It would be interesting to see what they measure at 80*C.
MC2100 To Do's
- Thread starter jbailey930
- Start date
While I understand that he is experimenting with this very beatup derelict iof a MC2100, these amps were built to be run HARD, expected to be run hard, and at some time I hope he takes off the kid gloves, does a 1 hour FTC style preconditioning and really wrings his prototype driver boards and the amp out.
I would also like to see the distortion trace on his scope as he tests the amp at what we found that they could typically do at + 130 watts.
I would also like to see the distortion trace on his scope as he tests the amp at what we found that they could typically do at + 130 watts.
Hunted11
Active Member
I agree. Years ago I used my 2100 for a band. It was being used for the PA one channel for the main PA nd the other for the monitors. The bass player blew his head unit. I disconnected the monitors and ran his bass into the left channel and connected the output to his speaker cabinet. The right channel stayed for the PA. I don't know how hard it was being hammered, but the left channel was HOT and it kept on running. The good old days.
Gregory
Soundco Kid
I'd not recommend using his boards, but don't regret posting the videos. Best thing to do is update the original PCBs with the correct parts. To be fair, that amp didn't have any PO boards at the start, so he built some. He's likely mistaken about the `protection circuit´, describing it as designed to prevent clipping, but it's not Power Guard, that was in the next Gen amps. I believe it's the Sentry Monitor circuit.
-Greg
-Greg
Gregory
Soundco Kid
This is going to sound terribly geeky.......but.....
After unloading his rental and then setting up his bench for the amp clinic the next day DOB and I went out for dinner.
It was at this dinner that my vacuum tube adventures trying to acqiure proper 6l6 replacements for the 3 Mc240s I had came uphe told me of and some new transistors that Mac engineering had just cleared as replacements as well as samples of prototype devices that they were studying for future production uses.
It was over this dinner that he gave me the color codes that Mac used to identify which devices passed Q/C and engineering's excitement ( again geeky) over the quality and tight tolerances they were discovering in this new replacement devices.
These devices from Toshiba the sc2240bl and sa979bl were so cosistsntly tight to the published specs the grading system that was in place was no longer needed.
This to him was a big deal because these to new parts replaced over 3 dozen previous parts.
Why do I bring this up, when I looked at the published curves that Toshiba publishes for the drivers xraytony is using they are so tight between the NPN and PNP they are obviously decades improved over the 60s original or the u07 and u57 motorola parts Mac used in the 70s amps.
With the awkward use of the quasi constant current source used in this 60s design and some of the basic early circuit compromises I would not expect these prototype boards to deliver sudden sonic nirvana, I do hope that they prove to offer a reliable solution to issues that so many MC2300s ran into over the decades as they were put under overtime stress.
Since xraytony is looking to market these boards I do hope he tries to break them while stressing the amp out like we know Mac owners are inclined to do.
After unloading his rental and then setting up his bench for the amp clinic the next day DOB and I went out for dinner.
It was at this dinner that my vacuum tube adventures trying to acqiure proper 6l6 replacements for the 3 Mc240s I had came uphe told me of and some new transistors that Mac engineering had just cleared as replacements as well as samples of prototype devices that they were studying for future production uses.
It was over this dinner that he gave me the color codes that Mac used to identify which devices passed Q/C and engineering's excitement ( again geeky) over the quality and tight tolerances they were discovering in this new replacement devices.
These devices from Toshiba the sc2240bl and sa979bl were so cosistsntly tight to the published specs the grading system that was in place was no longer needed.
This to him was a big deal because these to new parts replaced over 3 dozen previous parts.
Why do I bring this up, when I looked at the published curves that Toshiba publishes for the drivers xraytony is using they are so tight between the NPN and PNP they are obviously decades improved over the 60s original or the u07 and u57 motorola parts Mac used in the 70s amps.
With the awkward use of the quasi constant current source used in this 60s design and some of the basic early circuit compromises I would not expect these prototype boards to deliver sudden sonic nirvana, I do hope that they prove to offer a reliable solution to issues that so many MC2300s ran into over the decades as they were put under overtime stress.
Since xraytony is looking to market these boards I do hope he tries to break them while stressing the amp out like we know Mac owners are inclined to do.
kevzep
Its all about the Music
I'm sure he will, he is actually very good at taking advice from viewers too, so feel free to email him or make a comment on the YouTube channel.....
I want to see him test one to destruction too, it has to be done!!
Gregory
Soundco Kid
Have some test results to post on the MC2100.
All transistors on the Power Output board have been tested, and I haven't really seen any bad devices.
How does the test data look to you? The measuring gadget is Atlas DCA55 Semiconductor Tester.
Sorry about the blurry images, they were sharp before uploading.
Q1–Q4 were tested `on-board´ because the circuits were basically open.
The main problem is RIGHT inboard heat sink overheating. Could be oscillating? We've never tested it with Sig Gen and dummy loads.
-Greg
All transistors on the Power Output board have been tested, and I haven't really seen any bad devices.
How does the test data look to you? The measuring gadget is Atlas DCA55 Semiconductor Tester.
Sorry about the blurry images, they were sharp before uploading.
Q1–Q4 were tested `on-board´ because the circuits were basically open.
The main problem is RIGHT inboard heat sink overheating. Could be oscillating? We've never tested it with Sig Gen and dummy loads.
-Greg
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jbailey930
AK Member
The right channel was also distorted and output was lower than the left......perhaps time to process the updates and retest?
edwinh
Active Member
In 1978, I bought a 2105 for my bass rig. Then it was a PA amp and got dragged around the country for several years. It became a rehearsal PA amp and then it resided in the basement for a while and I had it serviced and it made it into my home stereo. Then, one day a driver board let out the magic smoke and I took it to another place (and discovered the guy who previously serviced it did things like replace the main filter caps with 17k mfd caps. Sheesh. They rebuilt it from the top down and did the FSB. It sounded amazing and has made more forays on stage. Next step is to replaced the barrier strips with banana jacks and put it in some kind of case. As a bass amp, it outperforms Crest and other high powered modern amps. Looks like hell and sounds like heaven.
Gregory
Soundco Kid
It's time to start reinstalling parts on the Power Output boards. But I haven't found ANY bad transistors on either board. John informed me the RIGHT inboard heat sink bracket was broken, and was in danger of shorting to the chassis. The problem could be the OUTPUT transistors!
Here are the IR temperatures from the first day we hooked it up to the dummy loads.
The RIGHT side are original outputs, the LEFT have been updated before.
Which has a higher chance of OSCILLATION? updating to Darlington Sentry transistors? or installing the newer OUTPUT devices?
I'm trying to make the case for keeping the original Sentry transistors Q7–Q10.
-Greg
Here are the IR temperatures from the first day we hooked it up to the dummy loads.
The RIGHT side are original outputs, the LEFT have been updated before.
Which has a higher chance of OSCILLATION? updating to Darlington Sentry transistors? or installing the newer OUTPUT devices?
I'm trying to make the case for keeping the original Sentry transistors Q7–Q10.
Code:
Sentry Pol hfe min hfe Ic Vbe Ib
Q7 NPN 90 102 2.5 0.739 4.200
Q8 NPN 90 180 2.5 0.734 4.210
Q9 PNP 90 149 2.5 0.722 4.222
Q10 PNP 90 159 2.5 0.725 4.216-Greg
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Gregory
Soundco Kid
Driver transistors Q11–Q14 that came with the update kit are compared to the original transistors.
I'd say the originals are ok, but will install NEW devices and heat sinks.
The transistor gadget
-Greg
Code:
Old Drivers
Pol P/N hfe MIN hfe Ic Vbe Ib
Q11 NPN 132-038 40 48 2.5 0.703 4.244
Q12 NPN 132-038 40 76 2.5 0.703 4.243
Q13 PNP 132-039 40 119 2.5 0.718 4.230
Q14 PNP 132-039 40 110 2.5 0.725 4.222
New Drivers
Pol P/N hfe MIN hfe Ic Vbe Ib
Q11 NPN 132-153 40 114 2.5 0.701 4.241
Q12 NPN 132-153 40 125 2.5 0.720 4.228
Q13 PNP 132-154 40 181 2.5 0.716 4.225
Q14 PNP 132-154 40 182 2.5 0.726 4.218I'd say the originals are ok, but will install NEW devices and heat sinks.
The transistor gadget
-Greg
Gregory
Soundco Kid
>>Which has a higher chance of OSCILLATION? updating to Darlington Sentry transistors? or installing the newer OUTPUT devices?
Ok right, do a search for answers (edit the URL to change key words).
https://www.google.com/search?q=MC2105+"oscillation"+site:audiokarma.org
https://www.google.com/search?q=MC2105+oscillation+site:audiokarma.org
https://www.google.com/search?q=MC2100+"oscillation"+site:audiokarma.org
https://www.google.com/search?q=MC2100+oscillation+site:audiokarma.org
https://www.google.com/search?q=2100+"oscillation"+site:audiokarma.org
https://www.google.com/search?q=2100+oscillation+site:audiokarma.org
This project has been going on so long that I forgot what happened in the early stages—it's NOT my project, it's John's. I told him it was going to take weeks, and weeks, and weeks. And after this is done I'll be able to service amps.
It was the LEFT outboard heat sink with the broken bracket (square end of chassis). The original RIGHT side outputs (070s) are likely toast.
Time to start pulling and testing outputs.
-Greg
Ok right, do a search for answers (edit the URL to change key words).
https://www.google.com/search?q=MC2105+"oscillation"+site:audiokarma.org
https://www.google.com/search?q=MC2105+oscillation+site:audiokarma.org
https://www.google.com/search?q=MC2100+"oscillation"+site:audiokarma.org
https://www.google.com/search?q=MC2100+oscillation+site:audiokarma.org
https://www.google.com/search?q=2100+"oscillation"+site:audiokarma.org
https://www.google.com/search?q=2100+oscillation+site:audiokarma.org
This project has been going on so long that I forgot what happened in the early stages—it's NOT my project, it's John's. I told him it was going to take weeks, and weeks, and weeks. And after this is done I'll be able to service amps.
It was the LEFT outboard heat sink with the broken bracket (square end of chassis). The original RIGHT side outputs (070s) are likely toast.
Time to start pulling and testing outputs.
-Greg
Last edited:
Gregory
Soundco Kid
Didn't look at this doc/booklet until a couple weeks ago, and have the devices sorted out pretty well now.. used it to populate the test data spreadsheet. John had the same doc with a green-colored cover.
-Greg
SOME possible oscilation issues occurring in SOME random MC210x repairs.....
Output subs MJ15003g have slightly higher gain than the original Motorolas.
Differential pair mismatches in either the input section of the amp or the negative feedback loop of the output section.
Wirewound resistors without enough inductance were a problem in the next series of Mac amp's creating a circuit modifaction for those amps. This was relayed by my last contact within engineering and could very well be why the hit and miss oscilation issue crops up in the current repair of MC210Xs.......as Terry has suggested a different driver device than a MJ15003g might be the best solution for this possibility.
It is not uncommon to bench test these amp's and find them partially functioning.
Unsymmetrical clipping can reveal sentry monitor issues. Notch distortion can show up a bias resistor with creeping up resistance; it is not uncommon to find the output stage partially working with only one of the two driven output devices working, the one having failed open instead of shorted.
The most common failure of a Mc2100 is probably a cage, having had something dropped on it, shorted to a "hot" heatsink. A Mc2105 if the glass has not been broken due to the above mishandling and a heatsink insulator failing because of the rough handling, a failed output due to age.
Of coarse in due proccess a recap will be in order as the originals are well past their expected 20-25 year old lifespan.....BUT will not fix the most common failure modes of these amps.
ABCs of bench testing before any restoration attempts are needed and then said ABC stress testing after complete is really mandatory.
I still believe a list of what should be expected restoration procedures for all these vintage units would be a positive for all current and prospective owners.
Output subs MJ15003g have slightly higher gain than the original Motorolas.
Differential pair mismatches in either the input section of the amp or the negative feedback loop of the output section.
Wirewound resistors without enough inductance were a problem in the next series of Mac amp's creating a circuit modifaction for those amps. This was relayed by my last contact within engineering and could very well be why the hit and miss oscilation issue crops up in the current repair of MC210Xs.......as Terry has suggested a different driver device than a MJ15003g might be the best solution for this possibility.
It is not uncommon to bench test these amp's and find them partially functioning.
Unsymmetrical clipping can reveal sentry monitor issues. Notch distortion can show up a bias resistor with creeping up resistance; it is not uncommon to find the output stage partially working with only one of the two driven output devices working, the one having failed open instead of shorted.
The most common failure of a Mc2100 is probably a cage, having had something dropped on it, shorted to a "hot" heatsink. A Mc2105 if the glass has not been broken due to the above mishandling and a heatsink insulator failing because of the rough handling, a failed output due to age.
Of coarse in due proccess a recap will be in order as the originals are well past their expected 20-25 year old lifespan.....BUT will not fix the most common failure modes of these amps.
ABCs of bench testing before any restoration attempts are needed and then said ABC stress testing after complete is really mandatory.
I still believe a list of what should be expected restoration procedures for all these vintage units would be a positive for all current and prospective owners.
Gregory
Soundco Kid
Since all but TWO of the transistors have been removed from the Power Output PCBs, I went back and remeasured the resistor values with a Fluke 87 III, noting the tolerances and put them in a spreadsheet.
From there it was easy to `drag´ math functions from row R1 to `fill in´ the rest.
It shows most drifted high in resistance.
The table is still in v_01 so there might be some errors. Will be advising to order in L-R pairs since these components are in expensive.
What your you put in? carbon composite or metal film?
-Greg
From there it was easy to `drag´ math functions from row R1 to `fill in´ the rest.
It shows most drifted high in resistance.
The table is still in v_01 so there might be some errors. Will be advising to order in L-R pairs since these components are in expensive.
What your you put in? carbon composite or metal film?
-Greg
clinic-audio
all on YAMAHA untill 1990
>>Which has a higher chance of OSCILLATION? updating to Darlington Sentry transistors? or installing the newer OUTPUT devices?
Ok right, do a search for answers (edit the URL to change key words).
https://www.google.com/search?q=MC2105+"oscillation"+site:audiokarma.org
https://www.google.com/search?q=MC2105+oscillation+site:audiokarma.org
https://www.google.com/search?q=MC2100+"oscillation"+site:audiokarma.org
https://www.google.com/search?q=MC2100+oscillation+site:audiokarma.org
https://www.google.com/search?q=2100+"oscillation"+site:audiokarma.org
https://www.google.com/search?q=2100+oscillation+site:audiokarma.org
This project has been going on so long that I forgot what happened in the early stages—it's NOT my project, it's John's. I told him it was going to take weeks, and weeks, and weeks. And after this is done I'll be able to service amps.
It was the LEFT outboard heat sink with the broken bracket (square end of chassis). The original RIGHT side outputs (070s) are likely toast.
View attachment 1740730 View attachment 1740731
Time to start pulling and testing outputs.
-Greg
Hello Greg
I think that you don't look at the right place
If you have one heatsink too much hot , this is not coming from the output power transistor . If the temp is increasing that mean that your transistors are working . Checking them with your PEAK is not comparable with professionnal measurement system . I am talking about values that you get . This little tester is very good and give you informations that your TR is not shorted and don't leak . You can't make comparaison with hfe in the data sheet .
Regarding your problem , I will strongly recommend you to measure the input DC volt you have on each channel coming in the driver board .
Come back to us with report
