Marantz 250 Transistor Replacements

[Stoddrob]

In a separate post titled Marantz 250 Restoration Project 2026, I mentioned a Marantz 250 Complete PLUS Ultra rebuild kit offered by a fellow AK member. I purchased a customized version of this kit. While it did include many necessary component replacement, it left out many others. So maybe not so complete and not so ultra after all.

The benefit of the kit was that the transistors included were "matched."

I would like to post some of the components NOT included in the kit, and my measurement (components removed) of those original components, and ask for opinions as to whether there are any that appear solid and reusable. So let me present what was in these amp boards (right and left channel) and their testing results. I am using a new FNIRSI LCR-P1 Transistor Tester.

Read left to right. ID is provided in the first row for each transistor location; Then right channel component; then left channel component; then type of transistor. Then note.
Test data is on lines below that. First line (L-R) is right channel component test result, then left channel component test result.

Column spacing was unfortunately eliminated.

Location: Right Ch. Left Ch. Type Note:

Q501/Q502 -- Orig. 2N5961 replaced in each channel with new replacement 2N5961 from kit


Q503 Motorola I50 MPS A65 PNP Darlington
128 hFE 12770 hFE.
991uA N/A
607 mV Ube. 1176 Ube

Q504 SPS1951 SPS 1951 NPN
120 hFE. 110 hFE
1.11 mA. 1.02 mA
608 mV Ube. 599 mV

Q505 -- Orig. 2N4125 replaced with 2N3906 from kit
Q506 -- Orig. 2N4123 replaced with 2N3904 from kit

Q507 -- Orig. S39613 replaced with 2N5416 from kit
Q508 -- Orig. SJ2582 replaced with 2N3440 from kit

Q510 -- Orig. SJ2586 replaced with 2SC4793 from kit
Q511 -- Orig. SJ2585 replaced with 2SA1837 from kit

Q516 MPS A43 MPS A43 NPN
37 hFE 69 hFE
576 mV 560 mV

Q517 MPS A93 MPS A93 PNP
46 hFE 89 hFE
603 mV 614 mV

Q518 MPS 6519 MPS 6519 PNP
215 hFE 232 hFE
663 mV 644 mV

Q519 1928 1928 NPN
409 hFE 452 hFE
665 mV 672 mV

Q520 2N4123 2N4123 NPN Note: Kit recommended replacing original MPSA20 with new kit-provided MPSA20
71 hFE 89 hFE
646 mV 618 mV

Q521 MPS 6519 MPS 6519 PNP
215 hFE 265 hFE
660 mV 643 mV

Hopefully when I post this these columns will stay intact and the summary of components will be useful. Thank you!

 

[Stoddrob]

Well...column width spacing was removed and the columns collapsed....but I think you can still read each component location going left to right and see results of right and left channel component testing.

 

[Stoddrob]

Motorola MPS A65 (Darlington) EBC Pinout (Image in second two photos with test results last photo)
Q503 PNP

Original Component (same as listed above). Image in first two photos.
12770 hFE
1176 mV Ube

Five NOS Motorola Components Tested (see image):

10514 hFE
5.05 mA Ie
1126 mV Ube

22992 hFE
5.23 mA Ie
1106 mV Ube

26039 hFE
5.20 mA Ie
1138 mV Ube

29585 hFE
5.22 mA Ie
1137 mV Ube

29865 hFE
5.21 mA Ie
1148 mV Ube

 

[Stoddrob]

Motorola BC547 — CBE Pinout
Q504 NPN (Right Channel Amp Board)
(AK Post Recommended Replacement of Original Motorola SPS1951 with EBC Pinout)

Test Results of Original SPS1951:
118 hFE
1.09 mA Ie
611 mV Ube

Ten (10) of 43 NOS Motorola BC547 Components Tested:
Majority in 500-600 hFE range.

Low:
445 hFE
650 mV Ube

450 hFE
646 mV Ube

High:
588 hFE
645 mV Ube

638 hFE
642 mV Ube

 

[Stoddrob]

Motorola MPS A93 — EBC Pinout
Q517 PNP

Original Component Test Result - Right Channel (First two images) :
46 hFE
603 mV Ube

Original Test Result - Left Channel:
89 hFE
614 mV Ube

Ten (10) NOS Motorola MPS A93 Test Results:

107-117 hFE Range. Average: 113 hFE
628-631 mV Ube

Note: The only concern here is that the NOS transistors do not have the color code on the back and do not have the gold leads. But the test results are extremely consistent. These were purchased from Orchid Sound Electronics in Phoenix, AZ.

 

[Stoddrob]

Fairchild 2N5961— EBC Pinout
Q501/502 (Differential Pair)

Original Left Channel Set Test Results:
217 hFE
1.96 mA Ie
671 mV Ube

511 hFE
2.70 mA Ie
655 mV Ube

Note: They should be closely matched especially in hFE….so this pair needed to be replaced.

Original Right Channel Set Test Results:

304 hFE
2.74 mA Ie
665 mV Ube

353 hFE
2.10 mA Ie
660 mV Ube

Note: These two were closer in matched results but low hFE compared to replacements below.

I purchased twenty (20) Fairchild 2N5961 transistors. These have the same markings as the originals except the NOS ones have a green and partial white stripe mark on the backs. The results, in ranges, were were consistory between 500 and 600 hFE (15 out of 20). Low was 278 hFE and high was 624 hFE. Nearly all Ube were 650. Ie results were between 2.51 mA and 3.04. Most were 2.75-3.00 mA.

I was able to get some very closely matched sets from this purchase.

 

[Stoddrob]

Motorola MPSA43 — EBC Pinout
Q516 NPN

Original Left Channel Test Result:
69 hFE
657uA Ie (.657 mA)
560 mV Ube

Original Right Channel Test Result:
37 hFE
358 uA Ie (.358 mA)
576 mV Ube — Note: Ube is the Base to Emitter Voltage of a Bipolar Junction Transistor (BJT).

Note: First two images are of one of the two original transistors from the left amp board at Q516

I tested 10 (NOS) MPSA43 from a reputable Seller. The leads are not gold and there is no color code on the backs. However, the test results were very consistent. Range was 67 To 81 hFE with most between 76 and 81. Only two were under 70. All were in the 600-610 uA range — or .6 to .61 mV Emitter Current.

It looks like my Right Channel transistor needed to be replaced but the Left Channel appeared to be OK.

The other strange thing is that the FNIRSI LCR-P1 showed the Pinout on these new NOS Motorola MPSA43 to be CBE. This has been the case several times with this tester. As I understand its a well-reported problem with this tester. So don't go by the tester for Pinout. Its not the best tester (by far) but the other test result parameters tend to be very consistent from component to component. However, the Motorola datasheet and the original transistors both make it clear they are EBC.

 

[Stoddrob]

Motorola MPS6519 — EBC Pinout
Q518/Q21 PNP

Original Motorola MPS6519 Right Channel Test Results:

215 hFE
2.00 mA Ie
663 mV Ube

215 hFE
1.93 mA Ie
660 mV Ube

Original Motorola MPS6519 Left Channel Test Results:

232 hFE
1.57 mA Ie
644 mV Ube

265 hFE
1.73 mA
643 mV Ube

Originals are shown in the first two images.

These are some of the most difficult replacements to find (I believe). There are lots of Chinese copies on the market. I came across a supply of Original NOS with Motorola stamp mark and color coding on backs (see last two photos). While my originals tested relatively good (especially right channel ones), I wanted to find good matched sets for each channel. These NOS are shown in the second two images. They do not have the gold leads, however. I could and might actually use the right channel transistors again.

Out of ten (10), five tested between 232 and 234 hFE; three tested at 245 hFE; and 2 registered 260 hFE and 268 hFE.
All were 1.60 — 1.70 mA Ie and 650-670 mV Ube (average around 655).

 

[Stoddrob]

Fairchild BC550C — CBE Pinout
Q519 NPN
(AK Post Recommended Replacement of Original Motorola SPS"1928" with EBC Pinout)

Original Motorola "1928" Right Channel Test Results:

409 hFE
3.67 mA Ie
665 mV Ube

Original Motorola "1928" Left Channel Test Results:

452 hFE
4.04 mA Ie
672 mV Ube

Originals are shown in the first two images. They have gold leads. The left channel transistor has a BETA paint blotch on the back.

Twenty (20) NOS Fairchild Semiconductor BC550C were tested for replacement of originals (second two images):

Five (5) have 440-470 hFE with 3.95-4.20 mA Ie and 650 mv Ube;
Seven (7) have 490-505 hFE with 2.6-2.65 mA Le and 630-640 mV Ube;
Eight (8) have a 460-480 hFE with approx. 2.5 mA Ie and approx. 635 mV Ube (insignificant variance of Ie and Ube)

Why such a disparity on Ie results in the first five? 1 mA to 1.5mA variance to all the others.

Which to use? Reinstall originals? I would lean towards using four of the first five with mid-400 hFE but higher Ie and Ube like the originals.

Note: As an update, I decided to reused the original SPS 1928 transistors. They test good.

 

[Stoddrob]

Q503 PNP
Right Channel
Motorola I50 Transistor
128 hFE
991 uA Ie
607 mV Ube

I have not seen this transistor in any post on a Marantz 250 power amplifier. Usually you will find MPSA65 (Darlington) or maybe a SPS1952. Do you think a Motorola I50 the same as a Motorola SPS1952?Or do you think a SPS1952 is a MPSA65 (Darlington)?

Why would the type of transistor in the two amp boards be so different? I mean, a Darlington in one and a normal PNP in the other (at least the Service Manuals say it is a PNP)? This was definitely a factory transistor and not a replacement. It had faded brown coloring on the top of the transistor.

Also, the Marantz 250M Service Manual says Q503 is a PNP MPSA65. That would apply to both channels.

I replaced both Q503, Right and Left Channel, with MPSA65 transistors. They were both tested at just shy of 30,000 hFE with identical 5.21 mV ie and nearly identical Ube (1141 and 1143 respectively).

Would there be any reason to be concerned with this choice?

I have never found anything on the SPS1952 in terms of datasheet and I can’t find anything on a Motorola I50 either. See images.

 

[Stoddrob]

As a final post, I have attached a labeled amp board with the locations of the components I have replaced and substituted or reused and labeled the components used which relate to the detail above. Maybe it will be helpful to someone. It would have been helpful to me.

 

[Jose Jimenez]

Where are you at with this amplifier?

 

[Stoddrob]

Where are you at with this amplifier?

I have been delayed due to illness and too many other things to also do. I hope to power-it up and do some testing again next week. I was having problems getting any voltage reading from pre-driver transistors Q507 & Q508. I did install the output drivers but could not get a BIAS reading at R531 & R532. I want to first try to find out why I’m not getting a voltage of .6v from the metal covers of the pre-driver transistors and then to try to get a BIAS reading from either R531/R532 or R552/R553 test points.

 

[Jose Jimenez]

OK, get well and when you feel better you will be able to get it done! I enjoy working on this amplifier and find it similar to the 16/16B amps before. I will look to see if I have a clear service manual and schematic copy. I do not know how good yours may be. Take care.

 

[Stoddrob]

OK, get well and when you feel better you will be able to get it done! I enjoy working on this amplifier and find it similar to the 16/16B amps before. I will look to see if I have a clear service manual and schematic copy. I do not know how good yours may be. Take care.

Jose, I got some time this last week to work on the amplifier. I changed the pre-driver transistors (Q507 & Q508) to install tested NOS Motorola 2N5415s instead of new 2N5416s. See Marantz Service Bulletin from August 1976 below. I also removed both sets of potentiometer in both channels to clean them and test them. That gives me peace of mind. I replaced the differential set Q501/Q502 with NOS Fairchild 2N5962. Both sets were significantly above 500 hFE and matched as closely as possible. Which was an improvement on the old ones which beer more like 225 hFE and not that closely matched as I was led to believe.

Check out my latest post. Marantz 250 Repair Testing

I included some images of testing done with a handheld oscilloscope and signal generator. I got a good sine wave at 1k Hz and with 100mv. Also at 200mv. Next step is to test right channel and then hook-up my new Siglent oscilloscope and see how that looks.

Rob

 

[Marty R]

I’m curious as to how you connected the collector of Q511, in the photo it is soldered to the screw however I believe that screw is isolated from the circuit? Did you run a jumper on the foil side?

 

[Stoddrob]

I’m curious as to how you connected the collector of Q511, in the photo it is soldered to the screw however I believe that screw is isolated from the circuit? Did you run a jumper on the foil side?

Yes, I followed the example of another AK Member and attached and soldered to the screw. I also believe that the instructions I received from the "kit" when I bought the parts including the transistor for Q511.

While it seems to work (as far as I can tell) I recognize that there are different variants of the 250 and the one I have may be different from the earlier designs and therefore you may be right. But would it even work if there was no collector connection? I did not add a jumper.

Further, I had an issue with the failure of transistor Q508 on both channels which caused the resistor R528 to start smoking and burn through badly. On both channels. I was thinking -- why this would happen? What is the root cause? I doubt both Central 2N3440 would fail and short out and cause the resistor to burn through.

The first two testing photos are after replacement of Q508 and R528 in both channels. I'm afraid the same thing will happen if I don't figure-out source of problem.

Any thoughts?

 

[Jose Jimenez]

We are thinking, but late for lunch. I just came across your post again.

 

[Stoddrob]

I’m curious as to how you connected the collector of Q511, in the photo it is soldered to the screw however I believe that screw is isolated from the circuit? Did you run a jumper on the foil side?

Here's a photo of the schematic. The screw appears to be the collector on Q511. The question is if its the other screw? It may be as you say — isolated at the other screw where I soldered the middle lead (collector lead?)

 

[Stoddrob]

We are thinking, but late for lunch. I just came across your post again.

BTW…I received the BK tester and test cables but have not used it yet.