My Amp Keeps blowing a fuse...

zingo

Two months ago I upgraded many of the caps in my Shuguang Treasure 300B amp. The addition on the Jantzen caps has been fantastic for the sound quality, and all was going well. Then two nights ago after the amp had been on about 10 seconds, the amp shut off which I found to be the fuse had blow. I opened up the amp and found that one of the leads between two caps has been a cold solder joint and come loose, but I don't know if it touched the positive lead to that cap. I soldered it back in place, replaced the fuse, and started up the amp again. Holding my breath, I saw all the lights come on and the tubes start to warm up, but around 10 seconds in again, the fuse blew. That seems like a very weird and specific issue to have as it doesn't seem like a direct short. Maybe an issue with a cap as it would have to charge, thus the elapsed time after start-up? I looked over the amp again and couldn't find any components that looked burned, bulged, or odd. I'm currently working on getting the schematic, but any help would be very much appreciated!

disneyjoe7

Does the new caps match the old caps in value? Also could one of those electrolytic capacitors could be installed backwards.

zingo

All the new caps were exactly the same values as the old caps, and all are non-polar polypropylene. I've marked the loose lead I found the first time the amp cut out, and the cap where it was soldered. (Red is the lead, Yellow is the cap it was attached to)

I'm trying to figure out if anything else happened when the lead broke loose, because the amp worked great for two months.

disneyjoe7

I wonder if that cap is bad.

michaeljhsda2

Do the Jantzens have a metallic outer shell? It looks like the 10 uF cap is touching the small transformer (lower left) in one place and then it's touching another metal part (tube socket?) in another possibly creating a short?

zingo

I'll check when I get home tonight, but I believe the first thing I did was test them with a multi-meter to see if they were conductive. However, showing a short on a multi-meter and being about to conduct and discharge some static electricity or otherwise are two different things, and would be a good thing to look at again to make sure everything is insulated.

zingo

I just heard back from Grant Fidelity, and here was their response along with the schematic for the amp:

Hi Jake,

That sounds very like a rectifier tube has gone south. Rectifier tube is the tube being run the hardest in the amp as it converts AC to DC and will last 1000-2000 hours. It is not expensive but once it goes, usually it will take out the fuse. The amp use 4 amp fuse - I will send you a few spares when sending you the rectifier tube.

When you had the amp on before it blew the fuse, did you see one of the rectifier not lighting up by any chance?

I have attached a schematic for the amp for you. Try putting in new rectifier tube and new fuse in to see if it fixes the problem. If not, you need someone to measure voltage inside the amp to trace down the exact problem on problematic parts, if any.

Do you use a power conditioner with your tube amp? If not, it's highly recommended as it will regulate the power and help prevent spikes, hence save your tubes, especially the rectifier

Best,
Rachel

zingo

I heard that a good way to test if the rectifier tube is bad or if it an electronic components is to take all the tubes out of the amp, replace the fuse and turn on the amp. If the fuse blows then you probably have a shorted filter cap or in extreme circumstances, a blown power transformer. If not, it's probably a tube. Has anyone heard this before?

heiney9

I wouldn't run a tube amp without tubes until you investigate further.

IMO

H9

zingo

Hopefully a new rectifier tube will do it, but tonight I will check a few of the caps for shorts, and make sure that the Silver Z-Caps are insulated if in fact they are conductive.

When I test the caps with my DMM and they do have a short, that will be easy enough to detect with the continuity setting. However, could a cap have a degree of failure, or with a new cap that originally tested to spec, would it be good or bad?

TECHNOKID

heiney9 wrote: »

I wouldn't run a tube amp without tubes until you investigate further.

IMO

H9

+1! Powering your amp without the tubes may simply worsen your problem(s).

zingo wrote: »

Hopefully a new rectifier tube will do it, but tonight I will check a few of the caps for shorts, and make sure that the Silver Z-Caps are insulated if in fact they are conductive.

When I test the caps with my DMM and they do have a short, that will be easy enough to detect with the continuity setting. However, could a cap have a degree of failure, or with a new cap that originally tested to spec, would it be good or bad?

Checking caps for continuity with your DMM will provide you with very limited data on the condition of the cap. It will only tell you if the cap is shorted or open but will not confirm other potential damage to the cap.

IMHO, an ESR meter is the best way to check if capacitors are good/bad. I had a lot of success fixing TV sets sets and other electronics in the past using an ESR meter. Normally, the LCR value of a capcitor will change as it ages however, if the broken lead of your cap has touched something else, it is not impossible that this has affected its LCR value.

There are 2 options, if the cap you have replaced is not too expensive, you could replace it again or... The second option would be to invest in an ESR meter which would serve you for future troubleshooting or modding if you do much of it.

You can read on the purpose of an ESR meter here; http://www.noahtec.com/esr-meter.htm

Heck, you can even built your own; http://www.qsl.net/iz7ath/web/02_brew/15_lab/06_esr/

I am not familiar with this one as I personally bought a DIY kit but do not remember who engineered it all I can recall is that it was from oversee. I'll check if I can easily find it but I think nowadays there are easier to use on the market but it is all a question of many $$s one is willing to pay for.

zingo

I tested the two caps I had in question with my DMM and they were not a short; a good start I guess. I currently do not have an ESR meter, but that is a much better way to test the caps than a LCR meter?

TECHNOKID

First, REPORTED SPAM in post #13!

zingo wrote: »

I tested the two caps I had in question with my DMM and they were not a short; a good start I guess. I currently do not have an ESR meter, but that is a much better way to test the caps than a LCR meter?

I managed to find some info on the ESR meter kit I bought a few years ago (http://www.amazon.com/BK-Precision-Meter-Synthesized-Circuit/dp/B000LDHSW4). I am not sure if they still carry the one I have (actually, just found out mine is no longer made; http://members.ozemail.com.au/~bobpar/esrmeter.htm) but the Blue meter Kit seems to be a new and improved version of it.

An ESR meter is for reading the Equivalent Series Resitance built into the capacitor as described below.

ESR is the sum of in-phase AC resistance. It includes resistance of the dielectric, plate material, electrolytic solution, and terminal leads at a particular frequency. ESR acts like a resistor in series with a capacitor (thus the name Equivalent Series Resistance). This resister can cause circuits to fail that look just fine on paper and is often the failure mode of capacitors.

While an LCR meter has the capability of measuring L lnductance values, C capacitance value and finally R resistance value (impedance) using specific frequencies (http://www.ehow.com/facts_5007276_what-lcr-meter.html). IMO, LCR meters would more likely be used for project building rather than troubleshooting.

Applications
?The automatic detection mode helps technicians identify unknown components. For precision circuit building, an LCR meter lets you sort a batch of parts by value, so the components are well-matched.


Read more: What is a LCR Meter? | eHow.com http://www.ehow.com/facts_5007276_what-lcr-meter.html#ixzz1G0WnCNHY

Now, depending on available budget, one can buy a combo ESR-LCR meter which I would beleive would be in the hundreds of $$$ (IE: http://www.amazon.com/BK-Precision-Meter-Synthesized-Circuit/dp/B000LDHSW4).

zingo

Thanks for all the info. I'm getting both new rectifier tubes for the amp, so I'll know that is not the problem when I plug them in. If the issue still exists, I can look towards hardware, but Ian and Rachel from Grant Fidelity both think the issue is as easy as the rectifier tubes.

I have not heard a better amp than this Shuguang Treasure 300B amp, but I'm haunted by a comment that Ian made in an email, "You should always have spare rectifier tube(s), any decent power spike will take them out, but they sound so nice!" I remember the trouble free days of SS amps with no maintenance and glass to break...

heiney9

If you buy NOS rectifier tubes like Mullard, they may last as long as you. I have yet to see any of my rectifier tubes go, but I use expensive NOS vs. the cheaper and IMO, more poorly built current production rectifers. The NOS Mullard and Brimar sound sooooooooo much better than current Chinese or Russian production it's......AMAZING.

I should clarify my term "poorly built" part of that has to do with materials and purity of materials not being available today like they were in the 40's 50's 60's. So when I state "poorly" built I'm not entirely passing judgment on the Chinese or Russian's just the process is not the same as it was in the "glory" days.

H9

heiney9

I remember the trouble free days of SS amps with no maintenance and glass to break...

I will also add in the 2 years I've been messing with my 4 tube units other than dirty pins I've not had a single issue. I have 3 integrated amps and 1 pre-amp. I haven't even had to reset the bias on the 6V6 push/pull based integrated. It's still right there.

But, I also don't use any current production tubes............perhaps that's the reason or most of the reason. Perhaps not.

H9

disneyjoe7

Is that cap that was fixed is that C5 on the schematic?

Face

Glass is a pain in the ****. :biggrin:

megasat16

zingo wrote: »

Thanks for all the info. I'm getting both new rectifier tubes for the amp, so I'll know that is not the problem when I plug them in. If the issue still exists, I can look towards hardware, but Ian and Rachel from Grant Fidelity both think the issue is as easy as the rectifier tubes.

I have not heard a better amp than this Shuguang Treasure 300B amp, but I'm haunted by a comment that Ian made in an email, "You should always have spare rectifier tube(s), any decent power spike will take them out, but they sound so nice!" I remember the trouble free days of SS amps with no maintenance and glass to break...

Funny thing about tubes is that they can only go open circuited. You can look for the pin layout of rectifier Tube and check the pins for continuity test with an ohmmeter. If you find something opens that shouldn't has been, you got your culprit. I hope it's simple as rectifier tube gone south.

megasat16

heiney9 wrote: »

If you buy NOS rectifier tubes like Mullard, they may last as long as you. I have yet to see any of my rectifier tubes go, but I use expensive NOS vs. the cheaper and IMO, more poorly built current production rectifers. The NOS Mullard and Brimar sound sooooooooo much better than current Chinese or Russian production it's......AMAZING.

I should clarify my term "poorly built" part of that has to do with materials and purity of materials not being available today like they were in the 40's 50's 60's. So when I state "poorly" built I'm not entirely passing judgment on the Chinese or Russian's just the process is not the same as it was in the "glory" days.

H9

A good rectifier tube is a good rectifier tube. If you are paying premium for so called NOS tube compared to the good modern tube for rectifier stage , you got the soul things carried a bit too far into it.

zingo

disneyjoe7 wrote: »

Is that cap that was fixed is that C5 on the schematic?

C1 ground lead was loose and may have contacted C5 positive lead. Both caps look good and test open with my DMM, so I will wait for the new tubes and hope that is it.

heiney9

megasat16 wrote: »

A good rectifier tube is a good rectifier tube. If you are paying premium for so called NOS tube compared to the good modern tube for rectifier stage , you got the soul things carried a bit too far into it.

Respectfully, you have no idea what you are talking about. A tube is not a tube is not a tube.

In the beginning I didn't believe it either..........in some cases the rectifier makes more of a difference than the power tube as far as influencing the sound. Believe what you want but, old tubes last a lot longer than new tubes.

H9

disneyjoe7

Well I would try a new tube or two in the rectifier tube department. If still having issues I would think a bad C1 which could have been damaged by a spike in voltage to it, could cause a high voltage drain to blow fuse. Just a thought, again change tube first.

zingo

disneyjoe7 wrote: »

Well I would try a new tube or two in the rectifier tube department. If still having issues I would think a bad C1 which could have been damaged by a spike in voltage to it, could cause a high voltage drain to blow fuse. Just a thought, again change tube first.

Good thinking about C1. I may have a spare cap of the same value which I could swap in...

I tested both tubes and they have continuity across pins 2 and 8; check that test off my list.

megasat16

heiney9 wrote: »

I should clarify my term "poorly built" part of that has to do with materials and purity of materials not being available today like they were in the 40's 50's 60's. So when I state "poorly" built I'm not entirely passing judgment on the Chinese or Russian's just the process is not the same as it was in the "glory" days.

H9

What kind of material and purity of materials that you refer that were used in the 50s, 60s, 70s Tubes as opposed to today's tube?

Of coz, most Chinese made tubes and Russian Tubes are cost effective and they don't likely have the best materials in there. But it doesn't mean the better tubes can't be made today coz of the lack of materials or technology.

heiney9 wrote: »

Respectfully, you have no idea what you are talking about. A tube is not a tube is not a tube.

Ok! I confess I neither have any love affair with Tubes nor believe Tubes add soul to music; etc. But I know different Tubes does alter frequency response of equipments in certain ways...So, it doesn't mean I was wrong or anything yet.

"A Tube is not a Tube is not a Tube" must mean just a Tube.

In the beginning I didn't believe it either..........in some cases the rectifier makes more of a difference than the power tube as far as influencing the sound. Believe what you want but, old tubes last a lot longer than new tubes.
H9

You can believe in NOS tubes. I was saying if you are paying a premium price for the NOS Rectifier Tube over a good freshly made Rectifier Tube, you are rubbing (touching) it in the wrong place. But ultimately, it's your coins anyway. Rubbing a couple drops of oils on the NOS tube doesn't hurt anyone.

megasat16

zingo wrote: »

Good thinking about C1. I may have a spare cap of the same value which I could swap in...

I tested both tubes and they have continuity across pins 2 and 8; check that test off my list.

So, Rectifier Tubes may likely be fine but chances are electrodes may be given out. If you still blow the fuse after replacing with new rectifier tubes, it's time to disconnect the main power transformer and test for correct voltage. You can unsolder the wire from the rectifier tube socket.

zingo

megasat16 wrote: »

If you still blow the fuse after replacing with new rectifier tubes, it's time to disconnect the main power transformer and test for correct voltage. You can unsolder the wire from the rectifier tube socket.

I hope to God I don't end up there...

TECHNOKID

zingo wrote: »

C1 ground lead was loose and may have contacted C5 positive lead. Both caps look good and test open with my DMM, so I will wait for the new tubes and hope that is it.

As I pointed out checking capacitors with a DMM is near useless. You have proved your capacitor is not shorted however you have not proved that it is not open. When using your DMM, do you do your test both ways (talking neg and pos leads) as if you do thant the value should slowly change as the capacitor charges/discharges (the DMM battery) as this will give you an idea if the capacitor is not open. If it does not charge/discharge when moving your leads around, the capacitor may well be open.

zingo

Because you've been very helpful and knowledgable Technokid, I'll point this one toward you. I was just playing around with my DMM and found that one setting had a capacitor symbol. I hooked it up to a new cap I have laying around and the DMM showed that is measured right on. Since I'm now assuming that the cap setting on the DMM works correctly and that I'm using it correctly, couldn't I desolder the questionable caps from the amp and test their value? Wouldn't them testing with a correct value deem that they are working correctly, or would I still need to test them with an ESR meter?

FTGV

Does the fuse blow right at turn on?If the tubes prove to be good then I would test for a shorted cap,starting with those in the power supply.(C6-C11)I would check bridge rectifers VD1, VD3 as well.As for your meter measuring capacitance it might be limited to values <10uf.

zingo

The fuse blows after about 10 seconds Fred.