#1
Hey guys,

I'm looking to relamp a Randall RGT100ES, and I'm woundering what the tubes does.

You can see the diagram here:
http://www2.randallamplifiers.com/images/stories/manuals/RGT100-RGT100ES-RGT100HT-OwnersManual.pdf
(page 3)

Now, I'm looking to use it for a power amp to start with, so I'll swap the 6L6 first.

Then, 12AX7 are for pream, right? So if I want to play around with the pream I'd need to change them.

But what about the 2 smaller ones: 12AT7 and 7025? What are thoses for?

Another question, I'm looking to "disable" 2 of the 4 power tube to tone it down, which one would I disable and how do I do so, just unplug them?

Thanks!
#2
Why would you swap the tubes right away?
Because if you wanted to buy real good quality tubes, you would be better off buying a power amp alone and spend more for the tubes.

Yeah, 12AX7s are in the preamp, and 12AT7s, 7025s as well as 5751s, 12AU7s and 12AY7s are lower gain tubes, swappable without having to change anything else.

To make it half the power you just pull out 2 tubes.
They should be wired in parallel so no matter what you unplug.
Name's Luca.

Quote by OliOsbourne
I don't know anything about this topic, but I just clicked on this thread because of your username :O
Quote by Cajundaddy
Clue: amplifiers amplify so don't turn it on if you need quiet.
Quote by chrismendiola
I guess spambots are now capable of reading minds.
#3
Well, surely I'll try it before, but from what I know, they are totally due!

Lower gain tubes are for a cleaner tone?

Thanks for the input!
#4
that diagram doesn't really help much

one of the preamp tubes might be the phase inverter, too, which is normally considered to be part of the power amp. i'd suspect the 12at7, but that's just a not-very-educated guess.
I'm an idiot and I accidentally clicked the "Remove all subscriptions" button. If it seems like I'm ignoring you, I'm not, I'm just no longer subscribed to the thread. If you quote me or do the @user thing at me, hopefully it'll notify me through my notifications and I'll get back to you.
Quote by K33nbl4d3
I'll have to put the Classic T models on my to-try list. Shame the finish options there are Anachronism Gold, Nuclear Waste and Aged Clown, because in principle the plaintop is right up my alley.

Quote by K33nbl4d3
Presumably because the CCF (Combined Corksniffing Forces) of MLP and Gibson forums would rise up against them, plunging the land into war.

Quote by T00DEEPBLUE
Et tu, br00tz?
#5
Quote by Dave_Mc
that diagram doesn't really help much

one of the preamp tubes might be the phase inverter, too, which is normally considered to be part of the power amp. i'd suspect the 12at7, but that's just a not-very-educated guess.


the 12at-7 does indeed seem to be the PI according to the schematic

http://elektrotanya.com/randall_rgt-100_sch.pdf/download.html

a 7025 is just another name for a low-noise 12ax-7.
punk isn't dead, it's always smelled that way.

"A perfection of means, and confusion of aims, seems to be our main problem."
-ae
#6
If I'd use the amp just for the power and not for the preamp, would I need this tube?

Thanks for all the info, I'm kind of a newb in all the valve amplification era!
#7
If you want a tube power amp, look at a used peavey Classic 20/20,50/50 they are great and cheap used.

Those Randall amps are not that great. My friends band used them briefly and they quickly dropped that endorsement because of that
2002 PRS CE22
2013 G&L ASAT Deluxe
2009 Epiphone G-400 (SH-4)
Marshall JCM2000 DSL100
Krank 1980 Jr 20watt
Krank Rev 4x12 (eminence V12)
GFS Greenie/Digitech Bad Monkey
Morley Bad Horsie 2
MXR Smart Gate
#8
Can't get a poweramp for the price i'm paying!

I've read great things about this amp thought, something like it's in between an 5150 and JCM800, which I like!

Anyway, first step is to use it as a power amp, next will be to test out the tone!
#9
You may want to dig deeper on the pulling tubes business.

I do that too but really only to save on power tube costs long term. I probably would not have gotten all SED =C= if I had to buy a quad

Some amps the pair work as inner two/outer two and some amp are staggared (Laney's IIRC and maybe some Peaveys).

Like this:

ABBA (pull the A's)
vs
ABAB (pull the set furthest away from the phase inverter)
or
AABB (pull the B's) ( i have no clue on that just guessing) Maybe that is the same thing ABAB

But consult with Randall or someone who knows more about this amp.

Are you running the guitar into the FX return or something?
Last edited by 311ZOSOVHJH at Dec 18, 2013,
#10
^ Nice ABBA refrence


My Marshall are AABB for the pairs
2002 PRS CE22
2013 G&L ASAT Deluxe
2009 Epiphone G-400 (SH-4)
Marshall JCM2000 DSL100
Krank 1980 Jr 20watt
Krank Rev 4x12 (eminence V12)
GFS Greenie/Digitech Bad Monkey
Morley Bad Horsie 2
MXR Smart Gate
#11
Quote by Robbgnarly
^ Nice ABBA refrence


My Marshall are AABB for the pairs



"you can dance...
you can jive...
having the time of your life...
oooyhooo...
see that girl...
watch that scene...
dig in the dancing queen...
ooooooh ouuuu ooooooh ouuuuu"


Wow. Did I just say that


I'll add your combo to the mix
#12
Quote by 311ZOSOVHJH
"you can dance...
you can jive...
having the time of your life...
oooyhooo...
see that girl...
watch that scene...
dig in the dancing queen...
ooooooh ouuuu ooooooh ouuuuu"


Wow. Did I just say that


I'll add your combo to the mix

Whats more disturbing is that you know the words by heart
2002 PRS CE22
2013 G&L ASAT Deluxe
2009 Epiphone G-400 (SH-4)
Marshall JCM2000 DSL100
Krank 1980 Jr 20watt
Krank Rev 4x12 (eminence V12)
GFS Greenie/Digitech Bad Monkey
Morley Bad Horsie 2
MXR Smart Gate
#13
Quote by 311ZOSOVHJH
You may want to dig deeper on the pulling tubes business.

I do that too but really only to save on power tube costs long term. I probably would not have gotten all SED =C= if I had to buy a quad

Some amps the pair work as inner two/outer two and some amp are staggared (Laney's IIRC and maybe some Peaveys).

Like this:

ABBA (pull the A's)
vs
ABAB (pull the set furthest away from the phase inverter)
or
AABB (pull the B's) ( i have no clue on that just guessing) Maybe that is the same thing ABAB

But consult with Randall or someone who knows more about this amp.

Are you running the guitar into the FX return or something?


Yes, I'll be running a ToneLab trough the Effect Return

By looking on how the circuitery goes, would I likely be able to know which tubes to pull?

Thanks for all the help again!
#14
If I'm looking in the PDF linked earlyer, the 6L6 tubes seems in parallel before the speakers output, in a BAAB order, am I correct?

And the 12AT7 seems to affect the power section of the amp?
#15
^ Edit: Yep. BAAB pull the B's

I'm sure that 12AT7 is the phase inverter and yes it is very important to the power section. It feeds the power tubes a signal. Lots of people say to change that tube whenever you change the power tubes. A 5751 works real well in that slot too. Roughly the same gain level as a 12AT7 but is real clean and real quiet. Look at the JAN Phillips brand of 5751. I think they are about $25 these days, maybe a bit more.


Based on my limited knowledge of tube amp schematics it looks like it is

Maybe gumbi, Robb or Cathbard can confirm.

If that is true then pull the two outer power tubes and rebias. That is the most common set up anyway. You won't blow anything up but do watch your tubes very closely for red-plating and get yourself some Dioxit.
Last edited by 311ZOSOVHJH at Dec 18, 2013,
#16
Pull the 2 inner or the 2 outer tubes it does not matter which ones.

Be advised that when you do this you have to set your ohms differently. If you have a 16 ohm cab you need to set the amp to 8 ohms and if it is an 8 ohm cab you use the 4ohm setting. (You can not run a 4 ohm cab doing this)
2002 PRS CE22
2013 G&L ASAT Deluxe
2009 Epiphone G-400 (SH-4)
Marshall JCM2000 DSL100
Krank 1980 Jr 20watt
Krank Rev 4x12 (eminence V12)
GFS Greenie/Digitech Bad Monkey
Morley Bad Horsie 2
MXR Smart Gate
#17
just keep the mantra of "half tubes half ohms" i go back and fourth on my splawns every once in a while. they are KT88, so half power isn't a bad thing regarding the cost of kt88's.
WTLT 2014 GG&A

Quote by andersondb7
alright "king of the guitar forum"


Quote by trashedlostfdup
nope i am "GOD of the guitar forum" i think that fits me better.


Quote by andersondb7
youre just being a jerk man.



****** NEW NEW NEW!
2017-07-07 2017-07-07 Update and a Chat On Noise Constraints *** NEW FRIDAY 7/7
2017-04-13 RUN AWAY from COMPUTERS!!! TCE? RANT ALERT!!!
2017-03-02 - Guitar Philosophy 1001- Be Prepared For the Situation (Thursday 2017-03-02)
2017-02-21 How to Hot-Rod the Hell of your Stratocaster for $50! (Tuesday 2017-2-21)
Resentments and Rambling from a Guitar Junkie
---> http://trashedengineering.blogspot.com/
#18
The 7025 will be V1. That's where you put your low noise tubes. This is a head, no? If so, stick a JJ ECC803 in there. You'll love 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
#19
Yeah, it's a head!

What is the use for the low noise tube? Does it impact the preamp or the poweramp?
#20
preamp
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
#21
Quote by gumbilicious
the 12at-7 does indeed seem to be the PI according to the schematic

http://elektrotanya.com/randall_rgt-100_sch.pdf/download.html

a 7025 is just another name for a low-noise 12ax-7.


I'm an idiot and I accidentally clicked the "Remove all subscriptions" button. If it seems like I'm ignoring you, I'm not, I'm just no longer subscribed to the thread. If you quote me or do the @user thing at me, hopefully it'll notify me through my notifications and I'll get back to you.
Quote by K33nbl4d3
I'll have to put the Classic T models on my to-try list. Shame the finish options there are Anachronism Gold, Nuclear Waste and Aged Clown, because in principle the plaintop is right up my alley.

Quote by K33nbl4d3
Presumably because the CCF (Combined Corksniffing Forces) of MLP and Gibson forums would rise up against them, plunging the land into war.

Quote by T00DEEPBLUE
Et tu, br00tz?