How much headroom should I expect out of my Silverface Vibrolux?

Freedom35

Member
Messages
51
I know this has been discussed a bit, but I have been reading some threads here and wanted to get some input from you all. I have a mid-late 70s Vibrolux Reverb, late enough to have the pull volume knob (which I never use...) I've had it forever, and lately have been using it in a band doing funky, jazzy, R&B and hip hop, with a rather loud drummer. I'm finding myself wanting more clean headroom for rhythm playing.

I haven't played in such a loud group for years, but I don't remember the amp breaking up so early in the past. Plugged into input 2, I can get some breakup with the volume on 4 or 5, and 6 gets downright crunchy if I play hard chords. This is with humbuckers or my tele with the volume up high on the guitar. I am noticing it more and more at gigs, and it's getting to the point where I'm afraid something has gone awry in the amp circuit. Basically anything over 4 and I'm into breakup. Does that sound about right to you all? If this is what's normal, that's fine, I will make some adjustments to my rig, but I'm trying to get a sense of what could be wrong so I can explain myself to the amp tech eventually.

Tonight I spent some time and cleaned all the pots, tube sockets, switches and jacks. I re tensioned the tube sockets as explained here. The power tubes were new about 4 years ago and I swapped some preamp tubes for new ones and nothing changed. I'm still using the stock blue fender label speakers, I believe they're CTS ceramic? My laymen eyes couldn't see any broken or loose solder joints in the chassis, but I didn't probe too much.

Let me know what you all think!
 

MoBigBro

Gold Supporting Member
Messages
1,047
If you need more headroom, the best fix is a pair of very efficient speakers.
I'm guessing that your CTS Ceramics are no more than 96Db sensitivity.
If you put speakers with sensitivity over 100Db in your Vibrolux you will absolutely notice the difference.

I have a 2X10 cab that I play with a BF Bandmaster head (So, quite similar to your SF Vibrolux). I have an Eminence Ragin Cajun and Red Fang Ceramic in the 2X10 and it is really loud and sounds great. The Red Fang is no longer available, but a Ragin' Cajun - Ramrod mix would be similar. If you want more American voicing, try a Ragin' Cajun - Copperhead mix. Or two RCs.

If you're anywhere near where you need to be now (volume wise), this will push you over the top.

Cheers,

MoBigBro
 

smolder

Gold Supporting Member
Messages
14,716
Yah… speakers are the key.

Silverface amps seem to be louder and stronger from the late 70’s… even amps that didn’t go ultralinear.
 

MitchA

Silver Supporting Member
Messages
114
I have the very same amp from the 70's and had breakup at about 5 until I put in Weber 50 watt 10F-150T ceramic speakers. Then it got way louder and less breakup. In fact, I eventually switched to Jupiter 25 watt alnico because I missed the earlier sweet breakup and got tired of soundmen telling me to turn down. I put a set of TAD STR 6L6 tubes which also helped headroom a bit. That SV Vibrolux is no twin and will breakup about 6 no matter what you do but it sounds good to me but its loud at 6! Been a love- hate relationship but mostly love. good luck!
 

Trunkard

Member
Messages
398
Breakup starting anywhere from 3-6 on the volume knob is normal. There can be differences in how the knob is mounted on the pot shaft relative to the actual pot position, not to mention differences in pot tapers.

My first question would be: have the filter caps been changed, and if so how recently?

If the caps under the doghouse are original, they're almost guaranteed to be worn out and need to be replaced. Tired or leaking filter caps will rob an amp of power and headroom, and can make the bass muddy/farty.
 

Freedom35

Member
Messages
51
Thanks for the input everyone! Sounds like what I'm experiencing is normal and my amp doesn't need an immediate visit to the tech.
Buy some late break up power tubes.

I had new power tubes installed about 4 years ago. They are JJ 6L6. Is there a recommendation for cleaner sounding 6L6 types?
I have the very same amp from the 70's and had breakup at about 5 until I put in Weber 50 watt 10F-150T ceramic speakers. Then it got way louder and less breakup. In fact, I eventually switched to Jupiter 25 watt alnico because I missed the earlier sweet breakup and got tired of soundmen telling me to turn down. I put a set of TAD STR 6L6 tubes which also helped headroom a bit. That SV Vibrolux is no twin and will breakup about 6 no matter what you do but it sounds good to me but its loud at 6! Been a love- hate relationship but mostly love. good luck!
Oh it's all love with mine... yes I have been considering speakers.
Breakup starting anywhere from 3-6 on the volume knob is normal. There can be differences in how the knob is mounted on the pot shaft relative to the actual pot position, not to mention differences in pot tapers.

My first question would be: have the filter caps been changed, and if so how recently?

If the caps under the doghouse are original, they're almost guaranteed to be worn out and need to be replaced. Tired or leaking filter caps will rob an amp of power and headroom, and can make the bass muddy/farty.
Good question, I had the tech do filter caps a few years back when he did power tubes. All but one of the preamp tubes are, I believe, original. And I think they'll all fine because I swapped a couple out for new ones and found no difference!

Anyway, it sounds like the Vibrolux is healthy as a horse and I might think about finding some different power tubes and speakers. I have considered speaker swaps in the past but never pulled the trigger. I've got some reading to do!!!
 
Messages
6,445
@Freedom35, what are your tone control settings? When the volume is pushed with BF/SF circuits, the tone controls need to be taken down. I use 5s on the volume and tones as a baseline for Bf/SF circuits. With guitar settings dimed, these amp settings will/should produce lively cleans with any but the hottest guitar pickups if one uses a medium pick attack. If you take the amp volume control higher, the tones need to be lowered.
That said, plus one on high efficiency speakers yielding more volume than any other aspect of an amp….and low efficiency speakers cutting the output more than any other change.
There are a lot of good 10” speakers available.
 

Geetarpicker

Member
Messages
3,170
I couple years ago I restored two 70s era Vibroluxes, and yes somewhere between 4-6 (guitar and player dependent) they will start to breakup. A friend ended up buying one of these 2 amps recently, for use with pedal steel. He immediately swapped out the stock ceramic speakers for 2 new Eminence Ragin Cagun 10s, to get enough headroom for steel. He said the amp wasn’t even useable without the speaker swap. The Ragin Cajuns are one of the most efficient speakers out there, but they are stamped steel frame which keeps them light weight compared to something like JBLs or EVs.
 

MoBigBro

Gold Supporting Member
Messages
1,047
Thanks for the input everyone! Sounds like what I'm experiencing is normal and my amp doesn't need an immediate visit to the tech.


I had new power tubes installed about 4 years ago. They are JJ 6L6. Is there a recommendation for cleaner sounding 6L6 types?

Oh it's all love with mine... yes I have been considering speakers.

Good question, I had the tech do filter caps a few years back when he did power tubes. All but one of the preamp tubes are, I believe, original. And I think they'll all fine because I swapped a couple out for new ones and found no difference!

Anyway, it sounds like the Vibrolux is healthy as a horse and I might think about finding some different power tubes and speakers. I have considered speaker swaps in the past but never pulled the trigger. I've got some reading to do!!!
Just to clarify:
With more efficient speakers, your amp will still be breaking up at 5 or 6 (if that's what it is doing now) but the sound pressure going out your speakers will be louder, which is what you need in a band setting.
If you increase the sensitivity of your speakers from around 95Db to 100Db, that will increase sound pressure (volume) about the same as doubling your amp's wattage.

Changing tubes is not likely to make as much increase as speakers: You are using JJs and those are among the "high headroom" 6L6 Tubes.

In my opinion, a Vibrolux is just about the perfect gigging amp. If you still need more headroom after changing to more efficient speakers, you need to have a chat with your drummer....

Cheers,

MoBigBro
 
Messages
6,445
If you increase the sensitivity of your speakers from around 95Db to 100Db, that will increase sound pressure (volume) about the same as doubling your amp's wattage.

A 6db increase in speaker efficiency will double the apparent volume, ime and as I have read. That increase 8n efficiency would be akin to increasing amplifier output power by a factor of 10. Doubling amp power output is not increasing apparent volume by a factor of 2, even. Maybe more like an increase of 25%??.
 

WillLane

Member
Messages
2,573
I had new power tubes installed about 4 years ago. They are JJ 6L6. Is there a recommendation for cleaner sounding 6L6 types?

Anyway, it sounds like the Vibrolux is healthy as a horse and I might think about finding some different power tubes and speakers. I have considered speaker swaps in the past but never pulled the trigger. I've got some reading to do!!!


I have a '68 Custom Vibrolux Reverb. I'm sure it's not 1:1 to your amp but I bet it's a similar sonic footprint and volume output.

For mine, in input 2 of CH2 with a Telecaster, it doesn't break up until around 6. Equivalent of around 4.5 through input 1 of CH2. With inefficient speakers (95-96dB like your CTS's) it's moderately loud and full at this point, good gigging and monitoring level with a nice touch response.

I've installed Eminence Ragin Cajun's into my amp, 100.5dB sensitivity each. That's around a 8-10dB sensitivity increase total. It turned my amp into a mini Twin; now it's a bit too loud for the average gig; really punchy, percussive, full, round. I'd say this would be your first step.

I like Tung-Sol 6L6GC's. Wasn't a fan of the stock Groove Tubes in my amp which were relabeled JJ's, which is what you have in yours. If you install the 6L6's yourself, be sure the amp is biased correctly; the Vibrolux is not a "plug and play" cathode biased amp if I'm correct. Should be fixed, adjustable biased if it's like my '68 CVR.

While you're there, I'd inspect all the preamp tubes and the rectifier as well. If they're the original tubes, they should be fairly stout but it's possible they're failing and sucking away your headroom. JJ ECC83s is fine, I prefer the ECC803s but you may run into a little mechanical microphonics; generally it's not enough to bother me. This is a good guide on what preamp tubes do what.
 

harvey j

Member
Messages
1,810
I know this has been discussed a bit, but I have been reading some threads here and wanted to get some input from you all. I have a mid-late 70s Vibrolux Reverb, late enough to have the pull volume knob (which I never use...) I've had it forever, and lately have been using it in a band doing funky, jazzy, R&B and hip hop, with a rather loud drummer. I'm finding myself wanting more clean headroom for rhythm playing.

I haven't played in such a loud group for years, but I don't remember the amp breaking up so early in the past. Plugged into input 2, I can get some breakup with the volume on 4 or 5, and 6 gets downright crunchy if I play hard chords. This is with humbuckers or my tele with the volume up high on the guitar. I am noticing it more and more at gigs, and it's getting to the point where I'm afraid something has gone awry in the amp circuit. Basically anything over 4 and I'm into breakup. Does that sound about right to you all? If this is what's normal, that's fine, I will make some adjustments to my rig, but I'm trying to get a sense of what could be wrong so I can explain myself to the amp tech eventually.

Tonight I spent some time and cleaned all the pots, tube sockets, switches and jacks. I re tensioned the tube sockets as explained here. The power tubes were new about 4 years ago and I swapped some preamp tubes for new ones and nothing changed. I'm still using the stock blue fender label speakers, I believe they're CTS ceramic? My laymen eyes couldn't see any broken or loose solder joints in the chassis, but I didn't probe too much.

Let me know what you all think!
A change in speakers would give you more clean headroom.
 

PierreL

Silver Supporting Member
Messages
3,270
I also play funk, jazzy stuff and R&B, in two bands. I use a 1982 SF Vibrolux, basically the same amp as yours, stock speakers.
My amp volume stays on 3 and it’s plenty loud at that point.
My guitars are an ES-330 or a Telecaster, but I never use them with the volume full up on the guitar, which makes a big change.
I also use a 5751 in V2.
Never had a problem with clean headroom with that setting. But my drummers are that loud. I still have to compete with horns in one of the two bands as it’s a big band…
 




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