Fender "Custom" Vibrolux Reverb problem!

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by apgwheeler, Dec 17, 2009.

Am I an idiot?

Poll closed Dec 31, 1969.
  1. Yep.

    3 vote(s)
    13.0%
  2. Nope.

    13 vote(s)
    56.5%
  3. Only a little.

    1 vote(s)
    4.3%
  4. Should have asked a tech in person instead of just TGP and local players

    4 vote(s)
    17.4%
  5. Who cares, this amp sucks anyway.

    4 vote(s)
    17.4%
Multiple votes are allowed.
  1. apgwheeler

    apgwheeler Member

    Messages:
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    Location:
    Albany, NY
    I am probably preaching to the choir here, you guys generally know WAY more than me! But of course, the Fender CVR is a "fixed" bias amp. I don't mess with Power Tubes. But, I do mess with preamp tubes. In the Fender CVR, the valves are
    v1 = channel 1 "Normal" 12AX7
    v2 = channel 2 "bright" 12AX7
    v3 = Reverb 12AT7
    v4 = Gain Stage 12 AX7
    v6 = phase inverter 12 AX7
    v7 = power tube 6L6(gc)
    v8 = power tube 6L6 (gc)

    So, at the recommendation of board members and the local (highy esteemed) guitar shop, I felt it was "OK" to "tube roll" and swap out some tubes in V1, V2, and V4.

    I played around with different configurations, but ended up with
    V1 = Empty (I don't use normal channel)
    V2 = 12AY7
    V4 = 12AT7

    The rest, stock , as described above.

    My goal was "calm down" the amp a bit, get some more headroom, and less breakup. I know, the opposite of most players. Well,this all worked beautifully. Played a gig, great! Tone heaven.

    Then last night, with that configuration, a terrible screech started and Valve 8, the first power tube you see on the left when viewing the back of the amp, was crackling and burning really hot. I mean white hot and blue. I hit the 'standby' switch and almost burned the skin on my finger!!

    Then, I put in a new pair of matched 6L6's, it happened again.

    So, I just dropped it off to my local tech guy. I have not had to use him yet, hope he's good. There's only 2 guys around locally that really deal with this stuff and he's one of them.

    So, did I mess up this amp or break it? Seems "tube rolling" is super common in these amps, don't know why I would have broken it...
     
  2. mark norwine

    mark norwine Member

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    I have no earthly idea what "Tube rolling" is / means, but:

    1.) messing with preamp tubes has zero effect on the power tubes.
    2.) your problem seems to be in the power section and is unrelated to the preamp tubes (see #1, above)
    3.) the power tubes are fixed biased; the preamp tubes are cathode biased. You seem to imply otherwise [or am I misunderstanding?]
    4.) If I could take one guess, I'd say you've lost bias to one or both power tubes. You need to visit your tech.

    EDIT: I voted "NOPE, not an idiot".
     
    Sam Sherry and twangbanger like this.
  3. apgwheeler

    apgwheeler Member

    Messages:
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    Joined:
    Nov 23, 2009
    Location:
    Albany, NY
    Hi Mark,
    You see I am in a bit above my head. Thanks so much for your points. re: your 3.) - I didn't know that. I thought the Preamp AND Power tubes were fixed bias in a "fixed bias" amp. See I've just been getting bits and pieces of info here and there. I guess I better read up a good book on tube amps (reading "The Soul of Tone" - fender Amps, right now as an easy/intro thing).

    Well I'm glad I took it to a tech then.

    I liked the sound of the amp with v1 pulled and a lower gain 12AX7 sub in V2 and V4. I guess if that's a sound I like I should probably tell the tech so he can cathode bias it right...

    thanks a mill! Any book or video suggestions?
     
    Last edited: Dec 17, 2009
  4. mark norwine

    mark norwine Member

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    If you want to understand how tube amps function: "Valve Amplifiers" by Morgan Jones.

    If you want opinions, based on how some people believe tube amps function, there's Weber, Torres, Pitman, et. al.
     
  5. taherbert

    taherbert Member

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    Dec 6, 2009
    Location:
    Durham, NC
    Dave Funk's Tube Amp Workbook is another great read. It also has schematics for all the old Fender amps included.
     
  6. taherbert

    taherbert Member

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    Dec 6, 2009
    Location:
    Durham, NC
    Slang term for substituting tubes en masse to tweak an amp's sound.
     
  7. TweeDLX

    TweeDLX Member

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    Location:
    Port Angeles, Washington
    No need. The bias for the pre-tubes is already set and works on any flavor. 12AY7 will work fine in a slot formerly occupied by a 12AX7, and vice-versa. Any of the 12A_7 types will...

    Mike
     
  8. mbratch

    mbratch Member

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    Another thing to consider is that the Custom Vibrolux does not have negative feedback, whereas the blackface amps do. This will give a looser, a little louder, more presence/bass, and more gainy (more breakup) sound. You could add in a bit of negative feedback and that would tighten up the sound and make it less "gainy". You'd be turning the volume knob up a little more for the same amount of volume, but the sound should be cleaner.
     
    Sam Sherry and twangbanger like this.
  9. Manolian

    Manolian Member

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    Mar 1, 2009
    Location:
    Miami,FL
    My experience with this amp ( bought it new back in '98), has been with the pots and input jack in the normal channel. It had been sitting in storage for a few years ,so when I took it out to play recently ,it was unusable making all sorts of noise and humming like a banshee.
    Ever since it was new I had trouble with the input jack in the normal channel though.
    I took it apart and cleaned all the pots with De-ox-id ,then I re-soldered the input jacks to their small PC boards,and cleaned their contact points, now it sounds beautiful,reverb and vibrato work great , and even the infamous hiss is some what lower,( it still has all original tubes ,and blue alnico speakers made by Eminence).
     
  10. GenoBluzGtr

    GenoBluzGtr Supporting Member

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    Location:
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    I don't understand something. You mentioned that your goal was to ' "calm down" the amp a bit, get some more headroom, and less breakup', but by pulling V1, you're doing just the opposite. Pulling the tube from the unused channel, increases gain, reduces headroom and causes the amp to break up earlier. You are compensating for this by using much lower gain tubes in the other channel. This happens because current that normally is coursing through that unused channel 1 circuit is now being added to the available current for the vibrato channel, and is creating 'hotter' conditions in that channel (earlier breakup, less headroom).

    Try popping a tube back into V1 and ALSO using the lower gain tubes in Channel 2. That will give you much more headroom and less breakup than you have now. Another quandry is that you have a 12AX7 in the Phase Inverter. That should be a 12AT7. Using a 12AT7 in that slot should produce more headroom and less breakup as well.

    Try this... http://www.kcanostubes.com/content/newsletter_details.asp?ArticleID=5
     
  11. rednefceleb

    rednefceleb Member

    Messages:
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    Joined:
    Apr 1, 2009
    I am new to The Gear Page. Hello Gear heads. I was fortunate enough to find a pristine Vibrolux Rev. Custom on E-Bay last week. I got in touch with Brian @ Tube Depot for advice on replacing the tubes. I keep looking for a tube diagram for this amp. I read what the person who started this thread wrote. I was wondering what V-5 is for. He did not list that. Maybe one of you guys will send out the exact tube diagram and purpose for each one. This is one of the best sounding Fender amps I've owned. Thank You.
     
  12. Baxtercat

    Baxtercat Member

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    just west of Monterey, CA
    Good info in this one!
     
  13. Blue_n_Jazz

    Blue_n_Jazz Member

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    Mar 11, 2010
    Actually, These were design and came stock with 12AX7 in the Phase Inverter. Now, I agree that reduce gain here should help. They are not a "reissue" amp that many people mistake. All they have in common with the Vibrolux of old is the name. Thay are a totally different beast. Most people love or hate them.

    I have one that is worn out. Needs new tubes in a bad way. Mine came with Jensen P10R. The first time I heard one it had the Eminence. Emi are much much better tonally. I put Rajin Cajun in her. Needing tubes, not sure if I made the right decision. We shall see..............
     
    Last edited: Sep 22, 2011
  14. phsyconoodler

    phsyconoodler Member

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    Location:
    calgary canada
    Well I had one of those amps and they don't respond kindly to having v1 removed.They share plate resistors and when you pull out v1 it makes v2 unstable and can cause all kinds of issues like oscillations.
    When Fender did this amp they simply took a Vibroverb PC board and took away some components and added others.One is the negative feedback.
    Then they added reverb to both channels.
    When you remove v1 it removes again stage and changes the relationship of the rest of the amp to the phase inverter.
    Even if you use just a lower gain tube in v2 it upsets the balance caused by the shared plate resistor and sometimes the amp won't make any sound at all.
    To get the amp to really work properly and get all the headroom you want and a better reverb,I suggest doing the Moyer Mods which essentially returns the amp to being a Vibroverb,a far superior sounding amp IMHO.

    TweedDLX said:"12AY7 will work fine in a slot formerly occupied by a 12AX7, and vice-versa. Any of the 12A_7 types will..."

    Not so in the Custom Vibrolux as it's not even close to an AB763 circuit.It won't work properly.
     
  15. Blue_n_Jazz

    Blue_n_Jazz Member

    Messages:
    195
    Joined:
    Mar 11, 2010
    I tried putting a 12AU7 in V1, no sound. Its a funny beast. I like the heart of the beast. It could use some tweaking. Verb is could but could be better. Love the Vibrato. Warms my heart. All in all, good amp. Get a used one, tweak it with the Moyer or Frommel mod, and its a killer amp.
     
  16. David16

    David16 Member

    Messages:
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    Mar 30, 2013
    Location:
    Santa Maria, CA
    I was searching for some information on my 2007 Custom Vibrolux Reverb Reissue and found your's dated back in 2009. I've always was told that if I change out the power tubes in this amp that I had to be sure to bias the power tubes by using the bias pot to ensure the tubes were not running too cold or too hot. IS THIS NOT TRUE??? By what I read in this write up, it sounds like there is no bias pot and no adjustment is needed. Also, I was thinking of going the the Tung sol power tubes, and changing the speakers to two Celestion Gold 10's or the Eminence Legend 1058's . Have you any experience or comments on either of the tubes or the speakers. Does anyone who might read this have comments.
     
  17. Sam Sherry

    Sam Sherry Supporting Member

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    Location:
    Portland ME
    Do you "have to?" Let's take this step by step:

    1) Fender hard-wires the factory bias lower than some people like it. They do that not so much for sonic reasons as to keep tubes from red-plating no matter what you toss in. The interwebz says, "You Shall Like 70%" but that's not the law of gravity. There are a gazillion recordings made on Fender amps with the factory-stock bias and people often call that sound 'iconic' until they find out that the interwebz 70% Rule has been flouted (again).

    2) It is extraordinarily unlikely that a properly-functioning modern power tube will red-plate with the Fender factory setting. Based on that fact, you do not "have to" rebias when you put new properly-functioning modern power tubes in an unmolested Custom Vibrolux Reverb.

    3) But like many people you might find that you like the sound of your CVR at a different bias setting than the Fender stock setting. Or you might want to try some odd piece of old glass. Or you might just be very unlucky. That's why it is best practice to check your bias when you change power tubes.

    I've got modern Tung Sol 6L6s running one of my amps and they sound fine. It's parallel single-ended so they're running pretty hot, and they're taking it steady.

    For me changing speakers has a lot more sonic effect than changing power tubes. IME once the band kicks in the sonic difference between brands of properly-functioning modern power tubes is marginal. That last bit is counter to TGP and the interwebz generally, so a lot of people think I'm dead wrong.
     
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