Grit with my grind

guitarpkr76 · Post by **guitarpkr76** » Sat Jul 23, 2005 4:36 pm

dobbhill,

What part of LA. are you in? I'm in Alexandria.

-Brenton

Jackie Treehorn · Post by **Jackie Treehorn** » Sat Jul 23, 2005 7:00 pm

dobbhill wrote:I tried the lower B+ and have to say that I like it better. I worked on my layout a bit and the distortion quality that was bothering me is much better. The amp is still extremely bright. I can play it with the treble turned off and it still has a good bit of high frequency content. I guess I just like a dark sounding amp. My JTM 45 is not near this "top-endy." Can you think of anything else I should look at that may be causing excessive HF content? Also, what is the "correct" value for the coupling caps between the PI and output tubes: 0.22 of 0.1 uf ??
D

You've examined your caps, what about your resistor composition? Metal films in the signal path definitely brighten things up. Using a carbon comp as the power tube grid resistor (or other grid resistors) might get you a softer top end. Another approach is to run the wires to the plate and cathode of the preamp tubes to get a little capacitive coupling/negative feedbaclk between them, which gives a really nice, subtler top end.

HiGain · Post by **HiGain** » Sun Jul 24, 2005 12:58 am

Hello,

I am about to begin building the Two Rock kit. Could you please explain what you mean by running the wires to the plates and cathodes?

Thank you for the great info.
Jake

Robert · Post by **Robert** » Sun Jul 24, 2005 1:41 am

Jackie,

I would also like to know what you specifically mean by "running the wires to the plate and cathode."

BTW Jake, be certain you fit your PT to your cab BEFORE you begin your build. I had to move the PT 1/2 inch in from the side and 1/2 inch back from the front to fit the TR cab.

Robert

glasman · Post by **glasman** » Sun Jul 24, 2005 1:56 am

Robert wrote:Jackie,

I would also like to know what you specifically mean by "running the wires to the plate and cathode."

Robert

As a guess, probably meaning running the Plate and Cathode wires parallel to one another and very close together. This would add some capacitance between the plate and cathode and soften the top end. You can get the same effect by putting a 100 to 500 pf cap between the plate and cathode or by bypassing the plate resistor with a 100 to 500 pf cap. One of the express prints shows this type of arrangement.

Gary

HiGain · Post by **HiGain** » Sun Jul 24, 2005 3:57 pm

BTW Jake, be certain you fit your PT to your cab BEFORE you begin your build. I had to move the PT 1/2 inch in from the side and 1/2 inch back from the front to fit the TR cab.

Thanks for the heads up, Robert. I actually have another Two Rock Ruby-- their 12/18W EL84 version-- to go by. It will be interesting to compare the tones of the two...

BTW, your pictures look really great.

Jake

HiGain · Post by **HiGain** » Sun Jul 24, 2005 4:06 pm

As a guess, probably meaning running the Plate and Cathode wires parallel to one another and very close together. This would add some capacitance between the plate and cathode and soften the top end. You can get the same effect by putting a 100 to 500 pf cap between the plate and cathode or by bypassing the plate resistor with a 100 to 500 pf cap. One of the express prints shows this type of arrangement.

Gary

Thanks, Gary. Makes you wonder why KF didn't add some treble filter caps somewhere, such is in the dumbles. From what I've read, I guess it was in his nature to achieve results through layout instead of parts. There's so much to learn!

Jake

glasman · Post by **glasman** » Sun Jul 24, 2005 4:24 pm

HiGain wrote: Thanks, Gary. Makes you wonder why KF didn't add some treble filter caps somewhere, such is in the dumbles. From what I've read, I guess it was in his nature to achieve results through layout instead of parts. There's so much to learn!
Jake

Hi Jake, I think the differences have to do with layout and the types of voicing that HAD and KF were trying to achieve. The HAD style has a smoother and thick midrange overdrive with tons of bass. While the KF has a brighter, more raw type of tone that gets better as the volume is cranked. I like both!! I will say that the KF style is easier to play while the HAD requires a different pick attack to get the goods. Ham hands don't work well with a HAD.

Just remember, one mans "thats too bright" is another mans "please turn the treble and presence up".

Gary

Jackie Treehorn · Post by **Jackie Treehorn** » Sun Jul 24, 2005 5:20 pm

HiGain wrote:Hello,

I am about to begin building the Two Rock kit. Could you please explain what you mean by running the wires to the plates and cathodes?

Thank you for the great info.
Jake

Basically, Gary covered it. You can parallel the wires from the turret board to the plate and cathodes of the preamp tubes and vary the distance between them to get the result you like. Gerald Weber talks about this approach in his first book, too, under amp stabilization. I don't think it's the same as bypassing the plate resistor (which doesn't sound very good, to me) but would be similar to taking a small cap and going from plate to grid or plate to cathode. Some kind of oscillation could also be happening in the range above hearing which could be making the audible frequencies sound ragged, so getting a bit of local negative feedback would help in that area, too.

glasman · Post by **glasman** » Sun Jul 24, 2005 5:44 pm

Jackie Treehorn wrote: I don't think it's the same as bypassing the plate resistor (which doesn't sound very good, to me) .....

You are very right, this is not a very good sounding fix as it takes the plate straight to AC ground. I prefer the plate to cathode approach in my amps.

Gary

Wayne Alexander · Post by **Wayne Alexander** » Mon Jul 25, 2005 5:12 pm

As I was installing a better bias knob (a really nice one that records which turn of a 10 turn pot you're on, and is calibrated with 100 little numbered notches on the outer edge, so you can make note of exact knob position when you've got the bias right on different sets of tubes, allowing tube swaps without pulling out your bias-test equipment, highly recommended) I checked through my Express clone trying to figure out how to increase high-end in my amp, I realized that I had a wrong value cap as the coupling cap between V1a and V2a. It was supposed to be a .0022, I was using a .022. When I fixed that, it brought my amp back to the bright microphonic metallic regions that you'd expect. So if any of you want to darken the amp significantly, use a bigger cap value between V1b and V2a, maybe .01 (the .022 was too dark).

dobbhill · Post by **dobbhill** » Thu Aug 11, 2005 7:17 pm

I had to put down my TW project for a while before it drove me completely crazy.

I believe my problem (the buzzing quality riding on top of distorted notes) has been related to layout and oscillation. Is there a diagnostic tool/procedure/technique that any of you could share with me in my quest to find out what is possibly wrong? I have an analog scope, a signal generator, and good meters.
Thanks again for all the suggestions.
D

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