Hi,
I bought a very cool and well regarded Proton D1200 "Dynamic power on demand" amplifier from 1987 the other day. I figured of course its a bit of a gamble with such an old thing, and I will have to replace the caps and stuff, but thats ok since i enjoy these things. I listned to it playing so it is in working condition.
But when I got it home and opened it up I found that the output transistors on one channel have been replaced at some point in it´s lifetime. On one side are the original Sanken A1386A/C3519A transistors, four of each in parallell. On the other channel are Toshiba 2SA1302/2SC3281´s instead.
I'm not experienced enough to know what this means. I figure it might well affect the sound of course, if it means both channels don't sound the same, but also stability and reliability perhaps?
So I wonder what the best course of action is with this? Is it worth the effort to try to restore it to a more original state with the right transitors if I can get them? Or is it best to just leave it alone? Or cut my losses and throw it away even 😱 ?
Thankful for any guidance on this!
I bought a very cool and well regarded Proton D1200 "Dynamic power on demand" amplifier from 1987 the other day. I figured of course its a bit of a gamble with such an old thing, and I will have to replace the caps and stuff, but thats ok since i enjoy these things. I listned to it playing so it is in working condition.
But when I got it home and opened it up I found that the output transistors on one channel have been replaced at some point in it´s lifetime. On one side are the original Sanken A1386A/C3519A transistors, four of each in parallell. On the other channel are Toshiba 2SA1302/2SC3281´s instead.
I'm not experienced enough to know what this means. I figure it might well affect the sound of course, if it means both channels don't sound the same, but also stability and reliability perhaps?
So I wonder what the best course of action is with this? Is it worth the effort to try to restore it to a more original state with the right transitors if I can get them? Or is it best to just leave it alone? Or cut my losses and throw it away even 😱 ?
Thankful for any guidance on this!
Just use it. What you have are run of the mill Sanken LAPT’s - not their top of the line - up against probably the best high fT output transistor Toshiba has ever made. Spec sheet wise they are in the same league. The originals probably have a slight edge in distortion, but either would be below audibility in that circuit. If the Toshibas were fakes, they probably would have smoked the first time you turn it up loud. If they were C5200’s I would say put them back to the originals but I’d leave 3281’s in there... if they fit and are installed properly. The originals and replacements are not in the same package - C3281 is larger. Or at least it is supposed to be.
It appears the Sankens are still available, but of course the 3281 is long since history. Any you buy now WILL be fakes. The On Semi version MJL3281 is not the same thing. They have bigger dies and more capacitance. Still very good devices but they will affect the open loop frequency response and it needs to be designed for. InterchangeBle in a lot of the big pro amps that aren’t trying to get single digit ppm distortion but need something rugged.
It appears the Sankens are still available, but of course the 3281 is long since history. Any you buy now WILL be fakes. The On Semi version MJL3281 is not the same thing. They have bigger dies and more capacitance. Still very good devices but they will affect the open loop frequency response and it needs to be designed for. InterchangeBle in a lot of the big pro amps that aren’t trying to get single digit ppm distortion but need something rugged.
The Sanken pair are still an LAPT type that is unique to Sanken and probably among the best type of power transistor for use in Audio power amplifiers. The Toshiba transistors (if they are indeed original Toshiba parts) are another audio type that is also excellent, but was more economical when these transistors types were in production.
Both are excellent audio transistors and as long as the stereo channels sound exactly the same when fed the same signal or played in mono to test that properly, there is no need for concern. You could probably leave well enough alone there if you were happy with the sound quality and didn't drive the amplifier to constant clipping level.
Ideally, you could replace both pairs with matched transistor pairs of similar types of transistors that are currently in production. Not all manufacturers or audio enthusiasts are so particular about their audio quality and perfect matching in all technical details, though, since this is expensive and it isn't a simple task without some DIY building or repair experience and suitable tools and instruments. YMMV
Both are excellent audio transistors and as long as the stereo channels sound exactly the same when fed the same signal or played in mono to test that properly, there is no need for concern. You could probably leave well enough alone there if you were happy with the sound quality and didn't drive the amplifier to constant clipping level.
Ideally, you could replace both pairs with matched transistor pairs of similar types of transistors that are currently in production. Not all manufacturers or audio enthusiasts are so particular about their audio quality and perfect matching in all technical details, though, since this is expensive and it isn't a simple task without some DIY building or repair experience and suitable tools and instruments. YMMV
Ok, thanks for the input! Good news! The Toshibas are a little bigger package but they seem to fit nicely. I gather I can go ahead doing some recapping for the time being, trying not to spend excessively in that department. I will do some mono listening and se if there are any anomalies.
If I want to change the transistors down the road do you think it's a valid option to just get a bunch of original ones and installing them on one channel without doing any serious matching? I don't have the tools or expertise for that really, beyond what I can get with a DMM maybe. Or do I really need to change both channels as Ian suggests to get the left and right channels to match properly?
Also, Is there any chance I can get original Sankyos off Ebay from China? Or is there another way? They seem to be in production but the only reputable reseller I have found are a company called profusion. They only carry A1386/C3519 without the "A" suffix. I am not sure if there are interchangeble?
If I want to change the transistors down the road do you think it's a valid option to just get a bunch of original ones and installing them on one channel without doing any serious matching? I don't have the tools or expertise for that really, beyond what I can get with a DMM maybe. Or do I really need to change both channels as Ian suggests to get the left and right channels to match properly?
Also, Is there any chance I can get original Sankyos off Ebay from China? Or is there another way? They seem to be in production but the only reputable reseller I have found are a company called profusion. They only carry A1386/C3519 without the "A" suffix. I am not sure if there are interchangeble?
Profusion or Digi-key only. E-bay and China is how you get fakes. “A” suffix is the voltage grade, I beliieve. Current production would be the A - that’s what Digi-Key has.
the D1200 is a very good amp, a bit rough formwork, but with monster bass.
on the other hand, beware of PCBs, they are fragile and think to take a selection
voltage higher than the original for capacitors, because they are all too fair on the original model
on the other hand, beware of PCBs, they are fragile and think to take a selection
voltage higher than the original for capacitors, because they are all too fair on the original model
Great advice! No drilling through the PCB to fit capacitors then 🙂 I'll see if I can find 22000 caps with higher voltage that will still fit.
Do you have experience recapping this amp? And if so, any advice on the big 15000 cans on the sides? I'm not sure if I can find replacements that fit. I think I will leave the originals in there for starters but maybe I will have to change them eventually.
Change the big caps when they become a problem (like changing the outputs - only if there’s a problem). You change out all the little electrolytics on the board because there are easy, and when they do get leaky they can cause all sorts of nuisance problems that are often hard to diagnose.
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