#1
Hi friends
after reading through 311's extremely informative amp biasing tutorial http://profile.ultimate-guitar.com/311ZOSOVHJH/blog/?to=on&date[month]=2&date[day]=25&date[year]=2010
I now feel ready to ditch the stock valves in my plexi for something nicer. I bought it used (barely) a couple of months ago, and just finished paying off my credit card debt (i'm a full time student working my ass off to support gear fetishes, I'm sure many of you are the same ). Anyway I've managed to save some extra cash for new valves and a bias probe etc but before I proceed I just have a couple of questions.

I'd like to preface this by saying I have an intermediate experience level with electronics and am good at following instructions, and I plan on following all of the relevant safety procedures when I do this, having been electrocuted several times in the past (not by amps!)

After reading Cathbard's advice on valve selection in an earlier thread, I'm considering a matched quad of Mullard EL34's for the power section and a JJ ECC803 in V1 of the pre, and two Mullard ECC83S's in V2 and V3, and the Eurotubes pro-one bias probe (not wanting to use my cheapo multimeter). Basically I'm just wondering is it worth paying for a matched quad? Thoughts on gold pins? I'm not keen on paying for NOS but I've heard good things about new mullards.

Also, some of the pots are pretty scratchy, especially the presence knob, I took a look inside the back of the amp the other day and everything was very clean with no sign of dirt or corrosion and minimal dust. I'll change the valves first but plan on using some contact cleaner on the pots after, any recommendations for a good contact cleaner? (in Australia) Pretty sure we don't have deoxit or super 10 here. Cheers for reading, please excuse the essay, I promise gut shots and a video of the final product cranked in my backyard when I'm done!
#2
Thanks

Yes, you want a matched quad
Don't worry about gold pins - that's snake oil
I have a matched quad of Mullard EL34 and I was pretty happy with them. Replaced with SED =C=
Marshall amps are known for having scratchy pots. If it is just the presence knob I wouldn't worry about too much for now. Not sure if it would even be worth trying to replace/fix.
Dioxit is what I use, but Cath or someone else can help you with an alternative.
Good luck
#3
Quote by 7thString
Basically I'm just wondering is it worth paying for a matched quad?


yeah, you'll want a match quad.

i would prefer a set of JJ EL34's myself. i have not been impressed by my experiences with new mullards.

Quote by 7thString
Thoughts on gold pins? I'm not keen on paying for NOS but I've heard good things about new mullards.


i will sometimes use a gold pin tube in the V1, sometimes it'll sound a bit more firm. i have a couple gold pinned 12ax7's around and i'll try them out. more of amps just run a normal 12ax7 in v1 though.

also, if cath were here i think he might recommend a 803 in the V2 slot as well. i generally have enough tubes around were i'll try some different things out and see what i like.
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
#4
Okay thanks for the advice guys, I'll experiment a bit with the pre after I'm happy with the bias of the new EL34's. Or should I do this the other way round?
#5
I don't think it matters too much. Assuming you have all new or good preamp tubes. Now if you want to experiment and do some 'tube rolling' then def bias the amp first. If you are having problems with the amp and suspect it may be a bad preamp tube then by all means swap it out.

I would get the amp biased to sound its best first. That mean minimal cross-over distortion. Go with your ears but do not play through the amp while the probe is installed. It is a bit of hassle having to wait for the tubes to cool down and then putting the probe back on etc etc but your ears will tell you what is right (along with the reading on the probe). Too cold and thin, turn it up a bit and then play again. To fuzzy or 'warbly' turn it down a bit and play again.

Now if you have a bad preamp tube then yes, that could skew this exercise but lets assume all the preamp tubes, and more importantly the phase inverter tube, are in good working order.
#6
If anyone is interested, here's the guts Please excuse poor photography Seems that 'Denise' did ok..? Sprayed some contact cleaner into the pots and that seemed to get rid of any scratchyness.
The tubes were stock as expected. I still haven't decided on brand / type to replace with, but am likely going with JJ ECC803 in V1 and JJ ECC83S for the other two, but so many ****ing opinions on the net about plexi power tubes. I read one fairly convincing argument for 6550's giving a solid hendrix tone, but I think personally I prefer EL34's so am likely to just get a full retube kit from Eurotubes, because I can get a bias probe from them too. Anyone had good / bad experiences with Eurotubes in the past?
#7
I wouldn't have said that, I would have said JJ everywhere, ECC803 in V1, ECC83S everywhere else and either EL34 or EL34L, preferably L's. Unless you can afford SED EL34's. I certainly wouldn't have said Mullards - unless they were British.
This is of course unless I was discussing NOS. That's a whole 'nother ball game.
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
I would use SED EL34 if I were you. Much better tubes than JJ (not that JJ are bad) in a Marshall. SED can handle a larger plate voltage than JJ's and Marshall amps are always high plate voltage's than most other amps. www.tubesandmore.com has the best prices on SED in the USA $157 a quad. SED is all I use in my Marshall
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
#9
SED are best, no doubt. They're just gonna keep getting more expensive too. If you can afford them, buy them. If you can't, JJ are the go.
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
#10
Ok cheers, I respect your opinion so I'll get a quad of JJ E34L's (E34L's right?) and probably pull the trigger on some Winged C's in a few weeks (when I have money) to compare and likely stow away until word of the apocalypse
#11
Quote by 7thString
Ok cheers, I respect your opinion so I'll get a quad of JJ E34L's (E34L's right?) and probably pull the trigger on some Winged C's in a few weeks (when I have money) to compare and likely stow away until word of the apocalypse

Yeah SED's are worth getting, I have a set in my Marshall and a spare set just in case. I also have a spare set of JJE34L for it also, but I have yet to try them out.
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
#12
I've got a quad of JJ EL34L's in the Randall. They rock. You run them hotter than normal EL34's. They hammer.
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
#13
Done! Was actually simpler than expected once I knew what I was doing. The only issue was a blown fuse in my DMM before I even started measuring, ended up having to drive 30min to Jaycar to find a half amp fuse for the P.O.S Anyway big thanks to 311 and Cath for their advice, huge improvement in clarity and overdrive tone when compared with the stock tubes.
This was my workspace, pillows to attempt to save it if that inch of chassis holding it up were to slip off

The factory bias wasn't actually as cold as many people say online, around 34.65 mA. I ended up around 33.3mA, and it was reassuring to find that all four tubes had been matched close to this (Eurotubes). I couldn't notice much difference in the sound from about 28-38mA but with the VR1 pot all the way CCW (~50mA) it definitely matched up with 311's description of being 'warbly' and similarly at full CW (~20mA) it was slightly thin / icey.
On an unrelated note, saw Jimmy Barnes play a couple of weeks ago, and it was epic. Here's a crap picture I took whilst completely drunk and stoned. Ian Moss joined him later for a bit of nostalgic fun and earlier in the evening Brett Kingman pumped out a great set with James Reyne / Daryl Braithwaite.. (Cant remember who )