My voltage readings and bias question(s) on my new build

[steelerfan88]

 I recently built the "Phat-Ass" circuit (see attachment for layout) but used an EL34 output section. The amp sounds pretty good but there is ALWAYS room for improvement....right ?....LOL ! Anyway.....Here are my final readings on the power section. Please look them over as well as the attached layout and throw me your suggestions

PT used: Weber WO25130
Secondary B+ tap used : 340-0-340@ 150ma (diode rectified w/ (2) 5408 diodes)
Output valves used: JJEL34 (2)
Plate to cathode reading (pins 3>8): 412VDC
Cathode resistor value: 300R/10W
Cathode bias cap: 470uf/50V
Voltage measured across cathode resistor: 31VDC

Modifications I made to this layout: #1) I did NOT use the shown input toggle switch but rather wired in two separate input jacks in the standard Hi/Lo parallel configuration and used two 33K input resistors instead of the usual 68K.
#2) I left the screen resistors on pin(s) 4 at 1K each but used 5W wire-wounds instead of the shown 2w for extra security. #3) I lowered the bias resistor bypass cap from 1000uf/50V to 470uf/50V. # 4) I changed the .0047uf cap feeding the volume pot to .01uf.  #5) I changed the cap on the tone pot from .0047uf to .01uf. #6) I changed the last filter cap down to 22uf/500V. Everything else on the layout has remained the same as shown in the attachment.

 Plugging these readings into the Weber bias calculator tells me I am dissipating approx. 20w per tube with 49ma plate dissipation per tube. Am I in a "good place" with these voltages ?
 I am getting 423VDC on the screens (pin(s) 4 measured to ground) this seems a little high to me.....your thoughts ?

 Any other suggestions would be greatly appreciated ! Like I said, The amp sounds pretty good but if I can improve on it and learn something.......I'm ALL EARS 

[steelerfan88]

 on another note....I used 1M audio log pots for both volume and tone. The tone knob does not really do much until i rotate it almost 3/4 the way round. Would using a 1M linear give me a more useful/drastic sweep on the tone ? 

[jjasilli]

Yes, try a linear tone pot.


EDIT:  also try the Duncan tonestack calculator.  From its help page:  "Next set the potentiometer style.  Linear uses a linear track where the resistance is in proportion to rotation of the potentiometer.  Log A has 30% of the full value at half-way position, and Log B has 10% of the full value at half-way position."

[PRR]

> Am I in a "good place" with these voltages ?

If the load is 6.6K, I like it very much. If you also take the G2 resistors to 2K or so, it has the maybe-advantage of being pretty darn abuse-proof (my goal when fixing amps for school use). A Jazz guitarist I respect thought it played nice, and stole it for his teaching studio. Probably 20W-25W actual output before clipping.

If you use the Marshall-like 4K loading with these conditions, it technically "strains" when pushed to/past its limits. This sound may be bad or good; hard to predict and suitability does depend on the player and genre.

Your tone-stack questions.... get a pile of pots and caps, try different things. Caps and pots and the stuff which drives them all interact. You perhaps should have stayed with the presumably "good" values for the first build... I assume someone did try them and liked it. Of course we all different and you may like another flavor (set of values).

The other reason I am dodging the question is I don't see a schematic, only a layout without all values marked. How-it-works is easier to see with the circuit abstracted to the basic electrics.

[steelerfan88]

Thank You "PRR" for your in depth opinion. After changing the tone pot to a linear, I am pretty happy with it now. It has a much more usable/quicker sweep. I left the volume with a 1MA log. I am going to increase the screens resistors to 1.5K and petty much call this one done as it sounds pretty damn good......Like a really good Lite IIB circuit being pushed with EL34's......whats NOT to like about that kinda' tone ! I am using a 4K load but I don't think the amp is struggling by any stretch. I'll play it off and on over the next few weeks to give it a good test.

[steelerfan88]

Here's a few pics of the finished chassis.....