More Fender Trivia/History: The first Fender Vibrasonic (5G13) was made in the early 60's, brown tolex, a single 15' speaker (usually a JBL), 2x 6L6GC power tubes, presence control, solid state rectifier and no reverb. It has the rare distinction of having it's front panel Volume control not adjacent to the input jacks (like almost evey other Fender amp) but 'two knobs down' between the 'speed' and 'treble' controls! It was superseded soon after by the 6G13-A, which changed to 2x 5881 power tubes and added an extra vibrato (tremelo) tube. These brown amps are not a bright as later Fenders and without reverb and two 2x 6L6GC power tube compliment, they are probably not the first choice amp for steel players. However, they are incredibly sought after as guitar amps and collectors pieces and undoubtedly trade for stratospheric prices due to their unique features, age, and how few of them were made.

Next came the Vibrosonic Reverb (silverface), notice no 'a' in the name, which is the'Twin Reverb with a 15" speaker' that has been mentioned before in this thread. With 4x 6L6GC, reverb and usually, a big orange JBL 15" speaker (does anyone know the letter designation of these orange JBL 130 15"speakers?) This was a good steel amp, a variation on the Twin Reverb theme. Does anyone have of of these without a master volume control; I've never seen one without that and that would, indeed, be rare!

Then came the 135 watt Vibrosonic Reverb in the mid/late 70's. (My files show 2/78 but I wouldn't bet my life on it). You can tell it by: 4 amp fuse, no choke, and line out/recording jack on the back panel. It has a ultra-linear taps on the output transformer and is very similar to the corresponding Twin Reverb of its era. Another good steel amp. This amp could be modded to use a choke for improved performance.

And, lastly, is the Custom Vibrasonic Amp (back to the'a' in the name), a blackface re-issue of sorts but not of any particular amp. It has 4x 6L6GC, reverb (in both channels!), no negative feedback and a 4 ohm 15" speaker. These amps actually have a channel marked 'steel' but, except for a little extra headroom in the preamp and a few bells ('sweet switch'), they bear a great resemblance to the usual Fender circuitry we seen since the beginning of the Blackface era (AB763). The 15" speaker is of no special pedigree. (I know how particular, or is that peculiar, steel players can be about their choice of speaker!) Has anyone put a Black Widow in one of these amps? Or any other speaker? Steel players, let's hear how you like these amps for steel!

Does anyone know the story on how the 'A' got changed to an 'O' and back again?

"Just yesterday, I took one of
my 2-EL84 amps with no negative feedback and a fixed/cathode bias
switch, adjusted the bias for equal plate currents, and asked a friend
of mine, who is one of the best guitarists I know, to do a blind A/B
test. He picked fixed bias *every* time as sounding the best, using
terms like "fuller", "better definition", "better tone", "my sound", etc.
Most people automatically assume an EL84 amp should be
cathode-biased, but sometimes fixed bias does indeed sound better."

The speaker is a knowledgeable amp builder named Randall Aikens.

I believe that Fender came out with their "master volume" gimmick in '72, which was near the time that they released the Vibrosonic. So I don't know if there is such a thing as a "none" master Vibrosonic.

In the new Vibrasonic, they used a 50 pF cap for the "sweet" switch instead of the normal 120pF bright cap. The speaker is the "heavy magnet" Eminence 4 ohm which sounds amazing with Tele, but is a bit brittle and lacking in the mids for steel guitar, IMO. For a 100 watt amp, that thing is not all that loud. I suspect they held the gain back a bit to keep 'er clean.

Bob, Gary Brandin came by today and he is still singing praises about his "Rick". On a Supro Thunderbolt, what would be the ballpark for the cathode current (6L6)?

I have to evaluate the whole power amp section, really.
It's a complex bouillabaisse. Want to bring it by? Or email me?

Bob

In my case, I re-biased after every modification, the last one being the removal of the cathode resistors. The actual bias voltage didn't change more than a volt or so from where it was before the resistors were removed. I've exchanged quite a few emails with Bob Metzger regarding the biasing subject, and have found a bias value that works for me. I think I ended up at about -48.5V.

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bterry.home.netcom.com

My next project is to try some different things in the preamp section, but I'm real happy with it as is for now.

Thanks to all for the suggestions and advice.
Bill

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bterry.home.netcom.com

When I bought this Custom Vibrasonic, it had some hissin', spittin-type problems, so I took it to the Nashville Fender Custom shop. Ronnie, the amp guy, said that these new amps are very inconsistent from the factory. He came up with some kind of a mod that fixed it. It has a really nice Fendery, shimmery "compression distortion" as you say.

I dropped a 15" Black Widow in her and she really came alive. I play everything through the guitar channel, better tone.

I use it on sessions and engineers LUV it. It really makes my Zum blend, yet jump off the speakers.

I'll be out in Irvine,CA with Terri Clark on wed, Aug 2. If you or any of your friends/family want to come, be my guest. Email me with tix requests before this Th.

Seriously, would you please consider posting the Custom Vibrosonic/Ronnie mods? (With his permission, of course). And was that Black Widow a 1502 or a 1501-DT or a 1501-SB? (it says on a little white tag adjacent to the speaker terminals!)

Thanks everyone for contributing!

Good luck with it,

Kevin Post, I would also like to hear about the Custom Vibrasonic mod.

Thanks guys, this thread changed my mind about getting rid of the Twin!

Dave Z

[This message was edited by Dave Zirbel on 19 July 2000 at 08:53 AM.]

Dan Torres has a very good tube amp book for beginners: "Inside Tube Amps". He is very knowledgeable about tube amps; I don't really know if he's setup amps expressly for steel guitar but he is well acquainted with the principals of what would make a successful steel amp. On the other hand, he is flamed daily on another BBS by the 'preservationist' vintage amp guys because he has invasively modded many Fender amps (May I say the 'D' word on the forum): he's drilled a few holes for extra features. I don't find anything wrong with him but he is compared daily to Hitler, Idi Amin, Pol Pot and a number of other well-known amp builders. I've never had any dealings with him one way or another but I did install one of his 'amp kits' that he sells in a friend's amp, which turned a mediocre amp into a great sounding amp. My advice: If I were in your shoes, I'd go to him. He knows his stuff. Go thru this thread and pull out the actual tech stuff; leave the prose behind; he (or any other tech) doesn't have time for that. OTOH, you could ask bOb, who is a hop, skip and a jump from you about any tube amp guy in Sonoma who has steel on the brain (not a metal plate, though!).

Too bad, My wife and I are planning to move to Sonoma but not for a few years yet. I'm glad to know that there's a few tube amps left up there and it's not all grapes (yet!).

Good luck,

b0b Lee, does Mike do mods?

By the way, Dan said his mod for a Custom Vibrasonic would be to rip out the circuit board and start over with regular components.