Bare Knuckle Pickups Forum

Forum Ringside => Tech => Topic started by: MDV on April 12, 2007, 07:27:39 PM

Title: Can anyone give me a hand (e-hand, even) biasing a screamer?
Post by: MDV on April 12, 2007, 07:27:39 PM
As per title.

I have valves
I have multimeter
I have good sense not to touch any contacts when the amps on
I know to leave it for some time to heat up to get the right voltage

and blah blah blah, I have biased one amp before: my TSl. But that was soooooooo easy: its just got a screw.

Looking in the back, I'm not even sure where the bias pot is on the screamer!

Help required please, in case I do something.....udoable!
Title: Can anyone give me a hand (e-hand, even) biasing a screamer?
Post by: MDV on April 12, 2007, 07:34:36 PM
I just found out the bias pot on a powerball is inside. I'm guessing from what Ive seen the screamers the same

Damnit.
Title: Can anyone give me a hand (e-hand, even) biasing a screamer?
Post by: MDV on April 12, 2007, 08:10:05 PM
OK, I'm going in, cover me!
Title: Can anyone give me a hand (e-hand, even) biasing a screamer?
Post by: MDV on April 12, 2007, 10:18:01 PM
Found the bias pot, but I dont know which conacts which!!
Title: Can anyone give me a hand (e-hand, even) biasing a screamer?
Post by: noodleplugerine on April 12, 2007, 10:18:31 PM
Sounds like fun :D
Title: Can anyone give me a hand (e-hand, even) biasing a screamer?
Post by: Mavet on April 12, 2007, 10:28:32 PM
Here are two guides for ENGL biasing + pics.
one is for a powerball ond one for the mighty savage.
I hope you'll find common grounds with them and the screamer

http://www.lordriffenstein.com/phpbb/nfphpbb/viewtopic.php?t=621
http://www.lordriffenstein.com//phpbb/nfphpbb/viewtopic.php?t=79
Title: Can anyone give me a hand (e-hand, even) biasing a screamer?
Post by: MDV on April 12, 2007, 10:34:04 PM
Mavet, you are a schollar and a gentleman. Thank you very much!

*puts helmet back on*

Aaaaaaaaaaaaaaaaaaaaaaand again!
Title: Can anyone give me a hand (e-hand, even) biasing a screamer?
Post by: Mavet on April 12, 2007, 10:38:36 PM
It just prooves that I spend to much time on the net and to little time playing (guitar  :roll: ), glad I could help.
Title: Can anyone give me a hand (e-hand, even) biasing a screamer?
Post by: Mavet on April 12, 2007, 10:41:05 PM
*takes helmet off*
Title: Can anyone give me a hand (e-hand, even) biasing a screamer?
Post by: Kilby on April 13, 2007, 04:14:56 PM
Listens for screams !
Title: Can anyone give me a hand (e-hand, even) biasing a screamer?
Post by: dave_mc on April 13, 2007, 09:26:59 PM
major apologies in advance, it just came to me, and as you all know, I can't resist a cheap joke.




















let it read the daily mail.

*rim-shot*

sorry. :oops:
Title: Can anyone give me a hand (e-hand, even) biasing a screamer?
Post by: hunter on April 13, 2007, 11:14:02 PM
I received this long time ago, when I had a screamer myself, might be useful schematics...
http://www.thegutbusters.com/temp/ENGLBIAS.pdf
Title: Can anyone give me a hand (e-hand, even) biasing a screamer?
Post by: BloodMountain on April 13, 2007, 11:14:58 PM
haha dave!
Title: Can anyone give me a hand (e-hand, even) biasing a screamer?
Post by: Muzzzz on April 14, 2007, 10:23:34 AM
I don't get it...  :?  :oops:
Title: Can anyone give me a hand (e-hand, even) biasing a screamer?
Post by: noodleplugerine on April 14, 2007, 12:35:04 PM
Quote from: dave_mc
let it read the daily mail.


You win the internet.
Title: Can anyone give me a hand (e-hand, even) biasing a screamer?
Post by: Kilby on April 14, 2007, 12:44:37 PM
Quote from: Muzzzz
I don't get it...  :?  :oops:


The daily mail is very biased in regard to politics

Baically theyre somewhat to the right of Hitler
Title: Can anyone give me a hand (e-hand, even) biasing a screamer?
Post by: HTH AMPS on April 14, 2007, 03:34:39 PM
try this on for size...

http://www.angelfire.com/electronic/vtubes/Theory/JCM900Biasing.html

 :twisted:
Title: Can anyone give me a hand (e-hand, even) biasing a screamer?
Post by: dave_mc on April 14, 2007, 09:40:00 PM
Quote from: Muzzzz
I don't get it...  :?  :oops:


the daily mail is a newspaper, with quite a right wing bias.



Quote from: noodleplugerine
Quote from: dave_mc
let it read the daily mail.


You win the internet.


*fist pump*

"that's what i'm talkin' about!"

EDIT: lol at rob, maybe that's a little far... (though didn't they support mosely back in the day?  :lol: )
Title: Can anyone give me a hand (e-hand, even) biasing a screamer?
Post by: _tom_ on April 14, 2007, 09:51:22 PM
^
(http://img356.imageshack.us/img356/5091/o6ybwauo6yeac7kjlt7efu7ek1.jpg)

:lol:
Title: Can anyone give me a hand (e-hand, even) biasing a screamer?
Post by: Kilby on April 14, 2007, 10:06:57 PM
Quote from: dave_mc

lol at rob, maybe that's a little far... (though didn't they support mosely back in the day?  :lol: )


Nope they disowned him for being too soft
Title: Can anyone give me a hand (e-hand, even) biasing a screamer?
Post by: MDV on April 15, 2007, 02:59:56 AM
Hunter, that was a massive help, thank you.

I think I can cobble together this information now to get this done. Its all making much more sense now. I'll print that off on A3 at work and sit and correlate it with the actual board for a bit.

All this just to turn one bloody screw by the right amount!!

P.S. Dave: the screamer reads the sun, but never gets past page 3!

The TSL is well biased...I'll have to check for daily mails in the back of it!
Title: Can anyone give me a hand (e-hand, even) biasing a screamer?
Post by: dave_mc on April 15, 2007, 07:16:09 PM
^, ^ ^ and ^ ^ ^

 :lol:
Title: Can anyone give me a hand (e-hand, even) biasing a screamer?
Post by: MDV on April 16, 2007, 09:29:13 PM
Well, I think I fried my multimeter  :lol:

Its just...well was just an argos thing.

I'm still not sure what points to test  :lol:

Its not clear what goes where looking at the back of the PCB: you cant see the componets, wires just end and what have you. First time inside an amp. More confusion than doing.

Anyway. I hope these are clear...

This be re-post of hunters most good schematic

http://www.thegutbusters.com/temp/ENGLBIAS.pdf

This be bias trim pot and valves

(http://i96.photobucket.com/albums/l198/D_Man666/DSC00016-1.jpg)

This be output transformer connections from valves

(http://i96.photobucket.com/albums/l198/D_Man666/DSC00017-1.jpg)

This be whole thing

(http://i96.photobucket.com/albums/l198/D_Man666/DSC00019-1.jpg)

This be dead

(http://i96.photobucket.com/albums/l198/D_Man666/DSC00020-1.jpg)

Can anyone help me, in baby talk, find where to check the idle current please? It would be much appreciated!

P.S. HTH, your post on the JCM900 was alarming. Please tell me I dont need to solder anything yet! I'd like to do this with a DMM (a new one, not touching THAT contact again: interesting way to find which connection the plate voltage runs through to the valves though).

P.P.S. I havent changed the valves yet and played though it: its fine. Sounds better even: I uderbiased it from factory just a tad (in case...I dunno...I am actually quite cautious about this stuff...bar blatent disregard for the welfare of my multimeter) took some harshness that started this whole thing out of it).