18 watt express

[dcribbs1412]

Its hot outside.
This will be a stay busy in AC build done mostly with parts on hand,
far from the classic parts and layout.
Thanks to xtian for his layout and ideas.
Pre board (small E-caps are 22uf 400V)

D

[RJ Guitars]

Its hot outside.
This will be a stay busy in AC build done mostly with parts on hand,
far from the classic parts and layout.
Thanks to xtian for his layout and ideas.
Pre board (small E-caps are 22uf 400V)

D

Hot in Arizona in the summertime... that's not a big surprise I guess.

I have made more Express builds in deviation from the classic build than I have with it, so I am already a fan of this amp. The more this happens the better chance we have of understanding those critical areas of layout and instability in the Express circuit... not that I hope you have to work too hard to make this stabile but any troubleshooting you do helps us all when we color outside the lines in our Wreck building adventures ?

Will you use fixed bias on the output tubes?

Can we assume you'll be using a pair of EL84's or maybe 6V6's?

[xtian]

Really interesting coupling caps!

[Bob S]

Nice layout Darin - kinda TW meets Dumble meets Marshall.
Not sure why, but for me the Liverpool is much more forgiving than the Express with regards to layout. Power section makes that much difference to the magnetic soup I guess.
I likes STKs too.

[dcribbs1412]

I have made more Express builds in deviation from the classic build than I have with it, so I am already a fan of this amp. The more this happens the better chance we have of understanding those critical areas of layout and instability in the Express circuit... not that I hope you have to work too hard to make this stable

RJ,
Thanks
Yes pair of fixed bias 6V6's
I'm hoping for a decent amp in the end without too many problems.
Like I mentioned in another post the probable outcome of this will be contacting you for the parts for a proper build.
I have not built a full scale TW amp yet.

xtian
Russian caps I had on hand 1000v(silver) and 630V(green) supposedly PIO not sure how they will sound or holdup in this circuit.

Thanks Bob
layout is actually from xtian
I have a donor amp I may try the quad 84 Liverpool circuit in down the road.
I see Mojo sells the STK's as NOS caps

D

[dartanion]

STKs are great!! The fact that Mojo is selling them as NOS is completely horseshit. You can order them directly from STK.

[dcribbs1412]

Got her fired up.
got sloppy with the heater wiring
Voltages are a little low 10-15V (290V PT), but in the ballpark...
will roll some tubes and hope to get pre voltages up a little
V1..192, 170
V2..250
V3..196, 205
385 on plates
B+..392
biased at -31v
Freakishly loud for 2 6v6 amp...crap!
Hope to spend some time and learn this circuit.


D

[xtian]

Yeah, your mismatched heater wiring is really sucking the joy out of it. No, it's a beauty! I know what you mean about LOUD. Mine gets PPIMV. Rock on.

[dcribbs1412]

Thanks xtian
If I learn to play/use it correctly I will go back and redo heaters
Amp is surprisingly quiet(normal hiss) even dimed.
Too late to give it some run time. Hope to soon...PPIMV may be a good idea.
Again thanks for your time and layout

D

[RJ Guitars]

D, very good work and a great rework of a donor chassis... at first I didn't see the PI tube and I was thinking you did some voodoo or something but I got it now.

Anytime you get a quiet Express you've scored some bonus points. I see the ceramic caps across the diodes on the power supply and also that filtered power socket. Did you do anything else out of the ordinary to kill unwanted noise? At a glance I don't see enough filter caps to be what we call the standard power supply... they must be there somewhere?

I like the compact sized power supply and bias board, and the outside access to the bias control. I especially like it that the PS board is not parked on top of the power transformer. I created something similar in a PCB board... makes it easy to add fixed bias to a build.

[M Fowler]

Nice job on the Express D.

rj that is a handy PCB to have.

[dcribbs1412]

Thanks RJ
Did nothing knowingly as far as lowering noise(goofy heater wiring). Luck?
Filter caps are small 22uf 400V on board with green and red leads.
Nice pcb bias board...what is the 1M to ground off the HT tap?

Thanks Mark



D

[lumox0013]

Great work I love it when the parts bin creates FranKen-Amp . when only using 6v6s what do you gentelmen feel is needed power suppy wise are you still running 200-300 ma? Ive gotten the impresion reading here that kens transformer choices played a large roll in the express sound. anyone who has done it with different transformer options please chime in im preparing for my first express and will use 6v6s but dont want to lose the harmonic richness.

[dcribbs1412]

Thanks lumox0013
This build was mostly parts on hand
iron was sitting around. I'm hoping a decent amp comes from this
but I'm sure it's nowhere close to a full Express
If I were to go from scratch I would certainly use the
proper iron for a full build, even if using 6V6 glass.
YMMV

D

[RJ Guitars]

Thanks RJ
Did nothing knowingly as far as lowering noise(goofy heater wiring). Luck?
Filter caps are small 22uf 400V on board with green and red leads.
Nice pcb bias board...what is the 1M to ground off the HT tap?

Thanks Mark
D

That is one of my best friends - it bleeds the voltage off the filter caps and lets me stick my hand in there with some hope it won't bite...