#1
Okay so I replaced my fuzzed out tubes for the first time yesterday, and now the high popping/static sound has left with my broken tubes which is great, but with these new ones my amp now sounds astonishingly quieter. It still works, just with settings cranked it sounds about 1/4th it's potential volume level.
Also, the tubes are 6L6GCMSTR. Any help would be great, thanks!
#2
What were in it before?

Take them out, spray the pins with contact cleaner, put them back in.
Spin 'round carousel when your horse isn't screwed in.

My band:
Fractured Instinct
(For fans of Death/Groove/Prog Metal)

Ibanez RGA42E
Ibanez S420
LTD H-301
Ibanez RG520
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#3
The same kind of tubes were in before except what were once Ruby's and now J.J Electronic. And thanks, I'll try that.
#4
make sure you bias the amp, even if you put the same type of tubes it...likely the Bias has drifted over time and the new tubes will have different optimal settings. Assuming that cleaning the contacts/sockets doesn't solve the problem.
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#5
Thanks for the tip and yeah, I'm just noticing now on the back it has a 'Power Bias' set-up and a tiny flathead-screwdriver shaped thing inside it, which Im guessing Im supposed to turn but Im not sure.. From most youtube videos this one seems a lot more automatic as opposed to opening up the motherboard and manually adjusting the voltage.. It's a newer model of amp and like I said this is my first time replacing them.
I might bring over someone who knows more what they're doing in this area but in case it's an easy adjustment Im curious to ask if anybody else is familiar with this 'Power-bias' set-up?
#6
What amp?
Quote by DeathByDestroyr
See, it's important that people clarify when they say "metal", because I pretty much always assume they are a Cannibal Corpse fanboi.
#7
Quote by R45VT
What amp?
This. Without knowing what amp it is we are just pissing in the wind.
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
Sorry, the amp is a Randall 50 Watt RT 50 (if Im not mistaken?)
#9
That has the same system as my RM100. They aren't self adjusting but they are the easiest amp to bias on the planet.
From the manual.

The RT Series of products from Randall takes the danger and mystery out of bias and puts it safely into
the users hands. You will need a decent quality digital voltmeter capable of measuring in the 100 millivolts
DC range. This is a very basic type meter available at any electronic supply house or Radio Shack. They
typically cost anywhere from $10 to $25. About the cost of one bias adjustment from your local amp tech.
You will also need a small, flat blade screwdriver to turn the adjustment control.
1) The amp should be on, standby in the “PLAY ” position and all knobs all the way down.
2) Turn the meter on and set for reading DC millivolts. Consult the meter instructions for how to do this
properly. Since all meters are different it is extremely important that you thoroughly understand what
you are looking at on the meter display.
3) Insert the Black (Negative) meter lead into the panel hole labeled “COMMON ”.
4) Insert the Red (Positive) meter lead into the panel hole marked “TEST POINT 1 ”
5) You typically will observe a reading between 25mVDC (25 millivolts DC/.25v) and 45mVDC (45
millivolts DC/.045v).
6) With your screwdriver, turn the “BIAS ADJUST ” control to obtain the proper reading for your
tube type from the chart below. Write this number down.
7) Next, move the red meter lead to the hole labeled TEST POINT 2. Write down the value. Both
readings from steps 6 and 7 should be within the range shown on the chart. Readjust if needed to get
both tubes into the proper range of readings. 8) Lastly, keep the red test lead in the TEST POINT 2
hole and move the Black meter lead to TEST POINT 1. You should read less than 5mVDC (5 millivolts
DC) or .005VDC. If the reading is greater, this indicates the tubes are not very well matched. It doesn ’t
necessarily mean they are defective, just not matched. If the reading is greater than 8mVDC (8 millivolts
DC) or .008VDC, we recommend replacing the pair with a closer matched set.
9) After completing the adjustments, allow at least 5 minutes for the tubes to warm up and stabilize.
Then recheck and read- just if needed. Lower settings will typically sound a bit cleaner and harder while
higher settings tend to be a bit more compressed and softer. Find a range you prefer.
BIAS READINGS:
6L6/5881 EL34/6CA7 E34Ls 6550
28mV to 35mV 30mV to 38mV 35mV to 45mV 35mV to 45mV
Meter displays differ from one meter to the next. Some may indicate for example, 30.0 for 30 millivolts.
Others may show .030 for 30 millivolts. Knowing how you meter works if of the utmost importance.


So 28 to 35mV for you.


In case you don't have it:
http://www2.randallamplifiers.com/images/stories/manuals/RT_Manual.pdf
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
Last edited by Cathbard at Nov 9, 2013,
#10
Funny. My brother has an RM50 and replace the tubes and had a lack of volume.

I found he was running 6 or 8mA.

You can just turn the knob a bit until you get volume back. If the tubes start to glow red turn it back down.

A bias probe and a multimeter are a good investment. Plenty of tutorials on the net. Cathbard posted directions. We'd be happy to help with any other questions.
Quote by DeathByDestroyr
See, it's important that people clarify when they say "metal", because I pretty much always assume they are a Cannibal Corpse fanboi.
Last edited by R45VT at Nov 9, 2013,
#11
Don't need no filthy bias probe with a Randall.

The way they do the biasing on the RM100 was a big selling point I must say. It's brilliant. Don't need no filthy matched tubes on a Randall either. Awesome machine. And you can run just about any octal tube you want. Best purchase I've made for many a year.
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
#12
Bias probe is universal. Works on more than just a Randall...
Quote by DeathByDestroyr
See, it's important that people clarify when they say "metal", because I pretty much always assume they are a Cannibal Corpse fanboi.
#13
Thank you everybody, my question has been successfully answered. You guys rock!