a micro hand drill with tiny drill bits for enlarging holes in PCBs. I don’t think it would be an issue. As for the pin placement, I don’t get it. As with all metal case transistors the pins are in a triangle formation, as are the holes in the pcb. So you just have to turn the transistor on an angle and the center pin will either go forward or backward. So in this pic the new transistors legs are directly over the holes they would go into and it’s under zero tension or stress from the legs being twisted. I’ve replaced other devices this way and have never had an issue. Now when the three pins are in a straight line, that’s when the twisting begins.
Dan
Dan
TTC004 TTA004 have higher Ft other specs are close.
If you have the MJE 243 253 pair try those and look for oscillation. Use of a variac or 60w incadescent bulb in series with the ac line power will reduce output damage if it oscillates.
If you have the MJE 243 253 pair try those and look for oscillation. Use of a variac or 60w incadescent bulb in series with the ac line power will reduce output damage if it oscillates.
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I would have suggested the Toshiba parts as well. Caveat - thicker legs, and ECB pinout.
Edit - It's a ganky solution, but I would consider cutting the pins on the TO-126 package a little short, and using bus wire and Teflon sleeving to make the connections. to the TO-39 pads. It may be possible to lay down the package and cut the leads to line up with the holes, using bus wire. Another option would be to try a TO-92L package like the 2SA965 and 2SC2235 - the legs will be closer to the size of the TO-39, though the pinout will still be ECB. The TO-92L will do a bout 1/2W comfortably - any more, and you would need to do a slip-on heat sink or glue a piece of aluminum sheet to the package.
A gob of hot melt around the bodge my provide enough strain relief to keep the legs from breaking under vibration.
Edit - It's a ganky solution, but I would consider cutting the pins on the TO-126 package a little short, and using bus wire and Teflon sleeving to make the connections. to the TO-39 pads. It may be possible to lay down the package and cut the leads to line up with the holes, using bus wire. Another option would be to try a TO-92L package like the 2SA965 and 2SC2235 - the legs will be closer to the size of the TO-39, though the pinout will still be ECB. The TO-92L will do a bout 1/2W comfortably - any more, and you would need to do a slip-on heat sink or glue a piece of aluminum sheet to the package.
A gob of hot melt around the bodge my provide enough strain relief to keep the legs from breaking under vibration.
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Thank you for the suggestion, it’s interesting that both you wrenchone are recommending the Toshibas. I was looking at that those since I have plenty on hand, but immediately dismissed them due to their specs.
The slightly lower Veb wasn’t too concerning when looking at them for a replacement regardless of circuit, but the Ic is rated at less than half the current. Figure that would be an issue in many circuits.
But the big thing was the Ft, it’s over double that of the TO39 devices (100 MHz vs 50 MHz ). I was under the impression that a fast device would be more likely to cause oscillation. With the MJE devices I’m asking about being 10 MHz slower than the TO39 devices, it is they that I would have to worry about? So being a slower device will introduce oscillation?
Regardless of which devices I try I’ll definitely power it up on. Dim bulb tested so that if there are any issues I would prevent damage. Weird, looking at the specs I would have totally guessed the MJE devices would be the better match, I guess which is why I eliminated the Toshibas from the running.
Dan
You would probably want to use a 47ohm or so stopper resistor at the base of any of those frisky devices...
Could you please explain?
And help me understand why the lower current capable TTC004b and TTA004b devices would be a better option than the MJE243G and MJE253G. Do I have my thoughts on Ft and oscillation all wrong?
Thank you,
Dan
I replaced the destroyed PC14 with blown 2n5320/5322 drivers and lifted lands with an AX6 board. Both boards driving NTE60 output transistors, likely reboxed MJ15003. With 6 mhz TIP41c/42c drivers the highs of the AX6 board were dull & lifeless compared to the surviving PC14 board. With 30 Mhz MJE15028/29 as drivers, the sound is identical as PC14. Except the AX6 board has more gain, which I correct with balance in the disco mixer. So I suspect 40 mhz driver transistors would be capable of good sound also.
That is what I expected as well, figuring the audible difference between the 50 MHz and 40 MHz devices would be minimal. I’m confused though why others would suspect that I could see oscillating with a device that’s 10 MHz slower. I’d imagine hearing that when going from 50 MHz to 100 MHz.
I think it’s possible that the Toshiba devices could possibly sound better being faster, but I was hoping to find a solution to anytime I see those TO39 devices are called and with the Toshibas having a much lower Ic (1.5A vs 4A) and lower Veb (6V vs 7v) I would have ti do the math on their position in the circuit to make sure these currents and voltages aren’t exceeded. Plus at being twice the speed I’d then be concerned about oscillating. Unless I have my thoughts on oscillating in relation to Ft wrong.
Dan
In the end, you can go with whatever solution you find most comfortable. The suggested 47 ohm resistor for the 100 MHz devices acts a stopper to prevent oscillation. The resistor forms a pole with the Miller capacitance of the transistor.
As a thought, the faster devices may make the overall amp more stable (less lag), as long as you set them up so that they don't oscillate by themselves. With very slippery devices like a mosfet, using a stopper resistor is imperative, as mosfets are more likely to oscillate when biased in the linear region.
As a thought, the faster devices may make the overall amp more stable (less lag), as long as you set them up so that they don't oscillate by themselves. With very slippery devices like a mosfet, using a stopper resistor is imperative, as mosfets are more likely to oscillate when biased in the linear region.
That is true, but I want to make as close to the “right” decision as possible. I just want to figure out your thoughts on why you think the Toshiba devices would make a better for here. I’d love to understand the thinking. Was it because they are 100 mhz devices? To be 100% honest, I’m not all that great at figuring out the math that gets me the current that the device would be under in that position. Which is why I was looking for something that equaled the devices I was wanting to replace.
If you do know, is there any chance you could tell me the current that this device in that position will be drawing? I’d love to be able to figure that out. Then maybe I could do that for the rest of the circuits.
I didn’t realize you were mentioning the 47 ohm resistor for only the 100 MHz devices. How are those wired in? Across the base to emitter?
Thank you again,
Dan
On the mechanical side, just make sure the heatsink you will use on the TO126s is properly supported somehow by the PCB. So there is no strain on the legs.
The problem with being able to advise you re the expected dissipation of the driver stage is that the schematic shown is partial and barely readable.. Both driver transistors have compensation caps from base to collector, so that may likely be the determining factor in stability rather than transistor ft.
I apologize, unfortunately that’s 1970s McIntosh for you. If I could post a larger file I would, or I could email you if you wish.
As for the drivers that have the caps across the base to collector, I actually believe those are the pre-drivers (Q111 and Q113), the ones I’m actually changing. From what I understand the drivers are mounded to the heatsink with the outputs. Looking at the schematic you’ll see that the next pair of transistors (Q115 and Q117), their emitters drive into the bases of the outputs.
As for the capacitors on the base to collector of the pre-drivers (C115 and C117) they are .0012 uF, McIntosh’s instructions are that after the transistors have been updated to this new pair the compensation caps are to be changed to 680 pF. So if I place either the MJE devices or the Toshiba devices, these caps across their bases to emitters could very well eliminate any oscillations?
Dan