71 sf Vibrolux issue's

[earthmud]

New Tranny Pics added! I've been chasing a fizz problem for a while now and have swaped out the speakers, cables, and preamp tubes. The fizz is still there. Another issue I've noticed seems to be a loss of volume and a really bright tone. My vibrolux on three should be really loud shouldn't it? When I turn it up(past three) I get ear fatigue really fast, though not from volume but from harsh brightness when using gain (using two weber 10f150's). I'd take it to a tech but funds are limited right now. If I swap out the power tubes do I need to have it rebiased in order to test it out? If its not the power tubes then it must be something electrical right (bad cap or output transformer)?

[RussB]

We can guess all day and night, and chances are, no one will get it right.

Rather than spending money recklessly, save up and find a good tech familiar with vintage Fenders. Has this amp been serviced in the last 15 or so years?

[slider313]

+1 on servicing. If the amp needs a cap job the symptoms you are hearing are only part of the big picture.

[earthmud]

It had a cap job and new tubes last year right after I bought it. I'm not real confident that the tech knows vintage fenders that well. The amp has plenty of volume when using pedals, but when clean with the volume on three I could easily talk over it. I've also swaped out guitars and checked the outlet voltage(which read 120volts in my old 2 wire house). I've had the amp for about a year and it seems that it has gradually lost volume and has gotten really bright and harsh. Do I need to have the power tubes biased if I'm just going to stick then in for a second to see if the fizz stops and volume returns? Should I replace the rectifier tube also?

[slider313]

What brand of power tubes are in it now? If your tech installed them he may know the plate voltage they were rated for. You could install another set, but I would watch them for red plating for the first couple of minutes. If they don't red plate then play it and see what you get.

[earthmud]

They are JJ's 6l6gc's. Not sure about the rectifier. I won't go back to that tech. There's another shop way across town that I'll try next. Very good rep but really far.What brand of power tubes are in it now? If your tech installed them he may know the plate voltage they were rated for. You could install another set, but I would watch them for red plating for the first couple of minutes. If they don't red plate then play it and see what you get.

[earthmud]

Gut shots. Let me know if everything looks okay.

http://i291.photobucket.com/albums/ll287/earthmud/DSC01355.jpg

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http://i291.photobucket.com/albums/ll287/earthmud/DSC01366.jpg

[earthmud]

Also I was wondering how to better secure the wire mesh in the top of the cab. It's pretty loose and vibrates when I play.

[earthmud]

bad cap?

http://i291.photobucket.com/albums/ll287/earthmud/DSC01368.jpg

http://i291.photobucket.com/albums/ll287/earthmud/DSC01370.jpg

[brad347]

You need a complete cap job. The amp is 1972.

[earthmud]

bad cap?

http://i291.photobucket.com/albums/ll287/earthmud/DSC01368.jpg

http://i291.photobucket.com/albums/ll287/earthmud/DSC01370.jpg


Supposedly I had one last year? Did my tech lie? I paid over 200$! Should I stop playing the amp?

[AL30]

$200 ? Your tech may have replaced your filter caps - you didn't provide a picture. But the on board electolytics are still original as is the bias cap. IMO these are part of the cap job. I don't wanna second guess your tech though. Did he tell "just the filters"? People have different views on what "cap job" includes.

Again, my opinion, but $200 for changing the filter caps (if that's all that happened) is ridiculous. Take a pic under the doghouse and see if they're new. That's the "pan" looking thing on top of the chassis. BE CAREFUL and don't touch any components when you do this. Just remove the screws, snap a few shots, and replace it.

AL

[earthmud]

http://i291.photobucket.com/albums/ll287/earthmud/DSC01371.jpg

I forgot that he did replace all the tubes also. The tech works part time at a shop by my house. I have found a new tech that has tons of experience but is really far away. I'm taking it in as soon as I have the cash. Notice anything else?

[brad347]

Those caps are new. BUT they are inexpensive imported Taiwanese caps made by a company called Illinois. Some people think they are fine. I prefer not to use them.

To me, though, it's not good practice to do a "cap job" and fail to replace the bias filter capacitor. The cathode bypass caps... okay, that I can live with someone wanting to leave them in the interest of keeping the amp "original," but the bias filter cap is critical and could take out other expensive components were it to fail. I'd reconsider a tech that left that step out of a "cap job."

For your current situation though, replace the cathode bypass caps and certainly the bias filter cap. Then see where you're at with the amp.

[JJman]

Some of the symptoms could possibly be explained by parasitic oscillation. Many of the wires are laying parallel to other wires. This is from "sloppier" assembly at the factory when compared to the '60s. The problem could be from just one set that are parallel. Hopefully it doesn't need to have many of the wires shortened and re-soldered. I've cleaned up many of the wires on my '71 DR since I've had it.

[brad347]

Some of the symptoms could possibly be explained by parasitic oscillation. Many of the wires are laying parallel to other wires. This is from "sloppier" assembly at the factory when compared to the '60s. The problem could be from just one set that are parallel. Hopefully it doesn't need to have many of the wires shortened and re-soldered. I've cleaned up many of the wires on my '71 DR since I've had it.

Even if that is the case, it's not too bad. Just find the wires going to the grids of the preamp tubes and shorten as many as possible.

[earthmud]

First of all thanks for all the help. I broke down this afternoon and drove across town to the new tech. I couldn't stand seeing her in peices like that. He was super cool. He loved the amp and said it was in a great shape. Turns out he worked for Fender back when my amp was built:AOK. She's in good hands. I just had some stuarts installed in my tele from same place and they did a great job. I'll post what the problems were when I get it back in a couple of weeks.


Thanks J