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Old 24th July 2011, 09:48 PM   #201
PB2 is offline PB2  United States
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Would your scans be the same as these? Just to save you the time:
Universal Tiger

People might be interested in the assembly instructions if you are up for scanning them.

I think the decrease of C8 to 100 pF, the output cap to .01, and increasing the 100 ohm resistors to 2W helped stability the most.
They would readily blow up with no load applied LOL!

VI limiting would certainly help with difficult loads.

Last edited by PB2; 24th July 2011 at 09:52 PM.
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Old 30th August 2011, 03:59 PM   #202
perrylv is offline perrylv
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This thread is very interesting. However, I have a pair of kit built Tiger .01s, one that has blown. Before I set out to repair, and not having the engineering background, can I be pointed to the current best thinking as far as stability mods and component substitution is concerned for this model amp? Might as well enhance it a bit while I am in there if there are some advantages to be had.
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Old 31st August 2011, 03:24 AM   #203
PB2 is offline PB2  United States
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I've only looked at the schematic for the .01 and have never worked on one or even seen one in real life. I don't know of any detailed discussions or mods for them anywhere.
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Old 31st August 2011, 03:14 PM   #204
bear is offline bear
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Universal Tiger

read this thread (print it out) and the other related SWTPC amp threads...

I think I'd sum it up this way:

- replace the polystyrene caps with NPO ceramics
- add degeneration to the input diff pair (per Nelson Pass)
- increase the output degeneration - bigger emitter resistors (per Nelson Pass)
- put a Baker Clamp on the driver (iirc)
- drop the B+ voltage 15% or so... (that calls for a "bucking transfomer" or other means)
- something else that I can not recall...

Also the layout - lead length and dress counts on this amp... although I don't know of a specific layout that is going to work, some of these amps were stable, others not, and it may be a function of lead dress and length...


PS. I think this would all hold for the .01 as well.

PPS. the VI limiter built in to the amp never kept it from blowing up...
http://www.bearlabs.com -- Btw, I don't actually know anything, FYI -- every once in a while I say something that makes sense... ]
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Old 24th November 2011, 10:06 AM   #205
gtc is offline gtc
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I have found this and the related threads a wonderful nostalgic read. Only last night I was having dinner with an old technician friend from 1970 and we finished up by discussing the amplifiers that we and other late teen or twenty-something hobbyists built back in the day.

To set the scene, in 1970 tech-heads like us were relied upon to drag party music equipment (turntable, preamp, amp and speakers, plus a pile of LPs) from one location to another and the upside was invites to lots of parties in rooms with posters of Hendrix and so on, lit with black light and thick with the scent of incense sticks to mask the smell of a funny weed people used to smoke. Of course, said equipment was expected to crack the plaster on the walls and get the cops called, so the motto was he who had the most powerful rig won. The challenge was to keep it all operating at full blast for the necessary number of hours. This usually involved fans across the heat sinks as a minimum.

Top of the list for mention over our dinner was the Tiger. In 1971, a mutual friend used to go around telling all and sundry about this wondrous circuit published in Popular Electronics in Oct ’70 -- the Universal Tiger. The opening paragraph of the article screamed in bold print: “It is virtually indestructible and our exhaustive tests reveal that no combination of input-output mismatching and short circuits can cause amplifier failure”. Statements like that, combined with the promise of insane output power, was music to our ears. Photocopies of the article were in great demand around the office and workshops.

Here was an amp promising performance akin to expensive top of the line brand amps for a build budget that young techs could afford. Parties here we come! The real challenge, we thought, would be to build affordable and luggable speaker boxes that could handle the power.

So, it was a great comedown indeed to get reports from early builders that the Tiger oscillated to the extent that a radio transmitter’s licence was needed, and blew up spectacularly, too. My friend looked at the problem and decided that the PCB layout was the cause. He went about redesigning that and had some success, but then lost interest in it.

My old friend never throws much away. After dinner, he pulled out a dusty file that contained the original article plus his hand-drawn negatives for the redesigned PCB.

When I got home I thought I’d Google Universal Tiger and discovered the threads on here. I think it’s terrific that you guys are employing 21st century software technology to try to determine and overcome the root cause of the Tiger’s design problems. I look forward to reading more on that.
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Old 24th November 2011, 11:12 AM   #206
Zero Cool is offline Zero Cool  United States
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@Bear: I think the bias stack resistors needed to be reworked as well if I remember correctly??
It's not about what you can BUY...It's about what you can BUILD!
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Old 24th November 2011, 01:33 PM   #207
Bonsai is offline Bonsai  Europe
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Scroll to the bottom of the page:-

Audio Amplifier Design and Circuits | hifisonix.com

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Old 27th November 2011, 05:26 PM   #208
JMFahey is offline JMFahey  Argentina
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For what itīs worth, I successfully built *a lot* of Tigersaurus versions in the early 70's.
How come?
There were some differences, although let me state that for me, the *main* factor in almost universal bad experiences in those years was lack of building experience in that (then new/groundbreaking) technology.
Specially regarding to grounding and layout.
Much more so than any "parts" problem.
1) Although still a Teen , I had somewhat more experience than my nerdy friends (the one-eyed leading the blind, he he) because some short time earlier, the "boom" were some of the "RCA" amps, mainly the 70W one, with a few "plastic" 40W ones thrown in.
"All" of them oscillated wildly, or so it seemed, and self destructed in a jiffy.
After blowing a few power transistors on mine, I finally tamed them into usability, by trying different wire layout and grounding schemes, until they were stable.
My friends (and friends_of_friends who had heard about that) called me to work on their amps.
Not much feedback or stability or phase shift theory used there, itīs just that after some time certain layouts "looked good" and others did not.
Many times I moved one wire end just one inch, pulling it and resoldering to the same busbar one inch further, or lifting one ground (later I learnt they were ground loops) or running separate ground wires to the PSU caps .
Nothing unusual ... today.
2) I had been building Guitar Amps, Tube of course, (there was nothing else) since 1969.
In 1972 Argentina got into Default, and Imports dissappeared, specially tubes.
I decided trying some SS stuff, and built my version of Tigersaurus with an Ampeg BT15 preamp, straight out of Jack Darrīs book.
3) Differences:
* used Motorola Aluminum MJ2955/2N3055 (original MJ802/4502 were inexistent here)
* used plastic TO66 TIP29/30C for Q3/4 and TIP31/32C for Q5/6
* Lowered +/- rails to +/- 35V
* junked C8 (the 220pF feedback capacitor) , I *never* had good luck with such compensation, which *increases* feedback at frequencies where you already have too much phase shift, added a 47 to 100PF cap on Q4īs BC (a "Miller" cap) which on the opposite lowers HF gain "internally".
Yes, I know it also causes its own phase shift but I guess that the HF loss is larger than that, and "wins the race".
Yes, I found this amp "dull", compared to my tube Twin clones, but I much attribute it to being SS, rather than anything else.
* I built almost 100 of these, which were used everywhere by Rock Musicians onstage, abandoning the design only because I moved on to higher powered 200W/2 ohm amps, with lots of selected RCA 2N3055H (the best transistor widely available way back then, in my market), which forced me to go quasi complementary.

*In a nutshell? I find these Tigersaurus amps very good, incredibly so for their era, where they were truly groundbreaking.
Itīs very easy to criticize *anything* 25 or 30 years later, hindsight is always 20/20.

Thanks a lot to all of you for making me revive fond memories of my youth.
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Old 27th November 2011, 05:45 PM   #209
Conrad Hoffman is offline Conrad Hoffman  United States
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I'm still using my original Tiger from the magazine article, completely scratch built, and it still sounds good. A couple observations that maybe I've mentioned previously. First, the output inductor is absolutely critical. Any effort to minimize it will result in instability, or subtle HF oscillations on musical peaks at the least. The problem is that nobody ever measures them and the values given in most schematics for most amps are just guesses. If anybody cares, I can measure mine and give an exact value and construction, as I have it near the test bench right now. Next, the wiring and ground points are critical. Good practice isn't good enough- best practice required. Minimize lengths, wire the LF returns as star but use the chassis for local HF bypassing right where needed. You can't get good HF grounding using long wires. FWIW, I found adding a miller cap was disastrous for sound quality; makes the amp sound dead as a door nail; just adjust the feedback cap as needed and note the different values used by SWTPC throughout the years and with different revisions and circuits.
I may be barking up the wrong tree, but at least I'm barking!
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Old 27th November 2011, 06:00 PM   #210
digits is offline digits
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I'd love you to Conrad.
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