Nakamichi RE-1 or Receiver 1 2SD313E 2SB507E Power Supply Transistors

[JayHam79]

Hello all... I've got a question regarding the NPN/PNP transistor pairings (2SD313E and 2SB507E) in the local power supply of this particular unit, which is prone to generate an excessive amount of heat. At ambient room temperature, the PNP 2SB507E (100-200 Hfe range) transistors Hfe measured 112 and 129 while the NPN 2SD313E (also 100-200 range) measured 121 and 103. Unfortunately, one of the D313E's legs broke off due to excessive heat and is unusable, hence the need to find a replacement and/or substitute.

Below will be a list of what I've been able to research on my own as far as substitutions are concerned and one pairing in particular seems to fit the bill nicely...

OEM from unit:
2SD313E: 121Hfe and 103Hfe (broken leg)
2SB507E: 129 Hfe and 112 Hfe

Options...
1: New STMicroelectronics from Digikey
TIP41C (NPN) and TIP42C(PNP). I've ordered 10 of each, all of which measured as follows:
41C: All measured 54 +/- 2
42C: All measured 135 +/- 2
Will a mismatch of 80 between the 2 cause issues in a power supply and if so, could this be offset by adjusting the bias.

Or...
2: 2SD313R Transistors from parts units I have laying around...
Utilizing the original OEM PNP 2SB507E transistors and pair them with a Sanyo 2SD313R that I have from a past Pioneer SX-450 restoration. I'm not able to locate specific data related to this proprietary transistor but it appears to have no Hfe gain range, and if so, could I substitute the R suffix by Sanyo for the E suffix that was supplied by the factory if the gain measurements are close enough?

My readings for the 2SD313R from the Pioneer at ambient room temperature...
(1)Hfe: 145
(2)Hfe: 137
(3)Hfe: 201
(4)Hfe: 155

Any input from the AK community is greatly appreciated and hope you all have a wonderful day.

 

[JayHam79]

Just a little update... I'm out of protect mode and temps seem stable. I hope... After a few more days of further research, I decided to install the 2SD313R with the 137 and 145 rated transistors from my SX-450 output section and so far it seems stable. I need to grab a higher wattage bulb for the DBT just to be safe. After that, Ill test the voltages at the transistors to see where Im at and then check the overall temperature to see how things have cooled. And don't forget... ADD HEATSINKS! Add them to any transistor in either power supply as they need to be cooled.

 

[JayHam79]

So... The schematic states the voltages for Q317/Q318 are 19v Base , 34.9v Collector and 18.5v Emitter. Q320 and Q321 are -19v Base, -35.6 Collector and -18.5v Emitter.
With my DMM, I measured the following...

Q317: 17.6v Base, 41.4v collector and 18.45v Emitter
Q318: 18.01v Base, 41.4v Collector and 18.48v Emitter
Q320: -18.64v Base, -42v Collector and -19.6v Emitter
Q321: -18.36v Base, -42v Collector and -19.6v Emitter

Unit is stable and the protect mode hasn't been activated but the collector voltage is a little concerning...

 

[sregor]

Looks good. FWIW I believe you reversed the base and emitter measurements...
Collector voltages are unregulated, so depend on line voltage and load (drop through resistors R340 and 350)

 

[JayHam79]

Looks good. FWIW I believe you reversed the base and emitter measurements...
Collector voltages are unregulated, so depend on line voltage and load (drop through resistors R340 and 350)

Thank you. It's quite possible the measurements were reversed. My brain gets confused and/or shuts off when Im viewing something translucent from behind or anything that is mirrored. The supply voltage from the system remote PCB (red lines) to R349 and R350 measured +54.3v and -54.3v at the test pin, which are now cool to the touch whereas before they would burn your finger sitting at idle in protect mode. Both resistors measured 223ohms out of circuit. Would an increase of 7v at the collector pose any stability issues?

 

[sregor]

Would an increase of 7v at the collector pose any stability issues?

No - these are just pass transistors, so stability is not an issue, anyway.
The more current that the circuit supplies, the higher the voltage drop across the resistors, and the lower the collector voltage. So no load at all would be 54 volts on the collector. I suspect it will change depending on what mode the receiver is switched to, depending on what is connected to the supply voltages - that's just the way it works. It could just stay the same, depending on how they (the manufacturer) did it...

 

[JayHam79]

No - these are just pass transistors, so stability is not an issue, anyway.
The more current that the circuit supplies, the higher the voltage drop across the resistors, and the lower the collector voltage. So no load at all would be 54 volts on the collector. I suspect it will change depending on what mode the receiver is switched to, depending on what is connected to the supply voltages - that's just the way it works. It could just stay the same, depending on how they (the manufacturer) did it...

Awesome. Once again, thanks for the info. I'm just thankful I had those proprietary Pioneer 313R's laying around that seemed to be a good match.

 

[tarior]

It's fairly common for the PNP of a complimentary pair to have more gain than the NPN. In that pass regulator circuit, it is of no consequence whatever.
Good call on adding heatsinks.

 

[JayHam79]

It's fairly common for the PNP of a complimentary pair to have more gain than the NPN. In that pass regulator circuit, it is of no consequence whatever.
Good call on adding heatsinks.

The heatsinks were a no-brainer for me, though I do I wonder how many cents were saved during production by excluding them

 

[JayHam79]

Figured I'd include an update on the Nakamichi' longterm functionality/reliability over the past month and a half...
I was a little worried about the possibility of heat related issues for the first few days and decided to limit powered on time to a few hours, slowly increasing that time over the course of week until I felt everything internally was stable. As of today, there haven't been any stability issues with either the local power supply repairs or the main power supply voltage regulator IC swaps with parts from an eBay parts unit...

 

[JayHam79]

Next item to address is the "noisy at times in the past" to currently non-existent tone circuit and channel balance functionality. If I am correct, the signal should be compromised by the transistors Q204/Q205 if they are in fact faulty. It appears to me the signal is processed through the transistors and balance circuit before the pre-out jacks. There was a noticeable thump and some noise generated when depressing the tone cut/engage button back in 2023, before the power supply failures.