[invstbiker]

Hello,

Have a pair of Canary M500 monoblocks with very low hours. Amps came with EH 300B's. Has worked fine for about two weeks since I've had them. Last week put in a new set of Emission Labs 300B's, set bias, then enjoyed. Today I was messin around with my PS audio power center. I turned the amp off then mistakingly turned it right back on about two seconds later. I got a flash on one of the 300B's then the amp went dead. Checked the fuse, and the fuse was blown. Replaced the fuse and turned the amp back on and after 10 seconds blew the fuse again. Any ideas:

Tube?

-or-

Amp?

Thank you

[Quiet Earth]

First, mark the tube that flashed so you dont get it mixed up with all of the other 300B tubes. Use a small piece of masking tape and attach it to the base of the tube that flashed.

Next, install another new fuse, making sure that it is not only the correct rating for volts/amps but also for either slow or fast blow.

Now,,, take the EML Tubes out and put the Electro Harmonic tubes back in the amplifier.

Turn the amp on again.

[avahifi]

Its not unusual to blow a main system fuse on a tube or hybrid amp if you turn it back on immediately after turning it off.  The hot amp can pull a large current input surge in this condition that will blow the fuse.

Check that main fuse and if it is a slow blow fuse make sure you replace it with an appropriate slow blow fuse.  A quick blow fuse probably will blow at turn on in a power supply application where a slow blow fuse was specified.

Good luck,

Frank Van Alstine

[invstbiker]

Thank you gentlemen for your thoughts. OK, so today I did the following with results of:

1. Replaced the fuse. turned amp on, fuse blew at about 15 seconds.

2. Changed the 300B's out to the stock tubes EH, replaced the fuse, turned on amp and fuse blew at 15 seconds.

So it would appear that something internal has gone out and I'll have to take it to the local amp guru 

Hopefully it's something simple.

[avahifi]

If you are sure you were using slow blo fuses, then next tell us if your amplifier has a rectifier tube, 5AR4 or similar.

If so, the next most likely culprit is the rectifier tube.  Replace it and the fuse once more (make darn sure it is the appropriate slow blow fuse) and hope this fixes the issue.

If not, then you probably do need the attention of your local tube guru.

Frank Van Alstine

[invstbiker]

The amp has:

4 300B's
2 6SN7's
2 5u4GB's

[BobMajor]

The 5u4GB are rectifier tubes. I had fuses blowing on an amp and finally replaced the rectifier tubes and haven't had a problem since.
If you don't have any spares here is one link for buying them:
http://www.thetubestore.com/5U4-Tube-Types

[BobMajor]

Here is a better price:
http://www.amazon.com/Electro-Harmonix-5U4GB-EH-Vacuum-Tube/dp/B000LL2YVQ

[invstbiker]

Thanks Bob, I will check those out...

[Quiet Earth]

You could also take the 5U4Gs from the good amp and put them in the bad amp (swap rectifiers) and perform the test one more time.

[invstbiker]

You could also take the 5U4Gs from the good amp and put them in the bad amp (swap rectifiers) and perform the test one more time.

YES, YES, YES. This is exactly what I did and "knock wood" problem solved. Thank you all for helping me go through these steps to resolve. I am going to replace all 4 of the 5U4GB's. This is out of the manual. Upon further investigation, the rectifier tubes that I am replacing are Sovtek 5AR4's which came with the amps. I am the second owner.

[Ericus Rex]

Probably the cheapest Sovteks you'll find:


http://www.dougstubes.com/rectifiers/5ar4-gz34.html




This place is having a 'going out of business sale' and has some really good prices on your tubes.  I'd probably go with the Mesa as they're sure to have been thoroughly tested.


http://tubebuilders.com/index.php?main_page=index&cPath=38_39

[Quiet Earth]

I think invstbiker is telling us that the manual calls for two 5U4GB rectifiers per amplifier, and that is what he is going to put in there. That's what I would do. Especially now considering what we know about blowing fuses with 5AR4s.

See the bottom of this page :  http://canaryaudio.com/M500.html