1. Win a Broadcaster or one of 3 Teles! The annual Supporting Member Giveaway is on. To enter Click Here. To see all the prizes and full details Click Here. To view the thread about the giveaway Click Here.

Fender amp techs...2 specific questions...

Discussion in 'Amp Central Station' started by LesTele, Nov 10, 2020.

  1. LesTele

    LesTele TDPRI Member

    Age:
    33
    Posts:
    84
    Joined:
    Jun 6, 2020
    Location:
    Richmond, VA
    Hi guys, so I have a Fender Super Reverb Reissue that I love but am needing new tubes for. I just have two quick questions. I think I know the answer to both of them but just want to make sure and check with the pros.

    1) In the pic below, is the hole circled that almost resembles an input jack the designated trim pot for power tube biasing? I think so but just want to make sure before I insert a screw driver in the amp when on.

    2) Also, I know I should get a match pair of 6L6gc power tubes but obviously the preamp and rectifier tubes don't have to match, right?

    You guys are always such a great help. I appreciate your time. As a bonus, if you have any tube recommendations for a SRRI, I'd love to hear it. Are modern tubes really that bad or should I limit to only NOS? thanks!




    SRRI pic.jpg
     
  2. Dacious

    Dacious Poster Extraordinaire

    Posts:
    9,314
    Joined:
    Mar 16, 2003
    Location:
    Godzone
    1. Not sure of, but I didn't think these had a bias pot standard, may have been added.

    2. Correct. Each triode is effectively its own unit in preamps.

    If the amp sounds good and has no problem in sound or operation, there should be no need to change rectifier or preamp tubes. They last decades normally. The only preamp tubes that make a big difference in tone are the first two from the right looking at the back.
     
  3. slider313

    slider313 Tele-Afflicted Silver Supporter

    Posts:
    1,403
    Joined:
    Jan 6, 2011
    Location:
    NC
    Yes, that's the bias pot. You will need a bias probe to determine the current draw, in mA, of the set of 6L6's as that will vary between sets; even of the same brand.
     
  4. LesTele

    LesTele TDPRI Member

    Age:
    33
    Posts:
    84
    Joined:
    Jun 6, 2020
    Location:
    Richmond, VA
    Perfect thanks guys!
     
  5. Wally

    Wally Telefied Ad Free Member

    Posts:
    38,229
    Joined:
    Mar 17, 2003
    Location:
    Lubbock, TX
    Unless you just want to replace all 6 12A-7s there is no need to do that. V1 and V2 make the most difference in the sound because they are the input stages for the two channels. V1 for the Normal and V2 for the Vib channel. V4 has one triode that is a tone processing gain stage for the Vib ch. if you wanted to go for one or more NOS 12A7s of different types to try out in the channel that you actually use, then I say go for it. V3, V5 and V6 are not tone processing tubes. A good 12AT7 in V3, which is the reverb driver, would perhaps be understandable. Some folks like to put a good NOS 12AT7 in the V6 phase inverter position.
    Power tubes....again, If you want to spend some money go for NOS. I do not know that most players would ever hear the difference there. And...the best NOS 6L6 type tubes, which would be the RCA 7581 imho, would cost more than half of what I consider that SRRI to be worth.....if you could find them. Everyone has there thoughts on their favorite modern 6L6. I have good luck with JJs. Ommv.
    Yes, that looks to be the bias pot there.....it is a full sized potentiometer rather than a ‘trim pot’. Do you have a bias meter tht reads current draw and plate voltage? If not, do you have a tech?
     
    Kevin Wolfe likes this.
  6. jhundt

    jhundt Doctor of Teleocity

    Age:
    66
    Posts:
    12,794
    Joined:
    Mar 23, 2003
    Location:
    Netherlands
    you don't really even need a matched pair of output tubes. There are many amp designers/builders/users who find that an imbalance in the output section is not a bad thing.

    All that talk about balanced output tubes is based on the old concept of getting maximum power out of the push-pull design. Maximum power does NOT equal 'best sound'.
     
  7. dogmeat

    dogmeat Friend of Leo's

    Age:
    70
    Posts:
    2,429
    Joined:
    Oct 12, 2017
    Location:
    Alaska
    yeah, and there will be a difference between tube sockets as well so a balanced set will be unbalanced when running. some say that having a difference is where the sweet tones come from. prolly a good idea to check it though
     
    Kevin Wolfe and King-of-Tone like this.
  8. VintageSG

    VintageSG Friend of Leo's Ad Free Member

    Posts:
    4,332
    Joined:
    Mar 31, 2016
    Location:
    Yorkshire
    Balanced output pairs are for Hi-Fi amps. A slight imbalance here and there can make an amp sound rather pleasant. It adds a sort of 3D depth to the sound ( I am no good at wording )
    Bias the to the hottest running valve, plug in, play, enjoy.

    Note that after a few hundred hours, probably less, the balanced pair will no longer be balanced. It's just the nature of things, and that's half the fun.
     
    Jared Purdy, Nickfl and Masmus like this.
  9. J. Bonkosky

    J. Bonkosky Tele-Meister Silver Supporter

    Posts:
    231
    Joined:
    Sep 7, 2014
    Location:
    Seattle Washington
    What brand of power tubes are in the amp now? Did you like the sound? If so just get a matched set of the same brand tubes. You could probably even skip the bias if you take that rout. Good luck.
     
  10. LesTele

    LesTele TDPRI Member

    Age:
    33
    Posts:
    84
    Joined:
    Jun 6, 2020
    Location:
    Richmond, VA
    For all the answers. That was really helpful. Yes, I am in need of a good bias probe. I see one from EuroTubes that sells for $99. I will probably get that.

    I didn’t realize the new output tubes were nearly just as good.I will definitely get something modern then
     
  11. LesTele

    LesTele TDPRI Member

    Age:
    33
    Posts:
    84
    Joined:
    Jun 6, 2020
    Location:
    Richmond, VA

    Thanks Wally! Is the rectifier tube considered an important tone tube that need to be replaced? The amp was made in 2011 so if the preamp tubes and rectifier tube is good I may not change them at all.
     
  12. golfnut

    golfnut Friend of Leo's

    Age:
    60
    Posts:
    2,724
    Joined:
    Jan 15, 2008
    Location:
    Canada
    From what I was told the rectifier tube is good till it doesn't work anymore.
     
    schmee likes this.
  13. Wally

    Wally Telefied Ad Free Member

    Posts:
    38,229
    Joined:
    Mar 17, 2003
    Location:
    Lubbock, TX
    lestele, I personally would have the amp on the bench to take voltage measurements. If the voltages looked good, then I don’t worry about the rectifier too much. And...it would depend on what rectifier is there. I don’t care for Chinese GZ34s. Ommv.
    It looks like you have a 9 year old amp, right?
     
  14. TwoBear

    TwoBear Tele-Meister

    Posts:
    411
    Joined:
    Mar 31, 2020
    Location:
    oc. CA.
    Rectifier tube is there at the beginning to solely change the AC into DC. It basically does what a set of diodes does. it doesn't have anything to do with your tone but then again it does, in that you can change it, in your case I think only down in other words I think it runs a gz34 which is at the top of what the amp was designed for and will put out the most voltage with the least drop.
     
  15. TwoBear

    TwoBear Tele-Meister

    Posts:
    411
    Joined:
    Mar 31, 2020
    Location:
    oc. CA.
    The rectifier tube is there solely to change the AC into DC, and as such performs the same function as a few diodes. it has nothing to do with tone but then again it actually does in the way that by changing it you can lower the voltage to your amp which will slow it down and compress it more. Pretty sure they still come stock with GZ 34, which is pretty much at the top of the Heap for that design in that it puts out the most voltage with the lowest drop and requires the least current to run it. If you wanted to lower the voltage in your amp you could check your power transformer respects to amperage current draw and what it will handle. Off the top of my head I think GZ 34 requires one and a half amps, some of the older less well-designed rectifiers can require two, three, maybe 4 amps. Changing them out used to be a way to mod your amp to lower the voltage and sort of sag it out. The rectifier that it comes designed with is also a soft start design so starting it on standby is not a big deal, it warms up slowly so as not to dump a bunch of power right onto the amplifier.
    And yeah JJ can be great there was also some 6v6s that were new a few years back that were so robust you could slap them in a twin reverb straight with no re-bias, I think they were either JJ or electro harmonix. I had a set of t a d that I got interrupted while I was rebiasing and came back and started up the amp with no negative voltage... They red plated and went on to last me years in my super reverb
     
    Last edited: Nov 10, 2020
  16. LesTele

    LesTele TDPRI Member

    Age:
    33
    Posts:
    84
    Joined:
    Jun 6, 2020
    Location:
    Richmond, VA
    yeah it was made in 2011. What are you thinking
     
  17. LesTele

    LesTele TDPRI Member

    Age:
    33
    Posts:
    84
    Joined:
    Jun 6, 2020
    Location:
    Richmond, VA
    wait, so I could also consider 6v6 as well instead of 6l6?
     
  18. LesTele

    LesTele TDPRI Member

    Age:
    33
    Posts:
    84
    Joined:
    Jun 6, 2020
    Location:
    Richmond, VA
    yeah, it should just be the stock one from the fender factory. So it’s to stay then? When will I know they are dead? I can pull them out. I do know the preamp tubes are jj don’t know if it’s aftermarket or what fender puts in
     
  19. Wally

    Wally Telefied Ad Free Member

    Posts:
    38,229
    Joined:
    Mar 17, 2003
    Location:
    Lubbock, TX
    Lestele, what does this amp do that you like? What is it that you might wish that it would do but does not do? This may be the t8me to question everything, right? LOL.... There are many other changes I would make to this amp before I used 6V6s in it, but there could come a time when I might try some 6V6s. I think JJ6V6s would stand up in there with no problem. NOS will too. I can’t speak to others.
    The amp can be made to be much more versatile with two distinctly different channels, effects on both channels, and a richer sounding output. However, if you have enjoyed the amp as it is, leave it as is other than new power tubes with a good Biasing and perhaps 2 or 3 9-pin changes.
     
  20. JRapp

    JRapp Tele-Holic

    Age:
    63
    Posts:
    594
    Joined:
    May 20, 2019
    Location:
    Phoenix, AZ
    The JJ 6V6S will handle a BF/SF Pro Reverb/Bassman/Super Reverb circuit. How it sounds is entirely another matter.
     
    Wally likes this.
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.