What Should Gene Build?

Discussion in 'Shock Brother's DIY Amps' started by The Ballzz, Jan 17, 2020.

  1. The Ballzz

    The Ballzz Tele-Afflicted

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    I'm considering a 5F8-A-ish build, but with using a 5E3 power section and adding a presence as per 5E4. I am however intrigued by the preamp of the 5E8-A, with the ability to use two full triodes in parallel for each channel and then even find a way to properly "jumper" the two channels! :eek: I really don't need more power/headroom, as I end up needing to attenuate my 5E3 by -7db most of the time anyway.

    See, here's what I got to work with (from a previous 6AQ5 build that I wasn't fond of), without buying anything, 'cept maybe a few caps/resistors:
    > Marshall style chassis from Modulus, with up to seven pot holes, if using only two jack holes and six pot holes, if using all four jack holes. It's punched for three novals and four octals, along with plenty of space for another noval, if desired.
    > ClassicTone 40-18085 power transformer
    > MPS OT20PP output transformer​
    My 5E3 is bone stock, except for a passive effects loop, it sounds amazing and does almost everything I want it to. I'm just looking to get a tiny bit more control over the shaping the mid range color. I regularly alternate between the members of the Holy Trinity of Strat/Tele Les Paul and have them all dialed in to coexist in the same amp setting universe, allowing each to shine its own special light! I'm an echo junkie and the loop has really liberated my Tweed life! I also love building and experimenting with amps!

    All Thoughts Appreciated!
    Gene
     
  2. Wally

    Wally Telefied Ad Free Member

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    How about a 5E7 with a 6V6 output section? Put a switch to OT from cathode to fixed biased? the 5E7 is my favorite tweed amp. The 5E7 is very similar to the 5E8A...especially if you pull one rectifier from the Twin. However, the Bandmaster has some different values in the feedback that make it ‘sing’ in a different manner than do its stablemates.....5E5A Pro, 5F4 Super, and that Lo-power Twin.
     
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  3. The Ballzz

    The Ballzz Tele-Afflicted

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    @Wally
    Funny that you mention this. It seems that if I lay it out right (I use turrets boards for my builds), I should be able to easily try all of the amps you listed by simply swapping in/out a component and/or jumper here and there? Yes, I realize this could all likely get set up to be "switchable" but I don't see the need for that operational complication. Once I find what I want, it will stay that way!

    There is the other consideration of the additional triodes in the input stages of the 5E8-A and what actually might be gained by judicious use of them. Though I may have missed a model, it appears that the 5E8-A and 5D8 Twins are unique in having two triodes in each channel's input section, with no 68K grid stoppers and still having a cathode follower/driver. Th 5E8-A is even more unique again by having "local feedback" surrounding said cathode follower/driver. This brings up the discussion and questions of "Black Magic/Voo-Doo" the next paragraph!

    The terms "negative feedback" and "local feedback" are often referred to and bandied about, but rarely discussed in a truly quantitative and qualitative manner. They seem to be the dark, secret science behind making a good amp become really great! While I kinda get what they do and seem to catch on that they are the true "cherry on top" of the sundae of a great sounding amp, it seems difficult to find details about the hows and whys of it's effective use. While we have tools like the Duncan TSC for graphic illustration of how tone controls and the various involved components work and interact, this does not seem to be the case for feedback and its components and usage. It almost makes me think that there is some special secret club and/or handshake required to glean such knowledge and expertise? Some discussions I've encountered seem to indicate that specific feedback use may or can have as much, if not more, impact on the final tone, response and performance of an amp than the topography of it's main components! You've made comments in other threads concerning how identical the 5E7, 5E5-A and 5F4 are, except for their "local feedback" treatment. This has helped confirm and fuel my suspicion of the importance of understanding the role this whole "feedback" phenomenon plays in amp design!

    And as may be obvious, the more of my questions that get answered, the more confused I get!

    I Want To Get It! I Yearn To Understand!
    Gene
     
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  4. Wally

    Wally Telefied Ad Free Member

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    Gene, looking at it, the 5E8A and the 5E7 are more similar than not, aren’t they. I have owned both. The 5E8A with two rectifiers is stouter.....the Bandmaster sings earlier and with more overdrive when pushed. Switching one of those rectifiers in the 5E8A would put it in the 5E7 camp, it seems. in my limited understanding, there might be a good reason for those input grid resistors. Iirc, Fender even added some 10Ks there i; the 5E7 RI. They added 1.5K’s to the grids of the 5E8A RI.
     
  5. The Ballzz

    The Ballzz Tele-Afflicted

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    Hey @Wally
    I kinda don't see the "more similar than not" thing here, unless you've got different versions of the schematics? As mentioned, the 5E8-A TWIN has two more triodes in the input stage of each channel and no 68K grid stoppers. Not intending to argue, simply endeavoring to understand. It seems that the 5E7's two channels equate to being more like just one channel of the 5E8-A, kinda/sorta? They certainly are fairly identical past the two volume pots though! And of course, the whole power supply "thing."

    Thanks A Bunch, Again!
    Gene
    Bandmaster-5E7-Schematic.jpg Twin-5E8-A-Schematic.jpg
     
  6. Wally

    Wally Telefied Ad Free Member

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    Gene, I see the differences prior to the first preamp stage. I am not too sure exactly how big of a practical difference there is, though. From the input grids of those input preamp stages, they are very similar. I do know which one prefer, though, if one uses the two amps as they are designed. I owned two ‘59 Bandmasters and a ‘56 5E8A Twin at the same time. The Bandmasters are without a doubt my favorite tweed. This is out of a fair,line of owned amps....5B5,5C5,5E5A,5F6A,5E3,5F1 in addition to the three I mention above. I have worked on a ‘49 Deluxe, a ‘53 Deluxe, a ‘54 5D6 Bassman, late ‘50’s Vibrolux and Tremolux. Although I remember all of these, the Bandmaster is the one that sticks in my tone memory most of all. I should have kept the least valuable one. Oh well.....I do have a ‘56 5E5A chassis that is empty.....all that was left from a fire. Wonderful patina!
    Good luck with the decision....and there is no way you could make a bad choice, ime.
     
  7. Wally

    Wally Telefied Ad Free Member

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    How about this, use four 12A-7’s but build both of those input circuits. You would have the two Bandmaster inputs and half the number of the Twin inputs. .??????
     
  8. The Ballzz

    The Ballzz Tele-Afflicted

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    @Wally
    That right there is an insightful (or is that "inciteful;)") suggestion! A slight modification of that idea, but with all else being equal, I could leave a few extra, open turrets and try it full blown, both ways. Also a piece of cake to experiment with local feedback values. Then, if I decide to like the Bandmaster better, removing the extra tube from the circuit would be fairly simple. Unless of course I decide to use those extra two triodes as some cascaded stages "ala" a LANEY AOR style fire breather!:p

    FWIW, I happen to have one of those "LANEY AOR PRO TUBE 100" amps, eight knob version, that I stole for pennies from a garage sale. It's an amazing monster thats fully capable of hot rodded JCM800 sounds, as well as other Marshall-esque stuff, while still giving up some fairly authentic VOX and Black Face Fender stuff. The most amazingly monstrous thing about it is that so much of the character and tone is developed in the preamp that the pre phase inverter master actually brings/tames the volume down without losing any of the tonal character. I'd actually love to use it regularly, but at 100 EL34 watts and nearly 60 pounds as just the head, it's simply impractical in this old fart's world, :( :cry: even though the volume is tameable!

    Thanx 4 All Your Thoughts Wally!:cool:
    Gene
     
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  9. The Ballzz

    The Ballzz Tele-Afflicted

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    Well @Wally ,
    While I'd rather not jump through all the hoops of adding the extra tube for the 5E8-8, just to "test" it's viability, I also don't want to miss out on something really cool, if valid. In hopes that someone already has tried what I'm thinking of, I'll post the same observations and questions I did over at the Amp Garage. They only pertain to the areas circled in red in the schematics above. I already know what I want to do for the rest of the amp.:

    "It appears that in the 5E8-A, when plugged into input #1 of either channel, it drives/feeds both triodes of that channel, in parallel and plugging into #2 drives/feeds only one triode of that channel? The are no grid stoppers, although input #1 appears to see a 500K to ground input/grid leak resistor and input #2 "sees" a 1MEG input/grid leak. I do also note the additional 100K "mixing" at the output of the first triodes on the 5E8-A that do not exist on the 5F8.

    With the 5F8, there is only one triode for each channel and input #1 "sees" a 34K grid stop, along with its 1MEG input/grid leak resistor and input #2 "sees" a 68K-ish grid stop and it's kinda voltage divider with the other 68K and 1MEG in series to ground.

    Am I reading and deciphering the above correctly, at least loosely?

    We are all aware of the mixed results of "jumpering" the 5F8 style input triodes in parallel. My questions and proposed discussion surround the possible benefits and/or pitfalls of combining the two dual parallel triode channels together, in parallel, with their separate volume controls, etc. Now I realize that a simple cable jumper won't work here, but a switch or hardwiring could. Is there any real benefit or am I just piddlin' in the wind?"


    Thanks To All,
    Gene
     
  10. JuneauMike

    JuneauMike Friend of Leo's

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    I wish we had more VOX builds. FWIW.
     
  11. Wally

    Wally Telefied Ad Free Member

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    Okay...dense I was being. I see what you are thinking, and you maybe correct about those two triodes being at work when running through input #1 of the 5E8A Twin. I have to admit that I was greener Back in the early ‘90’s when I owned that 5E8A, and I never took notice of that. I never once plugged into #2 input just out of curiosity, and my tech back then never illuminated that spect to me....if indeed it was noticeable in its effect. i don’t know how much if any gain is achieved by runn8ng both triodes in parallel.
    it appears that the 5E8A was the last of the Fenders to run that type of input circuit. All others had left that behind in 1955. They had adopted the 68K input grid stoppers in addition to the 1m grid leak. I suppose people were tired of radio signal interference??.
     
  12. The Ballzz

    The Ballzz Tele-Afflicted

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    Ya know @JuneauMike , throughout my many years, I've heard some the most amazing and pleasing sounds coming through VOX amps, but have never had the time with one to even come close to mastering the capture of any of them! It's always been a toggle between various Marshalls and Fenders, which are a lot more similar to each other than most folks want to admit! :rolleyes:

    I really do appreciate your comment, as well as your extremely insightful words in the "suggested reading" thread. I've always wished for a tutorial that equates to saddling up and riding on a guitar upon a journey from the input jack to the speaker, along with the opportunity to pause at various spots to view, absorb and understand the tasks being performed by each component! :D What a cool video that could be!

    Thank You Sir!
    Gene
     
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  13. JuneauMike

    JuneauMike Friend of Leo's

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    Yeah, Vox schematics give me a headache. There has to be a less British way of getting that British sound. Maybe that's why Matchless exists?
     
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  14. The Ballzz

    The Ballzz Tele-Afflicted

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    Hey @Wally my friend,
    To address the last part first. Notice that the subsequent designs utilized one less tube and add in the factor of Leo's "frugality" and there ya go! :rolleyes:

    My thought was surrounding actually ending up with the signal running through "FOUR" triodes, in parallel, prior to the driver/cathode follower. Not necessarily for gain "per se" but instead for dynamic intensity and tonal complexity. Of course then, I have some really cool stacked, dual concentric, 1MEG pots that could easily facilitate putting a pot on the output of each of the four triodes for some really bizarre insanity! :eek: Just wondering if anyone has tried it and/or if it is simply an exercise in futility! If I can't find any "experienced" answers in the next few days, I'm just gonna have to go ahead and do it! o_O

    Thanks Again For Playing Along!:cool:
    Gene
     
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  15. Wally

    Wally Telefied Ad Free Member

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    Build the Bright/Normal channel...leading out the Trem side....of a Top Boost Ac 30 and you have something very similar to a cathode-biased 4XEL-84 take on a 5F6A Bassman/5F8A Twin. Two gain stages prior to a cathode driver feeding the tone stack into a PTP phase inverter. I have read that Vox, like Marshall????, took their clue from Fender on this when they built the Top Boost addition to the first AC30.....which made do with a single gain stage prior to the phase inverter.
    Put a Pro Sonic into cathode bias and it will ‘jangle’ with the best of them.
     
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  16. The Ballzz

    The Ballzz Tele-Afflicted

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    Yeah, well then there's also that whole EL84 thing that simply hurts my ears if everything is not absolutely perfect!:p

    Just Sayin'
    Gene
     
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  17. Wally

    Wally Telefied Ad Free Member

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    Gene, I enjoy tonal complexity. I don’t know how much there would there, but I wish you success with the venture. as for El-84 tubes......imho and ime, it is the circuit and not the tube that has more to say about what comes out of the speaker.
     
  18. JuneauMike

    JuneauMike Friend of Leo's

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    Indeed. I sorta suspect that plate voltage is the critical thing there. But what do I know:

     
    Last edited: Jan 24, 2020
  19. The Ballzz

    The Ballzz Tele-Afflicted

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    @Wally
    You and a few others keep hammering on this ProSonic! o_O Up until a couple weeks ago, I never evn knew such a thing existed and now I'm getting a very severe case of GAS. The more I research the more it seems like the perfect amp for me, even though way more power that the 5 to 10 watts I actually need. I need to ask: "Can it actually do the Marshall side of the Tweed thing, or is it more Black Face in it's overall character?" Just saw a head version for $800? And it even has an effects loop! God Help Me!

    Got GAS! Must Resist?
    Gene
     
    Last edited: Jan 24, 2020
  20. johnDH

    johnDH Tele-Meister

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    Hi Gene, great project! I've got two thoughts: (and I'm just speculating, I've never built a tube amp)

    Would if be useful to you to be able to combine different cabs, maybe with different ohms ratings? If so, a full set of output taps direct to sockets can do that, 16, 2x8, 2x4. Plug a 16 cab to an 8 tap and a 8 cab to a 4 tap. You get even power share and no mismatch on the OT. (but would need two attenuators!)

    Vox amps secret is not only the el84's but also they have no NFB. This means that at small signals, they have a very high output impedance, which squishes down lower impedance as it's driven. This flattens the frequency response as you push hard, changing dynamically with volume. As NFB is added, there's less difference, as in most Marshall and Fender, changing the response. I have one Marshall with a Vox-ish output circuit, and at it's best it's very clear and dynamic.

    What I don't know is how to adjust a power stage to remove NFB as an option, and then compensate for what ever else that then requires to keep it working rightly.
     
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