6l6 in VHT Special 6

[kleuck]

[kleuck]

[kleuck]

Compresseur
Telecaster micros Tonerider Alnico III, VHT Special 6 'British mod), volume 14 h tone 12 h en clean mode ; cab loaded with an Eminence Ramrod ; tubes 6V6 Mazda & 12AX7 Siemens "smoothplate"
Sound files are tests of my compressor, so first amp only, then comp 10 o'clock, 12 o'clok, full tilt.

Deuxiéme first without comp, then comp 12 o'clock.

[NorCalTuna]

My buddy has one of these! It lives at my house and we gig with it to local coffee shops and such. I think it's a neat amp but I didn't like the tone control either. The boost is horrible! Why they didn't buckle another cap over the treble cap (unless randy owns a patent on this?) and get some smoother tone stack bypass action? Anyhow... I noticed that their design is essentially a champ with two tone stacks- the one knob one, and one typical t/m/b one fixed at the factory through resistors. Epic! Who knows whats next?

250K and 250K Concentric Pot | Allparts.com

It's not an audio taper but it'll keep me from drilling holes; I'll have the thing wired up tonight : ^) If anybody knows where to get a better pot, please indulge me!

I may also add a little NFB and a larger power tube cathode bypass cap but we'll see what the night holds.

[steve_rolfeca]

...The boost is horrible! Why they didn't buckle another cap over the treble cap (unless randy owns a patent on this?) and get some smoother tone stack bypass action?

250K and 250K Concentric Pot | Allparts.com

It's not an audio taper but it'll keep me from drilling holes; I'll have the thing wired up tonight : ^)

I'm not familiar with this mod- description/schematic/links to previous threads would be appreciated.

[NorCalTuna]

There's two mods there, I'm not sure which one you're asking about... So...

One thing I did to it last night was changed the tone pot to that concentric one, and pulled the tone knob and the voltage divider and other resistors which fix the response of the first tone stack out, so I could adjust the treble and bass like, uh, this, which is awfully close to the special 6 minus the vib.

http://www.ampwares.com/schematics/c...ibro_aa764.pdf

That mod is pretty badass, the amp is much friendlier now.

The next one I mentioned is the way VHT did the "boost"- it lifts the gnd on the first tone stack way up, basically taking it out of the circuit. This is cool but kinda brutal, a much sweeter way to reduce the loss of the tone stack involves placing a cap across the top of the stack, like a 680 or 750pf. You can see that here:

http://tubefreak.com/mk3-1.gif

one cap, one switch and one say 10m resistor to keep it from popping.

Next will be NFB-

[kleuck]

Some improvements i made, mostly to get rid of the remaining hum (in pink :Self between B1 & B2, R5 from 10K becomes a 33K etc)



I tested EL84 with the VHT adapter (and the "6P3S/6L6GT" bias resistor) and it's cool, hot distortion and gain, but i can see G2 glow in the tube, will have to drop the HT a little (50 volts) to use them on a daily base.
Tested 6P1P too, with another adapter (Ebay) and it's a cool tube too -will need a lower voltage too-

[kleuck]

Added a 50 volts drop zener with switch and led, to get a more vintage feeling, and to be able to use EL84 and 6P1P without frying them.

Back of the amp, with the self and the Vintage switch to the right.



Vintage mod's Led

[kleuck]

[diagrammatiks]

why did you cut the second cathode bypass cap and increase the first one?

I would think that would make the amp overly bass heavy.

[kleuck]

It's better to fully bypass the first triode (only) for a better 50 hz rejection, and i cut the second one to limit the lows,
Grid cap of the power tube is small too, same goal.
It's almost perfect with my open cab with a Emi Ramrod, but you can tune the circuit to your needs, i will perhaps limit a little more, but not on the first triode, only with the second and power tube grid cap.
You can too with the power tube's cathode cap, but i prefer to have a big cap here, to have a rock-solid bias, and it's necessary as i can use different tubes and different cathode resistors.

EDIT : i actually replaced the second triode cap with a 1µf one, tighter lows, and the tonestack (R9 >> 68K ) : sligthly tighter lows in Hi mode, and still enough in clean mode.

[kleuck]

La nouvelle self :





et les nouveaux chiffres.

[kleuck]

Mistakes in my voltages/power chart, here is the good one :

[kleuck]

The two leds :

Some tubes i use (6V6G ; E84L ; 6P3S ; 6P1P ; ECC83 smoothplate Siemens or TFK) :

BTW, i compared one more time 6P3S and 6L6WXT this morning, and the WXT doesn't sound as powerful, rich or musical as the 6P3S, so with my bias, i think that modern 5881 or 6L6GC are not a good choice, choosing a resistor for a 6L6GC would lead to a huge idle current, not sure the PT can stand it ; perhaps the best solution would be to use 5881 and bias for 23 watts.

I tried a 6P3S-E too a few minutes ago, and i sounds slightly more powerful than the 6P3S, more modern too (less musical compression) probably the best choice for max headroom and power, would need a slightly different bias to be at it's best i think (did not measure)

[J M Fahey]

Oh! , the might of the Placebo Effect !
Did you measure the actual RMS power increase?
Just wondering.