[kmcdonou4eq5]

My music stopped playing the other day and finally eliminated the upstream components to determine it is the Fet Valve.  I am wondering if it is a fuse.  Hard to imagine tubes went out for both channels.  I don't have another fuse to test it, but when I removed the main fuse it was opaque in color, sort of frosty white for the glass part of the fuse.  In contrast the quick blow fuses have clear glass.  Now, it might be just a different type of fuse and the frosty color doesn't have anything to do with it.  In short, is there a way  to determine if the main fuse is blown without having a replacement fuse at hand?

[thunderbrick]

Multimeter.

[kmcdonou4eq5]

What should the mulitmeter read, and what should it be set on to test?

[thunderbrick]

Remove each fuse, set the multimeter on ohms, and test it for continuity.  If you get a zero reading, it's toast.  If you get a high reading, similar to touching the multimeter leads together,  it's good.

[SJ David]

My music stopped playing the other day and finally eliminated the upstream components to determine it is the Fet Valve.  I am wondering if it is a fuse.  Hard to imagine tubes went out for both channels.  I don't have another fuse to test it, but when I removed the main fuse it was opaque in color, sort of frosty white for the glass part of the fuse.  In contrast the quick blow fuses have clear glass.  Now, it might be just a different type of fuse and the frosty color doesn't have anything to do with it.  In short, is there a way  to determine if the main fuse is blown without having a replacement fuse at hand?

I use the continuity method mentioned above. These mains fuses are often 5 amp slow blow and can be found at a local radio shack. If the fuse is blown, the other thing to consider is what may have caused the surge in power through the mains?

And the standard qualifier.... make sure the amp is not plugged in when working on it and always allow some time after the power is off before getting hands and tools in the wiring.

[mresseguie]

Just this week I called Frank asking about a blown fuse for my 240/3 AVA amp. He instructed me to buy "3ag" 3 amp QUICK blow fuses. He suggested I try Radio Shack. That is what I did. I bought a package of four fuses.

Furthermore, Frank said to use the quick blow. If someone used a slow blow (and there was a short/problem), one's speakers might (would??) be damaged.

In my case, I know what caused the fuse to blow out. I stupidly crossed my speaker wires for a fraction of a second while the amp was on. [I know.  ] Replacing the fuse fixed my problem. With luck, my stupidity has been fixed as well.

Best,

Michael

[kmcdonou4eq5]

Remove each fuse, set the multimeter on ohms, and test it for continuity.  If you get a zero reading, it's toast.  If you get a high reading, similar to touching the multimeter leads together,  it's good.

When I touch my leads together I get a zero reading. When they don't touch the reading is 1.  When I touched the leads to the left channel quick blow fuse (clear glass), I get a reading of 1.  When I touch the leads to the main slow blow fuse (with the frosty colored glass) I get a reading of zero.

It sounds like from what you are saying I have a blown fuse.  The only thing I wonder about is getting a zero reading when touching the leads together, which is contrary to what you said I should get.

Someone brought up the issue of finding out why the fuse blew in the first place.  I wasn't home, but my kids and their friends were quickly changing the volume from loud to soft via my Sonos, which is connected to an AVA dac and preamp and Fet Valve 600r.  Would a quick volume fluctuation cause a fuse to blow?

[thunderbrick]

Sorry, I had it backwards.       Either way, separating the VM leads is the same as a blown fuse.  No continuity, ergo, toast.   

Touching the leads to each other will give you the same reading as a good fuse, assuming the VM is working properly.

[kmcdonou4eq5]

Sorry, I had it backwards.       Either way, separating the VM leads is the same as a blown fuse.  No continuity, ergo, toast.   

Touching the leads to each other will give you the same reading as a good fuse, assuming the VM is working properly.

So a reading of 1, when the leads are separated indicates no continuity.  Correct? And, if I touch the leads together I get a reading of 0, which means continuity.  Correct?

So, a good fuse should have no continuity or continuity?  If no continuity (a reading of 1), then my left and right channel quick blow fuses are fine and my main slow blow fuse is blown (reading of 0).  Obviously if this is backwards then my left and right channel fuses are blown and my main fuse is fine.  So what is the truth here?

[Lefty052347]

The 10amp slow blow fuse is ceramic.  You need to test it with a multi meter set to ohms.  The meter I use will read 0.L for a blown fuse or 000.0 for a good fuse(000.1 would be okay).

Same for speaker fuses and the B+ fuses (quick blow).  You can also check the quick blow fuses visually.

Based on comments,  the quick volume changes would more likely cause a speaker fuse to blow; especially if the device used passed any transients to the 600R.  Also turning the amp on and off in quick succession can cause the 10 amp slow blow fuse to blow.  It happened to us at our demonstration with the Minnesota Audio Society.  If you have additional questions call us on Monday.

Regards,
Dean

[avahifi]

To clarify your fuse issue:

First, disconnect the amplifier from the AC power line!

Assuming a current production Fet Valve 600R amplifier, there are three back panel fuses.  The one closest to the IEC power jack is the 10 amp main AC line fuse.  It is a 250V rated ceramic slow blow fuse.  If this fuse fails the amp will be completely dead, no sound, no pilot lamp.

Remove the fuse and test it with an ohmmeter.  If the meter reads very low (near zero) this fuse is good.  If the meter reads very high or open, the fuse has failed.  It is a 3AG series 10 ampere 250V ceramic body slow blow fuse.  If it failed, replace it once.  If a new fuse holds and the amp plays normally, there is no other issue.  Once in a long time this type of fuse can blow from old age or from a power line transient overload.
If a second fuse promptly blows, call us.  651-330-9871

The other two back panel fuses are the left and right channel speaker fuses.  They should be no larger then a 5 ampere quick blow type.  Large system transients such as a dropped stylus, interconnect coming loose, or just trying to play way way too loud can blow these.  They will pass 200W continuously and are big enough for most rational speakers.  For very low impedance and very insensitive speakers, these fuses can be increased to 6 ampere quick blow types.  Test them the same way as above.

On newest Fet Valve 600R and 400R amplifiers there are four more internal fuses in two dual fuse blocks located on the floor of the amplifier to the left of the smallest vertical power supply board.  The two fuses in the left dual fuse block are the main power supply fuses for the output transistors and are 3AG 8 ampere quick blow types for the 600R and 3AG 6 ampere quick blow fuses for the 400R.  If one of these fails, the channel it protects will not play.  As above check the fuse with an ohmmeter and replace once if it has failed.  The right side dual fuse block contains two 3AG 0.25 ampere slow blow fuses that protect the high voltage but low current regulated power supplies for the vacuum tubes and small signal misfit.

In earlier amplifier production with an internal vertical power supply board with lots of heat fins, there are only the two main power supply fuses to the left of this vertical power supply board.

In the oldest generation amplifiers, the main AC power supply fuse is inside the chassis, in a fuse block near the right side (power transformer side) of the chassis

Note that production changes in the amplifier over the years has been to improve build ability and serviceability, there are no significant musical differences.

Again, call me for more help.

Frank Van Alstine

[SJ David]

Just this week I called Frank asking about a blown fuse for my 240/3 AVA amp. He instructed me to buy "3ag" 3 amp QUICK blow fuses. He suggested

Michael

Deleted due to Frank's reply posted while I was writing my original post.