Ok I am not too good (bad) with transistor amps and I want to resurrect my Sugden A21 series II amp.
When I bought this old amp the output transistors did not match and I want to right this poor beast before I put new PS caps in and fire it up.
The not to unusual problems is the original power transistor is a BDY38 and these are not available. I emailed Sugden and I was told that a TIP 35c or MJE2955 could be used.
Now I am confused. Totally. The original is an NPN type in a T0-3 case and while the TIP35C is NPN the MJE2955 is PNP and neither is T0-3 form. Now a MJ2955 is the right case but it is still PNP and the Sugden gentleman said that "PNP is Spec"? But wait the original iBDY38 is NPN
Then I read about the MJ1500X's being a good replacement in the JLH amps. HELP ME!
Perhaps someone is familiar with this Class A amp and I chose to put this request in this forum after reading about Nelson Pass working on the JLH (PLH).
Stephen
When I bought this old amp the output transistors did not match and I want to right this poor beast before I put new PS caps in and fire it up.
The not to unusual problems is the original power transistor is a BDY38 and these are not available. I emailed Sugden and I was told that a TIP 35c or MJE2955 could be used.
Now I am confused. Totally. The original is an NPN type in a T0-3 case and while the TIP35C is NPN the MJE2955 is PNP and neither is T0-3 form. Now a MJ2955 is the right case but it is still PNP and the Sugden gentleman said that "PNP is Spec"? But wait the original iBDY38 is NPN
Then I read about the MJ1500X's being a good replacement in the JLH amps. HELP ME!Perhaps someone is familiar with this Class A amp and I chose to put this request in this forum after reading about Nelson Pass working on the JLH (PLH).
Stephen
Only one is missing. It does not have a manufactuer designation on the outside of the can it just says BDY38 and under that 3K50.
The can has a little more depth (thicker) than other T0-3 types I have seen.
I do not know too much about the transistors in this amp failing but it is from the early 70's so... Perhaps bad caps caused it?
The can has a little more depth (thicker) than other T0-3 types I have seen.
I do not know too much about the transistors in this amp failing but it is from the early 70's so... Perhaps bad caps caused it?
portlandlay said:
Do you have a schematic and complete specs on the BDY38?
Do you know if parts were matched or selected?
I'd suggest, over the 2N3055A, the 2N3772 or even better 2N3773 which is a preferred part at On Semi.
But I have no experience with that amp.
These parts originated around the same time as the BDY38 but have much better SOA characteristics, and are probably better in every other way.
I've done many substitutions without problems, but I usually choose good designs to work with. One with marginal stability could easily oscillate with substituted parts.
Pete B.
I am not sure if the transistors were matched or selected but I do not think they were.
The schematic can be found in here http://www.tcaas.btinternet.co.uk/ navigate to "other class A amplifiers" and then to the Sugden 10w.
The ouput stage is a bit different but that can be found on page 6 of the associated article found at the same web address.
The schematic can be found in here http://www.tcaas.btinternet.co.uk/ navigate to "other class A amplifiers" and then to the Sugden 10w.
The ouput stage is a bit different but that can be found on page 6 of the associated article found at the same web address.
Thanks all for the ideas. I am going to order a few different sets. First the cheap 2n3055's to get it up and running. These should be pretty close to the BDY38's. I will get some MJ15003's and then some 2N3773's as well.
Thanks again and when it is up and running with these and new PS caps I will let you all know how it goes.
Thanks again and when it is up and running with these and new PS caps I will let you all know how it goes.
Hi portlandlay,
The only thing to really watch is the speed of the outputs. Most are fast now and that's why I really like Pete's suggestion to use 2N3773's.
Replace the electrolytics on the boards before you start. Some of the film caps might be bad by now too. I would not use 2N3055's. Waste of time unless you have them. Be aware the original spec for collector emitter breakdown voltage is 60V, not 100V as many manuals state. You would need 2N3055H labled parts.
-Chris
The only thing to really watch is the speed of the outputs. Most are fast now and that's why I really like Pete's suggestion to use 2N3773's.
Replace the electrolytics on the boards before you start. Some of the film caps might be bad by now too. I would not use 2N3055's. Waste of time unless you have them. Be aware the original spec for collector emitter breakdown voltage is 60V, not 100V as many manuals state. You would need 2N3055H labled parts.
-Chris
Hi Stephen,
The MJs are excellent parts but they're probably faster than the BDY38s, really even the 2N3773 is probably faster in todays technology but I doubt that you'll have a problem.
You might note the thermal resistance from the die to the package, which with all things equal is an indicator of die size. The 2N3773 is a bigger part than the 2N3055 which is also indicated by the higher power rating. It being high voltage will keep them out of secondary breakdown.
They're a preferred part indicating that they're going to keep on making them, probably because they're a superior substitute for so many of the older NPN TO3 devices. The larger die makes them slower which should offset the newer technology to some extent.
It is interesting that at a glance it might look like the 2N3055 has better hFE but you might notice that they're rated at different collector currents. The 3773 is tighter across temperature and higher across the more important 0 to 10 amp range as can be seen from the curves.
Matching is not an issue given that this is a quasi complementary design, but you probably don't want to risk any of the other parts failing and that's a good reason to change them all.
Pete B.
The MJs are excellent parts but they're probably faster than the BDY38s, really even the 2N3773 is probably faster in todays technology but I doubt that you'll have a problem.
You might note the thermal resistance from the die to the package, which with all things equal is an indicator of die size. The 2N3773 is a bigger part than the 2N3055 which is also indicated by the higher power rating. It being high voltage will keep them out of secondary breakdown.
They're a preferred part indicating that they're going to keep on making them, probably because they're a superior substitute for so many of the older NPN TO3 devices. The larger die makes them slower which should offset the newer technology to some extent.
It is interesting that at a glance it might look like the 2N3055 has better hFE but you might notice that they're rated at different collector currents. The 3773 is tighter across temperature and higher across the more important 0 to 10 amp range as can be seen from the curves.
Matching is not an issue given that this is a quasi complementary design, but you probably don't want to risk any of the other parts failing and that's a good reason to change them all.
Pete B.
portlandlay said:
Just as you were writing this I was filling my order for 4 2N3773's.
I did notice (newbie here) that it is a little hard to make fair comparisons at a glance as many of the data sheets do quote specs apples to oranges or at least tangerines to oranges.
Thanks a million all for the replies. I have also order 4 new PS caps and a couple of other caps that look suspect. I will put this together and then ask more questions about setting bias.
The web page I quoted earlier does have a quick procedure - will the new transistors change this?
Regards,
Stephen
I did notice (newbie here) that it is a little hard to make fair comparisons at a glance as many of the data sheets do quote specs apples to oranges or at least tangerines to oranges.
Thanks a million all for the replies. I have also order 4 new PS caps and a couple of other caps that look suspect. I will put this together and then ask more questions about setting bias.
The web page I quoted earlier does have a quick procedure - will the new transistors change this?
Regards,
Stephen
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