Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: maxupp on April 06, 2023, 03:58:02 am
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Hi folks,
thanks for accepting me to the board!
A few days ago I finished a 5E3 build, and while it does run with very little noise or hum, the sound is extremely dull to my ears and nothing like all the videos I've seen. (I had an oscillation problem at high Volume or Tone initially, but that went away after I tidied up my preamp tube wiring.) I've verified the wiring twice, and measured all kinds of voltages, which all seem okay, if a little low (see attachment, reference voltages are for 5AR4 recitifer.). The amp is running a 12AY7, a 12AX7, two JJ 6V6S and a 5Y3S rectifier.
The filament voltage is 6.39V. Plate dissipation is 11.4W or 81.4%, measured via the cathode resistor voltage drop.
I was hoping you guys could take a look at my measurements and tell me if there's anything amiss. If this is all good and how the amp is supposed to sound like, I'd also be grateful for recommendations for a bright speaker.
Here are some pictures: https://photos.app.goo.gl/QgeU1hJiEKPNTkyG7
I also recorded some clips, all using the Bright 1 input. Here it is with my '91 Fender Strat, before the oscillation fix:
And here it is with a PRS CE24: https://soundcloud.com/memories-on-polaroids/5e3-sound
The amp is running into a Captor8 loadbox and into some of the brightest cab sim IRs I could find.
I've also checked all the tube voltages:
5Y3S Rectifier:
1:
2: 340V
3:
4: -10V
5:
6: -10V
7:
8: 340V
6V6 1 (closer to rectifier):
1: 290V
2: ~0mV
3: 337V
4: 290V
5: ~10mV
6: ~10mV
7: ~0mV
8: 18V
6V6 2:
1: 290V
2: ~0mV
3: 336V
4: 288V
5: ~10mV
6: ~10mV
7: ~0mV
8: 18V
12AY7:
1: 115V
2: ~0mV
3: 1.63V
4: ~0mV
5: ~0mV
6: 115V
7: ~0mV
8: 1.63V
9: ~0mV
12AX7:
1: 141.2V
2: ~0mV
3: 1.1V
4: ~0mV
5: ~0mV
6: 174V
7: 14.9V
8: 40V
9: ~0mV
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Your post reports 18v on the 6V6 Rk, but the layout attachment says 22V.
Assuming it’s 18v, the current through the resistor is 66mA. 33mA each tube. Minus ~2mA screen current = 31mA plate current. Multiplied by the 319 plate-to-cathode voltage = 9.9W, which is too cold for this amp. JJ 6V6S are easily 14W tubes. No wonder you think it sounds lifeless.
Don’t be shy to heat those tubes up to 14W
Try rolling a few other 5Y3GTs , and or going to a 220R cathode resistor (or even 180R).
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I'm not sure this has anything to do with the sound but your B+ voltages are all much less than mine. My 5Y3S pin 8 is 375V. My 6V6S plates are both 368V. Maybe slightly different load lines. Your sound clips are all at high volume and clipping. How is the clean sound at about 2?
Here's the thread I started about my 5E3 bias. The sound was fine, just wanted to make sure I wasn't biased too hot. I also attached the typical voltages wire diagram from Weber. My voltages match this very closely.
https://el34world.com/Forum/index.php?topic=29644.msg326438#msg326438 (https://el34world.com/Forum/index.php?topic=29644.msg326438#msg326438)
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It not only sounds dull - it sounds muffled - maybe that's the same thing, I don't know. I assume it sounds the same into an actual speaker as opposed to the metaverse? :icon_biggrin: Sorry, old school here.
Anyways I could see Tubeswell's suggestion as plausible, but not the general lower voltage. I have a mongrel 5C3/5E3 (6SL7 preamp tubes in a 5E3 config) running at those lower voltages - plenty lively.
I note in the video that you crank up the volume in a couple places - amp should be screaming Neil Young Crazy Horse at that point. Somethin' ain't right IMO. Bad cap? wonky tube? I'd be looking at both those possibilities if changing the power tube bias doesn't get you there.
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That's bad!!!
Don't do anything to the amp until you connect it to a proper speaker. I use a Jensen P12N reissue and it sounds nothing like that.
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I was able to run it into my Orange PPC212 earlier tonight (though at mismatched impedance, 8Ohm out into 16Ohm cab), and it sounded pretty okay actually.
Still not a whole lot of drive, and still a bit wooly. Also there's some pretty noticeable humming, around 100Hz. German mains is at 50Hz, so it might be a harmonic of that...
The hum persists when I pull V1, but goes away when I pull V2. I redid the solder joints to the poti cases, one of which was pretty shit, but it still hums.
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If you’re not making appropriate power, your rectifier tube could be crappy. (As I said before, try some different rectifiers. If other tubes don’t improve the B+ current, then it could be that the High Tension winding on your PT doesn’t put out high enough VAC, and so then you could try heating up the 6V6 bias by reducing the Rk. Be aware that this will decrease the B+ voltage a bit).
5E3s have the mojo that they do because the 6V6s are idling at full bore. YMMV
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If you’re not making appropriate power, your rectifier tube could be crappy. (As I said before, try some different rectifiers. If other tubes don’t improve the B+ current, then it could be that the High Tension winding on your PT doesn’t put out high enough VAC, and so then you could try heating up the 6V6 bias by reducing the Rk. Be aware that this will decrease the B+ voltage a bit).
5E3s have the mojo that they do because the 6V6s are idling at full bore. YMMV
The transformer is putting out the exact 640V it is spec'd for. I will do as you say and order another rectifier tube. Let's see what happens
Any idea what could be going on with my hum issue? I've bent all the heater wires away from the signal wires on the preamp tubes, but I still have hum.
it only goes away when i pull V2. Pulling V1 has no effect. Maybe a ground loop? How would I test that?
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I think you are wise to wait for the new rectifier before further testing/changes - and hook it up to a speaker.
Two things that come to mind though. Have you swapped V1 & V2? Is the hum unchanged?
And I redid the solder joints to the poti cases, one of which was pretty shit, but it still hums
Are you relying on soldering to the backs of pots for grounding? That can be suspect. Most builders have stopped doing that and rely on a ground buss or star ground. You might check every component that is supposed to connect to ground and make sure that the resistance is darn close to zero.
And at the top of the Forum page there are two amp checking topics "Before posting..." and "How to check for things missed" Both have good advice.
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... 5E3 build ... the sound is extremely dull to my ears and nothing like all the videos I've seen.
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The amp is running into a Captor8 loadbox and into some of the brightest cab sim IRs I could find. ...
Plug it into a real speaker.
Your sound-problem is the IRs, and very likely not the amp. The original Jensen alnico speakers were pretty bright (though not as bright/harsh as the modern reissue Jensen alnico speakers). Even the same-IRs sound different when used with different loaders, so we can't trust them when evaluating the raw amp-sound.
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Looks like I completely missed the speaker sim thing. :dontknow: