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New adventures in 5E3

Discussion in 'Shock Brother's DIY Amps' started by theprofessor, Jan 11, 2018.

  1. theprofessor

    theprofessor Friend of Leo's

    Aug 8, 2016
    Chattanooga, TN

  2. theprofessor

    theprofessor Friend of Leo's

    Aug 8, 2016
    Chattanooga, TN
    Some findings. I took some measurements using the voltages I have now and the tubes that are in there. Today I've got;

    B+1: 384
    B+2: 344
    B+3: 252

    My Tung-Sol (Motorola label) is running at about 346pv and 40mA, meaning dissipating about 13.84W
    My Tung-Sol (Delco label) is running at about 346pv and 39.7mA, dissipating about exactly the same thing.

    One thing this tells me is that I have a very good matched pair of 6V6's, at least in terms of dissipation on the plates. I'm not going to change the common cathode resistor to the 6V6's until I get all the voltages down where I want them and see where things are then.

    Later this evening, I'm going to mount in two/ 13V zeners, which should drop around 22-24 volts. That should get me right at 360 or thereabouts. More on that later.

    Here she is in service:

    IMG_9975.JPG
     
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  3. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    Good on ya, Professor. Even before I tried jumper-ing, it took me a *really long* time to figure out the volume (and tone) controls on the 5e3. You always seem extremely well-read, so you've probably seen this. Setting aside the ABY, I like the "here's what will happen" settings for single-channel play. When not switching most folks just say 'active' and 'inactive' channel knobs.

    from Gerald Weber:

    Let’s look at another example, the tweed Deluxe. This amp is very unique because the volume controls are not voltage dividers!! Did you ever wonder why all tweed Deluxes seem to have an audio pot with too fast a taper? The volume control in a tweed Deluxe works by “loading down” the signal coming from the plates of the preamp tubes!

    If you are plugged into the instrument channel, the signal goes backwards through the microphone channel’s volume pot, through the microphone channel’s coupling cap, plate resistor, and filter cap to ground. You will get maximum mids in the instrument channel with the microphone channel’s volume control turned about halfway up. You will get a maximum midrange scoop with the microphone channel’s volume control turned full up. This would work the same if you switched channels and were plugged into the microphone channel and adjusting the instrument channel’s volume.

    This can be used to your advantage, especially if you have an A/B box. Set the normal channel all the way up and the instrument channel halfway up. Use an A/B box to select between the microphone and instrument channels.

    Here’s what will happen: When you select the instrument channel, you will get a fabulous clean tone. Since the instrument volume is turned halfway, you are not really overdriving the instrument channel that hard and since the microphone’s volume control is turned full up, you are scooping out the mids in the instrument channel. This gives you that “better than blackface Twin” clean tone-to die for.

    When you select the microphone channel (which is turned all the way up), you will get a fabulous lead tone. For one thing, you will be overdriving the output stage and because the instrument channel is halfway up, you will be boosting the mids as much as possible. This results in a thick, creamy, cello-like tone with incredible sustain.

    Of course, there are many other settings between the two extremes described earlier that will give very usable tones. This is where experimentation with your guitar, your playing style and listening will reveal the possibilities.​

    Sidebar: I always had trouble remembering that Instrument = Bright, Mic = Normal until I decided that M and N are next together in the alphabet.

    If you're a total glutton for punishment, I once tried to write a synopsis (not Cliff Notes, professors hate those) of the 32-minute Speed Shop video on 5e3 controls. I left out a lot of what Rondo says, trying to focus on the knobs. To add to the complexity, I'll list in parentheses the comments my amp-sensei brother added. Yeah, long and complicated!!! In my defense:

    A. It still doesn't take 32 minutes to read :D
    B. The two items I think are least obvious and most useful are #11 and 12

    1. Tone control is defeated as you max the volume on the active channel (the treble bypass side of the tone control is equalized out; it still works to bleed treble to ground when turned below about 5 on the dial, regardless of volume level)
    2. Tone control actually gets less bright from about 9 to 12 (only on the normal channel, where there is a little "ghost" tone control from the flowback through the normal channel; on the bright channel, it gets brighter all the way up, as long as the volume control isn't maxed out)
    3. Tone control acts as a gain / drive dial by giving more signal spectrum as treble is boosted
    4. The bright cap on Bright channel is also defeated as you max active volume (exactly as in #1)
    5. As a result, volume boost on Bright channel is also a bass boost (not technically -- it just reduces the treble loss that would occur through the volume pot's resistance without the bright cap)
    6. Active Volume 2 to 6 gives most of the volume change. (With some pots, it’s from 1 - 3, with small increase in volume above 3, but mostly more drive. This also means there is a ton of tonal variation between 1 and 3.)
    7. Volume 6 to 11 adds mostly distortion and sustain / compression
    8. Volume 11 to 12 adds mostly sag and bloom
    9. Maxing the inactive channel at 11–12 attenuates the active channel (this starts about 9-10 on the dial)
    10. Maxed active and inactive can give a tidier max distortion with more touch and tone control.
    11. Tweed cleans can be had with inactive ~ 6 and active ~ 2; try varying inactive. (I find the best tweed cleans at about 2 -3, tone about 6.5 -7, inactive channel off or at about the same setting as active.)
    12. Another clean area is inactive at 12 and active at ~8 — try varying active. (I get unpleasant levels of background noise with inactive anywhere above about 10 -10.5, and a muffling of the tone)
    13. You can use the tone control more easily in this area (YMMV here also)
    14. After you get a feel for the bright channel, try the normal/mic channel
    15. After you figure that out, compare your guitar’s pickups on the 2 channels
    16. After you figure that out, try out your other guitars the same way
    17. Now, try jumpering input 2 of the active channel to input 1 of the inactive. (Jumpered operation deserves many of the above variants. In particular, it allows lots of interesting blending of the two channels, as well as selecting either one alone, just by turning the volume knobs. Lots of good stuff between 1 and 3 here. And it really cranks the drive, cut and juiciness of the overdrive.)
     
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  4. Phrygian77

    Phrygian77 Tele-Holic

    820
    Apr 30, 2016
    Crawfordville, FL
    What 5Y3 are you using?
     

  5. Phrygian77

    Phrygian77 Tele-Holic

    820
    Apr 30, 2016
    Crawfordville, FL
    Never mind, I see where you posted the tubes about an hour ago.
     

  6. theprofessor

    theprofessor Friend of Leo's

    Aug 8, 2016
    Chattanooga, TN
    @King Fan ! I'm going to thank you for your magnificent post once I've read it so I can thank you more specifically. I got the zeners in.

    IMG_9976.JPG

    Here's the story: The line voltage here right now is 123.9AC, which is the highest I've ever measured it, I think. With the two, 13V (5W) zeners, my voltage now is as follows:

    B+1: 362V (a drop of 22 volts from the previous 384)
    B+2: 323V
    B+3: 236V


    The 6V6's are running now at about 330 pv and 37.3 mA. That's means they're dissipating about 12.3W--perfect! Now I can try out different flavors of 6V6's and see how they sound and how hot they run in the circuit.

    I think that 362V is great. And if the line goes down a bit, it will drop even lower. My goal was 350V-360V, so I'm going to say I hit it. With the drop of 22V, the sound is not as thick and fat. It is clearer and less clouded. Of course it thickens up as you turn up the dial, and I can always jumper channels for thickness, too. In my experiences, voltages on the lower side of the acceptable spectrum for a particular amp really sound better to my ears. The exception (of course) is a SF Deluxe Reverb, which puts about 120-130V more on the plates of the 6V6's than this 5e3 does!
     
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  7. JuneauMike

    JuneauMike Tele-Afflicted

    May 5, 2015
    Alaska
    Professor, can you talk about your zener string a bit. I wondered whether zeners gave you a 1 to 1 drop in voltages based on the value of the diode. It appears you got about 85% of the value (26v = 22v drop). I think robs website suggested a 10v 5w zener gets you 9 volts (90% close enough).

    Is there a formula to this? And does it change with the value of the zener (10v 5w vs. 25v 5w)?
     

  8. RLee77

    RLee77 Friend of Leo's

    May 15, 2016
    Silicon Valley
    Zeners are rated as a specific voltage @ a specific current. If you run them at lower current, the voltage will be lower. Some spec sheets show the plot of Vz vs Iz. It's probably around a 10 to 15% variance for common zeners, depending on how far off of the rated current you run them.

    I was wondering recently why it seems to be common practice to put zeners in the CT ground lead, rather than just putting them in series with the B+ connection to the first filter cap... then it occurred to me that some people used power zeners in metal mounting packages, where the cathode is the metal case, which made it convenient to mount the zener case directly to the chassis for great heat sinking.
     
    Last edited: Jan 20, 2018
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  9. theprofessor

    theprofessor Friend of Leo's

    Aug 8, 2016
    Chattanooga, TN
    Hey @JuneauMike ! @RLee77 responded with some expert knowledge. My only knowledge of the voltage drop per voltage rating is from using zeners two times. On my 5f2a, I used 38V worth of zeners and dropped 32 volts off of B+1 (88.8%). On this 5e3 build, I used 26V worth of zeners and dropped 22V off of B+1 (84.6%). I can't say why this slight variation, or whether there is a typical formula for it. But that is my limited experience. Is that what you were driving at with your question?
     
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  10. RLee77

    RLee77 Friend of Leo's

    May 15, 2016
    Silicon Valley
    That's a beautiful rig right there, prof. Congrats on a well-executed and informative build. I'll be eager to hear your impressions of the tones you get vs the 5f2a amp. Two great amp builds in a short time -- really makes me want to work through my backlog of partially finished projects so I can start my amp build. Long hours at work lately are really screwing up my hobby time! :mad:
     
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  11. RLee77

    RLee77 Friend of Leo's

    May 15, 2016
    Silicon Valley
    Thanks for that excellent description of the 5e3 controls, I'm going to save that off for later reference.
     

  12. awasson

    awasson Friend of Leo's Gold Supporter

    Age:
    54
    Nov 18, 2010
    Vancouver
    Off topic but... That sounds like a dangerous practice (running ground via zener). My line of thinking is that a diode can fail which would float the negative side of ~400 volts which will seek a ground somehow and electrify some other part of the circuit.
     

  13. clintj

    clintj Friend of Leo's

    Apr 4, 2015
    Idaho
    Zeners generally fail shorted on overcurrent, so if they did go out B+ would simply rise back to the original value. One of their many uses takes advantage of this: the power supply of some Klone pedals contains a 12V zener to protect the pedal from being plugged into a >9V power supply.
     

  14. theprofessor

    theprofessor Friend of Leo's

    Aug 8, 2016
    Chattanooga, TN
    I found my pair of power tubes. I ended up with a matched pair of the 1950's gray glass RCA 6V6GTs. Everybody agrees that these are great tubes, I think, and they're a good match for this circuit. I tried the Tung-Sol black glass for a while. They're clearer than the RCA's, with crisper, more defined treble and lower lows. They're fatter and, at the same time, clearer. I also tried a matched pair of Ken-Rad 6V6GT black glass, but they just didn't do it for me, as they normally do. They're matched, but I think they're a bit weak. Then I got out these RCA's that I purchased from Brent Jessee last year on his ebay page. They sound perfect. That mid-warmth that RCA's provide. The treble is plainer than either the Tung-Sols or the Ken-Rads, but it's also sweet (not plain like some Sylvania high-end that is a bit more generic in its plainness). This pair overdrives a bit early, too, and it sounds fantastic.

    If all I were after were clarity and punch, I would go with the Tung-Sols. But they can be challenging, I think (as the Ken-Rads can) for 5e3's with stock .1μF coupling caps that already pass a lot of bass. Both the Tung-Sols and the Ken-Rads have big bass. RCA's, on the other hand, have lows and low-mids, but not as much lower bass as those other two. And I think this helps the 5e3 from being overbearing in the bass. (In addition, I'm running a Raytheon LBP in the 12AX7 position precisely because of its thin tonal character, coupled with its clarity. I love Tungsrams, for example, but I think it's just too much low-end for this circuit.

    Anyway, these RCA's are running at about 331 plate volts and 36.2 mA, which means they're dissipating about 11.98W. Perfect!

    I've realized that I can tell the right tubes in an amp by using my Telecaster above all. I know what the middle position "should" sound like, and if that's right, the neck position and the bridge position will sound right, too. With the Tung-Sols, the middle position was too thick. With the RCA's, all the positions sound like what seems right to my ears.
     
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  15. theprofessor

    theprofessor Friend of Leo's

    Aug 8, 2016
    Chattanooga, TN
    Thanks very much, @King Fan ! That's a terrific post! While I've often read ahead, I didn't in this instance. I figured that I'd learn the interactive controls once they were in front of me. And now that I've (barely) begun, I'm exceedingly grateful to have your wonderful synopsis to use as a guide. I imagine I have a lot of what Weber says about the 5e3 in the three Weber books that I have, but I've never paid much attention to what he says about 5e3s, as I've never had one. But now... And thanks especially for the excellent and informative condensation of the long Tweed Deluxe Speed Shop video on the interactive volume controls. I knew about that, and I suppose I was going to force myself to sit down and watch it. But I find Rondo's presentations rather... soporific. And so I'm very happy that I can just get the gist by reading this seventeen(!)-point list. And that's making it simple!

    It seems that my relationship with the 5e3 will take a long time to develop, unlike the very immediate and simple 5f1/5f2. Thanks again!

    Thank you, @RLee77 ! I appreciate your encouragement. And I hope that it does indeed jump-start you to finishing your partially finished projects. I have an advantage in that my schedule is very flexible (since I'm a college professor and thus teach less than, say, a high school teacher), as long as I'm willing to put off important writing and editing projects... :) Sorry about your long hours as of late.
     

  16. awasson

    awasson Friend of Leo's Gold Supporter

    Age:
    54
    Nov 18, 2010
    Vancouver
    I know practical electronics but I don’t know enough about diode chemistry and physics to be certain of whether it will fail open or closed; I’ve read that over voltage will fail closed (shorted) and over powered (amperage) will fail open. The risk of it failing open, no matter how slim would put B+ looking for a ground and I suspect it would look on the audio cable so, a huge risk no matter how slight.

    EDIT: I feel like such a crotchety old dude worrying about a probable non-issue but it struck me as such a risky practice, I couldn’t leave it be. I spent nearly 20 years troubleshooting audio in another life and often watched power supplies search for ground.
     

  17. robrob

    robrob Poster Extraordinaire Ad Free Member

    Dec 29, 2012
    United States
    Some standby switches disconnect the power transformer center tap. It shuts off the source for all the DC electrons in the amp. It's not a safety problem.
     
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  18. awasson

    awasson Friend of Leo's Gold Supporter

    Age:
    54
    Nov 18, 2010
    Vancouver
    Yes, but unless I’m mistaken, we’re talking about grounding the DC circuit through a zener diode, not the AC circuit. In the unlikely event that the zener fails open, DC is still generated but it can’t complete the circuit so it looks for alternate avenues.
     

  19. SacDAve

    SacDAve Poster Extraordinaire Silver Supporter

    Age:
    66
    Dec 23, 2009
    Rocklin Ca.
    There have been a few threads about Zener's lately so I bought some (5W 10V) to experiment with lower B+. But the one thing I've heard no mention of how dose the Amp sound if you drop the voltage 20-V ? better ? If I recall the one advantage is extended tube life. On one the Weber it shows the B1-370 B2-318 B3-247 on the professors B1-384 B2-344 B3-252 is the professors way out of line? The reason I ask I just so I know when I experiment.
     

  20. robrob

    robrob Poster Extraordinaire Ad Free Member

    Dec 29, 2012
    United States
    The center tap is the source of all DC electrons in the amp circuit. Disconnect it and all DC current stops flowing. Electrons actually flow from the CT through the ground bus through the circuit and back to the rectifier and through the power transformer high voltage secondary wires.

    The center tap should only be tied to the chassis as a ground reference, not as a current return path meaning at the center tap-chassis connection the ground bus should be attached there too. If the chassis connection comes loose the center tap and ground bus should still be connected and everything is still safe.

    If the center tap and zeners did come loose and the ground bus separated from it, the chassis would no longer be tied to the power transformer secondary so the amp's high voltage AC and DC would be floating. There would only be voltage between the three secondary wires (HT-CT-HT). The DC power supply would not be hot since there is no circuit connection between the center tap and HT wires.

    You could touch either high voltage secondary wire or the center tap while touching the chassis without a shock.

    We would have a problem if that loose center tap wire (separated from the ground bus) made contact with with DC power supply though.
     

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