• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Has this Maggie bought the farm? (sorry, Bob)

gadget73 said:
Pics please? If the transformers haven't failed everything else can be fixed easily
Click to expand...
gadget73 said:
a shorted rectifier could be causing this, luckily 5U4's are pretty cheap. Still some pics to rule out obvious damage would be good, then test it with the rectifier out.

also you really shouldn't run amps with no speakers connected. It can cause the tubes to arc or damage to the output transformers if something is trying to make sound and the amp is not loaded. It should be connected to a dummy load if you don't want to risk speakers.
Click to expand...
Thanks, Gadget. I just got it back home. Attched is a photo my tech friend sent. The circled capacitor – if you bypass it, the rattle and sparks do not happen. However, the capacitor itself is good, he said.
 

Attachments

  • IMG_3031.jpeg
    IMG_3031.jpeg
    177.7 KB · Views: 50
dcgillespie said:
IMG_3031.jpeg
Gigantic said:
apples and oranges, but recently, my kitten "jarred" one of the EL-84s loose on my amp, causing almost exactly what you described. in my case, since my amp is ss rectified, it took out a couple resistors in the rectifier circuit, which were easily replaced. I suspect that the recommendations to replace the rectifier tubes or the associated filter caps to be not far off the mark. take off the bottom cover of your amp and let's see the innards. Those Maggies are dead simple and it shouldn't be too hard to spot any singed resistors or caps.
Click to expand...

The amplifier sounds tremendously unstable to me. Does it make the same sound through the speakers when they are connected? Is that without any input connected?

Dave
Click to expand...

Gigantic said:
apples and oranges, but recently, my kitten "jarred" one of the EL-84s loose on my amp, causing almost exactly what you described. in my case, since my amp is ss rectified, it took out a couple resistors in the rectifier circuit, which were easily replaced. I suspect that the recommendations to replace the rectifier tubes or the associated filter caps to be not far off the mark. take off the bottom cover of your amp and let's see the innards. Those Maggies are dead simple and it shouldn't be too hard to spot any singed resistors or caps.
Click to expand...
Thanks, Dave! As I mentioned elsewhere, if the circled cap is bypassed, the noise and sparks do not occur.
 
dcgillespie said:
The amplifier sounds tremendously unstable to me. Does it make the same sound through the speakers when they are connected? Is that without any input connected?

Dave
Click to expand...
No input was connected. And since no speakers were connected, I let it run just a second or two. I do understand that a load needs to be connected to those taps.
 
If yoy mean bypassed to ground you're killing the signal from the 6eu7 downstream, meaning the problem is somewhere in the 6eu7 or before it.

Looks like that orange transformer lead is awful close to the input jack in the back. If thats touching it might do this.

And 0 is the amount of seconds this should operate unloaded.
 
gadget73 said:
If yoy mean bypassed to ground you're killing the signal from the 6eu7 downstream, meaning the problem is somewhere in the 6eu7 or before it.

Looks like that orange transformer lead is awful close to the input jack in the back. If thats touching it might do this.

And 0 is the amount of seconds this should operate unloaded.
Click to expand...
Thanks, man! You may have nailed it! That orange lead should not be connected to the input, not no way, not no how, should it?! And the orange lead is actually twisted together with the red input wire (see photo)!!! Jeez, how could that have happened? I think that red wire should be soldered to the positive terminal on the RCA input jack, and the orange wire should be completely out of the picture (the transformer has 4, 8 and 12 ohm outputs, so two of the color-coded wires should not be hooked up at all). I'll try to fix that and report back!
 

Attachments

  • IMG_7199 3a.jpg
    IMG_7199 3a.jpg
    99.4 KB · Views: 25
I
Jalousie said:
I don't think severely jarred would cause a can cap to go bad. Maybe some wires touching together from the jarring?
Click to expand...
It looks like an input wire got somehow twisted with a transformer wire, which seems wrong as wrong can be. So you may have pinpointed the problem. Fingers crossed . . .
 
Ah, cool. We like an identifiable problem. Definitely seems like something went down twisted. [Bad '80s movie reference. I think Courtney Cox was in it.] Hopefully all fixable and nothing got eloctrocuted.
 
Thanks, everybody. I was able to deal with the crossed wires--an unused Edcor transformer 4 ohm output wire (there are 4, 8, and 16 options) touching a positive input-source wire. That solved the crazy high-pitched rattling, but no sound goes to the speakers. Next I should probably change the rectifier tube.
 
Ouch! That thing really looks chopped up. Who did the mods? If I were you, I would get a schematic and put everything back to stock and rewire it.

All four of those white coupling capacitors look to be in right place but I am really uncomfortable seeing a zip tie around the power transformer wires, and all of the off color wires connected together and rubber surrounds on their connections. Not to mention what Gadget saw and pointed out. :yikes:
 
Yes--quite horrific. Really have NO idea how the transformer and input wires got crossed. But I fixed that problem, and the amp no longer screams and rattles. But neither does any sound come out of the speakers.

Those Edcor transformers are heavy, and the amp fell hard. The rectifier tube was bent, and on further inspection, its notched center post was broken and glass is showing through (see photo). Any suggestions for what kind of 5U4 rectifier to use? Most seem to be 5U4G or 5U4GBs. Does it even matter to the sound?--they range from ridiculously cheap, as in a pair for 10 bucks, into the hundreds.

REGARDLESS, I'M HOPING A NEW RECTIFIER SOLVES THE PROBLEM!IMG_7210.jpg
 
Last edited:
Stock it would have come with a 5U4GB purely because thats what was being made when these were in production. The 5U4G has slightly lower current ratings, but for this amplifier its not going to make the slightest difference. It doesn't run high enough current to stress a 5U4G at all.

There is also a 5U4GA, same ratings as the 5U4G, but in a straight side bottle that is usually slightly skinnier than the 5U4GB. Don't see that one too often though.

the missing locator pin won't affect function but if you plug it in wrong it can make things extremely unhappy.

I would not pay dumb money for a 5U4 of any flavor. They were used in everything and they aren't exactly in short supply either in new or old production.
 
I have a bag of 5U4's I've pulled from various things. They're common as rocks. I wouldn't spent stupid high prices for one.
 
Same, have only rarely come into one that didn't work properly. One was actually a 5U4G, and I found it in my 9300 when it sounded all funny. A quick test showed the voltage dropping badly with any sort of volume, and the tube tester measured it well into the "its dead" zone.
 
I like the cool "bottle" type rectifiers, but I found a plain one for around 10 bucks with shipping. After I get it plugged in, I'll report the results. Thanks for all the guidance.
 
You must log in or register to reply here.
Back
Top Bottom