bench re-work amp

[Tony Bones]

I'm looking at the pic in post #33 and I don't see a pair of 1 ohm resistors. How are you measuring PA current?

Directly below the two blue bias caps on the board. Two itty bitty 1Ω/1W black resistors.

  I didn't recognize them as resistors.

[shooter]

going cooler, it's not my rig 
If it was mine it woulda been '34s self biased 

[shooter]

After 3hrs, I’m more convinced fixed bias makes no sense to me  

Idle NO signal

V5 446vdc  18mA  8.03W
V4 446vdc  13mA  6.10W

10 minute dynamic testing  (V5 reference measurments)
(math Max V * Min I, Avg V * Avg I, Min V * Max I)

Min power  447vdc * .016A = 7.2W
Avg power 438vdc * .034A  = 14.9W
Max power 411vdc * .068A = 27.9W

The problem I see using the min/max/avg, I have no clue how the data points shake out
Ie; 90% data =< avg?, or avg = just 1 max data and 1 min data?

All that said, the amp sound like it “should” to my Go/No_Go ears.  All the things the knobs control seem to change as expected, nothing smells outta the ordinary, (my favorite test  ).

On to the FX loop, final voltage checks.

Greatly appreciate the opportunity to do this build, and all the support I got in the process.

dave

[shooter]

Pam got home from a 12hr before I finished soldering, so guitar Monday.
I dropped the D & E taps from +33~ to -4 from original Tap volts.  Left the PI +32v  now 302vdc, 205 at plate.
need to tie in the FX B+ tap at C but I don't want to fly it that far, so thinkin.
the original build had the teal solder standoff up front, the new chassis is 1/2" higher, so after exhaustive standoff egg hunt, settled on a dab of superglue, cross thread the standoffs n call it a day 

[PRR]

> Min power  447vdc * .016A = 7.2W
> Max power 411vdc * .068A = 27.9W

A fix-bias amp idles cool when no load power is demanded. When working hard in a load the current rises, but some of the increased power goes to the load, does not heat the tubes.

I have NO idea what this amp is. 6V6? Two? 0.016 per tube or per pair?

Two 6V6 at OVER-voltage (>400V is a LOT for 6V6) "can" suck 2*28W= 56 Watts from power supply, and pass maybe 25 Watts to the load, leaving 31W/pair or 16W in each tube. This is hot for a 14W tube. But how long can your fingers keep it up? It may be fine. It may not be.

[uki]

V5 446vdc  18mA  8.03W
V4 446vdc  13mA  6.10W

How hot temperature does it run?

Maybe you are interested in this info about bias balance:

[shooter]

does not heat the tubes.

Thanks PRR, ya 6V6, once I dialed it back to the current #'s I could play full roar 10min and NOT leave fingerprints on the top of tube, sides might take some skin if you're not quick.

thanks UKI, it's gonna be the 1st 80degree day here AND sunny! so i'll try and watch tonight becasue I'm dragging the cab to the porch and playing till the neighbors start shooting 

[uki]

thanks UKI, it's gonna be the 1st 80degree day here ..

Oh I was talking about the tubes, in those videos the guy shows how hot the tubes are while unbalanced, 400° one side and way less in the other 260° ish, after balancing the cothode current, both tubes doing about 270°ish. Runs way cooler !!

V5 446vdc  18mA  8.03W
V4 446vdc  13mA  6.10W

Getting it around 15.5mA each tube it would do 7W ish each sides!

[shooter]

thanks Uki, imbalance in tubes has been going on before I could solder 
I will note it with the customer.  My guess, in time those really pretty NOS tubes will be swapped out for new skol, but, she sounds quite nice the way it sits.

I had to test-drive since dropping the pre volts, even to my non musical ears THAT change brought back some "magic sauce" lacking at the higher volts.  Before I couldn't dial the gain pots as far, my guitar volume controlled less than expected.  Now, once I set the gain pots and TS, all I gotta do is play with my guitar for compete "range" control.
the only downside, Mama's china dishes come close to jumpin outta the cabnit 

[Willabe]

...it's gonna be the 1st 80degree day here AND sunny! so i'll try and watch tonight becasue I'm dragging the cab to the porch and playing till the neighbors start shooting 

             

[shooter]

finished the FX, tested only using patch cord out back in, other than a small POP when I engaged didn't notice any signal change.  played her for about 1/2hr straight, no bullets!!, no smoke, no smells, shipit!

[sluckey]

So, what's the rest of the story?

[shooter]

UPS said it made it on the 1st
much as I know, hopefully it's too good to put guitar down   

[shooter]

I checked email n found this;

Incredible job on the amp, it really sounds great!
Thanks so much for taking this on!

thanks to all

dave