18Watt.com

hello,
interesting! we were recently talking about this,see "lite2 & lite3 difference" regarding the 470K to 220K resistors.
i ended up using a 180 ohm bias resistor in my lite2 to bring dissipation down to 11.25watts with a plate voltage of 355 volts.
i'm with zaphod_phil on this one,you have to stay within certain parameters or you start altering the character of the "18 watt" and i would'nt want it to sound like a "jangly vox" etc.

geoff 1965 wrote:hello,
interesting! we were recently talking about this,see "lite2 & lite3 difference" regarding the 470K to 220K resistors.
i ended up using a 180 ohm bias resistor in my lite2 to bring dissipation down to 11.25watts with a plate voltage of 355 volts.
i'm with zaphod_phil on this one,you have to stay within certain parameters or you start altering the character of the "18 watt" and i would'nt want it to sound like a "jangly vox" etc.

It's interesting. Now that I have tested this mod twice (I have 2 amps, for live and rehearsall), I can hear a tighter bass response and a way more balanced tone.

I don't find then jangly at all: it may remind me a bit more of a bigger Marshall, I'd say. But, once again, it's just one opinion against many others. Maybe we just have different tastes for sound.

I like low gain pickups (singles or filtertrons), and I use a pair of 25 watt G12M's. Tubes are JJs.

I also tried a bunch of cathode resistors, now I have 280ohm resistors for each tube and 47uF bypass caps. I will post voltages asap, I don't have my notes yet.

However, I could not have been luckier to find this forum: this thing is now exactly what I wanted. Sounds loud enough, drives beatifully and has enough clean headroom to meet my best expectations.

I would recommend a try to anyone who has an spare hour (and a need for more clean headroom).

fair comment!
everyone is different and if you are happy with it that's what counts! i'd like to know what plate dissipation you have with 280 ohm resistors?

geoff 1965 wrote:fair comment!
everyone is different and if you are happy with it that's what counts! i'd like to know what plate dissipation you have with 280 ohm resistors?

Here I am again

It's as if it had a single 140ohm resistor: plate dissipation right now is a bit more than 10 Watt.

JMPGuitars wrote:Welcome to the site! I'm curious, what values did you change to? Did you test your voltages before and after?

BTW- if you're still experiencing "fartiness" at all, that can be a sign that your electrolytics may need replacing. They typically have a life of 2000 hours, which is easy to surpass in a decade of playing.

Here I got my notes.

There's not a big difference in the power section, as I said: 0.6 volts less at the power tubes cathodes (from 10 to 9,40). Apparently same plate dissipation: around 10watts.

BUT: V1 has gone from 120 to 130V, and V2 anode 1 from 178 to 205 volts and anode 2 from 178 to 210volts. I didn't remember such a big difference, but here it is

hello,
10 watts PD and your resistor changes give you better clean headroom and i notice your V1 &V2 plate voltages are quite a bit lower than the forums voltage chart.do you know what your B+ and el84 plate voltages are?
i like to make notes for future reference "builds"
thank's

geoff 1965 wrote:hello,
10 watts PD and your resistor changes give you better clean headroom and i notice your V1 &V2 plate voltages are quite a bit lower than the forums voltage chart.do you know what your B+ and el84 plate voltages are?
i like to make notes for future reference "builds"
thank's

Hi Geoff,

Yes, I got all the main voltages, just for the record:

A is 314V
B is 295V
C is 273V
Plate Voltage (measured between plate and cathode) is 304V.
OT throws 311V
PIN 9 on Power tubes says 292V
Cathodes are at +/-9,5 V

Both of my amps were built partly out of junk parts, the PTs came from Tweed Deluxe projects: so I had to drop some volts down with a sort of a "solid state tube" rectifier (as Webber Copper Caps do).

So, actually, I could rise voltage quite a bit (but I think I won't do so, lol).

I was happy before, now I just can't wait to play it again

yeah you have plenty of room to play with the voltages if you wanted,so basically running the tubes "cooler" and the resistor mods give you more headroom,good to know.
i wonder if you brought the el84 plate voltage up to the "sweet spot" around 345V would you lose headroom?
thank's for the info!

geoff 1965 wrote:yeah you have plenty of room to play with the voltages if you wanted,so basically running the tubes "cooler" and the resistor mods give you more headroom,good to know.
i wonder if you brought the el84 plate voltage up to the "sweet spot" around 345V would you lose headroom?
thank's for the info!

Back in 2001 I messed a lot around with voltages, and I didn't get such a sweet spot.

I guess it's just a matter of balance, but, well, maybe next week I can jump the sag resistor and check it out again. I bet It won't make a big difference.

I also tried 12ay7 and 12at7 tubes, both at V1 and V2: you can notice a change, but if you put the volume up there's a moment in which you get to the same overdrive as if it was a 12ax7 (at least that's what it seems in my case, I might be wrong or a little deaf). So, I didn't win clean headroom itself, it was something as the "going up to eleven" joke: you just had to turn the pot a bit more to reach to the same problem.

This mod has definitely raised the clean headroom: I have the same volume pressure with a bit of a cleaner sound. Or that's what I can perceive.