YAOB (yet another one-zero-two build)

[aflynt]

The voltage is the same pre and post choke. It's high plate.

B+1 - 446V
B+2 - 446V
B+3 - 438V
B+4 - 370V
B+5 - 364V

Bias Range - -56V to -40V

-Aaron

[martin manning]

That's with no tubes in? Seems ok, you are only drawing a bit of current at this point, through the balance resistors and the FET. I'd put the tubes in and set the bias.

[talbany]

The voltage is the same pre and post choke. It's high plate.

B+1 - 446V
B+2 - 446V
B+3 - 438V
B+4 - 370V
B+5 - 364V

Bias Range - -56V to -40V

-Aaron

Under load you should have
430 PI
320 on B4 gives you 207/214
B5 should be around 315 should give you 190/200 in a high plate..
Still load it up and see what you get under load and with the tubes you have..

Good Luck!!

Tony

[aflynt]

Loaded some winged c pts and random preamp tubes and biased it to around 30ma. Plugged it in and everything functions. Seems to sound pretty decent too. I have to leave for a job in a few so I won't be able to get all the voltages right until tomorrow. Wish I could have brought it tonight. Thanks everyone!

-Aaron

[aflynt]

I played it a bit more really quiet after I got home from the job. The only thing I noticed that I didn't expect was that the jazz setting is a lot smoother and darker than rock. From the descriptions and clips I thought jazz would be more scooped and brighter, though it does seem to match the label more this way. This is my first time playing through a "D" style amp, btw.

Anyway... I'll futz with different tubes and voltages tomorrow. So far the amp seems very smooth and fat sounding but still very clear.

-Aaron

[amplifiednation]

Congrats Aaron!! Great looking build! Its always great when you don't have to troubleshoot! How are your preamp voltages? They will fluxuate as you change tubes. You'll find some that are perfect

[aflynt]

Okay. Here are the loaded voltages. I think they might be a bit too low.

Loaded Voltages:
B+1 - 432
B+2 - 431
B+3 - 411
B+4 - 301
B+5 - 294

Preamp Plates:
V1A - 171
V1B - 177
V2A - 189
V2B - 192
V3A - 288
V3B - 281

This with the power tubes biased a bit low at 30ma.

-Aaron

[Structo]

Try a few different preamp and PI tubes before changing the dropping string.

Particularly the PI tube.

You may need to drop the B3 resistor (2K7)

[martin manning]

Also see where your FET bias is running by measuring the voltages at the top and bottom of the 10k drain resistor. Look for about 20V at the top and about half of that at the bottom. The current draw there will affect all the other voltages a bit.

If you are good there, you may want to reduce the value of the 2k7 dropping resistor (if that's what you have in there) to bring everything downstream up 10 to 20V. An easy way to figure out what you need is to clip another resistor across the 2k7. Try a 5k1 or something around there (an extra power-tube grid resistor), 1W is enough to test, to reduce the resistance to 1k8 (calculate the value using the resistor you use) and see what you get for V1a and b plate voltages. Interpolate from there to select a value to replace the 2k7 with.

OTOH, it will probably sound pretty good as-is, and you can see if the higher voltages make an improvement to your ears when you clip another resistor across the 2k7. Slavishly matching the layout voltages is not always the best plan.

[aflynt]

Fet was about 24V at the top with a 22k dropping resistor. Didn't measure the bottom.

-Aaron

[amplifiednation]

You should try some different tubes like Tom suggested. In both of my builds I have noticed 20v+ swings with different tubes. Even just moving the tubes to different positions has made a difference. I have yet to have the need to change a dropping resistor, although I did have to adjust the bias network in my 2nd gen

[aflynt]

You should try some different tubes like Tom suggested. In both of my builds I have noticed 20v+ swings with different tubes. Even just moving the tubes to different positions has made a difference. I have yet to have the need to change a dropping resistor, although I did have to adjust the bias network in my 2nd gen

I tried a few different PI tubes. The voltages just went lower or stayed the same. I'm thinking I'll need to lower the B+3 dropper.

-Aaron

[talbany]

Like I posted the loaded voltages for the PI are 430...Your power transformer is giving you 431..I would put in a 1k there (bring it up a few volts) and try some different tubes in V1 that one is sucking some current...If you like it brighter and tighter you may have to go after the 22k next..This is really where my resistor substitution box comes in handy..

Tony

[aflynt]

Changed the B+3 dropper to 1k and the B+4 dropper (22k) to 15k. Just lowering the B+3 to 1k didn't affect the V1 values much (still in the 170s). Here are the new readings with the two droppers lowered:

B+1 - 428V
B+2 - 428V
B+3 - 420V
B+4 - 336V
B+5 - 329V

V1A - 193V
V1B - 199V
V2A - 211V
V2B - 215V
V3A - 289V
V3B - 283V

It's pretty bright, but was pretty bright before too. I might try a 18K instead of the 15k once I find one. I still have to wire up the Dlator too. And the footswitch. And mount it in the rack case...

-Aaron

[aflynt]

I put an MXR Carbon Copy in the loop and the amp sounds really really nice. Here are a couple quick clips with me noodling randomly.

http://soundcloud.com/aflynt/102-build-with-carbon-copy
http://soundcloud.com/aflynt/102-build- ... bon-copy-1

-Aaron