15W DC30/Rocket Type Amp

[ChrisM]

Finished this amp off today. The design comes from Trinity Amps here in Toronto (http://www.trinityamps.com). The design is essentially a 15W DC-30 (also very similar to the Rocket).

Anyways I added a few mods to the circuit. Having played the stock amp before building I knew a few things I could do.

- One tube reverb circuit to channel two (non-EF86 channel, TB channel). Single mix control to control reverb level/strength. Medium decay reverb tank mounted in the head cabinet. Reverb will be foot-switchable.
- Choke/Resistor switch. This three way switch functions as a switch that selects either a choke or resistor with the middle position being the standby function for the amp.
- Cascaded/Parallel switch. On Channel 2 the first tube parallels the two triodes. I am using a 3PDT switch to either select the two paralleled triodes or cascade the two triodes for a bunch for gain and sustain. When the triodes are cascaded there is a 70% increase in gain.
- Mid control (trim pot) on Channel 2.
- Phase Inverter limiter mod. This is a trim pot in series with the “tail resistor”. This trim pot controls how clean or dirty the signal is after exiting the phase inverter and is passed on to the output tubes.
- Mod Channel 1 (EF86) for more screen voltage. Better compression and feel.

Here are some finished pics.

[IMG:640:480]http://img.photobucket.com/albums/v610/ ... 0205-1.jpg[/img]

[IMG:640:480]http://img.photobucket.com/albums/v610/ ... CF0204.jpg[/img]

[IMG:640:480]http://img.photobucket.com/albums/v610/ ... CF0207.jpg[/img]


Here is the finished amp in it's cab, a very compact amp. The reverb tank barely fit, you can see how tight it is around the OT. It fit by mili meters.

[IMG:640:480]http://img.photobucket.com/albums/v610/ ... CF0323.jpg[/img]

[IMG:640:480]http://img.photobucket.com/albums/v610/ ... CF0325.jpg[/img]

[IMG:640:480]http://img.photobucket.com/albums/v610/ ... CF0328.jpg[/img]

Cab is a pine 112, Tone Tubby AlNiCo.

[M Fowler]

Chris that looks like a very good amp, I like your added features but 70% gain holy crappers Batman I would think oscillation would be abundant.

[C Moore]

Wow!
I do not think the average guitar player would appreciate what a great job you did with this amp. There is a lot of "stuff" going on in that chassis, a lot of features in a small amount of real estate so to speak. That could easily turn into a rats nest if the builder did not have some skill, patience, ability, etc. etc.
You did a good job.....

[Drumslinger]

Chris,

nice job on the amp. very clean and tidy. congrats on the new build!

[Gee]

Very impressive build and some creative ideas in there too.

Do you have a schematic of how you implemented the parallel/cascade switch? I'm keen to do something similar in my Spitfire clone.

[Noel Grassy]

No doubt Chris, one very fine looking build. Your execution beats the hell out
of anything the folks at TR are happy to charge $5K for! I'll go so far as to
say much more creative mods too.

Is the chassis Aluminum? Do you have a brake to make your own?

Nice job all around. I hope we see more good stuff from you.

Noel Grassy.

[ChrisM]

Thanks guys, it was a fun build.

Mark originally I had a the cascade setup so one tube went right into the other. On start up I had this constant oscillation that had nothing to do with lead dress. Put in a fixed voltage divider so the amp is on the verge of "wildness" with the cascade.

Gee if your interested I can draw up a schem. All I have now is a half ripped piece of paper with scribbles. Pretty simple though, 3PDT switch and a few components.

Hey Noel, the chassis is Al. I did not bend it though .

[KellyBass]

Chris, That is one very cool amp! Very nice work! Yeah, a schematic would be great...I'm a little curious about your ef86 circuit.

[Gee]

Gee if your interested I can draw up a schem. All I have now is a half ripped piece of paper with scribbles. Pretty simple though, 3PDT switch and a few components.

If you possibly could I would very much appreciate it.

[M Fowler]

Put in a fixed voltage divider so the amp is on the verge of "wildness" with the cascade.

ChrisM

Chris is that voltage divider at 220k/220k or 1M/100K?

[ChrisM]

Put in a fixed voltage divider so the amp is on the verge of "wildness" with the cascade.

ChrisM

Chris is that voltage divider at 220k/220k or 1M/100K?

Hey Mark, I forget the exact value. It was __K with 3K9 to ground. The values aren't anything special, just what worked for me. I had a pot in the circuit after I found the oscillation happening. So I tweaked the pot so the amp was on the verge of oscillation but stable. Measured from both sides of the wiper and installed the appropriate resistors.


Gee

[IMG:116:160]http://img.photobucket.com/albums/v610/kurtlives/th_scan0001.jpg[/img]

[M Fowler]

Thanks sound like a great amp buddy.

[Markusv]

Chris

I remember a few years ago when we spoke of your interest to build tube amps. Now you have gone to a very professional level. - my building is still in a pretty humble state

Excellent job and I think I may use you Parallel / cascade mod- looks like something I want to use in a Traynor Bass Mate mod

Markus V

[Gee]

Thanks for doing the Parallel Cascade schematic.

[10thTx]

ChrisM,

Any chance your amp looks sort of like this??? I did not draw the standby/resistor/choke switch.

If you have ExpressSCH (free download), I can email you the SCH version and you can edit it & post your schematic IF you are open to sharing it? Leave me a PM with your email address and I can get it to you.

With respect, 10thtx