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Yet another butchered 250

catrafter said:
Have you ever tried 2N6211 and 2N3583 in 240/250/1200 power amps that have TO-66 drivers?

Tom
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I would like to. However these seem hard to find, and the places I did find they were going for $30 or more each.
 
ocdecio said:
@rich l that is terrible. Welding the pins to the sockets is inconceivable.

What worked for me was the 2SA1011/2SC2344 pair from Sanyo with pretty close hFE and very high fT (which some people don't seem to like because it may lead to oscillations - I didn't experience that). Very hard to find though.

Other possibilities:

SC5171/SA1930 ;Toshiba
SC2238/SC4793
2SA1837/2SC4793 Toshiba

I also tried the MJE's but they don't work, and as you mention they are too far apart in hFE and caused the fluctuations you mention that in my case would show as hiss on the speakers and in some cases take it to protection with rails voltage at the output.
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I'm pretty sure the 'welding' had to have been corrosion or some such. When I cleaned everything up and plugged the transistor back in, both pins pushed into the case. Thinking it was shot, I pried the cover off and discovered that the internal leads were still connected, so I pushed them back out as I fed them into the inserts on the board and it still works. If it were stable, I might just leave it open, or epoxy the cover back on since it is my personal amp.
I'll search for the devices suggested, but it would be nice to purchase as matched pairs instead of buying by the dozen.
Its a hobby for me as well but I can only justify spending so much......I've got four more amps on cue waiting for bench space.
 
For what is worth I got 4 of each and used 3 pairs so far without any issues, they are true complementary with close enough hFE. Let me check the other subs.
 
So I measured the SC5171/SA1930 pairs and they came:

SC5171 172 172 172 172
SA1930 166 172 166 172

That would work for all pairs.
 
Try bdent and segor.de. You may need an online translator to talk to segor but their service is great.
 
rich l said:
The only place i find those is ebay. Is there a trusted source out there?
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You may get real parts on ebay, but more often you will get fake parts or poorly perrforming "replacements".
In this amplifier you probably do not need 100MHz driver transistors. Have you considered the 2SA940/2SC2073?
If you want faster parts them, 2SA1011/2SC2344 or You can also find the 2SA1930/2SC5171 there but if the amplifier was not designed to work with high ft transistors, it may oscillate and may self-destroy.
 
JoseHH said:
You may get real parts on ebay, but more often you will get fake parts or poorly perrforming "replacements".
In this amplifier you probably do not need 100MHz driver transistors. Have you considered the 2SA940/2SC2073?
If you want faster parts them, 2SA1011/2SC2344 or You can also find the 2SA1930/2SC5171 there but if the amplifier was not designed to work with high ft transistors, it may oscillate and may self-destroy.
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I am not sure if it is designed to work with high fT transistors, all I can say is that my 240 has been working for the last 3 months or so with a 2SA1011/2SC2344 pair. It doesn't mean it will never oscillate to death but it does have quite a bit of miller compensation capacitors in the circuit.
 
In any event, that company I suggested (with which i have no affiliation) has 3 kinds of drivers in TO220 for you to choose from, and they seem to be reliable and not too expensive.
 
ocdecio said:
I am not sure if it is designed to work with high fT transistors, all I can say is that my 240 has been working for the last 3 months or so with a 2SA1011/2SC2344 pair. It doesn't mean it will never oscillate to death but it does have quite a bit of miller compensation capacitors in the circuit.
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decisions,decisions. Haven't ordered from ampslab before but looks legit.I am waiting to see what goldswimmerb comes up with before I order.The more info I can gather, the better.
 
ocdecio said:
For what is worth I got 4 of each and used 3 pairs so far without any issues, they are true complementary with close enough hFE. Let me check the other subs.
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4 each of the 2N6211 2N3583 TO-66s?
Were they expensive?

I cry inside a little every time I have to use anything out of my small stash of ancient parts.

Tom
 
catrafter said:
4 each of the 2N6211 2N3583 TO-66s?
Were they expensive?

I cry inside a little every time I have to use anything out of my small stash of ancient parts.

Tom
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No - the TO220s. The TO66s I could only find for $30 or more a piece in places I don't know I would want to buy from. Your ancient parts stash is becoming more and more valuable!
 
Alright, so an update on my side of this thread.

Replaced the diff pair with 2n5089s matched to a reasonable degree. Replaced the MPSA20 with a modern replacement MPSA20
Used a BC560C for the SPS1952, and PN4250 for the 2N4250s.

Using MJE180G I seem to have stable bias now. It looks as if this revision is very sensitive to the gain of the diff pair!

Now onto testing for stability, I went with MJE parts for my driver's as the 2SC783/2SA483 I ordered were pretty far apart
 
goldswimmerb said:
Using MJE180G I seem to have stable bias now. It looks as if this revision is very sensitive to the gain of the diff pair!

Now onto testing for stability, I went with MJE parts for my driver's as the 2SC783/2SA483 I ordered were pretty far apart
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I am pleasantly surprised you were able to use MJE180G as a sub for SPS1950 (the epoxy transistor). Did you replace the diode as well?
 
ocdecio said:
I am pleasantly surprised you were able to use MJE180G as a sub for SPS1950 (the epoxy transistor). Did you replace the diode as well?
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Yes and yes.

So far seems stable, looks good on the scope, though I can't get full output with my test setup since my phone's preamp doesn't have enough output to bring the amp to 125w, and my test speaker on the bench starts to distort around 30 watts with a clean input.

With the test load everything looks good, though I may have to swap out the RCA connectors on the unit since the ones in there are very rough, and unfortunately riveted in.
 
ocdecio said:
I am pleasantly surprised you were able to use MJE180G as a sub for SPS1950 (the epoxy transistor). Did you replace the diode as well?
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Surprisingly the TO-66 parts I wanted to try as drivers were actually even further apart than the MJEs, if going by gain rank.
 
ocdecio said:
I am pleasantly surprised you were able to use MJE180G as a sub for SPS1950 (the epoxy transistor). Did you replace the diode as well?
Click to expand...

And my only conclusion, at this point, is that the gain of the differential pair is absolutely critical in getting the bias voltage correct on the positive half of the Amplifier.
 
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