Universal Tiger

Wow, an 18 year old thread.
I do have the answer for those wondering why the Tigersaurus would self destruct.
There are 4 10W 200 Ohm bias resistors in the 44010-44009 predriver stage.
Needless to say their idle power is about 6.25 watts each.
But, at 300 watts output they dissipate way more than 10 watts each.
So much so that they fractured the cement and I could see the nichrome elements glowing red hot through the cracks in the cement when doing like 300 watts output.
I blew up my pair of tigersauruses several times in their first few years to the tune of eight $5 outputs and eight $1 predrivers.
That was way too expensive in 1975 to resurrect a $155 amplifier but, still cheaper than buying a new one.
One time, replacing the predrivers, I noticed that the solder on the leads of all four 10W resistors was really crystalized.
Then it hit me, those suckers were getting so hot that they were unsoldering themselves in operation.
Open just one solder joint in that bias string and pow, there goes 8 outputs and 8 predrivers.
I remember distinctly that the instructions said to install all the cement resistors flush to the PCB with as short as possible leads.
The 5 watter's are OK. The 10 watter's are not. They unsolder themselves.
I removed the four 10W 200 Ohm resistors from the PCB. I then soldered eight 4-5 inch lead wires long enough to place the four resistors just under the mesh metal top of the amplifier.
I laced the four resistors into a block with 22 AWG magnet wire with a couple of flying ends.
I installed the lid while fishing the fly leads through the mesh.
Then a little twist tie action to mount the block of four 10W resistors just underneath the lid.
I mounted them bottom side up so I could monitor the glow from the elements through the mesh top.
The resistors would brighten and diminish according to the power output.
I operated those two Tigersauruses for another two decades until I'm sorry to say, they were stolen.
I took out alot a speakers but, I couldn't blow up those amps.
I could run above 100% meter into one 8 Ohm 15" woofer in parallel with a sweet 16 box of 6x9 ovals in parallel with 4 peizo tweeters.
That had to be close to a 3 Ohm Load.
I did have an 18" box fan mounted in the back of the road case.
I could run them at 100%, outdoors in the summer heat, all day and all night long until the party ended.
I never did blow them up after fixing the resistor issue.
Fix your 10W resistors and the Tigersaurus will run circles around any other amp. Except for maybe a crown DC300 in bridge mode.

P.S.
If anyone has a Tigersaurus transformer please consider a reply. I have a custom transformer builder on tap but, they would prefer to reverse engineer from an example transformer.
I'm thinking about reproducing the Tigersaurus but, I will have to weigh the cost of the original boat anchor power suppy versus a +-70 volt, 5 ampere switching supply.

All for now.
 
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Just a few photos of mine. My father bought most of the parts for this back in '71 after the article came out. Still have the original magazine. He didn't build it until around 1986-87. Metal shop at General Motors made the case and cover. Had to replace the switch today so I took some pics of it. Just happened to google the amp and found this page...

-Michael
I remember when that amp came out. Either in Popular Electronics, or Radio Electronics. Can't remember which one. I lusted for that in a big way, but I was heading off to college as a poor kid and didn't have the cash to spare. If only...
 
Wow, an 18 year old thread.
I do have the answer for those wondering why the Tigersaurus would self destruct.
There are 4 10W 200 Ohm bias resistors in the 44010-44009 predriver stage.
Needless to say their idle power is about 6.25 watts each.
But, at 300 watts output they dissipate way more than 10 watts each.
So much so that they fractured the cement and I could see the nichrome elements glowing red hot through the cracks in the cement when doing like 300 watts output.
I blew up my pair of tigersauruses several times in their first few years to the tune of eight $5 outputs and eight $1 predrivers.
That was way too expensive in 1975 to resurrect a $155 amplifier but, still cheaper than buying a new one.
One time, replacing the predrivers, I noticed that the solder on the leads of all four 10W resistors was really crystalized.
Then it hit me, those suckers were getting so hot that they were unsoldering themselves in operation.
Open just one solder joint in that bias string and pow, there goes 8 outputs and 8 predrivers.
I remember distinctly that the instructions said to install all the cement resistors flush to the PCB with as short as possible leads.
The 5 watter's are OK. The 10 watter's are not. They unsolder themselves.
I removed the four 10W 200 Ohm resistors from the PCB. I then soldered eight 4-5 inch lead wires long enough to place the four resistors just under the mesh metal top of the amplifier.
I laced the four resistors into a block with 22 AWG magnet wire with a couple of flying ends.
I installed the lid while fishing the fly leads through the mesh.
Then a little twist tie action to mount the block of four 10W resistors just underneath the lid.
I mounted them bottom side up so I could monitor the glow from the elements through the mesh top.
The resistors would brighten and diminish according to the power output.
I operated those two Tigersauruses for another two decades until I'm sorry to say, they were stolen.
I took out alot a speakers but, I couldn't blow up those amps.
I could run above 100% meter into one 8 Ohm 15" woofer in parallel with a sweet 16 box of 6x9 ovals in parallel with 4 peizo tweeters.
That had to be close to a 3 Ohm Load.
I did have an 18" box fan mounted in the back of the road case.
I could run them at 100%, outdoors in the summer heat, all day and all night long until the party ended.
I never did blow them up after fixing the resistor issue.
Fix your 10W resistors and the Tigersaurus will run circles around any other amp. Except for maybe a crown DC300 in bridge mode.

P.S.
If anyone has a Tigersaurus transformer please consider a reply. I have a custom transformer builder on tap but, they would prefer to reverse engineer from an example transformer.
I'm thinking about reproducing the Tigersaurus but, I will have to weigh the cost of the original boat anchor power suppy versus a +-70 volt, 5 ampere switching supply.

All for now.

That's good to know, I only ran my scratch built Tigersaurus on the bench at full power for about
30 seconds just to check it all out but I worried that it might have some sort of heating issue.
Mine never failed in home use, but when used for hours at parties, we put a box fan on top of it,
which also kept it safe. It has never failed.

I'd probably replace those with 20W resistors and space them 1 - 2" above the board. Or if 20W
are not available, use two 10W to make the final value also spaced well above.

If you are seriously considering a reproduction you might want to use high voltage outputs and
eliminate the series output stage. I did this in the LT Spice simulation model that is posted in
another thread. You might also want to look at older Bryston amps that are very similar but
much more complicated.
 
For those of you with MkII / 175a schematics I have this adventure to share

My Universal TIgers sat unused for the last ten years after R20 cracked. I replaced R20, but R16 would burn up. I figured that although the driver transistors ohmed out good, that the junctions may be breaking down at high voltage. I replaced Q6, with no improvement. I also replaced the output transistors (Q7 and Q8) and the input differential pair (Q1 and Q2) with no effect. R16 still burned. ( I had figured there could be trouble with an amp kit so I had bought spares for all the transistors. ) So...on to Q5. That changed things, R13 was now smoking. That finally made me curious to see what's going on with R13, so I put a multimeter across it. NO BURNING! Well, well. I took the first ceramic cap I could lay my hands on, without noting its pf value and soldered it across R13. The amp is now happy. Replacing transistors was a waste of time, none of them was bad. Moral of the story is that those "screams" can crop up anywhere in this design, and at any time. Before I commit the amp to daily service I'm going to build the "Speaker Protector" featured in the August 1991 issue of Radio Electronics. It's basically a device to prevent the amp's full up power supply voltage from breaking through to the speaker output transistors. Funny how the R20 resistor cracking had also blown fuse F2 on the negative bus which caused the full positive supply voltage to pass through Q7 and destroy the speaker. Bad fusing design. I didn't replace any caps, they all ESRed good, and checking with a scope there was not much ripple.

This is very interesting because I have one Universal Tiger that bursts into oscillation in many different ways.
But I have another that does not at all, and I assume that it might be variations in internal transistor capacitances
or performance characteristics.
The PNP vs. NPN output and driver devices have very different characteristics and capacitances so it is very
possible that one side would be more prone to oscillation. I'm not sure if the component references are the
same for the MKII version vs. the schematic in the first post but R13 in the OP schematic is protected by the
B-E junction of the output device and I've never seen that one burn. I'll look for the MKII schematic that I
have around here somewhere.
Here's the MKII schematic and R13 and R20 are in the same locations:
https://www.diyaudio.com/community/threads/universal-tiger.41926/page-9#post-2598334
 
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built quite a few, this is an amp that was awesome then, until I met the Leach Amps....
Because the Leach amps (especially the Double Barreled Amplifier) would do similar things, without all the drama. I have had to chase down oscillations in the stacked emitter follower before, but never had one actually be destructive. Annoying yes, but not destructive.

What I’ve found when working through it all is that a zobel is sometimes required at the emitter of the slave (upper) output bank. If that node drives ”too pure” of a capacitance (even collector-to-heat-sink) the reflected negative R at the base is troublesome. De-Q it and everything is fine. I’m not sure how well this will translate to the CFP-with-gain of the Tigersaurus, but fixes it with a stacked EF3. Even a big one with 10 transistors in series-parallel. It never blew one up, but had the “snivets” on the negative half cycle till I put the R-C loading on there. Quite audible when it happens, too.