Beefing up a VibroChamp?

[Rick1114]

I recently got my newly aquired 66 BF Vibro-champ back from a reputable tech who examined the amp replaced all the electrolytes, cleaned the pots and replaced the "brown turds" and installed a 3 prong cord & a 1/4 jack as well. The amp functions great now (before the controls had very little effect and not much volume), and I installed a Weber 8A100 speaker and put the original in a box for safe-keeping. So all the fuctionality and power is there that was missing before. He said my tubes were in good shape (mullard 12ax7 and RCA 6V6/rectifier) that came with the amp.

Now regarding the sound - the amp doesn't sound drastically different than it did before. The tech was only asked to bring it up to spec so no values were changed. I generally like the sound and the Weber actually does a great job with the bass for 8 inch speaker. I think I'm missing some sustain though - the amp sounds "Dry" to me for a lack of a better word. The note decay is quick and lacking some sustain until the amp is cranked to 10 and I cant do that all the time. Is that how a champ is supposed to sound?

I've read about the many mods, but I'd probably like to keep the tone stack. What are some good routes to beefing up the sustain and getting a fuller sound out of a BF Vibro-champ? (reversible of course!)

Thanks,

Rick

[cminor9]

I have read about people putting beefier output transformers on champs and princetons with good results. That might give it some more low end.

[Rick1114]

C-Minor - I'm not looking to do anything that involved. I played it with a LP tonight and it sounds much fuller with that guitar. I's a very articulate amp! I think I'm just not used to how a small alnico speaker sounds.

Anyway, I'd still like to add a little gain for blues playing - I've found a mod that suggests increaseing the plate resisitors between 110- 220k. Any opinions on this? I found it here: http://www.premierguitar.com/educati...r_tubetalk.asp

Also, I e-mailed my tech about it and he suggested raising the Cathode Bypass cap to 220/50V. Is that similar to adding a "fat" switch?

Any opinions on the best way to approach this?

[Rick Erickson]

Changing the cathode cap value would probably have little or no noticable effect on the sound. I would start by disconnecting the negative feedback loop. That should net you a few db's of gain.

RE

[Chuck H]

For a little more beef and sustain you could try the "Randall" style boost switch. It's just a 750pf cap bridged across the 250p treble cap to increase it's value. You could put the mod on a push/pull 250k pot and save the original pot with your original speaker. Pull the pot, get a "fat" boost. It works well. Mesa used it on a few amps too. But it is commonly seen on the Randall era silver face Fenders. Even though the SF amps have a bad rep, I like this mod. It sounds great for blues.

Chuck

[theunrulychef]

Not sure how long you've been playing on it, but I know you have to be patient with some of the Weber speakers break in times. I have a 8A100 I put in a small 50's Silvertone single-ended combo & I really kinda hated it at first. Flat, dull, boxy etc. I knew it needed to break in, so I took it to band practice & slaved it off one of my other amps at full volume. After doing that a few times and using it as my basement fx test amp, it's finally blossomed into one of my favorite speakers. It's still got a different vibe than the 10s & 12s I have, but it's really fat & musical. Also, breakup with it sounds much, much better.

In addition, I will also second disconnecting feedback loops as a good mod. After putting in an feedback on/off switch on my Princeton Reverb, I find myself never turning it back on. Super simple, reversable mod that has a quite pronounced effect on the tone.

[Rick1114]

Yes, I need to be patient. I have too much time at my boring job to think about this stuff! I asked Weber to break in the 8A100 but it still needs some more time - I can tell this is going to be a great speaker. Also I'm not used to playing through a smaller speaker & without reverb and that's probably most of what I'm hearing.

I actually put in GZ34, and that seems to have help quite a bit. It gave the amp more fundamental!