trinityamps.com

Mods: Marshall mod. on the PI, Cut control from a DC30.
Bright switch with 180pF and 270pF, Tone bypass.
Tested with Eminence 100W 8 ohm Speaker
Electro Harmonix 12ax7, Sovtek EL84

Very low noise level, no hum or other strange sounds, worked perfectly
the first time I plugged it in. Followed the Trinity 15 layout for some parts,
thanks Coco for making the schamtics and layout public on this board.And
for answering my questions.

ok, some measurements:
EL84 Cathode Bias Voltage= 12.47V 150 ohm resistor
EL84 Plate to Ground =357V & 357V
EL84 Screen Voltage= 357.5V & 357.5V

EL84 cathode current= 41.5mA
EL84 screen current = 4.4mA
EL84 plate current = 37.1mA
EL84 plate dissipation = (357-12.47)x37.1mA = 12.78 W
I know its a bit high....

With the master volume at '2' (in a 1-12 scale) this thing is loud..
I'm started to wonder if I had put in the correct 1M A pot for the
master volume, had to check twice

Cut control works like a charm, I find that the amp is not too bright
as it has been reported on other Spitfire builds. Just need to finish that
cabinet now.

Schematic and build photos:
http://home.online.no/~eber-ha/TubeAMP/amp_build/

Espen

Looks cool. I like your head cab. What did you use for the port holes?

jason

Nice looking build Espen.

Espen, Nice job. Cool cabinet too and some good ideas to add those switches!

How do you find the tone control works? Do you get enough change?

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

Thanks for those kind comments, I'm really happy
with how it turned out, gonna do a proper job on the faceplate pretty
soon,those stickers are already starting to come off.

I can hear a pleasant increase in gain/volume when I activate the 'bypass'
tone control switch. The sounds seems more 'up front' with tone bypassed.
So the tone control is definitely sucking some sound, even when its all the
way up. For my next projects the 'bypass' tone control switch is
something I'm going to use again.

Im going to disconnect the 180pF bright cap, so it will be 'no capacitor' or
270pF on the switch. The 180pF boost only the highest freq. a bit to bright
for my taste, 270pF suits me better as it also boosts slightly into the upper 'mid' frequencies.

The port holes are 12V downlight holders I had in my toolbox.

Next project is a AX84 High Octane. And then maybe a Trinity 18 sIII, I
really want one

Spring for the sIII straight away my friend no point in wasting time

Very nice build - are all transformers Hammonds?

Yeah, thats a pretty massive power transformer you have there!

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

Yes the transformer sure is big Its not a Hammond,
its a Novarria 2x280v 100mA 6.3V 4A+4A 5V 4A from Italy.
About half price of a Hammond transformer, and it does its job,
but next time I'm going to use a smaller one, there really is no need
for that amount of iron in a small amp.

Did a bit of soldering tonight removed 180pF bright cap,
so now its only 270pF / or no capacitor on the switch.
Also did a test with a lower value PI cathode resistor:
replaced the 820 ohm with a 470 ohm to thicken the amp's
overdrive tone but could not hear much difference so I
switched back to the 820 ohm. The bias:
820 ohm 1.24V
470 ohm 0.84V


Updated web page tonight: added voltages to schem, and
added turret board layout file:
http://home.online.no/~eber-ha/TubeAMP/amp_build/

Hi Espen,

Will you be posting some soundclips? I'm planning on building a spitfire and have heard clips on other sites but your setup is novel and has some of the functionality I am looking for. BTW, did you buy a pre-made chassis or did you cut it out yourself?

Thanks for your time,
Sean

Hi Sean

Its a pre-made chassis for a JTM45 that I modified slightly.
No soundclips yet but maybe in the future, but what I can say
about the sound is that the 'clean' sound is very good, Its bright
and the bass has a lot of punch.