I've been out of pocket for health reasons for a while but all good now. I finally got around to swapping out the resistors that were overheating in my stereo version and swapped out the PS caps with new mallorys.
The amp performs like a champ except for one thing that was also an issue with my universal tiger mono versions back in 1975, a faint 60 cycle buzz that can be heard in between tunes if preamp volume is at a relatively loud volume. Is there any grounding changes that could/should be made to the amp that might help in this respect? It's still got the original no-ground non-polarized cord cap but I'm assuming with the inputs and outputs being grounded to chassis that going to a earth grounded cord to chassis may not be advised?
The amp performs like a champ except for one thing that was also an issue with my universal tiger mono versions back in 1975, a faint 60 cycle buzz that can be heard in between tunes if preamp volume is at a relatively loud volume. Is there any grounding changes that could/should be made to the amp that might help in this respect? It's still got the original no-ground non-polarized cord cap but I'm assuming with the inputs and outputs being grounded to chassis that going to a earth grounded cord to chassis may not be advised?
I had bad experiences with SWTP designs - their preamp oscillated heavily and sounded like a waterfall I would have been better getting the Dyncco PAT-5 kit (chassis design was also lots better for the Dynaco kit). I have had much better luck with my own designs, where I verify stability using a gain-phase analyzer. I also take extra pains with grounding, which also may help.
You say with preamp at loud volume, this suggests that the problem is ahead of the
volume control. What preamp are you using, does it have fresh PSU caps?
Also good to hear that your health issues are better now!
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I've used it with two different pre's. A Denon that has no audible ac line noise when feeding a different amp and also a Marantz model 7 replica I built recently. All caps are good. An interesting note is the same line noise was present when running my two mono swtp amps from a Mac C22 back in 75'.
Perhaps we can divide the problem.
1. What noise do you hear when the input to the Tiger is shorted right at the RCA jack?
2. What noise do you hear when the input to the Tiger is shorted at the far end of the input RCA cable?
3. What noise do you hear when the far end of the input RCA jack is shorted and the ground of the jack touches the ground of the preamp?
1. What noise do you hear when the input to the Tiger is shorted right at the RCA jack?
2. What noise do you hear when the input to the Tiger is shorted at the far end of the input RCA cable?
3. What noise do you hear when the far end of the input RCA jack is shorted and the ground of the jack touches the ground of the preamp?
While I would like to take the steps you've outlined, I've been especially fearful of ever powering on a Tiger without inputs and outputs connected to a energized preamp and speakers due to the propensity for them to self destruct at a whim. Are you 99% certain the amp will not go into meltdown without a valid input?
Zero volts with zero source impedance sounds like a valid input to me. Certainly, zero volts, the sound of silence is valid...you might quibble that the short circuit on the input might cause oscillation...If it does, then something still needs to be repaired!!! R1, which is 2.2K Ohms, in series with the input base, would certainly be enough to keep funny stuff from happening. So I think 99% assurance is possible for the design reasonably close to the published version.
Still, be safe...always power down before changing input connections. Make sure they aren't flimsy and about to fall off at the worst possible time. If you're connecting an amp of uncertain condition to speakers, don't use your expensive speakers with the unobtanium tweeters...
Make sense?
Still, be safe...always power down before changing input connections. Make sure they aren't flimsy and about to fall off at the worst possible time. If you're connecting an amp of uncertain condition to speakers, don't use your expensive speakers with the unobtanium tweeters...
Make sense?
Please clarify #3 "far end of rca jack is shorted..." I'm assuming you mean far end of rca cable shorted and ground of cable touches ground of preamp rca jack?
I agree with you on your last post that there should be no issue with shorting the input and if it has a problem with it, there are some odd things going on.
I gifted one of my two stereo tigers to my son a few years ago and had been working fine until recently. I found the mains fuse and rectifier fuse had blown. There are no signs of any overheated components anywhere on the boards or power transistors. I assumed the power supply caps had finally given up and replaced them. I decided to bring up the voltage to the amp slowly with my variac to make sure there weren't other issues at hand. For the test, I installed shorting plugs on the inputs and some cheap 8 ohm test speakers on it's outputs.
When I hit 3 volts (AC mains), I noticed a slight 60 cycle hum from the speakers and brought it up to 10 volts which made the hum much louder so I stopped the test. I wondered if the hum was just the new caps not being up to voltage yet and possibly causing the hum. I decided to stop the test and see if my other (working) stereo tiger might do the same thing under the same conditions. Turns out it did the same thing but after going past 10 volts AC on the mains, the hum abruptly stopped and was able to bring up the voltage to full with no issues. So I decided to resume the test on my sons amp and when I got to 30 volts on the mains, the rectifier output fuse blew. So, i'm going to assume that one or more of the drivers or power transistors are shorted.
Is there a reliable way to test all of the transistors in-circuit with my Fluke 8060A or will I need to remove each one to test?
When I hit 3 volts (AC mains), I noticed a slight 60 cycle hum from the speakers and brought it up to 10 volts which made the hum much louder so I stopped the test. I wondered if the hum was just the new caps not being up to voltage yet and possibly causing the hum. I decided to stop the test and see if my other (working) stereo tiger might do the same thing under the same conditions. Turns out it did the same thing but after going past 10 volts AC on the mains, the hum abruptly stopped and was able to bring up the voltage to full with no issues. So I decided to resume the test on my sons amp and when I got to 30 volts on the mains, the rectifier output fuse blew. So, i'm going to assume that one or more of the drivers or power transistors are shorted.
Is there a reliable way to test all of the transistors in-circuit with my Fluke 8060A or will I need to remove each one to test?
What you want to do is to current limit the power to the circuit, turn the bias down or short
the bias network, and if you have a dual power supply with current limit set it low, say 100
to 200 mA. I didn't have a current limited power supply back when I was working on these
a lot so I'd fuse both rails and then either take dead fuses and solder 100R resistors across
them, or tack them across the sockets. This allows you to probe the circuit checking for
normal Vbe drops etc. to try to determine what's going on.
Often, I'd remove or desolder every transistor and test them out of circuit. If you remove
the small signal transistors then you can try to lift resistors around the metal can drivers so
that you don't have to remove them, worst case I removed those also.
A trick with a more normal EF output stage is to remove the power devices and jump the
feedback to the output of the driver stage in order to debug all of the small signal devices,
then install known good output devices. Not sure if you can figure out a way to do this with
the Tiger amps.
the bias network, and if you have a dual power supply with current limit set it low, say 100
to 200 mA. I didn't have a current limited power supply back when I was working on these
a lot so I'd fuse both rails and then either take dead fuses and solder 100R resistors across
them, or tack them across the sockets. This allows you to probe the circuit checking for
normal Vbe drops etc. to try to determine what's going on.
Often, I'd remove or desolder every transistor and test them out of circuit. If you remove
the small signal transistors then you can try to lift resistors around the metal can drivers so
that you don't have to remove them, worst case I removed those also.
A trick with a more normal EF output stage is to remove the power devices and jump the
feedback to the output of the driver stage in order to debug all of the small signal devices,
then install known good output devices. Not sure if you can figure out a way to do this with
the Tiger amps.
Thanks for the helpful tips from your previous repairs! I think I'm going to remove and test until I find the bad apple/apples. When I find them, I'm not thrilled with the prospects of trying to locate suitable replacements or substitutes after much reading through several forums. It sounds like most who have had success finding ones had to purchase quite a few of each type before finding ones that tested out well.
That particular Tiger implementation will work into a couple hundred ohm load with output transistors removed. Bias current path through the drivers isn’t interrupted, and it’s CFP is only unity gain. In those larger versions, you may lose the output stage gain when doing this, and be limited by the available swing in the front end. Tigersaurus may be a different story altogether, but probably can be jumpered in some way.
Good point.
If you disconnect the base connection to the output transistors then the drivers become
simple emitter followers. Then if you remove the screws mounting the power transistors
they will be isolated for test.
Test the driver section first at idle, then with signal noting that you won't get to the rails
due to the 100R resistors. You could short the 100R resistors across the BE of the outputs.
R12 and R14 load the output to ground.
This might be an interesting test for the amp in the OP here to determine if it still oscillates.
If you disconnect the base connection to the output transistors then the drivers become
simple emitter followers. Then if you remove the screws mounting the power transistors
they will be isolated for test.
Test the driver section first at idle, then with signal noting that you won't get to the rails
due to the 100R resistors. You could short the 100R resistors across the BE of the outputs.
R12 and R14 load the output to ground.
This might be an interesting test for the amp in the OP here to determine if it still oscillates.
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I pulled all of the drivers and output transistors. Only one driver tested bad, a Motorola SS1122 which was open and both output transistors in the left channel which were shorted.
I hadn't noticed before but that channel's pair of output transistors had been replaced by the guy who built the amp. He replaced the MJ4502 and the MJ802s in the left channel with a pair of HEP S7000 and S7001.
So, where to begin looking for a suitable complimentary pair of outputs and a good substitute for the SS1122? I unfortunately do not have the detective skills which will most likely be needed to avoid the counterfeits and other pitfalls.
I hadn't noticed before but that channel's pair of output transistors had been replaced by the guy who built the amp. He replaced the MJ4502 and the MJ802s in the left channel with a pair of HEP S7000 and S7001.
So, where to begin looking for a suitable complimentary pair of outputs and a good substitute for the SS1122? I unfortunately do not have the detective skills which will most likely be needed to avoid the counterfeits and other pitfalls.
I'm pasting a clip from a post by Piercarlo from 2007 in a thread about the SWTPC plastic tiger on substitution for an SS1122 and SS1123:
SS1122 may be replaced by a BD 138 and SS 1123 by a BD 137, which avoid using of the small (imho, nasty) heathsink for old TO 5 case. In the schematic voltages are missed. My advice is to limit to a +/- 25 Volt maximum.
Would these be acceptable substitutes for my Universal Tiger?
Also, any thoughts on best substitution for the MJ4502 MJ802 outputs? I've heard that one should steer clear of the NTEs and Mexico Motorolas.
SS1122 may be replaced by a BD 138 and SS 1123 by a BD 137, which avoid using of the small (imho, nasty) heathsink for old TO 5 case. In the schematic voltages are missed. My advice is to limit to a +/- 25 Volt maximum.
Would these be acceptable substitutes for my Universal Tiger?
Also, any thoughts on best substitution for the MJ4502 MJ802 outputs? I've heard that one should steer clear of the NTEs and Mexico Motorolas.