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Post new topic New, Slightly Confused Owner of a Fender Custom Vibrosonic
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Author Topic:  New, Slightly Confused Owner of a Fender Custom Vibrosonic
Nic Neufeld


From:
Kansas City, Missouri
Post  Posted 3 Dec 2019 3:58 pm    
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I just got a pretty good deal (just over 700) on a 90s Fender Vibrosonic, the one designed by Bruce Zinky with a steel and guitar channel, reverb, vibrato, with a 100 watt 6L6 "twin" type poweramp going into a 15" speaker. I'm mostly a nonpedal player playing Hawaiian and jazz predominantly. I wanted that big, fat clear Hawaii Calls sound when I strummed the low C on my 8 strings and I think this does it just fine!

So I'm excited, just a few anomalies I'm working out.

First is the reverb...if I turn it up past 5 or so, a high pitch whine starts. I haven't tried to troubleshoot tubes yet, but anyone had anything similar? It's a good reminder to not go too heavy on the reverb, anyway, but I'd like to get it back in fighting shape.

Secondly, there is a mysterious mini-switch on the far right of the back of the chassis...no label, and it doesn't look factory from what I can tell. I'm a bit scared by the switch and I'm not sure where it was originally when I bought it, but it seems to affect output slightly. I know the answer is "open the chassis and have a look", which I'm also a bit nervous to do, but does anyone know of any "usual" mods like this, and have a guess as to what it might be? Like I said, pulling the chassis and seeing what it is wired up to will probably help explain, I just figured I'd ask if there was some usual well known mod.

The amp was sold to the store in central Missouri where I bought it by a widow of a steel guitarist, so I hear. Hopefully I can keep it singing for him, whoever he was.
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Michael Butler


From:
California, USA
Post  Posted 3 Dec 2019 4:08 pm    
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sounds like it is oscillating. check to see that the cables are tight on the back of the amp and the reverb tank. make sure they are in the correct places. swap out the reverb tubes with known ones based upon the correct schematic for that amp.

the switch may be to lower the wattage or it may be a negative feedback switch. by your statement tho, it may be a lower wattage switch.

play music!
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Craig Bailey

 

Post  Posted 3 Dec 2019 7:32 pm    
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Is this the Vibrasonic with an "a"?
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Donny Hinson

 

From:
Glen Burnie, Md. U.S.A.
Post  Posted 3 Dec 2019 9:21 pm    
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Vibrasonic = 40 watts
Vibrosonic = 100 watts

The "howl" could also be a microphonic tube, or more rarely, a bad cathode bias cap.

The added switch could be a tone slope mod, or maybe an inverse feedback mod.
(I've done that mod to my old BF T/R.)

At any rate, I'd get the amp serviced. It's almost 30 years old, and the filtercaps are probably on their last legs.
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Ken Pippus


From:
Lake Oswego, OR
Post  Posted 3 Dec 2019 9:44 pm    
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Except the mid-90's Vibrasonic with an A, discussed here, which is 4 6L6's and about 85 watts.

Sort of typical mid-90's Fender. Inaccurate reissue of an amp they never built. But actually a pretty good sounding rig, and, as stated, over 20 years old, and potentially due for servicing.
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Dave Hopping


From:
Colorado, USA
Post  Posted 4 Dec 2019 1:01 am    
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The original VibrAsonic was the first brownface Fender,in 1959.Had a 15" JBL and 2 6L6's.The silverface VibrOsonic Reverb was essentially a Twin-Reverb with a 15".The OP's amp was a cool variation on the Twin-Reverb; I always wanted to take one out for a spin,but never got to.
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Nic Neufeld


From:
Kansas City, Missouri
Post  Posted 4 Dec 2019 4:11 am    
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Yep this is the "Custom Vibrasonic", not the vintage Vibra or Vibrosonics. Not a reissue, custom Bruce Zinky design made for a bit in the 90s.

About getting amps serviced...any idea of a reasonable rate range for that kind of service? I can't imagine it's cheap and will need to prepare The Better Half for new expenses Smile. Also, have never done that before (come to think of it, my Crate Vintage Clubs are probably closing in on 25 years) and want to know what is reasonable before I go quote hunting...

Thanks!
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Ken Fox


From:
Nashville GA USA
Post  Posted 4 Dec 2019 4:32 am    
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I agree with a Donny. Seen this before. If it is a bad cathode bypass cap on the reverb return circuit you can verify that by unplugging the reverb tank at the back of the amp. Turn up the reverb knob. If it oscillates then the cathode bypass cap at tube V4 or the tube itself is the likely culprit

Also check the tank to make sure the reverb pan is floating on its four suspension springs freely. A pan can get stuck on the two locating pins that are part of the reverb can during shipping. This will cause the reverb to squeal as well.
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Tom Gorr

 

From:
Three Hills, Alberta
Post  Posted 4 Dec 2019 7:28 pm    
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That Bandmaster reverb amp I bought based on (good!) forum advice a few years ago likewise gives an ear piercing after 4 on the dial.. nice to know the bypass cap is the culprit.

Now I have to fix it hopefully without electrocution.
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Erv Niehaus


From:
Litchfield, MN, USA
Post  Posted 5 Dec 2019 8:32 am    
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I believe the "Custom Vibrasonic" amp has two channels with one designated for steel. Very Happy
Erv
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Tim Whitlock


From:
Colorado, USA
Post  Posted 5 Dec 2019 9:21 am    
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The switch may be a low/high power switch, where on one side you get all 4 6L6s and the other side cuts it down to 2. It's a common mod and one I have on my Twin Reverb. It lets you cut out two of the 6L6s so you can turn the amp up a bit to get in the sweet spot. Cutting the two tubes, to my ear, gives you maybe 80% of the loudness you get from all four.
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Nic Neufeld


From:
Kansas City, Missouri
Post  Posted 5 Dec 2019 10:38 am    
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Tim Whitlock wrote:
The switch may be a low/high power switch, where on one side you get all 4 6L6s and the other side cuts it down to 2. It's a common mod and one I have on my Twin Reverb. It lets you cut out two of the 6L6s so you can turn the amp up a bit to get in the sweet spot. Cutting the two tubes, to my ear, gives you maybe 80% of the loudness you get from all four.


That's so far my best guess too just based on effect. Will have a look at it when I open it up but probably need to schedule a "wellness visit" with an amp tech, once I find one....


Thanks everyone!
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Calling and calling to me
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