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The 1 watt should work fine as the screen usually draws very little current (in normal operation). However if a tube develops a fault, often this resistor will smoke badly due to runaway excessive current. If a new tube is then inserted in the socket, there is a very real possibility, that the resistor will be high or open circuit due to the last tubes failure - in this case you will destroy your new tube very quickly. I ALWAYS measure the screen resistors before replacing output tubes.
The advantage with the 5 watt resistors is that they may survive a tube meltdown without frying!!
cheers
bajaman

thanks for the quick reply bajaman! i think i'm going to return them and see if i can get the 5 watters cus my amp has already had a few near nuclear meltdowns so i'd rather be a little safe than sorry

I just thought I'd follow up and say I finally performed these mods recommended by soulsonic and so far the results seems to be paying off, even though I haven't actually had a chance to play through the amp and see how it sounds. Before I did anything with the screen grid resistors I figured I'd use my newly acquired bias probe to see how cold the factory setting actually was. My plate voltage was reading 519v and the tubes were reading 5mA!! If I do my math correctly the 6L6GC is rated at 30 watts max so 30/519 = 57mA max dissipation so (0.005/0.057)100 = 8%!!!! I just started getting into this whole tube amp biasing thing but I've been hearing a lot of people recommend 70% as a good place to set it since there wouldn't be much crossover distortion here even though I would assume this differs from amp to amp.

Anyway I bought a new set of matched JJ 6L6GC for the Mace and I decided to only buy 4 instead of the 6 that the amp normally comes with. I also installed a trimpot to adjust the bias and at the moment I have the plate voltage at 488v and the bias set around 40mA. I didn't stick a choke in the amp yet and probably won't but the 470ohm screen grid resistors are in place and everything seems to be good. I'm running one 8 ohm speaker out of the 8 ohm tap and I figure that should help me out a bit with playing a lower levels and still sounding good. If I need more output when I play in a band situation I'll just hook the speakers up in parallel and run out the 4 ohm tap. I'll let you guys know how it sounds when I get a chance to rip it

Thanks a lot for the help soulsonic and everyone else who contributed to this thread.

I didn't stick a choke in the amp yet and probably won't

a pity then because this makes a significant improvement to the clarity of the amplifier.
bajaman

alright alright maybe i will

I wan to stress what bajaman said, also, read the article Aiken has on chokes, it might help to convince you.

http://www.aikenamps.com/Chokes.html

bajaman wrote:The 1 watt should work fine as the screen usually draws very little current (in normal operation). However if a tube develops a fault, often this resistor will smoke badly due to runaway excessive current. If a new tube is then inserted in the socket, there is a very real possibility, that the resistor will be high or open circuit due to the last tubes failure - in this case you will destroy your new tube very quickly. I ALWAYS measure the screen resistors before replacing output tubes.
The advantage with the 5 watt resistors is that they may survive a tube meltdown without frying!!
cheers
bajaman

I agree with checking screen resistors. Disagree as to the consequence. If a screen R goes open or high that will not damage the associated tube. Removing the screen supply does nothing but silence the tube. In fact a lot of old amps have a switch on the screen supply for a standby.

so I tried to contact Mercury Magnetics about using the 5150 or Butcher choke in my amp but I have not gotten a response. I'm just wondering if I could be looking for something different since my amp runs stock with 6 6L6GC in it, even though I'm only running it on 4. I'm sorry i'm new with tube amps and still learning. i should probably start a separate topic about it

speaking of running on 4 tubes, is that going to mess with the impedance of my speaker outputs? don't want to blow a trani while I'm at it

odd as mercury has always been very good about returning my emails... did you look at their site catalog? here are part numbers. first one in peavey list is for the butcher.


marshall type chokes:

ToneClone C MMC 3H 3.3H -- 200mA -- '73-'86
ToneClone C MMC20H 20H -- 200mA
ToneClone C M-67C '67 100 watt -- 2 Henry
ToneClone C MC10H 10H -- 100mA


peavey type:

Axiom C P-BUTCH-C Butcher -- Upgrade!
Axiom C P-CLASS30-C
Axiom C P-JSX-C
Axiom C P-VALVEK-C Valve King
Axiom C P5150-C
Axiom C P-6505-C

i know they have them for the butcher and 5150 but i don't own those models, i own a mace but from looking at their schematics i can see that all 3 use the same power supply resistor. i just didn't know if there is anything else i should know about them since chokes have all have a few different ratings.

get a Marshall reissue choke from Triode Electronics in Chicago
cheers
bajaman

what do the different choke specs mean in terms of the sound of the amp. my amp has a 20H choke would chanign to a 10h or even 2h change the sound at all? in what way?

from what I've been gathering the more henries the better. i think the more there are the more filtering there is. i've been studying that article a bit trying to better understand chokes.

Hi folks
I just registered to tell you that i did the mods suggested in this thread today. Adjustable bias and 470 ohm screen resistors. I set the bias to 32mA.

I must thank you all for giving me a new amp
That harsh nasty mid sound is gone and the clean channel is great now. It does not have those shimmering fender highs but that would require a revoicing of the tonestack, but a nice "twangy" or "honk honk" sound like vox if you know what i mean.

It breaks up very nice into old marshally crunch.

..and the lead channel ... Thick, smooth higain distorsion with that frosty bite in the treble that I always wanted. Really a high end sound now.

Again, I want to thank everybody for these tips and if anybody are i doubt, don't be, do it and be greatful to yourself ever after.

cheers!

It does not have those shimmering fender highs

add the choke filter
bajaman

Gaah! You planted a new project in my head again the very same day I got rid of my previous mod-itch.
In fact, I have been keen on it since I found this thread. The only choke that I have found available here in sweden is a Fender twin reverb replacement. Would be a good fit do you think, Baja?

just curious was the mod you did on a peavey 6505 as your name might suggest?

The only choke that I have found available here in sweden is a Fender twin reverb replacement. Would be a good fit do you think, Baja?

yes - ideal - just pull out the resistor and insert the choke.
cheers
bajaman

moltenmetalburn wrote:just curious was the mod you did on a peavey 6505 as your name might suggest?

Yes you are correct, I am sorry, should have stated that in my first post.
I was too exited I guess

By the way, a choke is ordered and on the way. I will check in and give a review of this mod aswell asap.

cheers

Now that i know it was a 5150 in disguise Im REALLY sure that your excited, that amp sounds like complete ass in stock trim IMO.

I have some experience with a few modded 5150s and I have to say that the mods youve done thus far do magical things for the amp but the finishing touch would be the OT, changing the OT has another HUGE positive effect on that amp, pricey but worth it.

Ive always used mercury magnetics transformers so I can attest that'd be a good choice, though I do hear that there are some other manufacturers trannys that make equivalent improvement and might be less costly. unfortunately none are coming to mind right now, someone else can surely chime in here.

If interested in the mercury, ted weber sells em cheaper than mercury does.