SAE Mark IIIC Repair

kwape

AK Subscriber
Subscriber
A Basket case to say the least. No cover and just a few useless output transistors. But I've fallen for SAE equipment and cannot resist. I have a detailed printout schematic. I'll try to post it later.

outputs on each channel:
Q15, Q16 SAE103 2N6284
Q17 SAE101 MJ802
Q18 SAE202 MJ4502 or MJ21193
Q19, Q20 SAE204 MJ11021

I still have the MJ802 & MJ4502 left over from the last project for both channels. Mouser has 2N6284 & MJ11021. Before I place the order, going to check components for any tells as to why outputs have failed in the first place. Hopefully this unit hasn't been messed with too much.


As to the missing cover, I have made a CAD drawing of the cover. If anyone knows a good metal fab shop that can make me a black anodized piece of aluminum to my specs that would be great, otherwise I'll try my luck asking around here locally.



This thread has been long awaited. NolaSally, this ones for you!



001.JPG 002.JPG 003.JPG 004.JPG 005.JPG AK002.jpg
 
mkiiicm_c_zpsjv6mukgd.jpg

mkiiicm_a_zps6rxlkgjg.jpg

mkiiicm_d_zpsamtykgj9.jpg
 
You have a sickness like me, SAE, GAS and SUMO. Sick sick sick!!!!!!!! This one is by THE MAN, JB.
 
holy ****. Finally have time to tear into this amp. It's been molested a little bit.....not too bad.

the beginning of these projects are a bit daunting. It's a new amp and I need to understand at least somewhat how it works. Thankfully I have the nicest schematics I've had for this project that can even make a dummy like me figure this out.:thumbsup:

I need to buy all new outputs except I have 4 of them on hand already (MJ802 & MJ4502). At this point I'm just going to check around for any cause to blowing outputs.

A diode I am unfamiliar with are all shorted. part number 11-0075 Diode Si (SAE 301) on my schematic. There're 4 of them (2 each channel). I have one original and 3 SBR5089 (Motorola part #). I cannot find any info on this Motorola diode. Does anyone know a suitable sub for the SAE 301 diode? wardsweb has it as a Schottky DO-1 but doesn't list an equivalent.


Also, I'm missing a choke resistor part number 22-0005 on one channel. no clue how I'm going to find that.

016.JPG 017.JPG 018.JPG 021.JPG 019.JPG 020.JPG 022.JPG
 
Last edited:
SAE301 is a Schottky diode, 1N5820G from Mouser will work just fine. Also the amp will run without them, their purpose is eliminate the high voltage drop across the .39 Ohm emitter resistors at high outputs. These same diodes were used by JB in his Ampzilla amplifiers. The first version of Ampzilla used the metal cased 1N5823 (5A/20V) and the later versions used the plastic 1N5820 (3A/20V).

Craig
 
Last edited:
thanks craig. It looks like original part number is 1N5823. I will go with that sub 1N5820G

I will post more info on that choke resistor assembly when I get a chance. I believe it is the L3 2mh coil in the schematic.
 
Last edited:
Try to find some those output networks from a Dynaco ST400/416., might be the same.

Craig
 
All four outputs are shorted in one channel. Everything else looks good so far.

Make sure to isolate those Schottkys they're in parallel with the .39 Ohm emitter resistors otherwise they look shorted.

The resistors in the output choke are much smaller than the Dynaco parts so never mind. You'll just have to wind your own on a 1/4" drill bit or round stock.

Craig
 
yeah I was thinking I could make one out of solid copper wire. I suppose I would just make a copy with the same amount of windings and same gauge wire and plug it in? I need a resistor too right
 
You need magnet wire as it has a insulation coating on it, plain old copper wire would be a short defeating the purpose. Any transformer companies in your area? All you need is pieces of scrap of 15 or 16 gauge. Pull the resistor out of the other one to see what value it is, it's going to real low, an Ohm or two. DMM virtually useless at these values.

Craig
 
nice! things are looking up. Got me a glass of a nice stout, couple problems solved thanks to llwhtt. Might just get this amp running after all.

yeah haha 2.2ohm L3 2mh choke
 
Last edited:
any chance you have a
2N6318 SAE(206) transistor? I will need at least one. eehhhh I'll see how many I really need and post back, if it's just one i'll grab it off mouser. only asking b/c they 13+ each.
 
Last edited:
I'm always searching for alternatives for these TO-66 transistors, no I don't have any. 2N6316, 2N6318, 2N3584, and 2N6421 are all of the TO-66s used in SAE and GAS equipment. I'm thinking about replacing the TO-66s in this MKIVD so I'm looking also.

Craig
 
After mucho cross referencing between SAE #s and GAS#s and looking at availability, the KSB596/ KSD526 pair from Mouser should work OK. It looks like only the (Y) high gain version is available from Mouser hopefully it's not too high. Maybe the other gain versions are available somewhere else. GAS used these as replacements for the 2N6316/18 pair. MJE15028/29 have also been used.

The other two pairs of TO-66s need to have a higher voltage rating, MJE15032/33 have been used for those.

The search goes on though.

Craig
 
Sounds like this might be a less troublesome rebuild.

eehhhh maybe. Too early to tell. I have learned a lot from the last sae amp in terms of how difficult it is to swap output transistors with modern equivalents. That was the real problem on the last amp. I should be able to avoid all that this time using wardsweb to reference part # that are known to work.
 
update:
all TO-66 transistors on the output board have tested good. I just have one odd ball Sony D291 in place of what was Q14 2N6316 ( not 2N6318). I'm thinking I should just grab a new one off mouser to keep all transistors the same part #s.

Now I'm assuming this transistor failed, and looking for causes the last guy might have missed. so far I've found R37 1.2ohm to ground is open. the search continues

many of these traces on the drivers are raising off the board. I'm using low-ish heat (680) but is there any tricks to sticking these back down? If not they should be fine anyways.

024.JPG 026.JPG


take a look at this driver board. The 1mh L1 & L2 coil on the schematic looks to have 14 ohm resistors in it's place. Just wasn't sure if that was correct or what.

027.JPG028.JPG
 
Last edited:
Back
Top Bottom