Express in single ended format?

[geoffrod]

i fitted the presence control, but it doesn't seem to do alot???

not sure if i was clear before, at the moment with the brief playing i have done, the amp cleans up fairly well with guitar volume turned back ,but i do loose a fair bit of volume that i am hearing, the amp means up real nice when the guitar volume is increased, but the volume increase is a fair bit, trainwrecks are renouned for clean to mean without a great increase in volume, is this possible with a single ended version???
if it is, how do i go about achieving it,

bigbeck, i was trying to stay away from the MV, just because i have read how they change and suck tone?

the amp is by no means silent as yet, that is a work in progress, but it is a heck of a lot better than it was a few days ago.

i need to get a couple of ferrite beads, it is very sensitive to outside transmissions.

firestorm, so changing the grid leak resistor to a lower value will smooth things out, but how do i know if i have gone to far, will i get voltage leaking thru again?

bigbeck,
i can get the highs down a far bit rolling the guitar tone pot back a bit.

im liking the harminics that come thru with it at full tilt,

[Firestorm]

i fitted the presence control, but it doesn't seem to do alot???

You do have the feedback loop connected, right? You could try a smaller value for R29.

trainwrecks are renouned for clean to mean without a great increase in volume, is this possible with a single ended version???

That's sort of true as long as you accept that the clean sound will also be LOUD. At least some of that characteristic may come from clipping the PI, which an SE amp does not have, but I would guess a lot comes from "saturating" the power amp, and in an SE amp, the PA is pre-saturated so it should do fine.

firestorm, so changing the grid leak resistor to a lower value will smooth things out, but how do i know if i have gone to far, will i get voltage leaking thru again?

There's no such thing as too far in terms of making the grid R smaller (except that as it approaches 0, you shut off the power amp). You can replace the resistor with a 250K linear pot wired as a rheostat (also connect a 1M resistor from the wiper to ground to protect the tube if the pot opens up). This will let you dial in any sound/volume you like. This is functionally a master volume. You won't have the same negatives with master volume use in an SE amp as you will in push-pull because the tube is running in Class A, thus already "maxed out."

[geoffrod]

i fitted the presence control, but it doesn't seem to do alot???

trainwrecks are renouned for clean to mean without a great increase in volume, is this possible with a single ended version???

That's sort of true as long as you accept that the clean sound will also be LOUD. At least some of that characteristic may come from clipping the PI, which an SE amp does not have, but I would guess a lot comes from "saturating" the power amp, and in an SE amp, the PA is pre-saturated so it should do fine.

"

so how is it that i go about making the clean louder???

the presence is conected as per the first schematic on page 1

[bigbeck]

bigbeck, i was trying to stay away from the MV, just because i have read how they change and suck tone?

I've put a lot of MV's in both PP and SE amps and never noticed this tone sucking. It's volume sucking,if anything. Like firestorm said, an MV is basically a variable grid leak. If you do put one in your amp,it becomes a volume control and the original volume control becomes the Gain control.

Basically,you have to try many mods for yourself,to see what YOU like. Everyone's got different ears. And when it comes to tone,we're all experts.

Clean & loud headroom is pretty much impossible with a single or even parallel 6V6. You really a bigger power amp. Raising preamp b+ by 40V or so will help but you're trading distortion for clean,and you may not like the tone - it's always a compromise.

[geoffrod]

bigbeck, i was trying to stay away from the MV, just because i have read how they change and suck tone?

I've put a lot of MV's in both PP and SE amps and never noticed this tone sucking. It's volume sucking,if anything. Like firestorm said, an MV is basically a variable grid leak. If you do put one in your amp,it becomes a volume control and the original volume control becomes the Gain control.

Basically,you have to try many mods for yourself,to see what YOU like. Everyone's got different ears. And when it comes to tone,we're all experts.

Clean & loud headroom is pretty much impossible with a single or even parallel 6V6. You really a bigger power amp. Raising preamp b+ by 40V or so will help but you're trading distortion for clean,and you may not like the tone - it's always a compromise.

i just had another play thru the amp, and it cleans up and is quite loud rolling the volume back on the guitar with the amp up past 12oclock, but when i turn up the guitar volume the volume out of the amp increases a fair bit, how do i decrease the volume level difference?

i have used a vvr before with good results, keeping the tone and touch at lower volumes.

cheers
geoff

[bigbeck]

when i turn up the guitar volume the volume out of the amp increases a fair bit,


cheers
geoff

That's what it's supposed to do! I'm afraid I don't understand what you're asking. Maybe my brain stopped working.

[Firestorm]

I think it's all experimentation now. 6V6s don't really have a clean sound when driven hard (unless they're Bendix 5992s), so try a 6L6, or an EL34 or even a 6550 (if your heater winding can cope). With all those, you'll have to fiddle the impedance selector (if there is one) since they'll prefer about half the impedance of a 6V6. These may increase the output power (or not, depending on the PT), but will likely be cleaner overall.

You could try leaving off the bypass cap on the output tube. This gets you some local feedback, reduced output and maybe a tad of compression since the bias will track the input signal. It's a simple experiment anyway.

If you have multiple output taps on the OT, make sure the feedback loop is attached to the 16-ohm tap itself (not the way the schematic shows).

Most SE transformers have a 40% tap for ultralinear operation. Try it. Even the Hammond 125s can be tapped at 50% for this purpose.

I'm guessing that one main reason an Express has "clean to mean" without appreciable power increase is that it hits the wall in terms of available current. If your power transformer can provide 300mA of current and you can push a pair of El34s (plus your preamps, plus resistive losses) up into that range with your guitar still on "5," turning up isn't going to get you any more power, but it will change the character of the preamp. Unless your PT tops out at, say, 50mA with a 6V6, you won't get the same effect.

Anyway, this is sort of the fun part now: messing around with things until you hear what you like.

[geoffrod]

when i turn up the guitar volume the volume out of the amp increases a fair bit,


cheers
geoff

That's what it's supposed to do! I'm afraid I don't understand what you're asking. Maybe my brain stopped working.

sorry my bad describing i suppose,
i mean i would like when i turn up the guitar volume, i increase the gain sound of the amp but the level of volume doesn't change much

[bigbeck]

Ok,now I understand. You want high gain(distortion),at a lower volume. I don't think you can do that at the guitar. An MV will allow you to do that. Or,use a distortion pedal.

Another easy mod is to use a diode clipper built on a push-pull pot. It's attached right after the last .022 coupling cap. The push pull pot allows you to adjust the amount of clipping (distortion) and also allows you to take it out of the circuit. However, it also drops a lot of volume but sounds really good if you choose the right diode and/or LED combination. I know it's cheating,using sand in a tube amp but your wife will love you for it!

Just do a web search for diode clippers. It's very easy to test the effect of a diode clipper by using just test leads to connect the diodes to the circuit to see if it's for you.

You may be able to build an amp in a day or two but the experimenting can go on for months. Hell, you can spend months just on tone stacks!

good luck

[moonbirdmusic]

Never mind -- had to log in -- duh

[geoffrod]

Ok,now I understand. You want high gain(distortion),at a lower volume. I don't think you can do that at the guitar. An MV will allow you to do that. Or,use a distortion pedal.
good luck

i suck at trying to explain things in writting lol

let me try again.

we are talkin trainwrecks here right.
what is the thing that trainwrecks supposedly do, they go from clean to mean with the turning of the guitar knob, they also do it with not a lot of volume output difference.
so how can i achieve this in my SE version.
do which section of the amp do i need to tweek,
the first or second stage, the power stage,
should i try and lift the plate voltage to the first stage, what about the last stae before the power stage has a pretty low plate voltage, and wont lifting ths voltage give the amp a feeling of more headroom?

i dont know maybe i am full of it so if thats true just tell me lol

i have some hum to get rid of as well.
some ferrite beads to install and some lead dress to do as well.

its my birthday tomorrow so i guess i will be able to do what ever I want, so hopefully i will be able to get to it.

cheers
geoff

ps, thanks for ll the helpfull suggestions so far.

[geoffrod]

i just changed the 2 10k resistors in the power supply line for 4k7's, and now i have motorboating going on grrrrrr

[dartanion]

Hey Guys,

Just a couple of notes. I was able to preserve a lot of what the Express does by keeping the PI and tweaking the preamp. Since the PA is SE, you feed the PA with just one side of the PI. Just make sure it's the correct side as you'll get positive feedback with the wrong side, just like in the PP version. I messed with the cathode resistors and bypass caps in mine to tune it for my tastes. Going with a smaller Rk on the clipping stage makes a big difference. I have been using values between 4k7 and 8k2 depending on the preference of my clients. To get more LOUD clean, you really need to use big bottles in parallel just to have the headroom. You can clean the amp up easily doing other things, but that changes how the amp responds.

Here's a recent video of my low B+ Absinthe:

http://www.youtube.com/watch?v=62aIXjySFYg

[geoffrod]

Hey Guys,

Just a couple of notes. I was able to preserve a lot of what the Express does by keeping the PI and tweaking the preamp. Since the PA is SE, you feed the PA with just one side of the PI. Just make sure it's the correct side as you'll get positive feedback with the wrong side, just like in the PP version. I messed with the cathode resistors and bypass caps in mine to tune it for my tastes. Going with a smaller Rk on the clipping stage makes a big difference. I have been using values between 4k7 and 8k2 depending on the preference of my clients. To get more LOUD clean, you really need to use big bottles in parallel just to have the headroom. You can clean the amp up easily doing other things, but that changes how the amp responds.

Here's a recent video of my low B+ Absinthe:

http://www.youtube.com/watch?v=62aIXjySFYg

hey dart,
i put and extra noval socket in for just that reason, to maybe try a PI, i also put in an extra octal socket just in case i wanted to go the parralel power tube.

i have been watching your vids lately, nice sound.

how is the b+ on your amps?

[dave g]

The clean to mean has nothing to do with exceeding the rated limits of the PT. No way in hell are two EL34s ever going to average 300mA. Even if you could manage to pull that much current, it's not going to sound cool. It's going to turn your power transformer into a chimney and probably trip a circuit breaker.

The clean to mean has just about everything to do with that 1K dropping resistor in the power supply between the plate and screen nodes. When you hit the power tubes with a large signal the screen current spikes, causing a voltage drop across that resistor that propagates to the preamp, changing the operating point of the PI and 3rd clipping stage and causing them to compress/limit more. You could even think of it as a weird sort of negative feedback mechanism.

You cannot completely replicate this in a SE design, because the output tube(s) are biased in class A and will be drawing too much current at idle. In a push pull power amp, both output tubes are biased near cutoff, so you are drawing far less current at idle, which means that the drop across that 1k resistor is comparatively small. That's really what the clean-to-mean boils down to; for smaller signals seen by the output tubes, the headroom of the preceding clipping stages (PI + 3rd stage) is relatively high. Increase the signal strength enough, and the headroom of those stages falls, leading to a voltage limiting compression effect.