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Hi all I just bought a Trinity amp from somebody off Craigslist. The amp is an old Plexi style build and sounds amazing. I actually got the schematic and took it too my amp tech to have a once over and he changed the cathode bias resistor from 250 that the original owners tech put in down to 150.

Would this change cause the amp to have to much high end? I mean I can roll treble all the way down and it still gives me ear fatigue and it's also so Frickin loud, I mean on 1 it's blasting. I am assuming them power tubes are running way hotter now and also when I bought this amp it had a bad rectifier tube in it and 1 power tube went. So now that I have legit power tubes and new Rectifier I am hearing this amp really for the first time the way it was meant to sound. When I 1st bought the amp it didn't have half the gain it does now and the feel was more sterile maybe due to it having an old nos rectifier that was barely working.

So I guess my question is where with the schematic would I have my tech look to tame high's a little. The amp isn't just high end either I get tons of bass and middle too so it sounds great but if I could have the perfect amp I would love to play while tech changed out some caps to tame brightness. You know what I mean when your ears hurt and it's not even on 2 that's loud.

Here is my amp schematic for reference and I thank and look forward to learning a ton from this site, Trinity amps your amps are amazing quality and tone!!!

http://www.trinityamps.com/docs/18WattP ... matic9.pdf

I just edited my post because after playing through the amp more I realized what I feel is the issue and maybe it's just the design of 18 watters i don't know but if I turn the gain down I get great cleans and blues tones for days and the eq is equal across all knobs as far as what i hear.

So this is maybe the design not sure but as I turn the gain up I don't seem to get lots of pre-amp distortion with the gain up and volume down. It's just kind of hairy but as I raise the volume the gain savagely goes up with the volume knob and thats when it tears your head off.

Another thing I remember was originally the guy had 12at7's in the preamp and straight off I said why? it calls for 12ax7's and even if you do like the tone of less gain, why a 12at7 I thought they had different voltages and weren't the best low gain tube to use for less gain in these stages. Maybe a 5751 or 12ay7,12au7 etc... So that coupled with a dodgy power tube and rectifier tube could of been why the gain wasn't blowing my head off then. To be honest it sounded good but I felt I was missing more tone and that's why I had to have a tech look into why this amp was eating power tubes and why he was using lower gain pre-amp tubes. Did he have the same issue and that was his way of taming the amp, just will never know.

There may not be anything wrong with this amp now that I have the power tubes and rectifier straightened out but would still like opinion on that 150 resistor that was put in for bias of el84s and I am going to try some JJ preamp tubes in place of these nos 12ax7's I have and see if they darken up the tone a little bit. I could deal with the volume and gain much better if it were more chewy and compressed, it's just got so much high end bite it hurts when turned up. I am used to amps giving up a lot of preamp distortion this seems to just want to give up el84 distortion.

Does that make sense that the amp doesn't get tons of gain with the knob dimed until i raise the volume up too around 3 or 4 then it's awesome gain but so loud, but loud in a harder way not the compression I'm used to feeling. Hate trying to describe tone and sound. Idk maybe somebody will understand what I mean. Thanks

From reading other posts it sounds like from Coco's explanation of the Slll Plexi variant that is what I may have. Every single word just hit me like yes, yes ,yup that's it. Now Idk because there were some mods done to my amp but you described my amp perfectly, less compressed, lots of gain on tap higher than 3/4 on volume, great cleans, instant AC/DC and way m0re if needed. That's everything i said above. I put some JJ preamps in the amp instead of the nos 12ax7's and I can't really tell right now cause I can't open it up at the moment.

I am however getting some great tones through the attenuator and just having fun with it. I know it's a badass amp I just want to be able to like I said earlier have somebody change values until it's mine.

VRM. - lowers voltage reduces the volume gain stays about the same. un less all the way down



no idea who it hat a 250R cathode resistor on the power tubes



Which speakers are you using ?

Hi I didn’t understand what you meant about the 250 ohm resistor. I have oversized Avatar cab with 2x12 heritage 20 watt greenbacks. They sound amazing lots of bass, mids and lots of high end. will the vrm be like an attenuators? I have a dr z airbrake that I just got used and it doesn’t do much until bedroom range by then the tone is so different and squashed.

I wouldn’t want to change anything about the tone except I can’t crank gain up and keep volume down and get awesome low volume tone. It’s either loud as hell with amazing full gain or I gotta turn gain down then it’s more bluesy tone. Sounds like power tube breakup unless I play clean with gain down.

Here's an older thread regarding the cathode bias resistor that you might find useful:
http://www.trinityamps.com/phpbb/viewtopic.php?t=1506
150 is pretty standard for these.

As for the desired "crunch"...a lot of the signature 18 watt sound comes from pushing the PI and output tubes into sweet sounding distortion. Turning down the channel volume and cranking the gain, you will mainly be getting preamp distortion, which is probably what you are experiencing.

I have a 1974 clone (normal and tremolo channels) and I basically dime the volume and tone and use the guitar volume to clean it up. Is it loud?...yes, but its only when pushed wide open does the magic of the 18 watt really happen (at least in my opinion).

As mentioned above, another option is to install a VRM. This will scale your DC voltage down to as low as 10%, allowing you to crank the amp but keep the volume reasonable, and still get that awesome distortion out of the power tubes. I've installed these in several of my amps and it works pretty well until you go way down on the voltage (in my experience). Installation usually requires some DC blocking caps on the input to keep the scratchiness tamed down. Stephen sells a VRM kit that is pretty easy to install. This may be a good option for you.

I've also used a Mini-Mass as well as a Brake-lite attenuator for this amp, and feel the MiniMass is a little better at preserving the tone especially at low volumes.

As far as tweaking the amp for tone...IIRC there are some "tweaker's notes" on the layouts/schematics for how to change the tonal character of the amp that may be worth checking out.

I appreciate your responses, I guess a lot of what I am experiencing is normal then. I played it this afternoon after work and nobody around to bother and it sounded really good. You are so correct about the magic happening when pushing those el84's. My amp is funny I don't get a whole lot of pre amp distortion, but soon as that volume knob goes up everything is pure rockNroll and the frequencies sound correct so i think i am good.

Just need to install vrm or figure out a setting on my airbrake that works. I still have time to return airbrake and may do so. It only goes down 1.8 db each notch until bedroom setting then it's a sweeping rheostat type dial, by then it's already so squashed it's not good tone.
I'll figure it out and it's fun learning in the meantime.

I had an atenuator it rolled off to mush high end

not sure I'm understanding what you mean sazafraz? I am using an attenuator as well but in all honesty by the time it gets to where the volume is decent the tone is squashed. I have to much high end if anything.

I have been rolling tubes in the pre-amp and I think I have some tubes that this amp just don't like, I can bend a note at the 4th fret D string and get this cry that sounds like robotic Matrix sound so I take the tube out put in another that's known too be good and it's fine. But that tube that was making strange noises will work fine in another amp.

Every time I think I have this figured out some weird noise or random crackling will happen. So i'm going to buy new 12ax7s as well and see what happens.

Edit: should the 1st channel with just tone and volume be pretty dirty from the get go? I thought for some reason I had cleans too but not after fixing power tubes and rectifier. I can get cleans on other channel but is the 18 watt inherently dirty on channel 1?

The first part was in regards to you saying your amp tech changed the 250r cathode resistor to 150 R

I had said I had no idea why there was 250 R in there
you said something along the lines of you did not know what I was referring too with the 250r


The next part was me referring to my results when using an attenuator .


The VRM adjusts the overall voltage of the amp

i.e. its quieter when the voltage is low and gets louder as you turn up the voltage . ( imho it does not effect the tone as much)

When your tech went thru the amp was the any value changes from the original schematic ?

Hi sazafraz I understand you now, My tech said all the voltages were exactly what they should be at different points checked out on the board and did confirm that some of the mods at the bottom of the schematic I posted were done. I'm not sure which one's I would have too take a pic and compare. I've never built an amp, I have some experience reading schematic not much, would rather pay my guy at this point. I'll start a project some day but right now isn't the time. At the beginning of this thread I posted pic of schematic, some of those mods were done to fatten up gain which worked really well. This amp is a beast and sounds like classic rock in a box with no pedals.

The amp has been too 2 different techs but both not mine. the first tech put the rectifier back in the circuit and got rid of a bunch of some solid state mess somebody did and then that owner sold the amp to me. My tech noticed the 250r and said it should be 150 per schematic and changed it. Plus the amp had bad power tube and old nos rectifier barely working when I tried it out to buy it and 12at7's in the preamp instead of 12ax7s but it still sounded good and being wired Ptp I knew I could have whatever minor issues fixed for cheap which I did.

I got all JJ's in the amp now and she sounds awesome, I am going to have the Vrm installed as soon as possible. I have been using my Dr Z airbrake attenuator and getting some tones that allows me to use amp at home without driving Mrs.Gadget crazy. I think a lot of the issue's I was having were bad tubes i thought to be good and also me just not familiar with how these amps need to be dialed in and how loud these amps can go. I thought my Victoria 20112 at 14 watts was loud and this amp is obviously a different animal and much louder.