SWTP Tigersaurus amplifier modification completed 

Nice! I miss SWTP and those good old days...

Nice work John! You have invested so much time for this project so I hope you will be well paid for such a work!

Awesome work John. This was so interesting. It's nice to see a redesign of a production amp with your explanations at each step. I once had an amp that I'd repaired and it blew up once per month. I worked with a technician from the parent company for hours, trying to sort out the instability. It turns out, it didn't like the mica insulators I had used on the output pair. Went back to silicone types and it behaved. It was so close to oscillation all the time.

Parts shortages should reduce significantly in the near future, lots of capacity coming on line.

John, sorry. The problem of the excessive heating of the power transistors with very low voltage in the PSU (±20VDC), was that I had the BIAS control in the ZERO OHMS position (maximum current conduction). I moved it towards 1k max resistance and the voltage issues were fixed and the power transistors cooled down for my peace of mind.  Feedbac

Great work fascinating process...cheers.

congratulations

You should ask the owner if he's willing to invest in making new PCBs for both amps with the modifications you made, to have them matched.

excellent analysis that eliminates possible oscillations, excellent video. I have a question about the changes .... the transistors Q3 and Q7 remain the original ones ??? . Thank you so much . Pedro .

Would like to see some tests VS the unmodified one as these two are a stereo pair. S/n, distortion, can the original pass the cap test, etc.

Glad to hear you got things sorted John. I will work on getting a Dayton trip on the calendar for pickup. I am with Anton on the testing. How about a head to head on the two units it isn't too much trouble?

I wonder if "FNIRSI toy scope" is good enough to display crossover notch. I remember Audio Expert from British "Practical Electonics" claiming a few years ago that only analog scopes can do it.

happy to see this completed so Q9 can be placed to Q10 driver thermally bound? I can do that I think

Well done! Is 3M tape or any other type of thermal pad better for power transistors than mica/grease?

What did the rails sag to under full output on this? Did you just test power at 8ohms? My 3 pair k134 j49 saggs to 59v rails from 69v idle at 4ohm i got 306w unclipped. This seems a bit more manly than mine. Thanks

Hi John, I don't want to make a long and boring letter. I am 61 years old and I have been a Piano Teacher all my life but my hobby has been electronics. When I saw the videos of the Tigersaurus modification, I was excited to repeat that modification on a Tigersaurus that had been broken I suppose by oscillations. I did everything as you showed it in the video. Using a Variac today , I was able to bring the voltage across the power supply filters down to just ± 20 vdc and touching the power transistors with my hand , I felt them get hot . It surprised me with so little voltage. Making measurements with the multimeter, with ±20vdc in PSU, in the Collectors of q20 and q22, q17 and q19 there was ±10VDC, but in the Collectors of the rest of the transistors it had voltage when in another Tigersaurus that is working it has ZERO Volt. I have a question: do you remember in the BIAS circuit in which position the 1k control was (maximum resistance or minimum resistance) when applying voltage??? . Answer me please. Thank you . Pedro .

Hi John , finally when you connect the amplifier to full voltage of +/- 74 vdc , both resistors R30 and R31 are replaced by two wires ??? . My question is because I don't see clearly in the final video of the anti-oscillation modifications the wires that would be used as jumpers of R30 and R31. Answer me please. Thank you so much . Pedro .

The SWTPC Tiger and Tigersaurus amps had strong "thumps" when coming up from the voltage drop (or power surge). Have you eliminated that problem with some of your modifications. Or do you have a soft-start circuit in the power supply for the finals. I keep worrying that I'm going to either blow my speakers or burn up the drivers on my Tiger pair. Have you resolved that issue with your mods?

By Jove John I think you've done it. I still say you should have just thrown a class D amplifier in the chassis and called it a day.

I realize this is super nitpicky, but just in case it might help visibility of the vid: I believe you have a typo in TigersAUrus in the title. ;)