Note that I don't suggest that anyone build this amp since it is overly simplistic.
The SWTPC Lil Tiger was their smallest amplifier with undersized TO-126 output devices that blew up
when driving 4 ohm loads. It was also overly simplistic as can be seen from the schematics. I was gifted
one channel circuit board and parts kit for Christmas in 1967, built it and it worked, and another a few
months later for stereo. It was my first SS amp that worked. I'd tried building some from Ge transistors
but none of them lasted for more than a few seconds. Mine blew up many times while driving 4 ohm
speakers and I didn't realize that larger output devices were needed. I still have it, not working, and
decided to simulate it for kicks back in 2016. I might rebuild it just to have it working as the first amp
I ever built.
I'd probably use BD911/912 or TIP35/36 as off board outputs if I rebuild this amp, then it should be fine
into 4 ohm loads and probably survive shorted outputs. I'd also use BD139/140-16 as drivers when much
bigger output devices are used. I also will post an EF3 output mod version simulation in another thread.
A zip file is attached with the LtSpice files, it is set up to run distortion analysis but it can be changed for
different .tran or AC analysis. Note that I used modern sensible replacements for the transistors from
Bob C's checked transistor model file. Again use bigger outputs rather than the ones shown if anyone
tries to build this.
Anyway, here are some pictures and a link to the full article from Popular Electronics December 1967:
http://swtpcemu.com/mholley/PopularElectronics/Dec1967/PE_Dec1967.htm
The SWTPC Lil Tiger was their smallest amplifier with undersized TO-126 output devices that blew up
when driving 4 ohm loads. It was also overly simplistic as can be seen from the schematics. I was gifted
one channel circuit board and parts kit for Christmas in 1967, built it and it worked, and another a few
months later for stereo. It was my first SS amp that worked. I'd tried building some from Ge transistors
but none of them lasted for more than a few seconds. Mine blew up many times while driving 4 ohm
speakers and I didn't realize that larger output devices were needed. I still have it, not working, and
decided to simulate it for kicks back in 2016. I might rebuild it just to have it working as the first amp
I ever built.
I'd probably use BD911/912 or TIP35/36 as off board outputs if I rebuild this amp, then it should be fine
into 4 ohm loads and probably survive shorted outputs. I'd also use BD139/140-16 as drivers when much
bigger output devices are used. I also will post an EF3 output mod version simulation in another thread.
A zip file is attached with the LtSpice files, it is set up to run distortion analysis but it can be changed for
different .tran or AC analysis. Note that I used modern sensible replacements for the transistors from
Bob C's checked transistor model file. Again use bigger outputs rather than the ones shown if anyone
tries to build this.
Anyway, here are some pictures and a link to the full article from Popular Electronics December 1967:
http://swtpcemu.com/mholley/PopularElectronics/Dec1967/PE_Dec1967.htm
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South West Technical Error Corporation.
Foregoing emitter resistors is an attempt to make it sound better. It can. To make the amp more ”rugged”, assuming the bias is stable, larger devices could/should be used. TIP41/2A’s would have survived 4 ohms. But as a direct replacement for the devices which were used it likely would result in thermal run away unless R6, the diodes types, or both are trimmed. 0.1 ohm emitter resistors and the problem goes away.
Foregoing emitter resistors is an attempt to make it sound better. It can. To make the amp more ”rugged”, assuming the bias is stable, larger devices could/should be used. TIP41/2A’s would have survived 4 ohms. But as a direct replacement for the devices which were used it likely would result in thermal run away unless R6, the diodes types, or both are trimmed. 0.1 ohm emitter resistors and the problem goes away.
Probably not. You could run these newfangled silicon transistors hotter than the old-school Ge’s. Even those old totem pole PNP Ge output stages often had emitter resistors, but LARGE heat sinks by comparison. By the time the heat sinks even got warm on those, the outputs were already blown due to excessive Tj. Those designs often had one of these Si TO-126/TO-202‘s as a driver running hotter than the blazes of hell and damnation in class A. But that transistor had a large bypassed emitter resistor. Thinking one can run a class B (AB) push pull stage that hot with no emitter resistors is a MISTAKE. No problem quiescent, but at war volume…… Poof!
They make 3-watt MOX’s in a really small form factor now, not much bigger than an old school half watt carbon comp. Put a bag of 100 0.1 (or .068) ohm on the next mouser order.
They make 3-watt MOX’s in a really small form factor now, not much bigger than an old school half watt carbon comp. Put a bag of 100 0.1 (or .068) ohm on the next mouser order.
