New 5E3 build bias check - am I ok?

[JPK]

I just powered up the 5E3 I've been working on for the past couple weeks. It sounds great, it's got that really nice glossy Fender high end with some amazing low end. Sounds big. I'm pretty happy with how a USA Strat sounds through this. The only issue is I think it's biased a little hot and will post the numbers below (Fluke 77, amp was warmed up). I calculated plate dissipation using both methods. Can you guys check my math to see if I'm doing this correctly? Also should I increase my cathode resistor?


Tubes: 2 x JJ 6V6S
OT CTR tap = 373V
Plate 1 = 368V
Plate 2 = 368V
OT BRN lead to plate 1 = 151.0 ohms.
OT BLU lead to plate 2 = 164.1 ohms.
Cathode voltage 20.1V
Cathode resistor 250 ohms.


-Plate dissipation using cathode resistor method (not as accurate):
I cathode = (20.1/250) = 80.4 ma. That's split evenly with the matched set of 6V6S so 40.2 ma per tube. I plate (is 5% less than I cathode) = 38.19 ma. P = 368 x .03819 = 14.05 watts. 14.05/14 = 103.5%

-Plate dissipation using OT resistance method (most accurate):
I plate 1 = 5/151.0 = 33.1 ma. P = 368 x .0331 = 12.1 watts. 12.1/14 = 86%
I plate 2 = 5/164.1 = 30.5 ma. P = 368 x .0305 = 11.2 watts. 11.2/14 = 80%

Since the JJ 6V6S is rated at 14 watts max. I should be ok or a little hot at 86% and 80%? I think it sounds good but I've heard that Fender used to bias these at like 70% ish. Cooler than where I'm at.

[JPK]

Also I'll post my gut pic even though it's not as pretty as ya'll's builds.    There were a few wires that were supposed to run under the board but I just said screw it and ran them on above. I wasn't crazy how the wires soldered up under the board. It seemed like the turret bottom ring wasn't taking the solder so well. Didn't give me a warm and fuzzy soldering feeling. Also there was no way to get 3 wires in one of those holes so I skipped doing those on the bottom. Two things crossed my mind when I built this thing. 10 pounds of $hit in a 5 pound box, and building a ship in a bottle. I'll stick to bigger chassis next time. It's pretty quiet so I have no complaints about it.

[shooter]

so, take the 3-reading added then divided by 3 I get 89.9%, perfect! 


the "should I adjust" test I use;
monitor the cathode voltage, my fluke has a min/max/avg function, us that to make life easy
play like you'd use the amp for 15 minutes, do the math, adjust bias as needed
repeat til you sleep well

[sluckey]

It's typical for cathode biased amps to run at 100%. Don't worry about it.

[JPK]

Thanks for both of your input. I just tried this amp with my Tele loaded with Custom Shop Nocaster pickups through a 2 x 12 bottom with Celestion Creambacks. Wow, this amp has got a very articulate tone, just ear candy. Also very loud. Fills the entire house with a nice reverb-sounding echo. Cool amp for sure. Glad I built it. You want a classic Fender sound, this amp nails it.

[shooter]

Wow, this amp has got a very articulate tone, just ear candy.

that's been the sentiment among most of the guitarist that have played through my cathode biased amps
things like "Man, you can't cheat with this amp, you hear EVERY mistake", "Very touch sensitive.."


you also found the other magic, good cabs n speakers


enjoy your creation

[mresistor]

@Shooter  does the Marshall 1974x also qualify?

[shooter]

If it's self-biased, I'm busy with 420 other things to look up the schematic 

[Voxbox]

JPK,


I've noticed that you are using a JJ 5Y3S rectifier.

I installed these in two Tweed Deluxe builds I am doing for friends just now, and I have some observations that you may find useful on the JJ.
I got the JJs as they are readily available if they needed to be replaced by my customers in the future. A rectifier is a rectifier, right?
Nope......

In doing an AB test using a Radial Engineering head switcher that switches one of two heads into one speaker, there is a noticeable difference in the response of the amp when using the JJ recto. And, to my ears, its not desirable for me.

Comparing the JJ recto build with own earlier build with a Sylvania 5Y3WGT, my perception of it is that the JJ recto makes the sound less dynamic. Both JJs that I have do this, so I'm pretty sure its not an individual valve that is acting this way. Installing the JJ in my own amp has the same effect on my amp.


A contact in the valve/tube supply business has found the same with the JJ valves, so its not just me!!    I've now installed a Sylvania in one amp and a Philips in the other, due to availability.

Having done some tests, I'd seriously recommend trying any one of the following -
Sylvania 5Y3WGT
Philips 5Y3WGT (It's really a Sylvania with the Philips name on it)
Raytheon 5Y3GT - gives an even higher B+ and even more responsiveness.
RCA 5Y3GT
Hytron 5Y3WGTA, limited testing but good initial impression
Philips Gold brand 5Y3WGTA, limited testing but good initial impression

I guess that the JJ affects the whole internal resistance of the power supply, making it higher? I'll let the valve experts on the forum give a technical explanation. 

BTW, The JJ 6V6s are fine for me and use them in my own amp.

I'd be really interested to hear your opinion if you try any of the other rectifiers out.
All the Best.....another rabbit-hole to go down 

Cheers, VB

[JPK]

@VOXBOX Thanks so much. I'll pick up one of those you listed and try it. I have nothing to compare since all I have is the JJ. Sorry I didn't see this post until just now. I should really subscribe to my threads. 


Edit: I just discovered the "Notify" button at the top of the thread and used it.

[Voxbox]

Grand!
Let us know how you get on sir