Yes if you have enough gain to kill off in NFB. Unfortunately, the 555 does not have that much gain to begin with, its a simple gain path with compromises. It needs a higher beta output stage to sound good. Pass designed it as a sum of all parts. Adcom ruined one part by putting low beta output devices in later models when toshiba stopped making 424/554's, they wanted the world to move on to their new star, the 1302/3281's
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Yup. I was never that crazy about the performance of Adcom. They were tough and sounded okay.
But the new star doesn’t fit! It’s a six pointed star in a 5 pointed hole! It’s really too bad no one ever made a regular production C3281 type device in a TO-3 can.
Could have charged fifteen dollars apiece for them and had a small sustainable market for decades. Drop them in place of D424 and it would do nothing but get better.
Could have charged fifteen dollars apiece for them and had a small sustainable market for decades. Drop them in place of D424 and it would do nothing but get better.
They ( MOT) did, but for some sinister reasons they stopped. They were the MJ1302/MJ3281. You probably know them as the Krell 48402/48481. Now those… cost $40-80 depending on what Krell wants to charge.
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“Could have charged fifteen dollars apiece for them” - at Mouser, in 25 piece lots, not “List” or “MSRP”. That would be 2-3X the onesey twosey price.
Back when Toshiba was making C3281’s there was still a decent market for TO-3’s. At on time I could still get D424’s and C3281’s from MCM.
Back when Toshiba was making C3281’s there was still a decent market for TO-3’s. At on time I could still get D424’s and C3281’s from MCM.
Yep. Now the only decent replacements ( apart from Retro fitting flatpaks) is the 2119x, which are closer to $10 shipped each now.
It is a sustained-beta type. Just not 30 MHz. I have no personal phobia of EF3’s, so 30 MHz outputs are not a hard requirement for me. A lot of vintage stuff was sort of designed around them, though. May or may not get back to original spec with 21193/4. Most of the time it “works” just fine even if originals were faster.
Which is why sometimes when I have the inclination, I do this... and LAPT out 😎.
Yes Chris, thats a 555ii.
The 2119x's use the same tech Toshiba used for the 424/554's and IIRC they licensed it to MOT, you can correlate the stoppage of the 424/554 with the intro of the 2119x timeframe. So the betas are a much closer match with the 424/554's.
Yes Chris, thats a 555ii.
The 2119x's use the same tech Toshiba used for the 424/554's and IIRC they licensed it to MOT, you can correlate the stoppage of the 424/554 with the intro of the 2119x timeframe. So the betas are a much closer match with the 424/554's.
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I can see your points, but did I mention that the bjt is soldered on to the copper adapter, its not mated via an insulator.
The two variables that offset that a bit, are there are holes/ spaces underneath in the existing mounting holes, that will cause gaps in conduction. So a spreader is needed here. The other thing to consider is that the TO-3 heat spreader is one of the reasons a 150w wafer can dissipate over 250w in This package. Being copper, it will wick away heat faster than the existing anodized surface with holes… at least that’s what it feels to me.
The bjt is soldered on to the copper adapter, so decent heat transfer is assumed.
As for dual backplates, that’s what the Sanken MT200 packages were. The 130w rated 2sa1294, welded on to a larger heatspreader ( along with its own Native backplate) is what the big brother 2sa1295 was, rated for an additional 70 w using the same wafer… it literally is a A1294 welded on a separate MT200 backplate.
As for the bushing, I don’t use it anymore, the backplate is soldered to the copper adapter, it literally is the collector, all I need is a regular screw to complete the circuit just like all other TO-3’s do.
Well that’s what logic suggests. I am happy to be corrected.
The two variables that offset that a bit, are there are holes/ spaces underneath in the existing mounting holes, that will cause gaps in conduction. So a spreader is needed here. The other thing to consider is that the TO-3 heat spreader is one of the reasons a 150w wafer can dissipate over 250w in This package. Being copper, it will wick away heat faster than the existing anodized surface with holes… at least that’s what it feels to me.
The bjt is soldered on to the copper adapter, so decent heat transfer is assumed.
As for dual backplates, that’s what the Sanken MT200 packages were. The 130w rated 2sa1294, welded on to a larger heatspreader ( along with its own Native backplate) is what the big brother 2sa1295 was, rated for an additional 70 w using the same wafer… it literally is a A1294 welded on a separate MT200 backplate.
As for the bushing, I don’t use it anymore, the backplate is soldered to the copper adapter, it literally is the collector, all I need is a regular screw to complete the circuit just like all other TO-3’s do.
Well that’s what logic suggests. I am happy to be corrected.
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Soldered is way better than using a TIM, if it’s void free. Not easy in a home brew setup. You have a vacuum reflow chamber? Hey, some people do, but not us through-hole holdouts who refuse to spend tens of thousands on “new tooling” to be able to use modern assembly techniques. Just properly weighted might be good enough here, but you still need your programmable pizza oven.
A bushing would be needed if a spreader wasn’t used. Otherwise the screw contacts the heat sink. That heat spreader could keep it aligned, especially if soldered because it removes a degree of freedom. Since my drilling is by hand and not CNC I tend to put sleeve bushings around the screws where it goes through, and pieces of heat shrink on the leads. I guess the Adcom heat sink was pre drilled so it should be pretty accurate.
A bushing would be needed if a spreader wasn’t used. Otherwise the screw contacts the heat sink. That heat spreader could keep it aligned, especially if soldered because it removes a degree of freedom. Since my drilling is by hand and not CNC I tend to put sleeve bushings around the screws where it goes through, and pieces of heat shrink on the leads. I guess the Adcom heat sink was pre drilled so it should be pretty accurate.
Yes, predrilled holes and you are right, without the adapter, the bushing would help align. By the way I am a cheapskate, I use Solder paste and a hot air station to solder these together. Two alligator clips keep them in place as I heat them... Takes time and elbow grease but gets the job done.
Drill 2 holes in a piece of wood or aluminum using the adapter as a jig, and use it to support the bottom when clamping, or you may have space issue / damage the pins when soldering.
A blow lamp or heat gun may work for soldering the paste, but oven will be easier to control. And a coal fired BBQ is ideal.
Heat gun, I have doubts unless it is very high watts rating.
A blow lamp or heat gun may work for soldering the paste, but oven will be easier to control. And a coal fired BBQ is ideal.
Heat gun, I have doubts unless it is very high watts rating.