New To The Forum...

[Murali]

Hi,
This is my first post, though I've used this forum as a resource. Thanks for all the great info and schematics, much appreciated.

I recently built a 'wreck and made some mods to the circuit that I've found very useful. They've probably been done and posted here before, so please excuse me if I'm being redundant.

I've done three things based on Version A1a of the wreckxpr.pdf schematic using EL34s:
1. I made the 500 pf cap to the Treble pot switchable to 250pf.
2. I inserted a 250kB pot in series with a 56k resistor in place of the 100k slope resistor in the tone stack, and
3. I inserted a 250kA pot (in series) between the 10k cathode resistor on the 3rd gain stage and ground.

Of the above mods, #3 has been the one I use the most, although the other two can alter the character of the amp nicely, too. I gig and record regularly and enjoy using and experimenting with amps I've built. I've also built a version of the Trainwreck above with a 2 EL84 Cathode Biased output 'cause the EL34 amp is too loud to use here in the clubs of Santa Fe, NM.

Being able to vary the sensitivity of that last gain stage is very useful and I've measured and marked settings of the pot that yield unity gain and also the output of a cathode follower. Using this in conjunction with the 250pf Tone Stack cap and adjusting the slope resistance results in being able to approximate some Fender amp tones.

I'd love to hear what you guys think of these mods. Or to know if they've been around before.
All the best,
Murali

[rooster]

Sure, I'll comment.

On #1, no, 250 is too bright I think. On #2, no leave the 100K and add a sweepable 50K trimmer for less midrange - you are going backwards, the amp already has a buttload of midrange. On #3, skip this idea, leave the stock 10K and instead sub R7 with a 100K resistor in series with a sweepable 50K trimmer. This controls the 3rd stage gain better than your method, IMO.

FWIW, I think you have altered and not tweeked. Tweeking means KF's design is still in the building, which is worth thinking about. In other words, consider that you started out wanting to clone an Express, don't be so quick to walk away from it.

The alterations I have suggested have been used by a few here, BTW. As you comb the forum you will find mention of them. Well, remember you asked for some feedback. Oh, and welcome to the forum. I am not attacking you so please don't read it this way. I'm just a big KF fan, that's all.

[Murali]

just testing the signature function

http://itunes.apple.com/us/album/enjoyi ... d418261590

[Murali]

You all know this "rooster" person is full of crap, don't you? [hey, nothing personal, rooster.]

Now, could I please hear from any of you who actually know something about amps, recording and performing?

Sure, I'll comment.

On #1, no, 250 is too bright I think. On #2, no leave the 100K and add a sweepable 50K trimmer for less midrange - you are going backwards, the amp already has a buttload of midrange. On #3, skip this idea, leave the stock 10K and instead sub R7 with a 100K resistor in series with a sweepable 50K trimmer. This controls the 3rd stage gain better than your method, IMO.

FWIW, I think you have altered and not tweeked. Tweeking means KF's design is still in the building, which is worth thinking about. In other words, consider that you started out wanting to clone an Express, don't be so quick to walk away from it.

The alterations I have suggested have been used by a few here, BTW. As you comb the forum you will find mention of them. Well, remember you asked for some feedback. Oh, and welcome to the forum. I am not attacking you so please don't read it this way. I'm just a big KF fan, that's all.

[Randy Magee]

Not a good start in a forum when you launch a personal attack... we're not here for drama...

[ampmike]

Amen to that!

[Bruciep07]

You all know this "rooster" person is full of crap, don't you? [hey, nothing personal, rooster.]

Now, could I please hear from any of you who actually know something about amps, recording and performing?

Good luck, don't let the door hit ya!

[rawnster]

Actually Rooster is one of the more knowledgeable resources on this forum...and one of which I gotten to meet in person. Murali, it would be wise to actually listen and heed his advice.

Seriously!

[bcmatt]

just testing the signature function

http://itunes.apple.com/us/album/enjoyi ... d418261590
_________________
New Mexico Music Awards Winner Best Pop CD 2011

Haha! Sure that's all you're really doing...

I never thought I'd say this, but I think I finally found a case where I prefer the regular spam-bots.

[angelodp]

How about some common civility. On your first post you insult a valued member? Re-think. An apology is in order.

[dreric]

How about some common civility. On your first post you insult a valued member? Re-think. An apology is in order.

This is what I love about this forum.

e

[M Fowler]

I like to use a 100pf and 350pf on DPDT bright switch because 500pf is too freaking bright on an Express.

I worked on a TAG members amp that had an adjustable slope trimmer pot and it worked well. He also had a trimmer on the tail resistor. Got great distortion with that, should be pots on the faceplate so you can use them externally.

The watts control didn't work well on my Express but works well on the Rocket controlling the signal to the PI. Besides that Express is not a four gain fire breather and no longer an Express

Mark

[vibratoking]

Wow! This must be some kind of record. His comments are wrong on so many levels. It's actually kind of comical when you look at it that way.

Rooster - aren't you glad you tried to help? I, for one, greatly appreciate the willingness of this community to help others.

[NickC]

You all know this "rooster" person is full of crap, don't you? [hey, nothing personal, rooster.]

Now, could I please hear from any of you who actually know something about amps, recording and performing?

Amps

Hmmmmmm. What do I know about amps? I started formal, academic studies of electronics with emphasis on tube technology in school in 1971. I've tinkered with them ever since, but I don't have anywhere near the knowledge of rooster. I read his posts (and many by other TAG power-users) and feel like a hummingbird that just scored a huge jackpot of flower nectar. Compared to him, I'm a complete hack.

Recording

I began multi-tracking when the Teac 3340s hit the scene. Have used various "Portastudios" and DAWs since those days. I have performed and engineered tracks released by roughly a dozen artists. I prefer to mic a good tube guitar amp and track it. But I've had to use digital emulators and solid-state boxes by demand of producers too. I don't like them, but I can use them. I've never had the privilege to run a big Neve or SSL console with a couple of 24 track analog tape machines slaved together, like some folks around here. In contrast to that level of experience, I am again a complete hack.

Performing

Been picking guitars for 40 years now. Semi-professional for 30+ (meaning I get paid for it, albeit not enough to support my family .... thus the day-job). I've played in the high-hundred's of gigs .... but not thousands like some folks hereabouts. I've played as a sideman for a multi-Grammy winning artist; a gifted, talented, wonderful performer. But I don't have her talent, stage presence, or charisma .... so I'm not the one in the spot-light .... and I'm completely okay with that. It has always been a supreme honor to play music for folks ..... whenever and wherever. Even though I am a relative hack at it, I show up on time, sober, prepared and ready to fulfill the code-of-the-road.


But I can't answer your technical amp questions. I've still got a LOT to learn. I'm extremely grateful for folks like rooster (and just about everyone here at TAG) for the incredible generosity to share knowledge and expertise. Thanks to all of you!

[surfsup]

On #3, skip this idea, leave the stock 10K and instead sub R7 with a 100K resistor in series with a sweepable 50K trimmer. This controls the 3rd stage gain better than your method, IMO.

I'm curious about the effects of his mod to add the 250k in series iwth the 10k on third stage. This gives a Rk range of 10-260k. At the high extreme (260k), this biases the valve very cold closer to cutoff, so the gain would be attenuated but in the form of heavy compression/clipping, correct?

V=IR so with a huge R, I is nearly zero so bias point shifts down to the bottom of the graph. Lets assume -1.5V grid curve. this is 0.006mA or 0.000006A current.

But with current going down, wouldn't the V drop across Ra be less so the graph will physically stretch up/down? But I'm thinking current is so low any input signal will get clipped heavily because you're riding the bottom of the graph?