a twreck build started - questions

[rockstah]

So when do we get to hear some clips?

soon.

[rockstah]

so i have my 1 meg resistors in place on the output tubes for biasing. ( pins 1 and 8 ties together and the 1 meg from pin 1 to ground.)
i dont know if many of you guys do it this way.
i do it like this on my marshall to be able to bias it.

anyway after i set bias to say 40mA with a B+ of 390 with this amp, when i play the bias shoots up and down depending on how hard i hit the strings.
i have never seen this with a marshall. does this sound right to you as far as the express? im talking the bias will go from 40mA to 57mA and back down. whats up with this? anyone?

Mark

[Zippy]

One MEG???

That's your problem - they should be on the order of nothing (more typically either 1 or 10 ohms, high precision). Your bias monitor resistors are literally one million times greater than they should be.

The reason that your bias is all over the map is that as you draw more current on the tube, it is dropping across the bias resistor, changing the reference to ground. You don't have a fixed-bias amp anymore - and it's not a cathode-biased amp either!

[rockstah]

One MEG???

That's your problem - they should be on the order of nothing (more typically either 1 or 10 ohms, high precision). Your bias monitor resistors are literally one million times greater than they should be.

The reason that your bias is all over the map is that as you draw more current on the tube, it is dropping across the bias resistor, changing the reference to ground. You don't have a fixed-bias amp anymore - and it's not a cathode-biased amp either!

i mean 1 ohm ( brown black gold )
i never noticed bias changing before with signal but then again i just may have never noticed - ya learn something new every day - thanks for the post!

[Ron]

If you still have the ticking sound, try a totally different set of output tubes (different brand or type). It seems unlikely with only 400 vdc on the plates, but cheap (sorry) tubes can "spit" at lower voltages. The internal insulators are not clean and the vacuum may be poor, so there can be a small arc across the surface of the insulators along the dirty spots every once in a while. It's not a tick but a spit!

BTW, the amp looks great!! Good luck in ironing out the final bits.

[rockstah]

If you still have the ticking sound, try a totally different set of output tubes (different brand or type). It seems unlikely with only 400 vdc on the plates, but cheap (sorry) tubes can "spit" at lower voltages. The internal insulators are not clean and the vacuum may be poor, so there can be a small arc across the surface of the insulators along the dirty spots every once in a while. It's not a tick but a spit!

BTW, the amp looks great!! Good luck in ironing out the final bits.

thanks Ron - i did get rid of the ticking by swapping out the Groove ( preamp tubes ) for JJ's .

[Ron]

I'm glad you found it. The only situation where I've had a preamp tube cause a ticking sound was in a few Fender amps with the optical tremolo. Choosing the right tube would make the ticking "inconspicuous."

[rockstah]

...this thing sounds killer... from crystal cleans to on - the - verge - of exploding - complex gain/distortion... all with just the volume on the guitar... its a nice amp... man its nice!

right now im experimenting with tubes. el34/6ca7 as well as big bottle 6ca7's. mullard, rca, silvania preaamp tubes as well.

Mark

[Normster]

After hearing those killer EVH clips from your Marshall, I have no doubt that you'll have one of the sweetest sounding Trainwrecks on the forum.

[Ron]

Don't forget to try a pair of 6V6s -- you'll be surprised at how different they can sound in this amp. It ain't your father's tweed Deluxe.

[rockstah]

After hearing those killer EVH clips from your Marshall, I have no doubt that you'll have one of the sweetest sounding Trainwrecks on the forum.

thank ya! i spent so much time tweeking my marshall build i almost feel funny doing anything to this circuit it sounds good the way it is.

perhaps ill just tweek it as far as tubes go first and then maybe later mess with the integrity of Ken's circuit.

i would like to get some good 22u caps to try instead of the sprague 25u's i have on the cathodes.

Ron ill get some 6v6's for sure!

Mark

[rockstah]

now i need a headbox.

[mightymike]

I have a bunch of .22uf/400v Mustards if you're interested.

[rockstah]

I have a bunch of .22uf/400v Mustards if you're interested.

hey Mike,

the cathode caps are 22u not .22u.


Mark

[mightymike]

Oh Ok rubs eyes..
25 makes more sense anyways.