Speak to me of Vibro Champs (NAD p.2)

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sookwinder
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Re: Speak to me of Vibro Champs

Post by sookwinder » Sun Dec 24, 2017 10:52 pm

The VC (and Bronco) amps are probably one of the few Fender designs (Princeton and PR also ) where there was little variation between BF and SF... so an early to mid SFVC (or Bronco) will satisfy just as much as a BFVC.

While the early BFVC had the blue moulded tone caps that are very desirable (I should say I do like the later "turd' coloured and "smurf" coloured tone caps as well), one could argue that the later versions of the BFVC and the SFVC are better than the early ones in as much as they had much larger power supply filter caps (cap can) and so had less hum. Obviously this hum is far more noticeable when you plug a larger external speaker (box) into the VC. Simple design, awesome tremolo, almost anyone can fix/repair them.

Hey lususnaturae.... nice looking Riviera... 1967 model ??
Also good to see the two mini HBs in the correct orientation.
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Re: Speak to me of Vibro Champs

Post by lususnaturae » Mon Dec 25, 2017 12:58 pm

Yes, the Riviera is a '67. And yes, the two mini HBs are in the correct orientation. I got the guitar from the original owner who didn't mod a thing. The guitar however did need a refret which I had my tech do the work. The Riviera is my best sounding guitar and such a pleasure to play.

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Re: Speak to me of Vibro Champs

Post by Gavanti » Fri Jan 05, 2018 11:52 am

So I ended up going for a '68 Bronco. It looks to have been re-capped and re-tubed, and has a 3-prong cord. New speaker, and it's missing the top back panel. Thanks Sookwinder and everyone else for the advice—I kept it in mind as I was looking. I'm keeping an eye out for a C8r speaker, but I'm mostly seeing 8 ohm ones at the moment.

Initial impressions: I have to get away from hearing the big 2x12 Slant 6V in my head while playing this. The Bronco is a way more raw tone without the low end, and it's generally less scooped and sparkly. It took me awhile to EQ it in, but somewhere around 7:30pm last night, I found myself just trancing out on a heavy riff without worrying about whether I was going to get hollered at to knock it off. So that's a major plus. It takes dirt and reverb pedals like a champ (sorry). My DLS on Super Bass is ok with it, but the SSBS Fuck sounds crazy good. This one stays pretty clean up until about 6 and then starts to get ragged quickly. In a small enough gig, I could likely use this and kick it over the line with a SHO. The tremolo is pretty great, and it actually plays pretty well with the Walrus Monument on my board. I don't think the 8" speaker is going to work for me ultimately, even around the house, but that's easy enough to fix with a cab (or maybe the Jensen would do it?). I'm going to try to run it through the speakers of one of my other amps to see how it sounds.

I'll give it a try for a bit. I've got an attenuator in the post, and I'm thinking it might be possible to bring the signal of the Slant 6V up enough to get a decent clean tone and then bring it down to a better home level with the attenuator. It's also possible I'll end up moving toward something just a little bigger like a Princeton, but in the meantime, I expect this to be super fun.

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Re: Speak to me of Vibro Champs (NAD p.2)

Post by sookwinder » Sat Jan 06, 2018 6:08 am

Bronco ... good pickup.


Some helpful hints for the VC and Bronco owners

1. The trem does not need a pedal connected for it to operate.
2. If the trem is starting (or is) soft, you may need a replacement valve... as this valve is not in the signal path any quality 12AX7 valve will work
3. If you are not using the trem, get a male RCA plug .. short out (connect) the two connections in the RCA and plug it into where the trem pedal will normally be attached. You will not loose as much gain through the trem circuit when you do this => amp a little louder
3. If you want to get a little more "rawness" into the sound, you can connect a switch that will turn off/on the Negative feed Back. The NFB normally smooths out the signal. With the NFB switched off, the VC / Bronco will sound a little more 50-ish... tweedish.. sort off. certainly more snarliness.
the mod is easy... you just cut the NFB return wire and place a toggle switch in. the switch can be secured to the chassis so you just put your hand up near the speaker/chassis and turn on/off the NFB
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Re: Speak to me of Vibro Champs (NAD p.2)

Post by Gavanti » Sun Jan 07, 2018 8:33 am

sookwinder wrote:
Sat Jan 06, 2018 6:08 am
Bronco ... good pickup.


Some helpful hints for the VC and Bronco owners

1. The trem does not need a pedal connected for it to operate.
2. If the trem is starting (or is) soft, you may need a replacement valve... as this valve is not in the signal path any quality 12AX7 valve will work
3. If you are not using the trem, get a male RCA plug .. short out (connect) the two connections in the RCA and plug it into where the trem pedal will normally be attached. You will not loose as much gain through the trem circuit when you do this => amp a little louder
3. If you want to get a little more "rawness" into the sound, you can connect a switch that will turn off/on the Negative feed Back. The NFB normally smooths out the signal. With the NFB switched off, the VC / Bronco will sound a little more 50-ish... tweedish.. sort off. certainly more snarliness.
the mod is easy... you just cut the NFB return wire and place a toggle switch in. the switch can be secured to the chassis so you just put your hand up near the speaker/chassis and turn on/off the NFB
Thanks! I might look into the NFB mod. Reading up on this has been an education. I think I'm finally starting to understand how amps actually work.

I have a couple of questions if you have time:

One thing I noticed is that the cathode bias resistor appears to have been changed to 400ohm (it reads 455ohm). The schematic suggests 470ohm, and reading around on several sites suggests these amps run pretty hot anyway. I saw a number of folks recommending swapping in 1kohm there. The power tube is a JJ 6v6S, which I believe can take a good bit more than older 6v6's. Is this too hot, or should I just keep an eye on the power tube when I turn it up?

Also, there's a wire (the green and white) coming out of the PT which just appears to be cut. Is this something that needs to be addressed? I thought it might be a changed PT, but the codes look right.

Thanks again!

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Re: Speak to me of Vibro Champs (NAD p.2)

Post by jdr1014 » Sun Jan 07, 2018 9:38 am

Nice score- congrats!!!

That mod speaker is probably not optimum IMO. As you said, you could use an ext. cab ...... or perhaps try some different speakers. Good thing is 8 inch speakers are pretty cheap. I have a WGS G8C ceramic (IIRC # correctly) in my SFVC and it is great for under $40. Amp sounds bigger and more bass with it.

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Re: Speak to me of Vibro Champs (NAD p.2)

Post by sookwinder » Sun Jan 07, 2018 3:18 pm

The cathode resistor on the original design is an echo from the tweed champ.. Leo fucked up.
I have had that resistor burn out and cause damage to the circuit board on a '75 VC.

me? if you are going to run the amp at mainly 3 -5 don't bother to change it.
But if you are likely to be playing for a long period of time above 5 (or even have the amp on for a long time - cathode bias amp designs are ALWAYS "on", so even though you may not be making any noise, the amp is still running "hot") - I would be changing the cathode resistor on the 6V6GT to a 2Watt 680 ohms, 750 ohms or 820ohms... maybe even go for a 5W ceramic resistor. I know this is not "original design" but from a saftey aspect, and a perspective of not having the amp destroy itself it is a good mod to do.

The wire... just tape it off.
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Re: Speak to me of Vibro Champs (NAD p.2)

Post by Gavanti » Sun Jan 07, 2018 6:18 pm

Thanks for the advice, sookwinder, and for the speaker recc, jdr1014!

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