SWTPC Tiger Amp Madness!
There are several threads on here about various Tiger amps that were construction articles in
Popular and Radio Electronics back in the late 60 and early 70s. Many people have commented
about how they brought back memories and how they went up in smoke or
even (probably brief) flames. I'll share some pictures here for laughs.
I built and repaired the Lil'Tiger and Universal Tiger (UT) (stereo version) many times. I scratch
built the larger Tigersaurus that never failed.
The UT (stereo) I worked on is my parent's amp and over the years I've picked up a few on ebay,
and various members and friends have given more to me. Tubelab (George) here sent me
two nearly completed UT boards and a pair of outputs transistors from 1976.
Michael Chua (Ampslab) sent me 5 pairs of much newer output transistors from the 1990s.
A local friend bought a pair of Plastic Tiger boards years ago that he tried to run on +/-45V not
knowing that the 40V in the article was a misprint and should have been +/-30V - his went up in
flames on turn on. He later had plans to build many more amps and offered his home etched boards and parts.
I was given a UT MKII mono block with incorrect output devices, I'm sure that it failed at
some point.
Here's the basic schematic of the original UT used in both the mono block and stereo versions, the boards are the same:
https://www.diyaudio.com/forums/att...217283-tiger-amp-madness-pe_oct_1970_pg32-jpg
The UT came in an open chassis mono block version and a closed chassis stereo version.
The stereo version used the same power supply but it was shared between the channels.
The mono block had one transistor per heat sink while the stereo version had the same
heatsinks but with 2 outputs on each one. They also deleted the thermal cut off in the
stereo version.
I bought this stereo UTS on ebay and it looks exactly like ours did when it failed, completely
burnt R12 and R14 with the board being charred even on the back side.
It is interesting that at audio frequencies and full power simulation shows about .9W in
R12, R14 and about the same in R15 and R16. The oscillation must be at high frequency
since plastic caps C3 and C4 melt and act to protect R15 and R16 forcing more power to
R12 and R14. The next and last revision of the UT increased R12 and R14 to 2W but left
the rest at 1/2 W when they also should have gone to at least 1W.
Here's a picture of the UTS from ebay with burnt resistors and melted caps on the top board:
https://www.diyaudio.com/forums/att...0684d1572213354-tiger-amp-madness-uts-top-jpg
The next is a close up of the top driver board:
https://www.diyaudio.com/forums/att...572213747-tiger-amp-madness-uts-top-board-jpg
An odd thing is that often one channel has severe damage like the top board but then
often there are damaged parts in the other channel. I don't know the details of how this
amp from ebay failed but the lower board has R13 slightly burnt. I should test all the
parts on that board. R12 and R14 are mildly burnt and the caps partially melted:
https://www.diyaudio.com/forums/att...572215741-tiger-amp-madness-sut-bot-board-jpg
When our amp failed, back in the early 70s, I did the repair and wrote this letter to SWTPC:
I found this letter recently in a folder with equipment manuals and it is very interesting to
note that the diff pair transistor Q2 failed, as well as the feedback shunt resistor R8 and a
mild burn to R12 and R14. The violent HF oscillation in one channel leaked into the other
channel. It is also interesting that both drivers failed in the badly damaged channel but
only one output device failed since probably the negative rail fuse saved the other output
transistor. I was 12 years old when I built that amp and 14 when I wrote this letter:
https://www.diyaudio.com/forums/att...7d1572214249-tiger-amp-madness-uts-letter-jpg
More pictures of the Stereo UT:
Front, ours had a stick on brushed gold front panel but otherwise was the same:
https://www.diyaudio.com/forums/att...98d1572215850-tiger-amp-madness-sut-front-jpg
Back:
https://www.diyaudio.com/forums/attachments/solid-state/790699d1572215913-tiger-amp-madness-uts-jpg
This one, actually a pair from ebay were built by Trout Audio Labs:
https://www.diyaudio.com/forums/att...00d1572216040-tiger-amp-madness-sut-trout-jpg
Here is the other in the pair from ebay, this one did not come with boards:
https://www.diyaudio.com/forums/att...01d1572216164-tiger-amp-madness-sut-2-top-jpg
There are several threads on here about various Tiger amps that were construction articles in
Popular and Radio Electronics back in the late 60 and early 70s. Many people have commented
about how they brought back memories and how they went up in smoke or
even (probably brief) flames. I'll share some pictures here for laughs.
I built and repaired the Lil'Tiger and Universal Tiger (UT) (stereo version) many times. I scratch
built the larger Tigersaurus that never failed.
The UT (stereo) I worked on is my parent's amp and over the years I've picked up a few on ebay,
and various members and friends have given more to me. Tubelab (George) here sent me
two nearly completed UT boards and a pair of outputs transistors from 1976.
Michael Chua (Ampslab) sent me 5 pairs of much newer output transistors from the 1990s.
A local friend bought a pair of Plastic Tiger boards years ago that he tried to run on +/-45V not
knowing that the 40V in the article was a misprint and should have been +/-30V - his went up in
flames on turn on. He later had plans to build many more amps and offered his home etched boards and parts.
I was given a UT MKII mono block with incorrect output devices, I'm sure that it failed at
some point.
Here's the basic schematic of the original UT used in both the mono block and stereo versions, the boards are the same:
https://www.diyaudio.com/forums/att...217283-tiger-amp-madness-pe_oct_1970_pg32-jpg
The UT came in an open chassis mono block version and a closed chassis stereo version.
The stereo version used the same power supply but it was shared between the channels.
The mono block had one transistor per heat sink while the stereo version had the same
heatsinks but with 2 outputs on each one. They also deleted the thermal cut off in the
stereo version.
I bought this stereo UTS on ebay and it looks exactly like ours did when it failed, completely
burnt R12 and R14 with the board being charred even on the back side.
It is interesting that at audio frequencies and full power simulation shows about .9W in
R12, R14 and about the same in R15 and R16. The oscillation must be at high frequency
since plastic caps C3 and C4 melt and act to protect R15 and R16 forcing more power to
R12 and R14. The next and last revision of the UT increased R12 and R14 to 2W but left
the rest at 1/2 W when they also should have gone to at least 1W.
Here's a picture of the UTS from ebay with burnt resistors and melted caps on the top board:
https://www.diyaudio.com/forums/att...0684d1572213354-tiger-amp-madness-uts-top-jpg
The next is a close up of the top driver board:
https://www.diyaudio.com/forums/att...572213747-tiger-amp-madness-uts-top-board-jpg
An odd thing is that often one channel has severe damage like the top board but then
often there are damaged parts in the other channel. I don't know the details of how this
amp from ebay failed but the lower board has R13 slightly burnt. I should test all the
parts on that board. R12 and R14 are mildly burnt and the caps partially melted:
https://www.diyaudio.com/forums/att...572215741-tiger-amp-madness-sut-bot-board-jpg
When our amp failed, back in the early 70s, I did the repair and wrote this letter to SWTPC:
I found this letter recently in a folder with equipment manuals and it is very interesting to
note that the diff pair transistor Q2 failed, as well as the feedback shunt resistor R8 and a
mild burn to R12 and R14. The violent HF oscillation in one channel leaked into the other
channel. It is also interesting that both drivers failed in the badly damaged channel but
only one output device failed since probably the negative rail fuse saved the other output
transistor. I was 12 years old when I built that amp and 14 when I wrote this letter:
https://www.diyaudio.com/forums/att...7d1572214249-tiger-amp-madness-uts-letter-jpg
More pictures of the Stereo UT:
Front, ours had a stick on brushed gold front panel but otherwise was the same:
https://www.diyaudio.com/forums/att...98d1572215850-tiger-amp-madness-sut-front-jpg
Back:
https://www.diyaudio.com/forums/attachments/solid-state/790699d1572215913-tiger-amp-madness-uts-jpg
This one, actually a pair from ebay were built by Trout Audio Labs:
https://www.diyaudio.com/forums/att...00d1572216040-tiger-amp-madness-sut-trout-jpg
Here is the other in the pair from ebay, this one did not come with boards:
https://www.diyaudio.com/forums/att...01d1572216164-tiger-amp-madness-sut-2-top-jpg
Attachments
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UTS-TOP.jpg131.6 KB · Views: 1,258
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UTS-TOP-BOARD.jpg129.8 KB · Views: 2,135
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UTS-LETTER.jpg120.4 KB · Views: 1,261
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SUT-BOT-BOARD.jpg136.2 KB · Views: 1,248
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SUT-FRONT.jpg117.3 KB · Views: 1,219
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UTS-BACK.jpg113.9 KB · Views: 295
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SUT-TROUT.jpg110.8 KB · Views: 286
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SUT-2-TOP.jpg162 KB · Views: 300
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PE_Oct_1970_pg32.jpg139.9 KB · Views: 873
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