Showman Head Troubleshooting Question

MBM · March 14th, 2004, 01:55 PM

I have an early 66 blackface Showman head. I was playing it when the sound all of a sudden a sound started occilitating up for a few seconds and then it went dead. The fuse had blown. Any ideas of what happened?

GilmourD · March 14th, 2004, 04:38 PM

Dead short inside a tube, maybe? Check the tubes themselves for any burn marks inside (outside of the getter flashes, which should be silver or turning white). Check the tube sockets for burn marks, in case they arced. And, I'm not sure what the output tranny should read as with a meter, but check that as well. One of the other guys here should be able to give you an idea of that.

Dacious · March 14th, 2004, 07:51 PM

The oscillation is a clue. It sound like the amp 'ran away' with ultrasonic feedback, causing it to eventually draw too much current through the power tranny. It may have toasted tubes, too.

This is a tech job, to work out what it is that is causing the problem - could be lead dress if any changes have been made recently. You may need to get the grid stoppers added to the power tubes.

GilmourD · March 14th, 2004, 08:38 PM

Quote:

Originally Posted by Dacious

The oscillation is a clue. It sound like the amp 'ran away' with ultrasonic feedback, causing it to eventually draw too much current through the power tranny. It may have toasted tubes, too.

This is a tech job, to work out what it is that is causing the problem - could be lead dress if any changes have been made recently. You may need to get the grid stoppers added to the power tubes.

If it's stock, it has grid stoppers on the power tubes. That's an AB763 circuit, if it's a totally stock '66 DS.

Dacious, as you know more about these than I do... What do you think about him turning the amp on in the dark and checking the glow of the tubes? Something in my gut says, though, that you've got an internally mangled 12ax7. I had a 1965/66 DS myself and I had a single power tube suddenly redplate and I lost half the power, but the fuse never blew. Just replaced it with a matched quartet from Andy Ruhl and things were cool. Would the grid in a 12ax7 suddenly connecting internally to the plate cause enough current draw for the thing to run away?

I by no means am any sort of expert (though I'm definitely trying to be :-D). Just tossing out a few ideas.

MBM · March 15th, 2004, 02:04 AM

Thanks guys,

It has a matched set of Groove Tube power tubes. The big orange G on the first tube now looks like a big brown G. The second tube started looking a little brown too. So, either something toasted the tubes or the tubes toasted the fuse. I hope the power transformer is still ok. I guess I will need to take it over to my trusty amp tech and have him do an autopsy on it.

Mike

GilmourD · March 15th, 2004, 02:34 AM

Quote:

Originally Posted by MBM

Thanks guys,

It has a matched set of Groove Tube power tubes. The big orange G on the first tube now looks like a big brown G. The second tube started looking a little brown too. So, either something toasted the tubes or the tubes toasted the fuse. I hope the power transformer is still ok. I guess I will need to take it over to my trusty amp tech and have him do an autopsy on it.

Mike

Actually, gotta love that GT paint on the tubes. Almost makes me wanna buy them sometimes. LOL

If for some ODD reason you decide that it's not worth it for you to fix that (I would suggest that it is), lemme know... I miss my old DS and would love another one. :)

MBM · March 15th, 2004, 03:04 AM

Gilmour,

I'd be happy to let you know. I sell a lot on eBay and was actually thinking of putting this baby on the auction block. It was gone through by an amp tech a least a couple years ago. It is absolutely pristine with hardly a scratch.

I was playing it through a cabinet with two 12" speakers of questionable ohmage so maybe ohms law stopped it for speeding. I will need to run it through a Showman cabinet next time.

Mike

March 14th, 2004, 01:55 PM	#1 (permalink)
MBM Tele-Meister Join Date: Jun 2003 Location: Texas Age: 59 Posts: 134	Showman Head Troubleshooting Question I have an early 66 blackface Showman head. I was playing it when the sound all of a sudden a sound started occilitating up for a few seconds and then it went dead. The fuse had blown. Any ideas of what happened?

March 14th, 2004, 07:51 PM	#3 (permalink)
Dacious Friend of Leo's Join Date: Mar 2003 Location: Godzone Posts: 2,623 35 Photos	The oscillation is a clue. It sound like the amp 'ran away' with ultrasonic feedback, causing it to eventually draw too much current through the power tranny. It may have toasted tubes, too. This is a tech job, to work out what it is that is causing the problem - could be lead dress if any changes have been made recently. You may need to get the grid stoppers added to the power tubes. __________________ My other Telecaster is a Thinline The Tele Bible, Ch 1, v 10 Love thy Telecaster, covet not thy neighbour's Strat!

March 15th, 2004, 02:04 AM	#5 (permalink)
MBM Tele-Meister Join Date: Jun 2003 Location: Texas Age: 59 Posts: 134	I took a look ... Thanks guys, It has a matched set of Groove Tube power tubes. The big orange G on the first tube now looks like a big brown G. The second tube started looking a little brown too. So, either something toasted the tubes or the tubes toasted the fuse. I hope the power transformer is still ok. I guess I will need to take it over to my trusty amp tech and have him do an autopsy on it. Mike

March 14th, 2004, 04:38 PM	#2 (permalink)
GilmourD Tele-Afflicted Join Date: Jul 2003 Location: Nutley, NJ Age: 29 Posts: 1,571	Dead short inside a tube, maybe? Check the tubes themselves for any burn marks inside (outside of the getter flashes, which should be silver or turning white). Check the tube sockets for burn marks, in case they arced. And, I'm not sure what the output tranny should read as with a meter, but check that as well. One of the other guys here should be able to give you an idea of that.

March 15th, 2004, 03:04 AM	#7 (permalink)
MBM Tele-Meister Join Date: Jun 2003 Location: Texas Age: 59 Posts: 134	Gilmour, I'd be happy to let you know. I sell a lot on eBay and was actually thinking of putting this baby on the auction block. It was gone through by an amp tech a least a couple years ago. It is absolutely pristine with hardly a scratch. I was playing it through a cabinet with two 12" speakers of questionable ohmage so maybe ohms law stopped it for speeding. I will need to run it through a Showman cabinet next time. Mike