#1
Just a couple of quick questions really.

1, how can I tell what bias my amp is?

2, if it's fixed bias, can i just replace the tubes with a matched pair and be done with it?

thanks guys.

(my amps a Randall RH50 if you need to know)
PRS SE Torero | Fender MIM Tele | Jackson RR3

Bugera TriRec Infinium | Randall RH50T

Marshall 1960AV

Soundcloud
Band Facebook
#2
Loosely speaking

1.) You can read the cathode current in milliamps if you have a multimeter and a bias probe.
2.) If it is fixed bias then that usually means you need to 'fix' the bias to the manufacturers specifications manually. Non-adjustable fixed bias and cathode biased amps are the ones where you can plug and play.

If any of that is foreign to you then pay a tech to do it or read up a bit more before attempting to do this yourself. It can be done, it can just be dangerous - especially if you have to open up the amp and the adjust the bias while the amp is powered on.

I did a quick google search and didn't find to much info on this amp. If you know what the plate voltage is supposed to be and what types of power tubes you need you can probably figure it out. In all honesty, if you ask a reputable tube dealer to match some power tubes for your Randall I bet it will be close enough to plug n play. Contact Doug at www.dougstubes.com and see what he recommends.
#3
Doesn't the RH50 have bias points on the outside of the amp? Doesn't the manual tell you how to do it?
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#5
Have you found a schematic at all? I did a quick search for one and found squat.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#6
i took a look on google and found that somewhere on the back pannel they do have test points but i couldnt find anything about what the bias is supposed to be set at. it seems like randall is boasting that its a "user friendly" bias section that can allow the user to switch back and forth between el34 and 6l6. other than that there is nothing.
Live Rig
Michael Kelly Custom Shop Plum Telecaster
Michael Kelly Custom Shop Plum Patriot


EVH 5153 50w
Jet City 2x12
Custom Board

It is NOT trash metal it is tHrash metal...get it right
#7
Doesn't seem very "user friendly" to provide test points but no documentation about how to use them - that's just being a tease.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#8
these are some of the issues why i didn't get one of these. i really wanted one but they have had a decent amount of issues and nobody knows squat about them.

TS id just contact randall and ask their tech support (if they have it)and hopefully they are more "user friendly" if that doesn't work take it in to a tech.
Live Rig
Michael Kelly Custom Shop Plum Telecaster
Michael Kelly Custom Shop Plum Patriot


EVH 5153 50w
Jet City 2x12
Custom Board

It is NOT trash metal it is tHrash metal...get it right
#9
Is this your amp? It is a head version of the RT50TC combo
http://www.gak.co.uk/en/randall-rh-50t/28494

This I thought was informative but I guess it is not
http://music-electronics-forum.com/t10791/

This looks to be about biasing a RH50 but it is in French
http://www.guitariste.com/forums/amplification,bias-du-randall-rg-rh50,180841.html

somewhat helpful...well not really
http://acapella.harmony-central.com/archive/index.php/t-1085252.html


Here - this one looks the most helpful. From the MTS forum. See the post second up from the bottom by jmgman70. That seems to make the most sense to me. There is a test point (as iheartgun said) for each power tube (right and left) and then a ground (middle). The recommended bias in mV seems on par with what I would expect.

http://mtsforum.grailtone.com/viewtopic.php?t=6233&sid=0936cb41af8631de7de8aa28b6dbdba9

Maybe Cathbard can figure out more.
Last edited by 311ZOSOVHJH at Oct 27, 2011,