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    Blowing my Fuses!

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    Tube Nube

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    Blowing my Fuses!

    Post by Tube Nube on Tue Aug 04, 2015 11:01 pm

    Greetings all.

    I turned on my ST 70 on the weekend, left it to warm up, came back to find it dead. Fuse was blown.

    Bought new fuses, 3A slo blow fuses, turned on the amp, it started to light up . . . so after 5 or 6 seconds, left it to warm up . . .

    Came back, and the fuse is blown.

    I can tell you this amp hasn't been bumped or jostled or abused in any way.

    Any thoughts? Should I change the rectifier as a precaution?

    Thanks in advance.

    Kentley

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    Location : Worcester, MA

    Re: Blowing my Fuses!

    Post by Kentley on Tue Aug 04, 2015 11:54 pm

    What's your rectifier? Sounds like a situation I had and it was in fact rectifier failure.

    peterh

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    Re: Blowing my Fuses!

    Post by peterh on Wed Aug 05, 2015 1:07 am

    Tube Nube wrote:Greetings all.

    I turned on my ST 70 on the weekend, left it to warm up, came back to find it dead. Fuse was blown.

    Bought new fuses, 3A slo blow fuses, turned on the amp, it started to light up . . . so after 5 or 6 seconds, left it to warm up . . .

    Came back, and the fuse is blown.

    I can tell you this amp hasn't been bumped or jostled or abused in any way.

    Any thoughts? Should I change the rectifier as a precaution?

    Thanks in advance.
    You should have it opened and with a DVM ready follow it's power on sequence.
    It might be a broken electrolytic cap, it might be a flashing EL34. Rectifier is the least probable.

    Tube Nube

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    Age : 53
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    Re: Blowing my Fuses!

    Post by Tube Nube on Wed Aug 05, 2015 1:36 am

    Thanks for the feedback guys.

    Ok, that's my project for after work tomorrow. Open it up and look for troubles.

    Tube Nube

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    Join date : 2008-12-06
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    Re: Blowing my Fuses!

    Post by Tube Nube on Wed Aug 05, 2015 1:38 am

    Kent', it's a Ruby 5AR4 rectifier tube.

    sKiZo

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    Re: Blowing my Fuses!

    Post by sKiZo on Wed Aug 05, 2015 9:20 am

    Seems to me there's a sticky here somewhere that gives step by step trouble shooting instructions for power up when you've got a problem ...

    First step is to remove all power tubes and see if that stops the fuses blowing, then re-install one bank at a time to see if you can localize whatever's causing it.

    Check the speaker wires for shorts. A single strand that got loose and crosses the terminals could shut it down.

    Also not a bad idea to retension all the sockets. A loose pin could also give you grief. That should be done every now and then anyway, even if you don't swap tubes. Clean the sockets and tube bases while you're at it.

    Bob Latino
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    Re: Blowing my Fuses!

    Post by Bob Latino on Wed Aug 05, 2015 9:40 am

    Tube Nube wrote:Greetings all.

    I turned on my ST 70 on the weekend, left it to warm up, came back to find it dead. Fuse was blown.

    Bought new fuses, 3A slo blow fuses, turned on the amp, it started to light up . . . so after 5 or 6 seconds, left it to warm up . . .

    Came back, and the fuse is blown.

    I can tell you this amp hasn't been bumped or jostled or abused in any way.

    Any thoughts? Should I change the rectifier as a precaution?

    Thanks in advance.

    The most common cause for a situation like this is a bad rectifier tube. Just because the rectifier lights up does not mean that it is good. Try a new rectifier tube and then rebias the amp. If that does not fix the issue, then there are other tings to try ..

    The tube amp troubleshooting guide is here > Tube amp troubleshooting guide ...

    Bob

    MontanaWay

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    Re: Blowing my Fuses!

    Post by MontanaWay on Wed Aug 05, 2015 9:48 am

    if an amp has been working fine for a long time and then suddenly starts to blow fuses, its a good chance that a component has gone south.
    But, as stated above, bad, loose or dirty contacts in tube sockets can get worse over time, until it gets to a point where it will cause issues.
    Remember, we are talking about fairly high voltages and in some cases fairly high currents, so any contact issues will eventually cause problems!

    Tube Nube

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    Re: Blowing my Fuses!

    Post by Tube Nube on Wed Aug 05, 2015 12:10 pm

    Thanks for these suggestions, guys.

    I'll swap the rectifier, as I have 2 more -- that's the easiest thing first. If the fuse survives it, I think I'll go ahead and clean the tube pins and sockets for good measure. If the fuse blows, then it looks like I'm into the trouble shooting procedure.

    Thanks to Bob for putting this together!

    deepee99

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    Re: Blowing my Fuses!

    Post by deepee99 on Wed Aug 05, 2015 1:32 pm

    Tube Nube wrote:Thanks for these suggestions, guys.

    I'll swap the rectifier, as I have 2 more -- that's the easiest thing first. If the fuse survives it, I think I'll go ahead and clean the tube pins and sockets for good measure. If the fuse blows, then it looks like I'm into the trouble shooting procedure.

    Thanks to Bob for putting this together!

    While you're swapping rectifiers, splash a little De-Oxit into the socket holes.

    Tube Nube

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    Re: Blowing my Fuses!

    Post by Tube Nube on Wed Aug 05, 2015 4:22 pm

    I dont ever remember hearing about de oxit back in the 80's, but seems to me that's a great addition to le repertoire electronique. I'll grab some on my way home!

    Tube Nube

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    Re: Blowing my Fuses!

    Post by Tube Nube on Wed Aug 05, 2015 8:39 pm

    Update: rectifier swapped out for new one, cleaned all rectifier and power tube pin slots with de oxit, and power came on with no issues. With power tubes in original positions, biasing was almost spot on.

    Patricia Barber is happily singing once again. Which piece, you ask? Why, "Light my Fire" of course. C'mon, baby!

    Thanks, team, for setting me a glowing once again!

    Kentley

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    Re: Blowing my Fuses!

    Post by Kentley on Wed Aug 05, 2015 9:17 pm

    Yay Alberta!!!

    deepee99

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    Re: Blowing my Fuses!

    Post by deepee99 on Wed Aug 05, 2015 10:44 pm

    The chorus of joy singeth your way.
    Get that tail-dragger down here! The Tylers get better by the hour.

    Tube Nube

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    Re: Blowing my Fuses!

    Post by Tube Nube on Wed Aug 05, 2015 11:48 pm

    Dave, I truly wish to make that trip down to visit you and your Tylers!

    Tube Nube

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    Re: Blowing my Fuses!

    Post by Tube Nube on Fri Aug 14, 2015 11:41 am

    Ahhhhhhh!!!!!!

    Well that was short lived!

    After enjoying my amplifier, believing I had the above problem licked, I accidentally left it powered on all night -- nothing I haven't done before a few hundred times.

    Arose this morning to see no signs of life! The problem has returned!

    Looks like it's time to follow the trouble shooting guide.

    It worked flawlessly last night, as far as my ears could detect.

    deepee99

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    Re: Blowing my Fuses!

    Post by deepee99 on Fri Aug 14, 2015 11:44 am

    Tube Nube wrote:Ahhhhhhh!!!!!!

    Well that was short lived!

    After enjoying my amplifier, believing I had the above problem licked, I accidentally left it powered on all night -- nothing I haven't done before a few hundred times.

    Arose this morning to see no signs of life! The problem has returned!

    Looks like it's time to follow the trouble shooting guide.

    It worked flawlessly last night, as far as my ears could detect.

    Noob, are you sure you didn't just have a power blip while you were snoozing? We've had tons of them down here as the thunderstorms rumble through. A quick power-off power-on cycle will send fuses and rectifiers a-cropper.

    Tube Nube

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    Re: Blowing my Fuses!

    Post by Tube Nube on Fri Aug 14, 2015 11:49 am

    That could be right! I still have a few more fuses. I can test that theory.

    I was reading on the web about how to check capacitors, and it looks like you have to take them out of the circuit -- that's going to be a bit of a head ache!

    deepee99

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    Re: Blowing my Fuses!

    Post by deepee99 on Fri Aug 14, 2015 11:51 am

    Tube Nube wrote:That could be right! I still have a few more fuses. I can test that theory.

    I was reading on the web about how to check capacitors, and it looks like you have to take them out of the circuit -- that's going to be a bit of a head ache!

    I don't think you have to take them out of the circuit, just test them whilst powered off. Somebody correct me if I'm wrong here.

    Bob Latino
    Admin

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    Re: Blowing my Fuses!

    Post by Bob Latino on Fri Aug 14, 2015 12:00 pm

    You can test the caps on the VTA amps in circuit. On the quad cap you will get readings higher than normal because the caps are wired together but if the capacitance reading does not rise and then stabilize at some point, then you could have a bad quad cap section.

    Two things ...
    1. Always do capacitor testing with the amp OFF.
    2. Don't leave a tube amp ON unless you know you will be going to go back to listening within an hour or so. Tubes wear even if there is no signal going though the amp .. Sort of like > You still burn gas with your car at idle even though you are not moving ..

    Bob

    Tube Nube

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    Re: Blowing my Fuses!

    Post by Tube Nube on Fri Aug 14, 2015 12:06 pm

    Thanks for these tips Bob. I'll be diligent about leaving it on, in future.

    With the amp having been off all day and I don't know how much of last night . . . I won't be in for a SHOCK from any of those caps when I get home this afternoon, if I go to test them will I?

    deepee99

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    Re: Blowing my Fuses!

    Post by deepee99 on Fri Aug 14, 2015 12:27 pm

    Tube Nube wrote:Thanks for these tips Bob. I'll be diligent about leaving it on, in future.

    With the amp having been off all day and I don't know how much of last night . . .  I won't be in for a SHOCK from any of those caps when I get home this afternoon, if I go to test them will I?

    Nah. Just unplug it and don't lick your fingers ...

    Tube Nube

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    Re: Blowing my Fuses!

    Post by Tube Nube on Fri Aug 14, 2015 12:53 pm

    Thanks Dave. I'll report back on what, if anything, I discover and accomplish.

    deepee99

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    Re: Blowing my Fuses!

    Post by deepee99 on Fri Aug 14, 2015 12:58 pm

    Tube Nube wrote:Thanks Dave. I'll report back on what, if anything, I discover and accomplish.

    If you're still alive.

    Tube Nube

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    Re: Blowing my Fuses!

    Post by Tube Nube on Fri Aug 14, 2015 1:03 pm

    Maybe I'll file an amplifier itinerary here before "taking off" the base plate. Then if I don't report back . . . you'll know to send assistance.

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