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When the Brown thread started, we promised Brent Bodrug from Sly-Fi for a first crack at it.

Specs included many Brown mods; cascade from Normal into TMB channel; Boost with .68; & VRM on PA only.
and we took it to Sly Fi Chapel Studios for a run with Brent - our favourite consulting recording engineer.

1. Normal Channel was PERFECT as it stood
2. TMB channel was EXCELLENT - a bit TOO bright (easily rectified) Treble on 1.
3. CASCADE is a really fun and a BONUS. It starts to get pretty close to Mesa. Pushing from Normal to TMB was good, TMB did brighten it up. Still need to tone it down in Brent's opinion.
4. Boost on TMB was not required - plenty of gain out of the box.
5. Adding the Boost in Cascade mode was crazy (unless you could really tone it down).
6. Power Amp VRM was a dissappointement - sound got fizzy and thin at lower volumes. Recommendstion was to scale the entire amp as we have always done.
7. LOUD - Loudest 18W I have heard to date.

BONUS
8. Unexpected cleans in both TMB and when cascaded mode. Beautiful Clean & loud - almost acoutstic - until about 4 on the Gain. Very useable indeed.

More to come on as the mods / testing progresses. Will get Brent to chime in.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Sounds really good. I want to hear more. And maybe some clips.

One thing on the TMB being too bright, did you have a bright cap on VR1? I have mine on a switch but I never use it. It is bright enough without it. Changing the V1 coupling cap (C1) to .0047uf will tame some of the treble. Also increasing cap across the V1 mix resistor (R42) up to 550pf. And lastly increase the treble cap (C3) up to 550pf.

I still have C1 at .0022 but I now have R42 and C3 at 500pf. I also have V2 cathode bypass cap (C20) sitchable between .68uf and 330uf. I call it the "FAT" switch as the 330uf brings in more lower-mids. I use it when not cascading. When cascading it can get a little muddy so I switch to the .68uf.

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Les

http://www.soundclick.com/unimind

Was that just power amp, or power amp + PI? The majority consensus of 18W builders and players is that power amp + PI scaling preserves crispness and definition better at low volume than scaling the whole amp. However, with PA+PI scaling it's *essential* to dial down the Volume level going into the PI as you dial down the voltage on the VRM, so that it doesn't get fizzy. I suspect that Brent didn't do that. The fizziness is a sign that too much drive is being applied to the PI+PA for the reduced voltage they're operating at.


This is an cool feature of some high-gain amps when you don't drive them too hard from the guiter. The Triwatt dos that as well in Overdrive mode.

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Great tones come in small glass jars!

^The PI + PA was scaled.
The original VRM is great because you don't have to worry about where volume/gain controls are set in relation to the VRM.


I also had a little experience with the amp.
No bright cap on the TMB channel

I'd make the treble cap (C3) 500pF. That has always been the value for the treble caps in Marshall's, I understand why you went with the 250pF though.



What's R42 at 500pF?

C20 the boost cap made the amp pretty gainy and crazy. I think coco mentioned before the boost was left off.

With that triode I'd just use a single 820R-1K resistor and leave it unbypassed. Biases the stage a bit warmer and brings you closer to a 50W Plexi in terms of architecture.

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Actually this amp was a collaborative effort with kurtlives so he's up on the details. The amp is really very close to finished.
We're betting that if you used 6V6 (driven harder) insted of EL84, it would be excellent as it stands, but the EL84s need to be tamed a little bit.



For the VRM, Brent did play with the controls on the PA/PI configuration to try to regain the texture but we all preferred the whole amp VRM. More intuitive & easier to control. We'll play some more with it. I'll get Mark Taylor involved.



We'll work on clips. Would you like to do them?

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Stephen.
Will there be an upgrade option for us original Trinity 18 owners. ie replacement turret board or maybe a small kit to do the mod? I haven't studied the plexi brown schematic to know how much is involved doing the mod on it's own.
Stew

You're viewing the New Design Turret boards, but you can do this with the old boards so an upgrade kit is a distinct possibility. Thanks for the idea.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

The R42 is the mix resistor for the TMB channel entering V2 and the 500pf is the bypass cap for that resistor.

I have highlighted the V2 and tone stack in the schematic below and that is exactly what I now have in my amp. Notice also the .68uf cathode bypass on V2A. That is where I have my FAT switch.

Incidentally, my amp now has the stock 1959/1987 spec. (i.e. no brown values)

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Les

http://www.soundclick.com/unimind

I would love to hear what it sounds like with 6V6s. From what I can tell the octals are designed to be pushed harder and have more bottem end. I bet it would sound great. And NO MORE FIZZIES. I did not order the V6 chasis so I will have to enlarge the holes to do the upgrade.

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Les

http://www.soundclick.com/unimind

But you *will* lose definition and crispness at the lower volume settings. That's the inevitable trade-off. Alternatively, you could also argue that the increased brownness is desirable...


You could always use 6CM6 tubes. They're 6V6s in a 9-pin bottle, and therefore limited to 12W dissipation (same as EL84s).

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Great tones come in small glass jars!

Damn that's the third time you have told me that . I would just need to re-wire the pinouts and figure out the bias resistor and cap. I guess I just need to order the damn things so I don't forget again. They are $7 at TubeDepot. http://www.tubedepot.com/nos-6cm6.html

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Les

http://www.soundclick.com/unimind

You'll probably need something like a 300 ohms or 330 ohms cathode resistor. 6V6s have a lot lower gain than EL84s, so you need the 18W stock 470k resistors on the grids, with 470R/22k PI tail vs the more usual 820R/56k.

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Great tones come in small glass jars!

Wonder how they compare to the 6V6 octal sound? Have you heard them?

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

What he said

Since they are almost identical specs to the 6V6s would I be able to just use the same values/design as for the Trinity V6?

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Les

http://www.soundclick.com/unimind

I have never heard them. I guess I am just going to have to try them and see.

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Les

http://www.soundclick.com/unimind

You get a tighter tone and less tendency for "fizziness" than EL84s. Some folks really rave about them. Unfortunately, they're not in current production, so they're not really suited for commercial amp designs, although great for DIY builds.


No - for two reasons. First of all a regular octal 6V6 can dissipate 14W. These ones are confined in a smaller space, and can only dissipate 12W. So you need a bigger cathode resistor. Secondly, IIRC the Trinity V6 still needs its PI optimised IMO to compensate for the lower gain of 6V6 tubes, with the 470R/22k values, which are closer to what you would have in a Blackface F*nder. It's just a small tweak, but it really helps get those 6V6s singing.

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Great tones come in small glass jars!

We have that design if you are interested and built our last v6 a new way.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Ok, so some of you may not know that testing the Plexi Brown first time coincided with a heart attack!

But since then I made the mods to the design and went back to the studio to see Brent.

I had Reduced treble cap; power scaled the whole amp; went to 820 ohms PI resistor; removed boost resistor and went with .68 fat cap; ignored the cascading. It is now as documented and as shipping.

The normal channel is still perfect, great bite and crunch. The changes in the TMB side brought it right on target for the tone were after - a hot loud Plexi with a bite to it. We still didn't think the cascading was perfect or worth the hassle to build it but the tone we were after was found when we simply jumped channels. So on builds, not kits, we will put in a pull switch that jumps the channels.



In a recording session on Jan 10, here is what Brent had to say:

" Your amps owned this session! ALL trinity!! Plexi is in both tunes - sounds AMAZING, band LOVED it and asked to use it on both (with my 50th anniversary Strat both times). We used it jumpered, just sounds like the best Marshall I never had! I want it!!!!! Also used Tramp, TC, and JTM. Strat, Rickenbacker, PRS Hollowbody. . "

More bands coming into the studio, so more feedback coming!

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps