Xits

C Moore · Post by **C Moore** » Sat Mar 16, 2013 7:21 pm

I built an amp that is pretty close to the Xits-10 schem.
It works OK. I am just in the process of "fine tuning" so to speak.
I have (in round numbers):
13 volts across a 150 Ohm Cat Resistor
315 Volts on the plates
320 Volts on the Screens

Seems like I am running the tubes pretty hard.?
Do I need to bring down the screen voltage.? Maybe via the voltage divider (wish I had saved the link) that I read about on TAG not too long ago.?

Thank You
This is a gutted Crate V18 btw

http://i111.photobucket.com/albums/n143 ... its004.jpg
http://i111.photobucket.com/albums/n143 ... s003-1.jpg
http://i111.photobucket.com/albums/n143 ... s002-1.jpg
http://i111.photobucket.com/albums/n143 ... s001-1.jpg
http://i111.photobucket.com/albums/n143 ... its005.jpg

Blackburn · Post by **Blackburn** » Sat Mar 16, 2013 7:26 pm

Why are your screens higher than your plates? That's a recipe for trouble! Try raising your screen resistors.

David

Blackburn · Post by **Blackburn** » Sat Mar 16, 2013 7:30 pm

I also just calculated your dissipation wattage, which is too high. You're dissipating above 13 watts with that 150 ohm resistor. If you go up to 200R or 220R you will be fine, but fix the screens first.

C Moore · Post by **C Moore** » Sat Mar 16, 2013 8:57 pm

Yeah.
10-4
I will do whatever it takes to knock the screens down below the plates.
I will see what kind of power resistors I have in the 200-250 Ohm range.
To be honest..... I was happy that I put power to this thing and am only looking at "minor" problems it seems.

It can be difficult to make one amp into another, but this chassis has a lot of room. I really admire you guys that are adapt at creating a good layout. That is an important skill when you are working from "ground zero" so to speak.
FWIW this amp has a Cut Control, SS Bridge Rectifier, and No Master Volume.
Will definitely let you know about the screens and bias when I get them under control.
Thank You

dorrisant · Post by **dorrisant** » Sun Mar 17, 2013 4:36 am

I've got 387 on the plates... 379 on the screens...
B+1 397
B+2 383

PT is Edcor XPWR107-120.
Cathode R is 125R... I will recheck the mA, I forgot to write it down.

I can give you more voltages/ mA if needed... just ask. I need to open it back up anyway.

I built strictly stock as far as possible. What schem are you using? What pt are you using?

I need suggestions to knock down the bass but otherwise awesome circuit (using greenback 10"). I love the tone stack (gonna steal it)!

Surf, Angeldop and Colossal are bound to have some insight here...

Tony

dorrisant · Post by **dorrisant** » Sun Mar 17, 2013 4:51 am

Stupid phone!!!

C Moore · Post by **C Moore** » Sun Mar 17, 2013 1:45 pm

I will take B+ all down the line (is that a Stones song.?) after I fix the screens and power tube bias.
I bought a PT from CE Dist. It is a Heyboer that was/is an upgrade for a Fender Blues Junior.
I used the schem from TAG. I did not follow it exact.
My power supply starts with bridge and a single 22/450 into a choke and then a 10/450.
I have no Master volume, and maybe a few other small changes, but the main amp is the same.

C Moore · Post by **C Moore** » Sun Mar 17, 2013 7:02 pm

OK
I have a 1k5 on the screens now. They are about 0.5 volts less than the plates... 327 vs. 326.5.

Have a 10 Watt 250 Ohm cat resistor. I now am at about 9.5 Watts for each EL84 at idle.

The phase inverter is 196 and 199 on the plates. Cat voltage is 70.

V2 plate is 225. The cathode is 2.8 volts.

V1 is 105 on Pin #1 and 180 on Pin #6.
Cat voltage is 0.960 on Pin #3 and 1.60 on Pin #8

Is this similar to what you guys are seeing.?
Thank You

dorrisant · Post by **dorrisant** » Sun Mar 17, 2013 7:13 pm

Does this help?

Sorry it is sideways...
I took B+ measurements as right after I turned it on, so they look a little low. Don't let that throw you.

Tony

LeftyStrat · Post by **LeftyStrat** » Sun Mar 17, 2013 7:30 pm

Don't mean to highjack this thread, but for those of you that have built the x10, how do you like it?

How does it compare to say, a rocket, or a liverpool?

dorrisant · Post by **dorrisant** » Sun Mar 17, 2013 7:52 pm

Great amp! More natural overdrive than a Rocket.
It can get a really good clean... but always seems to have some grit on tap.
It is pretty high gain... haven't built a Liverpool to compare it to.
The gain is warmer than in an Express.
Just a suggestion... this circuit needs the MV in order to get the full effect of the tone stack. You may never get the best clean tones without it.

I need to reduce the bass for the combo I have it in, bass control stays close to minimum at all times or it gets muddy. I don't want to change the ts values... maybe the pi caps are a better place to start... ?

I won't be gutting this in favor of anything else, it is a keeper fore sure!

Tony

Blackburn · Post by **Blackburn** » Sun Mar 17, 2013 7:55 pm

Well I've never heard one in person, nor have I even seen the schem, but I can say without much doubt that running EL84s that high won't be nearly as pleasing as Rocket or Pool specs. I mean, if you thought they were bright already...

This is what I gathered from the specs on Dorrisant's sheet anyway. I may or may not have read it right.

surfsup · Post by **surfsup** » Sun Mar 17, 2013 11:33 pm

Mine is 335 plates and around 320 screens...

I changed the TS to not make it so bassy. Also changed some cc's as well as the bypass cap on the first stage.

dorrisant · Post by **dorrisant** » Mon Mar 18, 2013 1:35 am

surfsup wrote:Mine is 335 plates and around 320 screens...

I changed the TS to not make it so bassy. Also changed some cc's as well as the bypass cap on the first stage.

What values did you change in the tone stack?

Gaz · Post by **Gaz** » Mon Mar 18, 2013 3:18 am

Try a 500KA bass pot.

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