More output from 5E3

[six_eight]

My BF Deluxe Reverb has a lot more headroom and volume than my Tweed Deluxe.  What would happen if I added a switch to the 5E3 that bypassed the 220ohm/25uF and connected the cathodes of the 6V6s directly to ground a la the AA763 circuit?   Would this make it louder and/or increase headroom?  What about heat?  The 5E3 already puts out a lot of heat.  Would adding screen resistors be a necessity?

[sluckey]

What would happen if I added a switch to the 5E3 that bypassed the 220ohm/25uF and connected the cathodes of the 6V6s directly to ground a la the AA763 circuit?

It would hum loudly until the 6V6s melted, possibly taking out your OT and/or PT.

What you're suggesting would put zero volts bias on the tube and tubes need to be biased negative (grid relative to cathode).

[phsyconoodler]

Get a more efficient speaker or add an extension cabinet to it.To speakers are significantly louder than one.
Use your deluxe reverb and your tweed in stereo.Then you get the best of both.

The more efficient speaker would be easy to try out.Just plug your 5E3 into another speaker cabinet to see what it sounds like.Maybe a 2-12 cabinet would float your volume craving boat here?

[six_eight]

What would happen if I added a switch to the 5E3 that bypassed the 220ohm/25uF and connected the cathodes of the 6V6s directly to ground a la the AA763 circuit?

It would hum loudly until the 6V6s melted, possibly taking out your OT and/or PT.

What you're suggesting would put zero volts bias on the tube and tubes need to be biased negative (grid relative to cathode).

Thanks!

So it could be done if I rigged a switch to simultaneously rebias the grid?  Which would need to be a fixed bias now instead of connecting the 2 x 220k resistor from the grid to ground, right?

[TubeGeek]

You would need to convert to fixed bias.  That involves adding a few more components to give you the negative bias voltage you need for the power tubes.  You should hopefully have a secondary tap on your PT that you can get the initial raw voltage for bias.  From there it needs to go through a combination of diode, resistors, capacitor and potentiometer so you can dial in the correct voltage needed.  Do some looking at other fixed bias amp schematics and go from there.

Here is something close to what you're asking for:  http://taweber.powweb.com/store/5e3p_layout.jpg

But...are you sure you want to alter the tweed deluxe tone?  It's pretty good cathode biased!

[six_eight]

Get a more efficient speaker or add an extension cabinet to it.To speakers are significantly louder than one.
Use your deluxe reverb and your tweed in stereo.Then you get the best of both.

The more efficient speaker would be easy to try out.Just plug your 5E3 into another speaker cabinet to see what it sounds like.Maybe a 2-12 cabinet would float your volume craving boat here?

Oh, that definitely does the trick.  But the problem with that is, I lose the "5E3" side of it....which I don't want to give up.

I was thinking of something more along the lines of just flipping a switch so that I could still have the 5E3 with all its deliciously low headroom and overdrive through the more "vintage correct" 1 x 12 P12Q, but if I wanted a little more headroom and volume out of it for clean tones, I could just flip a switch.

So if I were to connect the cathodes directly to ground and rebias the grid, would this give me more output and headroom from the power tubes?  Or would the change be marginal and not worth trying?

[six_eight]

You would need to convert to fixed bias.  That involves adding a few more components to give you the negative bias voltage you need for the power tubes.  You should hopefully have a secondary tap on your PT that you can get the initial raw voltage for bias.  From there it needs to go through a combination of diode, resistors, capacitor and potentiometer so you can dial in the correct voltage needed.  Do some looking at other fixed bias amp schematics and go from there.

Here is something close to what you're asking for:  http://taweber.powweb.com/store/5e3p_layout.jpg

But...are you sure you want to alter the tweed deluxe tone?  It's pretty good cathode biased!

That's why I want to put it on a switch, so that I don't have to give up the tone of the original cathode bias.  This leads me to another question...

Is the 5E3 classA or AB?  I've read conflicting things regarding this.  It sounds more class A to my ears.  And it puts out heat like it's in class A.  And it's not very loud for two 6V6 in push pull compared to amps with a similar output.  And I've read some people arguing that because it's cathode biased without a negative feedback loop, this makes it class A.  But most marketing claims it to be AB.

[six_eight]

You would need to convert to fixed bias.  That involves adding a few more components to give you the negative bias voltage you need for the power tubes.  You should hopefully have a secondary tap on your PT that you can get the initial raw voltage for bias.  From there it needs to go through a combination of diode, resistors, capacitor and potentiometer so you can dial in the correct voltage needed.  Do some looking at other fixed bias amp schematics and go from there.

I don't have the secondary tap.  The fixed bias tap is just a premature tap in the secondary high voltage winding so that the voltage is easier to bias to approximately 50v, is it not?  If I don't have a fixed bias tap on the PT it's just a matter of connecting to one side of the PT secondary before the rectifier with a diode, followed by an adjustable voltage divide(cathode of the diode pointing towards the PT)?  And then adjust the voltage divide for about -50v?

[printer2]

And after you end up with a fixed bias 5E3 how would you feel when you find you have no more volume than you started with? The cathode voltage across the bias resister is about 20V, you have about 80mA through them, a grand total of 1.6 watts.

[sluckey]

And after you end up with a fixed bias 5E3 how would you feel when you find you have no more volume than you started with? The cathode voltage across the bias resister is about 20V, you have about 80mA through them, a grand total of 1.6 watts.

Huh??? You just calculated the power dissipated by the 250Ω cathode resistor. The tubes would be dissipating considerably more. What am I missing here?

[jojokeo]

I have extra capacity trannies and a higher wattage cathode resistor so when playing larger venues or on outdoor stages with it I change to 5881s. Does the trick nicely and makes the amp really verisatile.

[six_eight]

And after you end up with a fixed bias 5E3 how would you feel when you find you have no more volume than you started with? The cathode voltage across the bias resister is about 20V, you have about 80mA through them, a grand total of 1.6 watts.

Hopefully, that's not the end result, but that's why I'm asking here first before I actually experiment.  You are aware that I intend to use a DPDT toggle switch to simultaneously remove the 250ohm cathode resistor and connect the cathodes of the 6V6s direct to ground while lifting the 220k grid bias resistors from ground and connecting them to the fixed bias?  I was not planning to leave the 250ohm cathode resistor connected while using a fixed bias.

[Willabe]

Oh, that definitely does the trick.  But the problem with that is, I lose the "5E3" side of it....which I don't want to give up.

I was thinking of something more along the lines of just flipping a switch so that I could still have the 5E3 with all its deliciously low headroom and overdrive through the more "vintage correct" 1 x 12 P12Q, but if I wanted a little more headroom and volume out of it for clean tones, I could just flip a switch.

Do you want this for playing live or at home?

If for home there's not much difference from fliping a switch or unpluging a second speaker cab.


                Brad       

[sluckey]

I had a cathode/fixed bias switch in my Tweed Deluxe Reverb. I played with it about a week and finally just removed it. I never noticed any change in volume.

I still have a cathode/fixed bias switch in my November amp. Again, no noticable volume difference. I do hear a slightly more compressed sound in cathode bias mode. I haven't flipped that switch in years.

BTW, since you will use a large resistor to drop the HT voltage down to a usable bias level, you can switch modes using only a SPDT switch. Your circuit might look similar to this...

http://home.comcast.net/~seluckey/amps/november/november.pdf

[jojokeo]

http://home.comcast.net/~seluckey/amps/november/november.pdf

Steve, how do you like the twin triode "plexi" set-up after having the amp for a while? Is it "worth it" and do you use the two gain stages' different settings much? Would you build it the same way or have the amp set up like this again or would you do it differently (if there was a "next time")?

[six_eight]

Oh, that definitely does the trick.  But the problem with that is, I lose the "5E3" side of it....which I don't want to give up.

I was thinking of something more along the lines of just flipping a switch so that I could still have the 5E3 with all its deliciously low headroom and overdrive through the more "vintage correct" 1 x 12 P12Q, but if I wanted a little more headroom and volume out of it for clean tones, I could just flip a switch.

Do you want this for playing live or at home?

Both, I reckon.  Mostly just to do it and see what it sounds like.

[six_eight]

I had a cathode/fixed bias switch in my Tweed Deluxe Reverb. I played with it about a week and finally just removed it. I never noticed any change in volume.

I still have a cathode/fixed bias switch in my November amp. Again, no noticable volume difference. I do hear a slightly more compressed sound in cathode bias mode. I haven't flipped that switch in years.

BTW, since you will use a large resistor to drop the HT voltage down to a usable bias level, you can switch modes using only a SPDT switch. Your circuit might look similar to this...

http://home.comcast.net/~seluckey/amps/november/november.pdf

That's brilliant use of a SPDT!  That's a bummer that it doesn't do much of anything.

[phsyconoodler]

So you said you were after more volume and headroom and don't want to lose the character of the 5E3? Do what I told you.
 Get a a 2-12 cabinet loaded with efficient low wattage speakers like eminence Red Fangs or Weber Blue Dogs or Warehouse speakers or whatever.You will still have the lovely grind but just at a louder volume.
 How easy can it get?

 Or simply install a C12K Jensen or something with more balls in your amp as it sits.
Better yet,just get a 1-12 extension cab and plug it in.Instant 3db more,just like adding another 12 watts.Put it under your 5E3 and get it all baby!

[sluckey]

how do you like the twin triode "plexi" set-up

I still like it just fine. I've got more hours on this amp than any of my others. The preamp is equivalent to a Plexi with the channels jumpered. The bright channel is a little too bright by itself and the dark (normal) channel is too dark by itself. But mixing the two together gives a full tone that I really like. I've built two November amps. The only change I made on the second one was to lose the bias switch.

[PRR]

> if I wanted a little more .., I could just flip a switch.

If that were possible, Leo Fender would have done it.

> I had a cathode/fixed bias switch ... I never noticed any change in volume.

With the *same* power supply and load impedance, there should be a 10% change from the 25V not-lost in the cathode bias resistor. That's hardly audible.

With fixed-bias (not a trivial change) *and* rigging for solid-state diodes instead of the lossy vacuum rectifier, you can get 25% more power. I used to do that. Decided it was a waste of time.

If you half the OT impedance, double the tubes (or use 6L6), and *double* the power supply current (bigger PT), then you get twice the power or 3dB. That's not a huge change, though it may get you out of a barely-too-weak situation.

As-is, use more/hotter speakers, or put a mike on it and run through the PA system.

[HotBluePlates]

My BF Deluxe Reverb has a lot more headroom and volume than my Tweed Deluxe. 

Ignore the numbers on the volume controls. Turn on both amps and slowly turn up each until they just start to get a little "not-clean". Now go back and forth to A-B each amp's volume at this point. Is on really that much louder than the other? Little-louder or WoW-louder?

"Headroom" is usually not well-defined by people, and could be an illusion in your amp. Rather than type 5,000 characters why that is, I wish I could just demonstrate in person.

Regardless, the B+ is about 50v higher in your blackface, and it's fixed-bias so the 6V6's have an additional ~20v across them, or ~70v total. Compared to the total voltage across the 6V6's in the tweed, that's ~25% more.

The OT load is probably reduced to about 6.6kΩ. That helps the 6V6's create a little more power in the blackface, when they are also given the higher B+. The combination of higher B+ and lower loading leads to a bit more current drawn under signal conditions. All that adds up to a little-more output power.

The impression of headroom in the blackface is due to the different tone circuit, such that you have to reach a higher number on the volume knob to get distortion. That doesn't mean more "real headroom" (as I'd define it, meaning more clean power), but the impression of more headroom because clean takes up more volume knob rotation.

I was thinking ... I could still have the 5E3 ... but if I wanted a little more headroom and volume out of it for clean tones, I could just flip a switch.

Plug your guitar into an A/B/Y switch and play through either or both amps with the click of a (foot)switch.

I used to do this with a '54 Princeton and a '67 Princeton Reverb. There's magic with having both amps going, midrangey distortion and mid-scooped clean with reverb, at the same time.

Plus, I think you're gonna go down a road of trying to turn a tweed Deluxe into a blackface Deluxe, and find that you have to lose one to get the other.

Kinda like when I kept trying to make a Les Paul Custom sound like a Strat. I got 80% of the way there with various pickups and switching mods, but I never nailed that sound til I just bought a Strat. Same with trying to make a Strat sound like a Tele.

Is the 5E3 classA or AB?  I've read conflicting things regarding this. ...  And I've read some people arguing that because it's cathode biased without a negative feedback loop, this makes it class A.

People argue because the only info they've absorbed are the watered-down explanations. That, and old-amp designers wouldn't really bother to get just a little-bit AB (with its higher output power); they'd raise B+, lower load impedance and switch to fixed bias to get well into AB territory.

An input signal (that's not rectified) is a 360˚ wave. If the output tubes each conduct for 360˚ of the input signal (never turn off), then the amp is class A. If the output tubes conduct for exactly 180˚ (are cut off exactly half the time), then the amp is class B. If the output tubes conduct for less than 180˚ of the input signal (cut off more than half the time), the amp is running class C.

Class C is only used in radio/radar transmitting (or the like) where the output is only 1 frequency.

Anything that has the output tubes conduct less than 360˚ (always on) but more than 180˚ (exactly half the time) is class AB. Closer to 181˚ could be called "cool" or "lean" class AB, closer to 359˚ could be called "hot" or "rich" class AB.

[HotBluePlates]

Strict technical definition of class B is hard to achieve with tubes, because they have a wide range from almost-off to absolutely-off. But there are guitar amps that are almost-B, and run very cool class AB.

Lean class AB is hard to do with cathode bias, because when the tube cuts off the bias collapses and tends to keep the tube on. A bypass cap can allow a cathode biased amp to run hot-AB (just straying a little ways into class AB) because a big bypass cap can source current for short off-periods.

It's also hard to bias the output tubes much-more-off with a cathode resistor. Cathode bias relies on tube current flow to help establish the bias voltage, so while you need more voltage, you're also reducing the tube current, which requires more-more-more resistance. Review ohm's law and the relationship between each of the quantities voltage, current and resistance. I figure it will take more than an 800Ω cathode resistor to try to bias the 5E3 the way the Deluxe Reverb is biased, if you kept a cathode resistor (and you'd need a lot more B+ to make up the difference of plate-to-cathode voltage between the amps afterwards).

I'd call a 5E3 a hot-AB amp. By the time it's breaking up, the output tubes are turning off for short times.

[printer2]

Well between sluckey and HotBluePlates that pretty much sums up the difference between switching from fixed bias to cathode, from a Tweed to a Blackface given the same output tubes. Nice to see some get it. Sorry I was not here to add to the discussion, I was out in the garage building a guitar.

While you may not have much more output (headroom) going from cathode bias and BF preamp rather than a Tweed, the fixed bias does tighten up the low end a bit and it would be nice to have both flavors of amp in one cabinet (oh yeah, I forgot to mention the NFB). Actually I do have a modification to get close to a BF sound out of a 5E3, A bit late to look for it, if there is any interest I could post it.

 

[HotBluePlates]

Does the mod involve adding a T-filter with a pot (wired as a variable resistor) to ground?

That could add a mid-notch when the pot is set for low resistance, or remove it if the pot is set for high resistance (or you could have a switch instead of a pot for 2 discrete settings).

[printer2]

Does the mod involve adding a T-filter with a pot (wired as a variable resistor) to ground?

That could add a mid-notch when the pot is set for low resistance, or remove it if the pot is set for high resistance (or you could have a switch instead of a pot for 2 discrete settings).

No, used a four pole switch to rearange the circuit and used dual pots for their respective circuits. Went down for the Tweed values and up for the BF, adjusted the caps to match. The tone circuit is built on the pots and conceivably you could leave the rest of a 5E3 board alone.

[worth]

Try decreasing the value of the first dropping resistor , ( thus increasing headroom by raising the voltages )from the stock 5K,  to a 2.7K , or even 1K.. then make it switchable.