Blackfacing a silverface Fender Vibrolux Reverb

[KirkP]

Have you tried different speakers? To avoid the trouble of removing and installing speakers I’ll sometimes plug the output of an amp in one cabinet to the speakers in another.
And if there’s another amp that you do like, you could try plugging it into the speakers in your VR cab to see if they are the problem.

[Little Jay]

What tone are you after? What is the amp lacking or what’s it doing too much?

The scooped Fender tone stack can leave something to be desired.....on of the best mods for SF and BF Fenders is to replace the 10k mid pot with a 25k pot (or if there’s no mid pot: put a higher value mid resistor of 15-20-25k). Then you dial in more mids and get more ‘wood’ in your tone.

Speakers are effective filters and can alter the tone of an amp substantially. You can try different speakers as KirkP suggests.

[KirkP]

I haven’t gone through it thoroughly, but this site seems like one of the better ones for info on AB763 mods. I’ve been considering a couple of minor fixes or mods to my amps, so this might help me decide.
AB763 Mods

[jpb]

Yes, I tested several speakers (original Oxfords, Lil Buddy; Warehouse G10C; Copperheads). Also different (brands) pre-amp tubes (12ax7, 5751, 12AY7). I prefer input 1, bright switch down for jazz. My preference of tone knobs is unvariably treble & bass ca 5, never much lower.

[sgosnell]

That tone setting doesn't sound good to me. On a Fender, I prefer treble all the way off, and bass up maybe 1 or 2. All the way off is flat on a Fender, and slightly increasing the bass actually reduces treble. If you're looking for a jazz tone, I suggest starting with the tone controls all the way off, and using the second input. On my VR, I also often use the reverb channel and remove the V1 tube, which is the preamp tube for the first channel. I prefer the sound of the reverb channel, with the reverb set to 2 or less. If you do want to use channel 1, try removing V2, which is the preamp tube for the reverb channel. This increases power to the other preamp circuit, giving a slightly thicker tone. It will not harm the amp in any way. This is the only way I can stand my VR. It still doesn't sound as good to me as my AI/RE combo, but it gets it into the ballpark. With the tone controls at midrange it sounds terrible. Putting the tone controls at 5 on a Fender is not a neutral setting, that's at zero (or 1 on the VR, which is the lowest number on the knobs). Fender's tone stack is not intuitive, and different from most other amps.

[KirkP]

For Fender amps I’ll usually start with treble and bass set near the minimum and mid fairly high, since this is where the tone stack’s frequency response is closest to flat. I’ll first adjust the amp’s volume knob, then I’ll bring the bass and treble up just enough to please me. Where they end up depend on the speaker, cabinet, acoustics of the room, the guitar, and the other instruments in the band, etc. Since adopting this method I’ve been much happier with my tone.

I also start with the volume knob on the guitar about half way down, raising the amp knob on the amp accordingly. There was a thread about that a while ago. The frequency response of magnetic pups vary with the guitar’s volume pot setting and are usually flatter when the pot is turned down a bit.

[jpb]

Today something strage happened: I took my VR and jazz box to the local music store to try my guitar on some other fender amps and to try other jazz boxes on my VR. But after pluggin in the my VR and my guitar all sounded fine; I could even dial the treble and bass to zero without complete sacrifice of my tone. Everything seemed better in balance.

At home I took a long power cable and plugged everything in a different power group and I had the same better tone as in the music store ealier today. Also, my other Fender amps an DV Mark Micro 50 sounded better and more in balance too. So, closer to home I guess :-) but still thinking on why different earthed power groups had such different results in tone. At least I live in a very old house, if that makes sense...

Tomorrow I take the VR to a session. I haven't gigged with it yet after the return from my tech so I hope everything is also better now at the session. Tomorrow's where the rubber meets the road; I'll let you know.

[Greentone]

jpb,

I have lived in old homes (I currently live in an old log home, in fact), and I have experienced this. My music room as it happens, is right above my workshop. Ugh! There is lots of florescent lighting in the shop. In a log home, the floor of one story is the ceiling of the story below--with no insulation, etc. So, the lighting is directly adjacent to the flooring of my music room. The amp sits directly on top of a florescent fixture. Aagghh!

Also, in an old home the grounding can be a bit dodgy in certain areas of the house. Add it all up and your amp can sound crappy in one location, better in another room. No big deal. I can always move. However, if I want to play along with the B3 or the piano...

[wsp]

The SF Vibrolux was optimized over the years for a later breakup and more headroom. If the amp is too clean there are some options: changing speakers (my SF VR had ceramics and I changed it to Alnicos Jensen P10q/r) or changing main power (export models). A typical SF sound is obtained at 220v, to get a blackface-type sound with earlier breakup you should select 240 or 245 V. Very easy "brown" mod (think variac) without any soldering job. Very easy, very quick, no risk!

[KirkP]

Today something strage happened: I took my VR and jazz box to the local music store to try my guitar on some other fender amps and to try other jazz boxes on my VR. But after pluggin in the my VR and my guitar all sounded fine; I could even dial the treble and bass to zero without complete sacrifice of my tone. Everything seemed better in balance.

At home I took a long power cable and plugged everything in a different power group and I had the same better tone as in the music store ealier today. Also, my other Fender amps an DV Mark Micro 50 sounded better and more in balance too. So, closer to home I guess :-) but still thinking on why different earthed power groups had such different results in tone. At least I live in a very old house, if that makes sense...

Tomorrow I take the VR to a session. I haven't gigged with it yet after the return from my tech so I hope everything is also better now at the session. Tomorrow's where the rubber meets the road; I'll let you know.

Were you in the same room? Acoustics can make a huge difference.
Seems unlikely, but could you have a voltage drop in one house circuit? A voltmeter set to AC would tell you. If so, could be a fire hazard.

[jpb]

KirkP, yes I kept the amp in the same place when changing the current group. Change was dramatic in the good sense. Ik could not measure any voltage difference in the AC mains wall sockets between the two groups (225V).

My amp tech did put the voltage switch on 240 and he explained why but I cannot recall his motivation for that.

Until I changed power groups, the sound of my amps changed from day to day, driving me crazy. Sometimes good enough, most of the times not too good. I thought it was my ears or something. Since I plugged my amp in the other power group, the sound is not only much better, but also stable. Nothing wrong with my VR is my conclusion. I'm glad
Greentone, the power group I played over before yesterday goes also out to a shed and my greenhouse with plant lamps etc. so one can assume that it is not a good thing for providing the correct current for an amp? I had some problems with this group in the past. I should have known earlier, damn!!

Thanks again for your kind contributions. It really helps.