Date: Sun, 06 Aug 2000 02:45:37 -0400 From: The Bernadettes Subject: [Fwd: Gibson Maestro... now,...Vibrolux questions]
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This is a forwarded copy of some off-list correspondence concerning tube swaps, amp mods for a SF Vibrolux Reverb amp that some people on the list were interested in seeing.
X-Mozilla-Status2: 00000000 Date: Sat, 05 Aug 2000 17:47:38 -0400 From: The Bernadettes X-Mailer: Mozilla 4.7 [en] (Win95; U) X-Accept-Language: en MIME-Version: 1.0 To: Optimal Tool Design Subject: Re: Gibson Maestro... now,...Vibrolux questions References: <002501bffeff$5c78cf00$513175~ptimal>
Optimal Tool Design wrote:
> Thanks for the reply Don. Pretty cool that Mr Amp uses a Vibrolux. I thought > you used an old Harvard or is that thing now too valuable to gig with?
Still gig with that also, frequently use both amps. Sometimes I slave the Harvard thru the Vibrolux, or sometimes I use the Harvard for harp and the Vibrolux for guitar. When I we host a blues jam, I usually bring the Harvard for the harp players to use, (ain't I great guy!!), though a lot of guitar players like playing through the Harvard also, (awesome slide guitar amp.)
> I've > been giging with a blackfaced Princeton Reverb which I think should be > similar to your Harvard.
They're pretty similar, though the Harvard circuit is a bit more primitive/simpler. I think the Harvard is a better sounding amp than a Princeton, though I dig the onboard tube/spring reverb on a Princeton Reverb.
> I want to know everyting about your Vibrolux you can tell me. Mine is a bone > stock silverface down to the original tubes. It's in store room condition. I > don't know the year but it is before the push pull volume knob thing. The > speakers are Alnico. I bought the amp from a 70+ year old guitar player who > seldom used it out of the house. I've aquired a few NOS tubes to do some > switching. I followed many of your recommendations when retubing my > Princeton. Any info will be appreciated.
The older silverfaces are better which likely yours is. First I would get it "blackfaced", any good amp tech can do this on a pre-push-pull model. And while the tech has it on the bench, you might as well have him check caps, etc. The fact that it has Alnicos is good, do you know what kind, model? Alnico's on a 70's SF Vibrolux would very likely be non-original. I'm pretty sure all Fender used on SF Vibroluxes were Oxford or Utah ceramics. Unlikely, but maybe Fender used Jensen Alnicos on very early SF's made in the 60's, could be yours is that vintage, these are the best silverfaces to get. I have seen original Alnicos on early SF Super Reverbs so it could be so. Pre-amp tube swaps: First I should tell you I use my Vibrolux for dual duty, (harp and guitar) so I made some compromises here and there to make it a good amp for both. I had my tech put reverb into both channels, I use the normal channel for harp, the vibrato channel for guitar. I use the stock 12AX7 for the first gain stage of the vibrato channel since I use this for guitar. I'm currently using a RCA NOS 5751 "Command Series" for the first gain stage in the normal or "harp" channel. This cuts the gain a bit but not much, but the tone on the 5751 is great for harp, rich, good bottom end but a lot less treble. If you're looking for a little more play on your volume knob try a RCA NOS 12AY7. I use this too, another great sounding tube, which cuts the gain a bit more. A lotta guys like 12AU7's which cut gain substantially, but I don't like 'em. I think they're a bit "flat, thin" sounding. I lot of guys wanna cut their gain so they can run their volume knobs up to "10", but I feel an amp sounds/runs better with a certain amount of extra gain running thru it. I use the stock 12AT7 for the reverb driver tube. A 12AU7 is a popular tube sub for this position, but I like to "drive" the reverb more, especially for guitar, but for harp you may wanna try this sub. I think a 12AU7 makes the reverb sound a bit thinner, I prefer the lush, wet sound of the stock 12AT7. For the reverb recovery position I use a NOS 12AY7. I find this gives me a little more "give" on the reverb knob and doesn't alter the richness of the reverb for guitar. For the vibrato I use the stock 12AX7 only for guitar reasons. Even if you don't use the vibrato function, your signal path does go through this tube so for harp purposes I would try subbing out this tube with a 5751 or 12AY7 to cut gain a bit and reduce some treble. I use the stock 12AT7 in the phase inverter position. Power tubes: I tried using 5881WGB 6L6 type tubes cuz they break up sooner but I found I like 6L6 GLC (the big kind used in Twins for clean headroom.) You wouldn't think this would be the best choice for harp, but these tubes have mucho, honkin, bottom end to them. Though cleaner sounding, I actually prefered them to 5881 type 6L6's. 5881's do breakup sooner but they don't push the bass frequencies like 6L6 GLC's. Rectifier tube: to help counteract the headroom of the 6L6 GLC's I swapped out the stock 5AR4 rectifier with a 5R4 to get a little more sag out of the amp. If you wanna get even more sag/compression you can try a 5Y3 but I don't think it would last long. I've used a 5Y3 for short periods of time, but I would recommend against doing this for long periods of time. A blown rectifier tube can sometimes blow other components in an amp when it goes, I don't think it's worth the risk. I've tried 5V4 rectifiers which theoretically would work and last longer than a 5Y3 but they arced out in a short while. Speakers: I'm currently using a pair of Mojo MP10R Alnicos in the amp. Though they were a bit bright when new, now that they're well broken in they sound great for both harp and guitar. (Nothing like playing heavy gauge strings with an agressive thumbpickin style to break in speakers.) Rated at 20 watts each this is real close to the limit that these speakers can handle. I always believe in living dangerously when it comes to speakers. I've always found that using the lowest possible wattage rating on speakers you can get away with without blowing a speaker gives you the best sound. A lot of guys like ceramics also, which tend to be warmer sounding than Alnicos, though I prefer the crunchy sound of Alnicos when pushed hard. I know that there is an internal mod which reduces the brightness in SF Fender amps. I think certain resistor values are changed. This is something to talk to your tech about, you may wanna look into that. Thats about it, lemme know how you make out.
Don D.
P.S. Steve, some others on the list asked if I can post my answers to you "on-list", is this OK with you?
