trinityamps.com

So, now that my Trinity 36 watter is complete, and sounding great, my build bug has taken me to a 50 watter. I recently completed the aforementioned JCM. Sounds pretty good so far, havent really stretched it out at all yet though. I was wondering, my bias voltages seem to be quite high. With my bias pot cranked all the way, I get about - 145 VDC. With it nearly off, I can get it in range to bias the EL 34's, but it does seem strange to me that it is so off from what I hear is the norm. Also, my plate voltages seem quite low, with no tubes in place I'm getting around 450 on pin 5 of V4 and V5, with tubes in place around 370 VDC. I am using a Mojo JCM transformer set with 360-0-360. That 370 plate voltage seems off to me. Anybody know much about these brutes?? Zaphod??

Cough, 370 VDC on pin 3 I mean....ahem......

Perhaps if you showed the schematic

Hmmmm....schematic huh?? Well I followed this layout pretty much to a T ......

http://metroamp.com/wiki/index.php/2204_chassis_layout

Thanks man. I believe most folks are getting voltages considerably higher, although I cant attest to what PT they are using. Seems low to me that I have a 360-0-360 PT, and I'm only getting 380 (yes revised I know) on my plates. On the other hand, I know nothing, and this is usually illustrated every time I post on this forum........

I know this isnt a Trinity issue, I parted this amp out from all over the place, but when it comes to Marshalls, you guys are the ones I have come to trust. Hell, I wish Trinity made a 50 watt kit (hint hint.....)

I built a 2204 a couple of years ago using Metro's Drake clone iron and I'm running around 415v with JJ KT-77's. It was around 425 with the EH EL-34's I originally had in there. There's a couple of pics in the Trinity gallery in fact...they built the cab. It's a JTM45 style chassis.

And it's a freakin ANIMAL of an amp. If that thing is 50w I don't think I'd want to be in the same hemisphere as a 2203 running wide open.

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SG + Brit tube head = Nirvana

What were the AC voltages on the PT you used Emohawk? If you dont mind me asking?

Even with my super low voltages, this 2204 also is an absolute beast!! It is sounding better by the hour as it breaks in too. Awesome amp for sure!!

I think I still have the docs on the PT at home. I'll do some diggin.

I think that amp might sound cool with lower voltages...probably a little "browner". I used the Drake clones (they're actually made by Heyboer BTW) to get a slightly more vintage flavor. It's really a plexi transformer.

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SG + Brit tube head = Nirvana

I figured out my problem. I had the wrong bias pot. Somebody, who will not be named, sent me a 500k pot instead of a 50k pot. I never checked it and just installed it, figuring it was the right pot. I discovered it last night, removed it, soldered the 47k directly to ground, and my bias voltage fell right in line. 33mv on one tube around 30 mv on the other. Also, my plate voltages fell in line as well, or at least much closer. I now have around 420 VDC on pin 3 of V4 and V5.

That big pot must have been bogging my PT down is all I can figure. Its all good now!!

Excellent! Those voltages sound right on the money. Mine runs a little higher but my line voltage is a a touch high also.

Enjoy it man...that design kills if you can stand the volume required to get it really singing.

Did you build the stock 2204 circuit or did you do some tweaking? I've done a few subtle mods on mine...clipped the "bright cap", removed the "treble peaking" circuits, slight gain boost in the first stage, plexi style presence circuit...I think that's everything. I actually put the two "treble peaking" circuits back in with one on a switch. Subtle difference - a little warmer. It's an animal in any configuration.

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SG + Brit tube head = Nirvana

I believe it is fairly close to stock. I built it using 3 or 4 layouts, and sort of mixing them. They were all very very close anyhow. Its mostly that layout from the MetroAmp forum, with a little Ceri@tone mixed in, and a pinch of Triode Electronics too. Even with all that, I think its stock -ish. Its been kind of a hairy build cause I messed some stuff up (go figure!), so I am gonna just play it for a week or so, I'm all soldered out for now. When I crack it back open in a bit though, I will do some of the popular mods. I would love a little help when that time comes if you dont mind??

Yes this amp is a beast. I dont think I'll ever need more volume..... Damn!!

No problem man. Most of my mod inspirations came from Tone Lizard's JCM800 writeup. I was also inspired by Joe Popp's build threads. My chassis, board & panels came from Ceri@tone so my layout is primarily Nik's, with some of the tweaks I mentioned above. I sourced the rest of the parts from Metro, Trinity & Ken Watts.

Here's a few that I had noted along the way. I've only actually tried #2 myself. Just haven't gotten around to fiddling with the others yet.

1. Locate the 68K input resistor (R3) and place a 330pf 1kv ceramic cap across it. This will beef up the mids and lows and make the entire amp feel more "meaty" and "thick".

2. Locate the 10K cathode resistor (R6 found on V1B) and replace it with a 4.7K resistor. This will beef up the gain. This seems to be the "sweet-spot" on these amps. If you want insane gain use a 1.5K (I wouldn't - it would be way too much & probably squeal like a MF. I have a 4.7k in mine & it's plenty - I never run it wide open).

3. Locate the 820ohm cathode resistor (R9 found on V2A) and place a .68uf cap across it. This will increase the gain a little. But mostly it gives you the nice "Plexi" midrange boost.

4. Locate the 33K "slope resistor" which is in the EQ section (R15) and replace it with a 47K resistor. This bumps the amp's entire midrange frequencies up a notch. The result is a very "fat", "thick" or "beefy" tone.

5. Locate the 22K Midrange knob (VR4) and replace it with a 50K Linear or Log pot. This is for those who are seeking more flexibilty out of the midrange knob.

6. Locate the .68uf cap (C1) which is found on V1A and replace it with a .47uf cap. This alters the midrange response and adds a "heavier" tonal quality to the amp.

Another couple I've tried are...

7. Bypass the "treble peaking" circuit running from the lo input to the pre-amp volume (R5/C4). Adds some "fatness" to the amp, especially at lower volume.

8. There's another "treble peaking" circuit - a 500pf or 470pf cap (C8 I think) in parallel with a 470k resistor (probably R10). Remove the cap for some added thickness/less shrieky top end (this is the mod I had on a switch).

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SG + Brit tube head = Nirvana

We did take a similar approach , I also followed some of Joe Popps blogs. I followed his lead and tried some very high end (and expensive) audiophile resistors I got from Angela's music. So far so good on those, although I really don't have anything to compare this amp to. I also got most of my parts from Watts, some from Mojo, the rest from Angela's, and Hoffman. I didn't realize there was much I could get here from Trinity, or I would have.

Excuse my ignorance,but where are you getting the component #'s from?? I looked at the Marshall schematic, and I cant see any numbering....... I'm pretty sure I know which components you are refering to, but not 100%.

I figured it out man. Thanks alot for the help. I tried 2 of the mods, 1)removed the treble cap, and 2) put the .68 cap on V2 cathode resistor. I dont want to do too many at once. I'll see how these play out first. Thanks a bunch!!

No problem man. Let me know how they play out for you. I've been meaning to try some things but just haven't gotten back to that amp. Too busy building other stuff (7 or 8 since I did that one).

BTW - I got the component numbers from the schematics. One of mine came from Triode I think & that one has the component #'s.

The only thing I actually got from Trinity was the cab really...and plenty of inspiration.

I didn't go crazy with the exotic components like Joe did. My amp is all 1/2w CF resistors except for the obvious stuff where you need more beef. Joe's may be a touch quieter (based on discussions I've had with him...haven't heard his amp other than clips). He was thinking about trying that gain mod but I don't know if he did. He doesn't run with a lot of gain anyway so it probably wouldn't really matter for him.

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SG + Brit tube head = Nirvana