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Post subject: Re: Blew up my Bassman
Posted: Tue Jun 11, 2013 6:00 pm
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Daniel,

It appears that your output tubes arc'ed between the heater line and the anode (pins 2 & 3 ). Definitely a shorted tube (must dsicard).

Now, onto did the tube short on it own. Or did something else caused this.

BTW... carbon tracing (burnt portion of socket) usually means you need new socket. The insulation characterisitics of the socket may been compromised by excessive current and heat.

Sorry...


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Post subject: Re: Blew up my Bassman
Posted: Tue Jun 11, 2013 6:10 pm
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Thanks BMW, it's very reassuring to be able to pinpoint at least one problem.

Very disappointed about the tube (Winged C! I love these things) but thankfully I have a backup pair of TAD 6l6 (the short bottles, which are very sweet anyways).

The socket was brand new. I'll see if I can get it replaced quickly.

Are there any pictures I could take that would help you discern whether the problem was caused inside the amp, or due to the tube?


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Post subject: Re: Blew up my Bassman
Posted: Tue Jun 11, 2013 6:16 pm
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demaria.daniel wrote:
Ok. So I took the amp apart and immediately noticed this:

Burn Spot on Power Tube Socket
http://www.flickr.com/photos/97332706@N05/9019542451/

Burn Spot on Power Tube between pins 2&3
http://www.flickr.com/photos/97332706@N05/9019542545/


OUCH!

Definitely need a new Amphenol there. A pity about that Winged C......

:(

Give it proper burial with full military honors.

Arjay

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Post subject: Re: Blew up my Bassman
Posted: Tue Jun 11, 2013 9:23 pm
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Bummer!!! The socket appears to be a China made porcelain unit. Best to upgrade. But the socket itself would not be the source of the problem. The socket could be cleaned of carbon, but the contacts may have been damaged. Like Beemer said, Why did the tube fail ??? Old age? Or some other components failure ??? Art

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Post subject: Re: Blew up my Bassman
Posted: Tue Jun 11, 2013 9:30 pm
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Daniel,

Take a photo of the back side of each 6L6GC socket. Need to check those grid stopper and screen resistors --- BEFORE putting in any new tubes.

You need to check the bias power supply circuit and the patency of the socket contact with the tubes.

Take a photo under the doghouse --- to see if any main filter cap and/or resistors in the power rail bit the big one.

When an output tube goes ballistic, you have a number of items to check before trying to use that amp, again.


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Post subject: Re: Blew up my Bassman
Posted: Tue Jun 11, 2013 9:42 pm
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Beemer is spot-on!!! But he made me look up the word "patency". Art

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Post subject: Re: Blew up my Bassman
Posted: Wed Jun 12, 2013 2:06 am
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BMW2002Ti wrote:
Daniel,

Take a photo of the back side of each 6L6GC socket. Need to check those grid stopper and screen resistors --- BEFORE putting in any new tubes.

You need to check the bias power supply circuit and the patency of the socket contact with the tubes.

Take a photo under the doghouse --- to see if any main filter cap and/or resistors in the power rail bit the big one.

When an output tube goes ballistic, you have a number of items to check before trying to use that amp, again.


+100

Something within that chassis caused a catastrophic failure. Start with the power supply first and work your way from there.

Arjay

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Post subject: Re: Blew up my Bassman
Posted: Wed Jun 12, 2013 5:42 pm
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Great news, the technician took the amp back in today and started work on it right away. He warrantees all his repair work so I won't have to pay for it. Finally, I have a replacement Winged C 6L6 (matched with the survivor!) arriving on Friday-- the Tube Store is located in Hamilton, just a short drive from Toronto.


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Post subject: Re: Blew up my Bassman
Posted: Wed Jun 12, 2013 6:35 pm
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I recommend measuring both the surviving Winged C and the replacement to see how closely matched they are.

Arjay

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Post subject: Re: Blew up my Bassman
Posted: Mon Jun 17, 2013 11:12 pm
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So. After a trip back to the repair shop and a rush order for a replacement tube, I took my amp to rehearsal Saturday night. The thing didn't last two hours!

This time to damage to the power tube and 'bear trap' retainer was REALLY bad. I'll take a picture because it's pretty remarkable.

I'll take it back to the shop (still under warranty right?) then maybe take it to ANOTHER shop for a second opinion, but I've got to find another amp. Find a home with a collector, or someone who can repair their own amp. Be very upfront that this is a problem child amp and see what I can get.


On the bright side, I had my first gig in 4+ years tonight and we KILLED IT. Using a rented Fender Twin RI. I pulled the preamp tube in the normal channel and plugged a Tung Sol into V2. And it was glorious. This amp could go neck to neck with the Marshall stacks that I've relied on when the Bassman failed.

For the money I could get for the Bassman I'm sure I could pay for a used Twin, two Warehouse Green Berets, maybe even some nice power tubes! Or, I may splurge and buy a used Marshall Bluesbreaker RI :twisted:

Our band is much louder and aggressive than when we started. Beautiful Fender clean tones aren't necessarily what I need right now, but I found a 65 Twin RI dialed in at its fattest setting fit the bill perfectly just the same. This whole Bassman project has been a great learning experience and I hope to find a good home for her.


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Post subject: Re: Blew up my Bassman
Posted: Tue Jun 18, 2013 7:11 am
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" This time to damage to the power tube and 'bear trap' retainer was REALLY bad. "

You definitely have some issue(s) with the power section. To generate enough juice to arc over the tube retainers is a dangerous amp. It sounds like tranny issues. Just a guess.

You need to have the tech really go through the amp, top-to-bottom.


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Post subject: Re: Blew up my Bassman
Posted: Tue Jun 18, 2013 6:01 pm
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BMW2002Ti wrote:
You need to have the tech really go through the amp, top-to-bottom.


Absolutely, I need to get this straightened out. It's just extremely frustrating that a thorough examination / repair by one of the most respected techs in town has failed to get this amp back in working order. Other technicians I've talked to have all said, "If he can't figure it out I'm not sure what I can do!"

However, it seems to me a second set of eyes may lend a fresh perspective. When I get the amp back from the first tech, I plan to bring it to a second tech to double check everything. After all, on Saturday the amp failed the same day I got it back from the shop.

Here's hoping I can put this whole thing behind me very soon!


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Post subject: Re: Blew up my Bassman
Posted: Tue Jun 18, 2013 6:37 pm
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Totally agree with Beemer. If there are no tube, component, socket, wiring issues; the output transformer should have a hi-pot test, or at least a substitute test. I would not advise just buying and installing a new transformer, until the problem is definately isolated!! Art

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