New TO-3 Output Transistors
- Thread starter EchoWars
- Start date
EW, just out of curiosity, do you happen to know the comparable specs on the NMA/NMC1012 outputs? I don't think I've ever seen them listed anywhere.
But it certainly seems like the perfect item to squirrel away in case there's a failure down the road. Thanks for the sleuthing... :thmbsp:
The Exclusively Sansui crowd would probably also be interested in this thread-
Herb
Some of the 'crowd' ARE interested and have been reading this thread with interest. :yes:
Me neither, but I suspect that they are similar to the 2SA1116 & 2SC2607, with a bit higher Ft.
Fred Longworth
audio fanatic
If you use a 25MHz device in a circuit designed for 5Mhz, the reactance in the feedback loop will overcorrect for the phase shift inherent to 5Mhz devices. If you use a 5MHz device in a circuit designed for 25Mhz, the reactance in the feedback loop will undercorrect for the phase shift inherent to 25MHz devices.
Both phase compensation errors lead to instability, but in my experience the worst is undercorrection, which comes from using low-bandwidth devices in place of high-bandwidth devices.
I've seen an unstable amplifier come up on a lightbulb tester or variac and seem, on first blush, to work normally. Then suddenly, when a load is connected, e.g. the inductive load of a real speaker, and the amp is cranked a bit, suddenly the amp goes up in smoke.
**********
Echowars, thanks a lot for this discovery!!!!
Fred
Both phase compensation errors lead to instability, but in my experience the worst is undercorrection, which comes from using low-bandwidth devices in place of high-bandwidth devices.
I've seen an unstable amplifier come up on a lightbulb tester or variac and seem, on first blush, to work normally. Then suddenly, when a load is connected, e.g. the inductive load of a real speaker, and the amp is cranked a bit, suddenly the amp goes up in smoke.
**********
Echowars, thanks a lot for this discovery!!!!
Fred
The assumption in your first sentence is that the dominant pole is defined in the feedback loop, which is not done all that often. That part of the amp is too vulnerable to the whims of the load, thus the dominant pole is usually before the driver stage, buffered from the output.
Still, it is good to make an honest attempt to replace devices with those who's unity gain freq. is in the neighborhood of the originals. The introduction of these devices makes that possible for a few amps that were orphans before. Now, if they'd release some intermediate speed devices (12MHz or so), we'd be stylin'.
Still, it is good to make an honest attempt to replace devices with those who's unity gain freq. is in the neighborhood of the originals. The introduction of these devices makes that possible for a few amps that were orphans before. Now, if they'd release some intermediate speed devices (12MHz or so), we'd be stylin'.
Fred Longworth
audio fanatic
Yes, it would be nice if the amplifiers I see lined up with theory. And yes, the dominant pole is supposed to "reside" primarily in the diff amp and class-A driver stages . . . however, a large number of amplifiers are crossing my counter, so to speak, that are load sensitive, and where the bandwidth of the output transistors matters a whole lot.
I have concluded that this is because, in a large number of cases, the lumped stray reactance as well as the lumped variance of expected reactance in the circuit has increased substantially as the components including the board itself age. Put simply, as circuits age, they get loose and sloppy, and thus, factors -- e.g. output transistor bandwidth -- that had a previously subordinated influence move into a position of far greater influence.
Fred
I have concluded that this is because, in a large number of cases, the lumped stray reactance as well as the lumped variance of expected reactance in the circuit has increased substantially as the components including the board itself age. Put simply, as circuits age, they get loose and sloppy, and thus, factors -- e.g. output transistor bandwidth -- that had a previously subordinated influence move into a position of far greater influence.
Fred
A general suggestion: any time parts are replaced, especially transistors that would need insulators, heatsink grease/paste, resoldering, removing and replacing circuit boards...you need the dim bulb tester to protect you against that possible dead short, miswired circuit, reversed polarity capacitor, or not quite isolated transistor.
Trust me, every tech worth his salt has seen it, most amateur audiophiles doing this work will let the smoke out every so often and that's with double and triple checking.
Vintage gear is always an adventure when trying to effect a repair or refurbishment.
no, because sometime down the road, sometimes immediately, sometimes later - the amp will emit a large cloud of smoke and stop working.
Might take a new set of speakers, or the day you crank it up for a party etc...
sort of like playing Russian roulette without spins in between each turn.
Fred Longworth
audio fanatic
The light bulb thing is invaluable. It's like testing a parachute while bungee-jumping. If the parachute doesn't open, the bungee cord keeps you from dying from the fall.
You can build a light bulb tester with hardware from Lowe's or Home Depot for under $20.
This is especially important when repairing complex DC-coupled amplifiers where, when the outputs short, the problem can work its way back into the driver and pre-driver stages. Since I own a repair service, I often see units where the owner has replaced, say, a 6-amp fuse with a 15-amp fuse -- causing the problem to spread.
Fred
You can build a light bulb tester with hardware from Lowe's or Home Depot for under $20.
This is especially important when repairing complex DC-coupled amplifiers where, when the outputs short, the problem can work its way back into the driver and pre-driver stages. Since I own a repair service, I often see units where the owner has replaced, say, a 6-amp fuse with a 15-amp fuse -- causing the problem to spread.
Fred
G9700/G8700db amp section
Had to go back and check.
In the amp section the differences in the 2 were.
9700 had heavier rectifiers, higher rail voltage, higher rated outputs and some changes on the drivers boards resistors to cope with different rail voltages.
Other then that aren't the driver boards are the same?
I'm assuming here, if the rest of the circuit can handle both types of outputs, couldn't both handle the better outputs?
Of course because of rail restrictions on the G8700, you wouldn't expect the same power.
Had to go back and check.
In the amp section the differences in the 2 were.
9700 had heavier rectifiers, higher rail voltage, higher rated outputs and some changes on the drivers boards resistors to cope with different rail voltages.
Other then that aren't the driver boards are the same?
I'm assuming here, if the rest of the circuit can handle both types of outputs, couldn't both handle the better outputs?
Of course because of rail restrictions on the G8700, you wouldn't expect the same power.
noveltone
Active Member
I am really excited to see ST investing in audio. I mean, they specifically designed this part for this purpose! Amazing. It's true, however, that audio isn't going anywhere, even though it seems that most people don't mind bad sound.
These fast TO-3's don't seem to hang around like vintage tubes, or are easier to counterfeit, or both. Anyway...
Glenn, thanks for sleuthing this out!
These fast TO-3's don't seem to hang around like vintage tubes, or are easier to counterfeit, or both. Anyway...
Glenn, thanks for sleuthing this out!
sanyofreak
Active Member
This thread entry clears it all up for me now, thanks for the info, dont think I've ever worked on an amp that required or utilized these types of devices, but great to know, and yeah, ST makes pretty good stuff otherwise as well, a trusted semi mfr....
Thanks
I don't think so. The C1586 and A909 are intermediate speed devices (which is why I said a 12MHz device from ST would be cool). As it is, I've worked on a lot of Sansui amps using these devices and replaced them (when necessary) with the On-Semi MJ21193/94 or MJ21195/96's, and could find no measurable change in output response from the original devices. The On-Semi transistors may not be ideal from a bandwidth standpoint (at least on paper), but they are apparently plenty good enough for replacing the C1586 and A909.
This is truly...........awesome.
