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.

Simplified 5E8a Layout

Discussion in 'Shock Brother's DIY Amps' started by nathanh, Dec 27, 2018.

  1. nathanh

    nathanh Tele-Meister

    Age:
    35
    Posts:
    285
    Joined:
    Oct 13, 2016
    Location:
    Bama
    In the spirit of learning I'm "building" a single input layout for a 5E8a. It seems to me that that unless you have a Y cable you can't just access both sides of V1 or V2 but you could jumper channels. That would be the same as using both sides of one tube, right?

    Im wondering if the two 5U4's have an impact on the sound. Could we just replace these with one 5AR and accomplish the same thing? I'd imagine those two 5U4s sound similar to just using a solid state rectifier.

    Any and all info is welcome!

    I've got a dead HRD that I would love to put this in. I already have a 5F6a and an AB165 (converted the normal channel to an AA864) so I figured this would be a fun circuit to add to the mix.

    conversion kit for Bassman head if interested:

    https://vintagefenderamprepair.com/products/ab165-to-aa864-plus-tweed-preamp-for-blackface-ab165

    Current layout: Im assuming the extra 100k's at the input were mixing resistors so I removed them. The goal is no shift in tone but simplified. What do you guys think?

    5E3 v3.png
     
    Last edited: Dec 28, 2018
  2. Mr Ridesglide

    Mr Ridesglide Friend of Leo's Silver Supporter

    Posts:
    2,152
    Joined:
    Dec 11, 2009
    Location:
    Bloomington, MN
    I've never played through a 5E8a, so perhaps someone else will verify, but IF you build it "stock", you will be able to jumper the two channels together simply by plugging guitar into one channel on the "1" jack, put another shorter cord from 2 on that channel, and put the other end of the shorter cord to the 1 on the second channel. You should be able to get a great blend of both channels that way, much like a Tweed Bassman, Deluxe, Pro, etc...
    I play a 5E5A for most of the gigs that I do, and I use both channels always.
    If you are looking to save real estate and make it a one channel amp, you will lose this capability.
    As for the 5U4's - we'll have to wait for someone else to pipe in for the "feel" aspect of this. The follow up model 5F8A, used a single GZ34 if that will get you where you want for space. 5AR4 and GZ34 are essentially the same tube if I recall correctly; one British, one USA branding.
    To save space on an amp faceplate once, I built an amp with two channels, but only used one input jack each, and put a switch on the amp to "jumper" the two channels. Food for thought -
     
    King Fan likes this.
  3. nathanh

    nathanh Tele-Meister

    Age:
    35
    Posts:
    285
    Joined:
    Oct 13, 2016
    Location:
    Bama
    My thought about the jumper is that on the 5E8a one channel (lo and hi) aren't sharing one half of the triode. For whatever reason they use both sides so channel two has its own tube as well and both sides are used there. So if when you jumper traditionally you're using the entire tube. When you jumper on this circuit, aren't you effectively using 1 half of V1 and one half of V2? So heck, one tube!

    Really interested in the rec solution! Would love to hear your 5E5
     
  4. Wally

    Wally Telefied Ad Free Member

    Posts:
    39,045
    Joined:
    Mar 17, 2003
    Location:
    Lubbock, TX
    If you pull one of the 5U4’s in 5E8A, the amp loses just a little power and gains a bit of sag. I do not know what a single 5AR4/GZ34 would do. WAG is that it would be somewhere between a single 5U4 and the 2x5U4’s. Of course, when you change the rectification in any manner, the voltage and bias changes.
    It looks as if you could use one triode for the bright channel and one triode for the normal channel. If you maintain the shared bypass circuit, that resistor would need to be an 820ohm to maintain the bias on that one tube.
    Re: the tweed Pro.... Mr. Ridesglide has a 5E5A Pro, which is very different from the 5E5. The 5E5 Pro is essentially a 5E3 Deluxe circuit that runs 6L6’s. The 5E5A is a very different circuit from that....With fixed biasing and a more complex preamp/tone section. The 5E5A and the Twin you are thinking of building are more similar to each other than are the two Pros. When you pull one of those 5U4’s from the 5E8A, you are very close to having a 5E5A....or a 5F4 Super or 5E7 Bandmaster since those three are stablemates...with their main differences being OT’s and speakers.
     
    H. Mac and nathanh like this.
  5. Mr Ridesglide

    Mr Ridesglide Friend of Leo's Silver Supporter

    Posts:
    2,152
    Joined:
    Dec 11, 2009
    Location:
    Bloomington, MN
    I was just looking at the schematic and layout for the 5E8A - seems that all four cathodes of the 12AY7 tubes share one 470R Resistor and Bypass Cap.
    Someone around here should know what your options are for this, while keeping true to the amps nature. You're getting out of my league now :)
     
  6. nathanh

    nathanh Tele-Meister

    Age:
    35
    Posts:
    285
    Joined:
    Oct 13, 2016
    Location:
    Bama
    Man its a little outta mine too but it should be fun! Im wondering if the more I compile this thing the more it starts to look like the 5E3 and 5F6a had an ugly baby. I'd imagine the shared cathode would be an 820 if it was just one tube. Fun times.
     
  7. nathanh

    nathanh Tele-Meister

    Age:
    35
    Posts:
    285
    Joined:
    Oct 13, 2016
    Location:
    Bama
    Good info! Thanks a ton.

    I'll get my layout up tonight or tomorrow. Would appreciate any and all opinions, ideas, beer, whatever.
     
  8. nathanh

    nathanh Tele-Meister

    Age:
    35
    Posts:
    285
    Joined:
    Oct 13, 2016
    Location:
    Bama
    Not quite done yet but here's where I landed for the night. I've still gotta fix V1 up and a few loose end.

    Gotta finish the Rec as well. Im surely not the first person to do this but like I said it's pretty fun to do and a great way to get a handle on the circuit.

    On the Recs: Im wondering if putting a weber cap there would be enough power to be equal to 2x 5u4's. Don't they have simulated sag as well?

    5E8a v1.png
     
    Last edited: Dec 27, 2018
  9. Wally

    Wally Telefied Ad Free Member

    Posts:
    39,045
    Joined:
    Mar 17, 2003
    Location:
    Lubbock, TX
    Weber caps come in a variety of types....pure solid state type of thing or emulators of various tube rectifier types.
     
  10. nathanh

    nathanh Tele-Meister

    Age:
    35
    Posts:
    285
    Joined:
    Oct 13, 2016
    Location:
    Bama
    Very true. I'll circle back to Weber. Time to learn some maths.

    Looking at this chart, what numbers should I be paying attention to? My 5F6a uses the 5AR4 so what about this amp requires so much more aside from availability in 1957?

    So which value here am I looking at here? What do I want to stay in the same ball park? Theres not that much difference in the between the 5AR4 and the 5U4-G. I'm wondering if having one less preamp tube will be a deciding factor.

    RectifierTubesVoltageDrop.png
     
  11. nathanh

    nathanh Tele-Meister

    Age:
    35
    Posts:
    285
    Joined:
    Oct 13, 2016
    Location:
    Bama
    Updated:

    5E8a v2.png
     
  12. Wally

    Wally Telefied Ad Free Member

    Posts:
    39,045
    Joined:
    Mar 17, 2003
    Location:
    Lubbock, TX
    Nathan, the 5U4 drops 44 volts while the 5AR4/GZ34 drops only 10 volts...big difference. I do believe that availability was the reason for the use of dual 5U4’s in that 1955 design of the 5E8 Twin and the revision 5ae8A.
    The 5D8 Twin carries two 5Y3’s. Dual rectifiers were used more often in organs and hi-if audio amps than in guitar amps.
     
  13. nathanh

    nathanh Tele-Meister

    Age:
    35
    Posts:
    285
    Joined:
    Oct 13, 2016
    Location:
    Bama
    So this voltage drop. That means if the the PT is pushing out 500v then post rec it's going to be 460v. Correct?

    Would the "Max ACV" be how much it can handle being hit with from the PT or is that how much it can output?

    Dumb questions to some people, but its how I learn :)

    Wally, new layout updated in comment 1.
     
    Last edited: Dec 28, 2018
  14. Wally

    Wally Telefied Ad Free Member

    Posts:
    39,045
    Joined:
    Mar 17, 2003
    Location:
    Lubbock, TX
    A solid state rectifier doesn’t drop any voltage. A tube rectifier drops some voltage with the type of tube determining that drop. There is a formula for a rough estimation of B+ with a solid state rectifier. Search engines are wonderful.
    Also, is that 500 volts on the primary or secondary side??? If on the primary, ime, it is more often thought of as voltage on each leg....250vac. That brings the rough estimate to about 350vdc for the B+.....kind of low for a tweed twin.
    If that is 500vdc on the secondary, that is too high for that Twin...by about 100vdc.
     
  15. nathanh

    nathanh Tele-Meister

    Age:
    35
    Posts:
    285
    Joined:
    Oct 13, 2016
    Location:
    Bama
    Oh that was just a random number have an easy equation to wrap my head around. Theres no actual amp or measurements happening at the moment. Just forcing myself into a thought experiment that will help me understand even more about amps. I clearly am lacking in this region.
     
  16. Snfoilhat

    Snfoilhat Tele-Afflicted

    Age:
    40
    Posts:
    1,396
    Joined:
    Apr 8, 2016
    Location:
    Oakland, CA
    I think this thread needs a schematic. I suggest getting a copy of the original 5e8a and annotating it, either in pencil on your bench or electronically on the thread. You can still use the thoughtful approach but folks in the conversation will have something concrete to refer to.

    Start w/ the power supply. Pick a wall voltage (like 117 VAC or whatever). Write that on the primary side of the power transformer. Then figure out what the secondary voltage is. There a a few ways of reckoning it. Remember it is still AC. Write it out from leg to leg and from leg to center-tap.

    Next tackle the rectification. That will turn AC into DC. Now we get into stuff like max AC and DC voltage drop.

    Then move on to your power tubes. Are you sticking with the vintage 6L6Gs? If so, you'll have a ballpark estimate of how much current they draw which will help you pick a rectifier solution. Also a range of working plate voltages to hit.

    Later when you start choosing real components like a PT, you'll know what the consequences are if any of the values are different from the original Fender 5E8a transformer -- and they probably will be! But you'll be on top of that stuff by then. Good luck!
     
  17. nathanh

    nathanh Tele-Meister

    Age:
    35
    Posts:
    285
    Joined:
    Oct 13, 2016
    Location:
    Bama

    Attached Files:

  18. nathanh

    nathanh Tele-Meister

    Age:
    35
    Posts:
    285
    Joined:
    Oct 13, 2016
    Location:
    Bama
    @Snfoilhat this has been quite the way to expand my knowledge. For my first build I was focused on signal path and how the circuit flowed and didn't pay attention to the power side of things because it was a conversion.

    @Wally I did quite a bit of re-reading.

    Ok what I've learned.

    How to pick a power transformer based on needed HV and current draw for the heaters (both 5v and 6.3).

    Different tube recs have a different multiplier when calculating AC to DC and needs to be considered when designing an amp, not while building.

    Chokes soak up around 10v of B+.

    Each rec has DC Drop. Seems to be an advantage.

    In the case of the 5E8a I was looking at the the dual rec as double the power output when I should have been looking at is as double the reserve. I got very caught up on the B+ being twice as much until I realized its not double the PT, its double the rec.

    I can build this with one 5AR4 or a weber cap equivalent and not change the sound for lower to mid volume but it will be different at higher demands. Im also considering modern voltages will give me a higher b+ and will help offset the one rec even more.

    I'll need to calculate the dropping resistors if I change the b+ so the preamp tubes are hit correctly.

    Let me know if I'm missing anything or if I need to be pointed in other directions!
     
  19. Wally

    Wally Telefied Ad Free Member

    Posts:
    39,045
    Joined:
    Mar 17, 2003
    Location:
    Lubbock, TX
    If I want a tweed amp, I want tweed era voltages. Ommv....
     
  20. nathanh

    nathanh Tele-Meister

    Age:
    35
    Posts:
    285
    Joined:
    Oct 13, 2016
    Location:
    Bama
    Fender in 2019: "yvmv"

    (your voltage may vary) :twisted:
     
    Wally likes this.
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.