Hummm.
I built one of the preamps too. It worked fine. I also built a couple of the 9 band equalizers, and a dynamic range expander. They all worked just fine (although I didnt like the expander). Did I just have extraordinary good luck, or ...? I just dont understand how all of the kits I built worked just fine for decades, and nobody else could get them to work. I just followed the directions. Odd.....
I built one of the preamps too. It worked fine. I also built a couple of the 9 band equalizers, and a dynamic range expander. They all worked just fine (although I didnt like the expander). Did I just have extraordinary good luck, or ...? I just dont understand how all of the kits I built worked just fine for decades, and nobody else could get them to work. I just followed the directions. Odd.....
I think whether or not you got a workable product would be pretty much the luck of the draw. I followed directions on assembling my preamp, and it howled like a dog (actually, it whooshed and swooshed and distorted like mad). In retrospect, I know now that the noises it made were from full-on RF oscillation, probably due to component variations and inadequate compensation. I have the equipment and experience now to fix such things or design them out in the first place - I didn't have them then. Today, I would also sneer at the cigar box construction, but it was probably all one could expect for the price.
To people that seem to be complaining about the SWTPC amplifiers:
did you build them right? (mine all worked)
did you follow the recommended chasis layout? (big problems when I didn't)
did you use the same wire lengths? (see above)
The only real problem I had with a factory kit was a Tiger .01 acting like a 2Mhz oscillator using the AC coupled input, it worked fine with the DC input. The problem was the tantalum input cap.
The preamp had some hum with the stock transformer, I replaced it with a wall plug type, no problem.
To those of you that think the CF pair is unreliable, look at a Bryston 3B, 4B, etc. The original 3B looks just like a Tiger .01 with another pair of outputs in parallel. Bryston retroactively extended the waranty on these early models to 20 years, a safe bet as the ones I saw for service usually just need filter caps. They don't sound half bad either.
did you build them right? (mine all worked)
did you follow the recommended chasis layout? (big problems when I didn't)
did you use the same wire lengths? (see above)
The only real problem I had with a factory kit was a Tiger .01 acting like a 2Mhz oscillator using the AC coupled input, it worked fine with the DC input. The problem was the tantalum input cap.
The preamp had some hum with the stock transformer, I replaced it with a wall plug type, no problem.
To those of you that think the CF pair is unreliable, look at a Bryston 3B, 4B, etc. The original 3B looks just like a Tiger .01 with another pair of outputs in parallel. Bryston retroactively extended the waranty on these early models to 20 years, a safe bet as the ones I saw for service usually just need filter caps. They don't sound half bad either.
DJK.
Hi D
Quote:
The preamp had some hum with the stock transformer, I replaced it with a wall plug type, no problem.
I remember that preamp because I had it for a while. It was by far probably the best sounding piece I can remember. I also owned some big Tigers I got from from you. The biggest mistake I made was getting rid of them.
I never owned a pair of the little Tigers that ever worked right. In retrospect I'm sure your correct. Proper attention to detail must be paid or the outcome will be crap.
There is no one I know of that puts the kind of detail into assembling something like you do. I wish I had some of the pictures to post so that others including myself could learn a lesson from it.
Thanks for the reality check.
Joe
Hi D
Quote:
The preamp had some hum with the stock transformer, I replaced it with a wall plug type, no problem.
I remember that preamp because I had it for a while. It was by far probably the best sounding piece I can remember. I also owned some big Tigers I got from from you. The biggest mistake I made was getting rid of them.
I never owned a pair of the little Tigers that ever worked right. In retrospect I'm sure your correct. Proper attention to detail must be paid or the outcome will be crap.
There is no one I know of that puts the kind of detail into assembling something like you do. I wish I had some of the pictures to post so that others including myself could learn a lesson from it.
Thanks for the reality check.
Joe
Re: 1973????
AHHH HA, we were both right...well sorta.....
What i have is a 1973 Popular electronics EXPERIMENTERS HANDBOOK that has the article "Assembling a universal tiger" on page 11
Also of note, i found i STILL have some original transistors if anyone wants them. some of the RCA driver transistors that have the built in heatsinks and a few motorola output transistors, but they look rough. they might work but the tops of the TO-3 cases have small dents in them???? I must have pulled them from something.
I also found my spec sheet for the 2 power transofrmers i have.
They have dual 110V primaries and dual 28VCT secondaries at 3 amps each. so you could wire them for 56VCT @ 3 amps etc and they will run 110 or 220V etc etc...
Zero
Jocko Homo said:
AHHH HA, we were both right...well sorta.....
What i have is a 1973 Popular electronics EXPERIMENTERS HANDBOOK that has the article "Assembling a universal tiger" on page 11
Also of note, i found i STILL have some original transistors if anyone wants them. some of the RCA driver transistors that have the built in heatsinks and a few motorola output transistors, but they look rough. they might work but the tops of the TO-3 cases have small dents in them???? I must have pulled them from something.
I also found my spec sheet for the 2 power transofrmers i have.
They have dual 110V primaries and dual 28VCT secondaries at 3 amps each. so you could wire them for 56VCT @ 3 amps etc and they will run 110 or 220V etc etc...
Zero
It would be nice if someone could take the Tiger 01 and SPICE it.
I would be really curious to know what the simulation says about the instability.
These are/were notorious for flaming out.
I have several that were flammed... and they definitely did not like having their inputs pulled out when they were on...
In fact I tried a complete rebuild and to stabilize them back about
1990 - couldn't manage to get them to stabilize... and couldn't really find the oscillation's source(s) (admitting inadequacies...).
It seems like layout plays a role too...
Also have some factory layout Tigers... smoked (the kits)... used
to see them all the time at hamfests, smoked.
Today you don't want to use the stock transistors, imho the newer 150XX series are superior anyhow...
_-_-bear
I would be really curious to know what the simulation says about the instability.
These are/were notorious for flaming out.
I have several that were flammed... and they definitely did not like having their inputs pulled out when they were on...
In fact I tried a complete rebuild and to stabilize them back about
1990 - couldn't manage to get them to stabilize... and couldn't really find the oscillation's source(s) (admitting inadequacies...).
It seems like layout plays a role too...
Also have some factory layout Tigers... smoked (the kits)... used
to see them all the time at hamfests, smoked.
Today you don't want to use the stock transistors, imho the newer 150XX series are superior anyhow...
_-_-bear
The Audio Amature article listed several reasosn why they smoked. the Bias Resistor stack was too small and some units had pecor brand Outputs that were bad, the Motorola outputs were good and didnt oscillate, but the Pecor units would.. etc...
Some other reasons but those were the 2 biggies..
Zero
Some other reasons but those were the 2 biggies..
Zero
What a timely thread. I was cleaning up the shop last week and came across the two Tiger .01's I built when I was in the 7th-grade! I worked for my dad all summer to pay for them. Memories, memories, memories. One still worked when I retired them a couple decades ago.
Hey Zero and Rick: Let me know if you decide to do anything with ‘em...
-Casey Walsh
Hey Zero and Rick: Let me know if you decide to do anything with ‘em...
-Casey Walsh
SPICE IT!!
Motorola transistors oscillated and destroyed themselves just fine, thank you.
Many made their way to the trash can. Along with the driver transistors...
As I said, I have factory kits, of the .01 style that fry themselves just for yuks... the requisite layout... so that's not the issue.
Obviously, something(s) are quite sensitive to positive feedback here, and maybe even some wire length in a critical area happens to work like an antenna or a high impedance depending upon position or length... but that's not a reliable way to set up an amplifier...
A few of mine did work for a while... but eventually they also decided to blow their own brains out...
So any of you SPICE wiz kids out there gonna run an analysis on the .01 circuit?? Let's get a definitve look at the circuit sans parasitic couplings??
_-_-bear
Motorola transistors oscillated and destroyed themselves just fine, thank you.
Many made their way to the trash can. Along with the driver transistors...
As I said, I have factory kits, of the .01 style that fry themselves just for yuks... the requisite layout... so that's not the issue.
Obviously, something(s) are quite sensitive to positive feedback here, and maybe even some wire length in a critical area happens to work like an antenna or a high impedance depending upon position or length... but that's not a reliable way to set up an amplifier...
A few of mine did work for a while... but eventually they also decided to blow their own brains out...
So any of you SPICE wiz kids out there gonna run an analysis on the .01 circuit?? Let's get a definitve look at the circuit sans parasitic couplings??
_-_-bear
It's been mentioned that this amp works just fine for some people and I've seen one in a system that was stable for over 20 years. But this very same amp blew up when used on the bench for testing speakers, where inputs and outputs were handled and changed often.
Anyway the obvious thing here is the Nyquist Stability Criterion, gain and phase margin which can be measured open loop, all that jazz. The obvious thing about this amp is that there's no dominant pole compensation from Q3's C to B. The Citation has 150 pF there.
There is a form of feedback system called integral control that is unconditionally stable with of course the tradeoff of slow response time. Way back in the early days when the 709 OP amp came out and blew up often because it was so unstable they discovered that a low frequency dominant pole (typically around 10 Hz) was similar to integral control as was seen in the 741. There is a similarity where the Tiger is like a 709 and the Citation like a 741.
A better approach is to have a high frequency feedback path from the voltage gain stage to the inverting input thus providing negative feedback for all the voltage gain stages, or most of them in cases where there's small gain in the output, and reducing the feedback from the slow output stage. The GFA 555 uses 20 pF from B to C at the voltage gain stage and 39 pF nested feedback from the voltage gain stage collector to the negative input.
Changes should not be made without measuring a prototype (and/or simulating) and providing enough margin to tolerate component variations and all load conditions.
Anyway the obvious thing here is the Nyquist Stability Criterion, gain and phase margin which can be measured open loop, all that jazz. The obvious thing about this amp is that there's no dominant pole compensation from Q3's C to B. The Citation has 150 pF there.
There is a form of feedback system called integral control that is unconditionally stable with of course the tradeoff of slow response time. Way back in the early days when the 709 OP amp came out and blew up often because it was so unstable they discovered that a low frequency dominant pole (typically around 10 Hz) was similar to integral control as was seen in the 741. There is a similarity where the Tiger is like a 709 and the Citation like a 741.
A better approach is to have a high frequency feedback path from the voltage gain stage to the inverting input thus providing negative feedback for all the voltage gain stages, or most of them in cases where there's small gain in the output, and reducing the feedback from the slow output stage. The GFA 555 uses 20 pF from B to C at the voltage gain stage and 39 pF nested feedback from the voltage gain stage collector to the negative input.
Changes should not be made without measuring a prototype (and/or simulating) and providing enough margin to tolerate component variations and all load conditions.
Thanks for your reply Dimitri it's always interesting to find out that others confirm what I heard. I see you've got quite a few publications concerning amplifiers and feedback, do you favor any particular approach?
I noticed years ago that Leach also modified his feedback values after he published the first article. Feedback is a difficult subject.
I noticed years ago that Leach also modified his feedback values after he published the first article. Feedback is a difficult subject.
PB2 said:
It's been many years, but I am pretty sure that my first course of action was to brute force "compensate" each and every B-C junction in that damn amplifier. Iirc, it still blew up.
It might be worth taking another look at it... but I wish some nice SPICE wizard would put the thing into the computer and see if the source of the instability could be isolated that way...
It definitely did not "like" to have its input disconnected while there was power going to it. Unstable for sure.
_-_-bear