Hi everybody,
got a strange problem.
My Vibroverb Project amp (all Mercury transformers) started to blow the 2 amp fuse, always when turning the standby on.
I removed the 6L6 and turned it on and off (power + standby) a couple of times with no challenge. I put in different 6L6, and it worked again.
After a couple of minutes the amp stopped working.
Actually, B+ was still there, but there was no filament any more...
The only tube on was the rectifier.
Then again, sometimes it blows fuses switching standby on, sometimes it works for a while and after a few seconds to a few minutes the filament goes away. Just no voltage any more. But full B+.
I exchanged the rectifier tube as well.
The filament has an artificial center tap with two 100 ohm resistors.
Any hint?
Stephan
Fuse blowing or filament goes away....
Moderators: pompeiisneaks, Colossal
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Littlewyan
- Posts: 1944
- Joined: Thu Sep 12, 2013 6:50 pm
- Location: UK
Re: Fuse blowing or filament goes away....
Something is shorting the filament circuit to ground or worse the power transformer is bad. Have you tried swapping the pre amp valves out? Does this fault occur every time you switch the amp on?
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Stevem
- Posts: 5144
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
Re: Fuse blowing or filament goes away....
You may have yanked on the filament wires too hard when twisting and wiring up the Pt!
When that 6.3 volt source quits on you unsolder those wires off of the PT and if they are dead, yet the B+ wires are still going strong than that is your issue!
If that's the case pull the PT bell off and see how far in those filament take off wires dive into the PT wrap, many times I have been able to peel it back and with a magnifying glass solder the output feed wire back onto the darn small filament winding!
I also think your short / fuse blowing issue is a output tube that has a short from its screen to heater, so you may have two problems going on here!
It will be a process of elimination to pin this one down!
When that 6.3 volt source quits on you unsolder those wires off of the PT and if they are dead, yet the B+ wires are still going strong than that is your issue!
If that's the case pull the PT bell off and see how far in those filament take off wires dive into the PT wrap, many times I have been able to peel it back and with a magnifying glass solder the output feed wire back onto the darn small filament winding!
I also think your short / fuse blowing issue is a output tube that has a short from its screen to heater, so you may have two problems going on here!
It will be a process of elimination to pin this one down!
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
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sbirkenstock
- Posts: 82
- Joined: Fri Oct 17, 2014 10:50 pm
Re: Fuse blowing or filament goes away....
Guy´s,
thank you very much.
One challenge was (kind of embarassing to admit) that the supply from the PT to the first output tube socket came loose...
Figured it out when I was trying to measure filament and touching the wire would turn on/off the filament.
It was just sticking in it´s hole. No idea when this happened, it certainly was good when I initially put it in.
I´ll put the 470 Ohm resistor going over the socket right now on the side the socket next time to give me a better view. Pretty tight around there.
I also exchanged the power tubes and the rectifier tube and now it fired up more than 10 times with no challenge
With the experiment of blowing to many fuses and running out of supply (Radio Shack is probably happy) I build a current limiter with a 100W light bulb, like Gerald Weber suggest.
Thank you very much,
Stephan
thank you very much.
One challenge was (kind of embarassing to admit) that the supply from the PT to the first output tube socket came loose...
Figured it out when I was trying to measure filament and touching the wire would turn on/off the filament.
It was just sticking in it´s hole. No idea when this happened, it certainly was good when I initially put it in.
I´ll put the 470 Ohm resistor going over the socket right now on the side the socket next time to give me a better view. Pretty tight around there.
I also exchanged the power tubes and the rectifier tube and now it fired up more than 10 times with no challenge
With the experiment of blowing to many fuses and running out of supply (Radio Shack is probably happy) I build a current limiter with a 100W light bulb, like Gerald Weber suggest.
Thank you very much,
Stephan
-
Stevem
- Posts: 5144
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
Re: Fuse blowing or filament goes away....
Make sure your output tube heaters are wired right with pin 2 feeding pin 2 and the same for pin 7!
Just to double check, you are using a 2 amp slow blow fuse right?
Just to double check, you are using a 2 amp slow blow fuse right?
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!