MA5100 transistors

c_dk

Addicted Member
I was trying to sort through these part numbers by memory Saturday night and while all the posts disappeared I did plan on checking my memory today and post at lunch.

The original MA 5100 Q1,3,and 7 were all 132-041 replaced in the 70s by 132-094 a BC414, replaced by 132-235 a 2sc2240bl in the 80s.

Q5 was a 132-051 or a BC107b replaced by 132-095 a x32w6047 replaced by a 132-235 a 2sc2240bl.

The 132-185 was a 2n6923 not the device I thought it was, a part of the sentry monitor, but a selected device for low noise; replaced by the 132-235 or 2sc2240bl.

The sentry monitor devices 021 and 032 became 132-171 and 172 or mpsa05 and 055.
 
It was my post that has disappeared...so to clarify, here is where I am at.

1. I'm working off Service Manual titled MA5100 Service Information Starting with Serial No 30H15 as that is the most recent one I could find and my MA5100 is SN 89Hxx.

2. Comparing the preamp board in this service manual, the board layout is slightly different as my board has the service bulletin caps for Q1 and Q2 added to dedicated locations on the board and not soldered to legs of those transistors.

3. In any event, this manual states the following for Q1-Q12, along with Semiconductor Data replacements and recommended replacements from that earlier post:

Q1,2 NPN 132-503 replaced by 132-093 (KSC1845F)
Q3,4 NPN 132-503 replaced by 132-093 (KSC1845F)
Q5,6 NPN 132-002 replaced by 132-095 (KSC1845F)
Q7,8 NPN 132-503 replaced by 132-093 (KSC1845F)
Q9,10 NPN 132-501 replaced by 132-093 (KSC1845F)
Q11,12 NPN 132-026 replaced by 132-095 (KSC1845F)

So maybe we are working off different Service Manuals (c_dk).

4. I started to type this up earlier this morning to get clarification on Hfes for the KSC1845 replacement for Q5:

So a couple of you were helping me find replacements for 132-002 --> 132-095 --> KSC1845F

My question is about sorting through 1845's to find one with desired Hfe. Should I be looking for a low Hfe or hi Hfe?

Looking at the Semiconductor Data doc:

132-002 had a min Hfe of 45 and a max Hfe of 180
132-095 had a min Hfe of 350 and no max Hfe listed

According to datasheet, KSC1845F has

Hfe1 min 150, typical 580
Hfe2 min 200, typical 600, max 1200

With the 1845, do I go with a low or hi Hfe?
 
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In the AKdatabase there is a MA5100 service manual and 1975 semiconductor data chart. I used those because they are readily available to members.

In the 80s Mac engineering made wholesale substitutions for semiconductors many of which are no longer available.

They used the high HFE BL series of the Toshiba devices for most of these subs.

As of a few months ago these Toshiba devices were available form Bdent, a typically reliable supplier.

I bought some of the BL devices from them and compared them to the BL devices I still have from Mac parts in the 80s.

The "new" BL graded high HFE devices barely met the BL grade while the devices shipped from Mac parts IN THE EIGHTIES, measured 3/4s plus of the BL grade.

The next time I ordered a batch of the Fiarchild devices and sorted them by HFE most all of them measured as good as the BDEnt shipped devices. When Fairchild was making and shipping a higher grade K** series they measured similar to the highest HFE BL graded devices.

Bdent wants 3.91 ea for a non Toshiba 2240bl......you can buy 10 ksc1845 for 2.10, 100 for $8.00.

Buy a bunch sort them for high HFE for the phono gain stage and move on.

Now that Fairchild is part of Onsemi I hope the restart production of the E series.
 
I reread your post....Mac engineering chose a higher HFE grade.....the BL grade from Toshiba.

Obviously they had some issues with containing the original semiconductors and added a number of capacitors to tame them.

When I rebuilt a MA5100 upon request I observed what engineering did for the C24 and C26, both with similar phono stages.

I have in the past experimented with a project C26, different transistors, caps etc.The biggest bank for the buck came from quieting down the power supply.
 
OK, I have ordered 10 of the 1845's. I'll select one that is at the higher end of the 2sc2240bl (350-700), replace Q5 and then report back if I'm still getting the low motorboating on the left channel with Phono. (Probably won't get the parts from mouser until Friday)
 
You could always take the transistor from the other channel and swap them to confirm it is the transistor if you really want to know.
 
Before I pull anything, I plan to put my meter and scope on it and compare schematic voltages along the signal path to see where the motor boating is initiating.
 
So I checked some voltages and everything looks good on right channel from Q2-Q6. But on left, voltage between Q3 emitter and Q5 base is constantly fluctuating between 1.6v and 3.2v. It should be 3.2v. Voltage there is steady 3.3v on right channel.

Q3 collector is 10.7v (10v)
Q3 base is 2.9v (2.9v)

Q5 collector is 39.5v (40v)
Q5 emitter is 1.8v (1.8v)
 
Ah, yes, voltage vanishing into the ether...electronics is truly voodo isn't it.

So which device are you going to replace?
 
Come on anytime you wake up your quantum physics to try to understand holes and charge potentials and electrons multiple states it does approach mystics if not outright voodoo.
 
Why the odd posts c_dk? Can we stick to the issue. I’m looking for assistance not dark humor.

Do you suspect Q3 is leaking or is this just due to the wrong transistor in Q5?
 
Well c_dk, there appears to be some mystical voodoo after all. Haha.

All the poking and prodding trying to measure voltages and view it on my scope has the motorboating coming and going. Though I still see the fluctuation occuring between Q3 and Q5.

My issue may be simply bad solder joints or poor connections in the transistor leg posts/sockets. Will reflow things this weekend and take more measurements. If it persists I’ll push forward with replacing Q5 and possibly Q3 as well.
 
I was going to bring up Schrodinger's cat, now that would be macabre, especially for the cat, but sometimes you just have to try a substitution.

I am assuming you have already replaced the caps and so it is time to sub in a replacement part.

I have already admitted to a memory lapse, a 132-185 was a acceptable replacement for Q5 and that all the phono transistors.....Q1,3, and 5 are all subbed by a 2sc2240BL.

At this point for $1.50 I would replace all 6 in both channels and recap and bypass the power supply.
 
Haha. Not familiar with that cat paradox but it might just fit :)

I have not replaced anything yet. The original owner had a few things replaced by McIntosh as I mentioned.

I have ordered electrolytics and transistors.

What does bypassing the PS involve and why?
 
Just a an off-topic comment. In the 60's when I was building home-brew electronic projects and and in college, 99.99% of the semiconductors I crossed paths with were 2Nxxxx. (and they were only germanium with three digit numbers too). The only place I ever saw a Japanese 2SCxxx part was in a Sony 6 transistor radio.
 
I was going to bring up Schrodinger's cat, now that would be macabre, especially for the cat, but sometimes you just have to try a substitution.

I am assuming you have already replaced the caps and so it is time to sub in a replacement part.

I have already admitted to a memory lapse, a 132-185 was a acceptable replacement for Q5 and that all the phono transistors.....Q1,3, and 5 are all subbed by a 2sc2240BL.

At this point for $1.50 I would replace all 6 in both channels and recap and bypass the power supply.

So it’s safe to say that Q1-6 can all be replaced with KSC1845F. I had planned on subbing 1-4 with BC549’s or KSA992’s and 5-6 with 1845’s. Any reason I would want to stick with 549’s/992’s

Also is there any reason to continue using the original McIntosh transistor leg posts? Seems a PITA. Can I just solder transistors directly to boards? Were those posts originally just sockets that transistors plugged into? On mine, a later year SN model SN 89hxx, all transistors appear to be soldered into each post/socket.
 
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The last time I tried to reuse the "leg posts" as you call them was when DOB laughed at me as I struggled trying to get all the solder out while I was hosting a amp clinic with him.

He just had me insert and solder the legs into the through holes. If you really want to reuse the posts you remove them with the transistor, heat and slide off the transistor and then insert post, insert shortened legs of the transistor and resoldered....just typing it makes me remember all the monkey business.

I thought that all the first 4 devices in each circuit were NPN devices but my memory could be faulty. Mac speced that all these NPNs were 2sc2240bl.....we have been using KSC1845 devices with good results. If you need a PNP they would have speced a 2sa970bl, we have been using KSA992 today.

I think the only PNP devices used are for the differential pair, neg. sentry monitor, and the driver for the coumpound neg. output.
 
Lol, yeah I think I will avoid/remove the posts.

My bad. All transistors in phono and preamp (Q1-12) are NPN. The amp boards have 2 PNP pairs.
 
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