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Robert

Robert

Oranges and lemons, say the bells of St. Clements.
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Camrose, Alberta, Canada - used to be Umea Sweden.
How bad does it look?

I just got this used Fender Pro Jr from UPS, so I installed the tubes, powered it up and smoke started coming out of them within seconds.

I opened it up and this is what I saw -

P6146876.JPG
 
E-w-w-w-w-w, that big filter cap and around it definitely isn't looking good! Actually, the cap may just be singed--looks like it was the resistor below it that went up in smoke.

Calling Tung, calling Tung.....come in, Tung!
 
I'm not an amph doctor, but it's just a cap and a few resistors. The real issue is what caused the blow out.. perhaps you didn't seat the tubes properly.
 
Here's a photo off Bill Machrone's site that shows how that section of the board should look. Looks to me like R32, the resistor below the 22 uf filter cap, is what let go:

fullboard.jpg


bcdon said:
I'm not an amph doctor, but it's just a cap and a few resistors. The real issue is what caused the blow out.. perhaps you didn't seat the tubes properly.
Click to expand...
Yeah, exactly. And pray that it didn't take out the power transformer with it....
 
duhvoodooman said:
Here's a photo off Bill Machrone's site that shows how that section of the board should look. Looks to me like R32, the resistor below the 22 uf filter cap, is what let go:

fullboard.jpg
Click to expand...
Is that picture a modded board? It looks like there are a couple of wires -- one yellow and one blue -- that aren't in Robert's photo. Maybe those had something to do with it?

Don't know, just my uneducated observation...
 
Eric said:
Is that picture a modded board? It looks like there are a couple of wires -- one yellow and one blue -- that aren't in Robert's photo. Maybe those had something to do with it?
Click to expand...
Good point! Those wires are part of one of BillM's mods for his Pro Jr. I was just trying to show what the unsinged components in that area of the board were....

BTW, here's a link to a Pro Jr. schematic:

http://www.ampwares.com/schematics/pro_jr.pdf

Looks like R32 is a 2.7 Kohm 2W power resistor that steps the B+ voltage down from 319 VDC to 294 VDC.
 
Robert it's not the 4th of July yet! I heard those were some bad caps but WOW! I haven't seen 'em light up like that before.Good luck with that one.Sumi:D :(
 
No way 2 know in hindsight, I s'pose, Robert...but...assuming that you know how to put tubes in correctly, could that damage have been done by the previous owner, which is why they were selling it in cyberspace, not face-to-face?

Their extortionate (isthataword?) fees aside, as bad as UPS can be (to whit: "What can Brown Do for You?"), blaming that frito-boardito on them may be a tad over-the-top. Although it is possible a solder joint cracked or connection came loose in transit, that could happen with the amp in the trunk of anyone's car hitting a bump in the road.

I think the amp was fried b4 it was packed and sent to you.
 
Who knows what happened to the amp. I can't say for sure. I think I know how to put in tubes correctly, but I should have looked at them as powered up the amp. Perhaps one of the tubes are busted.

The seller already offered to take it back, but I don't want to have spent all this UPS rip off fees for nothing. They charged me over $130 just to let me have this amp, so I would rather get it repaired than to put more money in their nasty little pocketses.
 
Thanks Vood for the schematics link! I dropped it off to a repair guy this morning and he said he needed the schematics before he could go anything. Now I am crossing my fingers that the amp can be fixed without costing me a fortune.
 
bcdon said:
I'm not an amph doctor, but it's just a cap and a few resistors. The real issue is what caused the blow out.. perhaps you didn't seat the tubes properly.
Click to expand...

Correct. That node is the B+ supply for the EL84 screens. The one good thing is that the resistor blew on top of the board, i.e., not on the trace side. The carbon can cause problems later on if it gets on the PCB's traces.

It is a fairly simple circuit, so any good tech should be able to fix it.

My guess based on the photos is that either one or both of the EL84's screen grids were damaged in shipping; they are not the most robust of tubes. But it is hard to say for sure as I don't have the amp in front of me. Your tech should probably check all the tubes to make sure they are good.

You will want to have the tech check R24 and R25 to make sure they aren't toasted as well. Those could be increased in size. right now they are 100 ohm. Anywhere from 470 ohms to 1.5K ohms would provide more protection for the EL84 screens.

Finally, I've heard bad things about the Illinois caps (marked "ic"). Depending on the age of the amp, you may consider having those replaced when the amp is serviced.

Sorry about your misfortunes with the amp, but hopefully it should be relatively painless to have it fixed.
 
Robert said:
The Gods are punishing me... perhaps because I have too many amps now?
Click to expand...
Allow me to take some of that bad karma, you got there buddy. Please ship all amphs marked "Marshall" to Vancouver and don't you dare use UPS!! :dance
 
All is good - I got the amp back today. It sounds great!

What was the problem? I am embarrassed to say - I put the power tubes into the preamp tube sockets, and vice versa... go ahead, slap me twice :thwap :spank :spank

Live and learn...
 
Haha. Well, live and learn. At least it works now!
 
Robert said:
All is good - I got the amp back today. It sounds great!

What was the problem? I am embarrassed to say - I put the power tubes into the preamp tube sockets, and vice versa... go ahead, slap me twice :thwap :spank :spank

Live and learn...
Click to expand...

Are you serious?

:spank :spank :spank

Doh! Ya newb! :dude
 
Glad to hear it's all good now,and that is an easy mistake to make.Your a good man to fess up to it.Sumi:D
 
How many swedes does it take to screw in a light bulb? ;)

Just kidding, not like I know anything about installing tubes. Glad it worked out!
 
Robert said:
....I think I know how to put in tubes correctly....
Click to expand...
NOT!! :poke :laughingatyou

As Bugs Bunny used to say, "What a maroon!"

Only joshin' with you, RR. To err is human as they say. Just glad that it turned out to be easily fixed and is running OK for you now.

Obligatory video demo forthcoming, we trust?!?
 

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