New Build - Express

[Firestorm]

It presumably was about 25k. I don't remember now. I would have to take it all the way out to check wouldn't I?

Measure from the point where the bias pot connects to R31, to the common ground connection (other two legs). See what happens to the resistance when you rotate the control. If stops significantly short of 25K, that's the problem.

[Zippy]

So was I positively wrong or negatively right?

Absolutely!

[Picker]

I checked it. Get 24.7k ohms so pretty close to the 25.

Off to jam with friends for a little while. I'll try to do a bit more on it when I get back

[Firestorm]

Okay. So maybe try 56K for R31.

[Picker]

Okay... I did some more reading and I have a better understanding now on how to correctly set the bias.

Hopefully, I will be able to bias it tonight and do the final checks. I may also go ahead and replace R31 first to the higher value. I'm still not sure why I would be only at a max of 29, but I think everything is wired correclty. Well see if I can get to it tonight.

[Picker]

By the way....

My girlfriend prior to learning about Trainwreck naming conventions had already started referring to my amp as "The other woman". Eventually, she even added a name before I settled on one myself. The name stuck and my new amp (once I get her running) now has a name.

May I introduce..... Jezebel

[surfsup]

My SPUD simulation of this bias circuit gets to max 28v as well. I'm trying to figure out the math for bias and its going slow but personally i'd rather understand it and build it once correctly than tweak later.

If someone who understands this circuit can explain how to calculate the range i would appreciate it. Also why is the 220k before the diode in unrectified ac?

[Picker]

Valve___Pin1_____Pin3_____ Pin6_____ Pin8
-----------------------------------------
V1_____ 198.9_____ 2_____175.1_____1.6
v2_____ 254 ______2.8 ___ n/a______n/a
V3_____ 205_____ 36_____217______ 36

V4 409
V5 405

Max negative bias still shows as -29

Install V4 & V5, set bias and check all voltages again.

I set the bias.
After I set it I measured 408v on Pin 3 of V5 and I set the bias to show 39.7m on the V5 resistor and 39.1 on V4

Removed the resistor and put back the ground wire. and got the following:

Valve___Pin1_____Pin3_____ Pin6_____ Pin8

V1_____191.6____1.9_____168.6______1.5
V2_____245______2.7_____n/a________n/a
V3_____197______34______209_______34

By the way... I didn't have a 56k resistor on hand so I left the 47k in place.

[ToneMerc]

Did you change the 47K or just straight ahead installed the power tubes?

TM

[Picker]

Left the 47k. I didn't have a 56k on hand

[Picker]

Do these last numbers look okay?

[Zippy]

How does it sound?

[Picker]

After I red-plated the one tube I have been shy about playing through it again until I got everthing straightened out. I think the whole problem may have just been that I hadn't biased the tubes correctly, but I'm not sure.

I was hoping for an "All Clear" signal from the pros before I jumped in again.

[M Fowler]

Even a pro turns the amp on and checks the status of the amp in situations like this.

Mark

[Picker]

Also, after completing the work on the amp last night, the girlfriend was getting jealous of all the time I was spending with my Jezebel, so I didn't get a chance to paly any. I'll plug in and make some noise tonight when I get home.

However, that said, the first time I turned on up until I red-plated she sounded AWESOME!