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Thread: SWR California Blonde goes insane!

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    Senior Member Sowhat's Avatar
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    SWR California Blonde goes insane!

    I got an SWR California Blonde in for repair with the complaint that it don't work… yeah! nice descriptive complaint. I Checked the external 3ASB power fuse and it was missing, cap and all, this could explain something here.

    swr_california_blonde_sch.pdf

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    After replacing the fuse holder and fuse I powered it up on a limiter with no signal and no load and it came up just fine. I took this opportunity to check the rails and check for DC on the output and everything looked good so I decided to hook up the signal generator, dummy load and scope to take a look at the output signal. Unfortunately I never saw any output because when I powered up I got a high current draw (greater than 2 amps) and my limiters lilt up the whole shop. I disconnected the load and it powered up just fine… mmmmm?

    Looks to be working good with no load but when a load is applied it goes insane! I don't know how to even approach this problem aside from shotgunning the whole amp, which is something I refuse to do. Are there any possible plans of attack out there to isolate this kind of misbehavior?

    I forgot to mention that I had installed it back into it's cabinet where it promptly blew it's new 3 amp slo-blo fuse which brought it right back to the bench where the limiter story comes in.

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    Supporting Member The Dude's Avatar
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    Were you trying to run the amp on a light bulb limiter? That will cause problems if so.

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    Senior Member Sowhat's Avatar
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    Quote Originally Posted by The Dude View Post
    Were you trying to run the amp on a light bulb limiter? That will cause problems if so.
    Yeah but I ran it straight on the mains too and the behavior was the same except going straight on the mains cost me a fuse.

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    Old Timer nosaj's Avatar
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    Quote Originally Posted by Sowhat View Post
    I got an SWR California Blonde in for repair with the complaint that it don't work… yeah! nice descriptive complaint. I Checked the external 3ASB power fuse and it was missing, cap and all, this could explain something here.

    swr_california_blonde_sch.pdf

    Click image for larger version. 

Name:	IMG_0382.JPG 
Views:	47 
Size:	1.15 MB 
ID:	48819

    After replacing the fuse holder and fuse I powered it up on a limiter with no signal and no load and it came up just fine. I took this opportunity to check the rails and check for DC on the output and everything looked good so I decided to hook up the signal generator, dummy load and scope to take a look at the output signal. Unfortunately I never saw any output because when I powered up I got a high current draw (greater than 2 amps) and my limiters lilt up the whole shop. I disconnected the load and it powered up just fine… mmmmm?

    Looks to be working good with no load but when a load is applied it goes insane! I don't know how to even approach this problem aside from shotgunning the whole amp, which is something I refuse to do. Are there any possible plans of attack out there to isolate this kind of misbehavior?

    I forgot to mention that I had installed it back into it's cabinet where it promptly blew it's new 3 amp slo-blo fuse which brought it right back to the bench where the limiter story comes in.
    What voltages do you get on the outputs with no load AC and DC. Kinda thinking oscillilation but curious about the voltages.
    nosaj

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    Supporting Member The Dude's Avatar
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    Agree with possible oscillation. Have you scoped the output with no load/no signal?

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    Senior Member Sowhat's Avatar
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    Quote Originally Posted by The Dude View Post
    Agree with possible oscillation. Have you scoped the output with no load/no signal?
    That could be, I didn't scope the output at no load/signal but I did read 0.01 something or another VDC, hard to tell values that low with my ancient meter and heavily damaged probes but I don't really see any DC on the output. As far as AC, didn't even think to look at that... maybe I should do that.

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    Perfect, I have a Super Redhead that just came in with an almost identical issue. I'll be watching this thread and commenting if I find anything helpful!

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    Senior Member Sowhat's Avatar
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    Had to check back in and give an update. I'm bobbing between 5 different tickets at the time so I don't get a large patch of time to mull things over. I decided to ramp up on a variac and bypass the limiter seeing just where I exceed 3 amps. With load and signal attached I ramped up the voltage while monitoring the current draw and voltage. It rose up to about 1-1/2 amps at 120 volts AC!!! what! no blown fuse? I must be seeing things, not only that but I get a nice clean symetrical sine wave out of the outputs, nice and controllable... what's up here the amp seems to work just fine, I brought it up and down a dozen times with no variance, so... I slap it back into the cabinet, attach the crossover and drivers, flip the switch and a loud shorted something or another buzz roars out and then silence... there goes my second and last fuse!

    There's got to be something wrong with the crossover or drivers but checking through all the components, everything looks good. I'm going to dynamically test the drivers tomorrow but they measure out just about what you would expect with a meter preliminarily, they look good. The crossover, which don't have much to it measures out to be doing it's job correctly... once again, mmmm..?

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    Supporting Member The Dude's Avatar
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    The odd thing here is that you said it also blew fuses on your dummy load (post #1)? At this point, I might hook up a tube amp to the crossover/speakers in the amp and see if it works. I say tube amp because a tube amp will be able to withstand a short for a small period of time. You might blow up another solid state amp if there is indeed a speaker/crossover problem. Also, if you check the wires going from amp to crossover (speaker out of amp), what do you measure. Does it show anything shorted?

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    Seems like it is "good on the bench" and "fails in the cabinet"? I think these can have the known SWR problem of cracked transistor legs, any chance of something getting pulled loose when you reinstall in the cab?

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    Old Timer nosaj's Avatar
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    Quote Originally Posted by Sowhat View Post
    Had to check back in and give an update. I'm bobbing between 5 different tickets at the time so I don't get a large patch of time to mull things over. I decided to ramp up on a variac and bypass the limiter seeing just where I exceed 3 amps. With load and signal attached I ramped up the voltage while monitoring the current draw and voltage. It rose up to about 1-1/2 amps at 120 volts AC!!! what! no blown fuse? I must be seeing things, not only that but I get a nice clean symetrical sine wave out of the outputs, nice and controllable... what's up here the amp seems to work just fine, I brought it up and down a dozen times with no variance, so... I slap it back into the cabinet, attach the crossover and drivers, flip the switch and a loud shorted something or another buzz roars out and then silence... there goes my second and last fuse!

    There's got to be something wrong with the crossover or drivers but checking through all the components, everything looks good. I'm going to dynamically test the drivers tomorrow but they measure out just about what you would expect with a meter preliminarily, they look good. The crossover, which don't have much to it measures out to be doing it's job correctly... once again, mmmm..?
    I will say this ...it could always be how it was put back together. I have a gk 250 lunch box and if you don't put the short screws in the right place you short the one of the outputs. The crossover is just a passive device right?

    Just for clarification, your nice clean sine wave was going to a speaker or a dummy load?

    nosaj

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    Senior Member Sowhat's Avatar
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    Quote Originally Posted by nosaj View Post
    I will say this ...it could always be how it was put back together. I have a gk 250 lunch box and if you don't put the short screws in the right place you short the one of the outputs. The crossover is just a passive device right?

    Just for clarification, your nice clean sine wave was going to a speaker or a dummy load?

    nosaj
    I never put in the mounting screws before the second fuse blow, just slid it into it's cabinet hole and plugged things in. The nice clean sine was on a dummy load (4 ohms). I don't have a 2 ohm load currently, just 16, 8 and 4. Now that I'm home and having dinner, I keep thinking about what could possibly be amiss... some hidden short that only manifests itself when hooked up to the SWR speaker wiring? I have not tried the amp through my shop test speaker cabinet (which is 8 ohms) but I bet it will work OK, that is once I stop at my local electronics supplier and pickup a few more 3 amp fuses.

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    Old Timer nosaj's Avatar
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    Quote Originally Posted by Sowhat View Post
    I never put in the mounting screws before the second fuse blow, just slid it into it's cabinet hole and plugged things in. The nice clean sine was on a dummy load (4 ohms). I don't have a 2 ohm load currently, just 16, 8 and 4. Now that I'm home and having dinner, I keep thinking about what could possibly be amiss... some hidden short that only manifests itself when hooked up to the SWR speaker wiring? I have not tried the amp through my shop test speaker cabinet (which is 8 ohms) but I bet it will work OK, that is once I stop at my local electronics supplier and pickup a few more 3 amp fuses.
    The dude or G1 has mentioned this before...the resettable circuit breakers you see on Traynors and wiring one in can save a lot of fuses till you work out the issue.

    nosaj

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    Senior Member Sowhat's Avatar
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    Quote Originally Posted by nosaj View Post
    The dude or G1 has mentioned this before...the resettable circuit breakers you see on Traynors and wiring one in can save a lot of fuses till you work out the issue.

    nosaj
    Those are real fuse savers but I don't have a 3 amp one around. I have one in my tube tester, my scope, my signal generator and even one grafted onto the side of my multimeter for current readings in which I always seem to pop the 10 amp internal fuse... what a chinsey idea to put a fuse in there, it should have been a circuit breaker.

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    Senior Member Sowhat's Avatar
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    Quote Originally Posted by The Dude View Post
    The odd thing here is that you said it also blew fuses on your dummy load (post #1)? At this point, I might hook up a tube amp to the crossover/speakers in the amp and see if it works. I say tube amp because a tube amp will be able to withstand a short for a small period of time. You might blow up another solid state amp if there is indeed a speaker/crossover problem. Also, if you check the wires going from amp to crossover (speaker out of amp), what do you measure. Does it show anything shorted?
    Maybe that's the impression I gave but it's not really what I said. The amp was on a limiter and showing in excess of 2 amps of draw with a load attached which is the limit of my limiter and it was full on. With the limiter fully engaged and the voltage showing somewhere around 40 volts full on I figured that was equivalent to well in excess of 3 amps bypassed to the mains. That's OK, I'm still scratching my head on that one in light of day 2's findings. Tomorrow, I'll get to the bottom of the speaker network by hook or crook and get this on put to bed.

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    Senior Member Sowhat's Avatar
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    Quote Originally Posted by glebert View Post
    Seems like it is "good on the bench" and "fails in the cabinet"? I think these can have the known SWR problem of cracked transistor legs, any chance of something getting pulled loose when you reinstall in the cab?
    All good checks and this gives me some additional things to check which I have not done yet. I'm sure it will be the last thing I check that turns out to be the problem... it always is.

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    Supporting Member The Dude's Avatar
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    I think it was George Carlin who talked about losing things. "You always find it in the last place you look".

    Of course you do, because you don't keep looking after you've found something.

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    don't forget the joker g1's Avatar
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    Not sure if this is of any help, you may know this already, or it may not be relevant in this case. But it could have led to a 'false positive' over-current reading initially.
    Some amps won't start up right on a limiter with a load connected. The output will stick to one of the DC rails and the bulb will light up and stay lit. Then you try it with no load and it doesn't light up.
    In those cases, start it up on the limiter without load, then connect the load while still powered on (with clips, not with 1/4 inch connectors).
    In your case, it still blew the fuse when put in the cab without limiter, so obviously there is a problem. Just didn't want you chasing your tail on the bench with a test equipment induced fault.

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    Supporting Member Randall's Avatar
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    I have a 2 amp push button breaker wired to clip leads. I use it all the time.

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    It's weird, because it WAS working fine.....

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    A word of caution on circuit breakers.

    They are only 'good' for so many 'hits'.

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    Senior Member Sowhat's Avatar
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    I've just about had it with this amp, here's what's up now. The picture attached shows how I have the amp hooked up... just like it is as it would be in the cabinet, speaker, horn, crossover and all. The only thing different is that my fuse is currently that red jumper wire. I ramp this up on the variac closely monitoring the current draw and damned if the thing don't fire right up, no shorting buzz, no funny business, works fine, low current draw.

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    Somehow between it being on the bench and it being in the cabinet something bad happens, but what?

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    Old Timer nosaj's Avatar
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    Quote Originally Posted by Sowhat View Post
    I've just about had it with this amp, here's what's up now. The picture attached shows how I have the amp hooked up... just like it is as it would be in the cabinet, speaker, horn, crossover and all. The only thing different is that my fuse is currently that red jumper wire. I ramp this up on the variac closely monitoring the current draw and damned if the thing don't fire right up, no shorting buzz, no funny business, works fine, low current draw.

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    Somehow between it being on the bench and it being in the cabinet something bad happens, but what?
    Check your screw lengths out of the chassis and see if there's a possibility of one them touching something it shouldn't. Look inside the cabinet to see if any shielding is loose also.
    nosaj
    nosaj

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    Does it power up fine on the bench directly into mains (no variac) and load connected?

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    Senior Member Sowhat's Avatar
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    Quote Originally Posted by nosaj View Post
    Check your screw lengths out of the chassis and see if there's a possibility of one them touching something it shouldn't. Look inside the cabinet to see if any shielding is loose also.
    nosaj
    nosaj
    I have not had a mounting screw re-installed since the beginning of this saga, I never get that far. I did notice that the HF driver + terminal was bent in such a way as to possibly touch the magnet but that should not make a difference, the magnet has no ground potential... a least I don't think it does. Didn't take a look at the cabinet shielding, if there is any, maybe that's a problem?

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    Old Timer nosaj's Avatar
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    Quote Originally Posted by Sowhat View Post
    I have not had a mounting screw re-installed since the beginning of this saga, I never get that far. I did notice that the HF driver + terminal was bent in such a way as to possibly touch the magnet but that should not make a difference, the magnet has no ground potential... a least I don't think it does. Didn't take a look at the cabinet shielding, if there is any, maybe that's a problem?
    It's usually some type of foil, which could possibly short something.
    nosaj

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    Senior Member Sowhat's Avatar
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    Quote Originally Posted by glebert View Post
    Does it power up fine on the bench directly into mains (no variac) and load connected?
    Ahhh... I don't know. I always go through the variac when on the bench, firstly to breaker at 5 amps and have the ability to monitor voltage and current, I don't want to work on stuff drawing more than that and secondly just because that's my closest available socket in relation to the amp jig.

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    Old Timer J M Fahey's Avatar
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    ALL SWR amps have the same problem: you turn them ON while plugged into a current limiter AND load connected and they stick to one rail. Always.
    G1 mentioned this earlier and I confirm it´s a "design feature" so don´t waste time chasing it.

    Just to retrace steps, basically to discard non problems :

    1) plug into limiter, no signal, all controls to 0 , NO LOAD : does it turn on fine?

    2) check all voltages: rails (which of course will be somewhat low), DC at output (less than , say, 150mV), bias current (drop across emitter resistors)

    3) connect load. Everything fine? Remeasure basic voltages.

    4) ´plug straight into mains, no load.

    5) same but now turn on with load.
    For peace of mind repeat basic voltage measurements.

    6) play it.
    Look at scope screen to catch any oscillation , fuzzies, etc. which might cause instability.

    Repeat connected to actual combo speakers, I think you´ll find it uses a Brazilian "Ferroelectric" LeSon Tweeter, a weird hybrid of piezo and magnetic.
    If it shorts, impedance is wild reactive and power amp may become crazy unstable, or plain oscillating.

    If dead, I guess Parts Express carries them or worst case replace it with a standard Piezo that fits (or enlarge hole) with a 47 ohm 2W resistor in series.

    Easy load for any amp but you´ll lose all sparkle (the main reason they used that weird Tweeter there)

    https://www.ebay.com/itm/SS-Audio-Tw...-/152011150540

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    Senior Member Sowhat's Avatar
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    Quote Originally Posted by J M Fahey View Post
    ALL SWR amps have the same problem: you turn them ON while plugged into a current limiter AND load connected and they stick to one rail. Always.
    G1 mentioned this earlier and I confirm it´s a "design feature" so don´t waste time chasing it.

    Just to retrace steps, basically to discard non problems :
    Yeah, I dumped the limiter a while ago because that was obviously causing mischief. On the dummy load it works good and once I gutted the speaker network out of the cabinet and put it up on the bench with the amp, it works good as a whole system as well. The exact same system installed in it's cabinet just 10 minutes before made a loud 120 cycle-ish buzz through the speakers and then popped the fuse. Sounds like a short to me. The only thing I have not done on the bench is slamming on the mains... up to this point I have been ramping up slowly and monitoring for current spikes because I'm not using a limiter, I don't need any fireworks. In the cabinet I used the amps power switch plugged straight into the mains and that's the location that blows fuses, not the bench. I certainly need to test this tomorrow morning.

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    Senior Member Sowhat's Avatar
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    We have a successful conclusion to this saga...

    I simply slipped the head into the cabinet and powered up with my hand hovering over the kill switch. All the way in I got a runaway short, max amps then, I slipped the chassis half way out and it came up just fine... slipped it back in and fireworks, slipped out nirvana. Well, I guess you know where this is going, what happens when I flex the chassis? BINGO! I can control the short. Long story short both the collector and emitter leads of Q4 (which is attached to the chassis heatsink) were cracked. Whoever it was who posted about cracked leads on that heatsink, give yourself a pat on the back from me.

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    I didn't even replace that transistor, I fired up the microscope and spot welded in some new leads... I love how I can do microscopic work now, makes me look like a genius, but we all know the truth about that.

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    Old Timer Leo_Gnardo's Avatar
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    Quote Originally Posted by Sowhat View Post
    makes me look like a genius, but we all know the truth about that.
    Yes we do. You're the one who knows where to put the chalk mark. Collect your genius award!


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    Old Timer J M Fahey's Avatar
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    Quote Originally Posted by Sowhat View Post
    We have a successful conclusion to this saga...

    I simply slipped the head into the cabinet and powered up with my hand hovering over the kill switch. All the way in I got a runaway short, max amps then, I slipped the chassis half way out and it came up just fine... slipped it back in and fireworks, slipped out nirvana. Well, I guess you know where this is going, what happens when I flex the chassis? BINGO! I can control the short. Long story short both the collector and emitter leads of Q4 (which is attached to the chassis heatsink) were cracked. Whoever it was who posted about cracked leads on that heatsink, give yourself a pat on the back from me.

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    I didn't even replace that transistor, I fired up the microscope and spot welded in some new leads... I love how I can do microscopic work now, makes me look like a genius, but we all know the truth about that.
    Modern version of:

    0 Not allowed! Not allowed!
    Juan Manuel Fahey

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