6l6 in VHT Special 6

[kleuck]

I'm not equipped for that, and actually not really interested, but why do you want to see a placebo effect ? I made repeated tests, i takes me a couple seconds to swap tubes, the amp is not powerful enough to make me deaf, so, i'm sure of what i say.
You can just give it a try you know ? Just a couple resistors and switches -and tubes of course- are needed.
Even different 6V6 do not provide the same power -by ear- i love the old RCA in metal case, but they do not sound as powerful as Mazda or Brimar 6V6 for example.

BTW, i was probably wrong, my anode current for 6P3S is already 67 mA, a true 6L6GC would need about 80 to 85, i think the PT cand stand this extra juice.

[kleuck]

Tried an old 6L6GC 'Dario Miniwatt) today, sounds as powerful as the 6P3S-E, muuuuuuch better sound.

[big_teee]

Tried an old 6L6GC 'Dario Miniwatt) today, sounds as powerful as the 6P3S-E, muuuuuuch better sound.

I read a similar test on another forum.
Another Tube Favored, was the Tung-Sol 5881 New issue.
Terry

[kleuck]

Interesting, with the stock bias or with same kind of bias and impedance trick as i do ?

[kleuck]

Tried a 6K6GT (RCA) today, with the amp on the "vintage" position (lower B+, around 300-310 volts) but also on on the regular position (not for too long, no redplating, but i will have to measure voltages an currents to see if at least the tube operates more or less in a safe zone), these tubes are nice, sligthly less power than the 6V6, a little "pentode fizziness" added

[tedmich]

you could try to mod the tone stack to a more "Ultra" topology and maybe add a few "depth" caps
https://docs.google.com/open?id=0Bx4...ViYjdkMzYwMzBl
^^big .png file



^^preview

[kleuck]

Why ?

[Rayman]

Why ?

A question for Klueck,

First...thanks for sharring all of your notes on these mods....I've learned quite a bit from your experience...I'm fairly new to tube amp modding so I've been trying to understand all that you have suggested...

Can you explain the reason for referencing the Heater to the Cathode....I noticed that early on you did not reference the two...simply adjusted the Cathode resistance to achive the correct bias...but later you decided to refrerence the two...From the tube datasheets the spec indicates a maximum +/- 200V...which we will never see...what other reason for referencing heater to cathode ?/

thanks,
Ray

[kleuck]

Just an old trick to reduce hum.
Cathodes pick hum from the heaters when their voltage is higher than the voltage of the heaters, which is actually 0 (average, as it's AC)
Connecting the virtual ground of the heaters wiring to a higher DC voltage (instead o ground) reduces the hum, you can do that with a divider from the high voltage line (would be more efficient, as you can achieve a floating 40 volts or so) but it's so easy with a cathode-biased amp to simply use the power tube cathode voltage
Merlin has a complete page here : The Valve Wizard
Did not do this at first, cause i was finding it a little tricky -first time i've done so much mods in a tube amp, did not want to fry it or myself etc.

[kleuck]

Bias was a little cold to my taste (especially when using a 6L6) -not center-biased- so i modified the cathode resistors. 6V6 are now between 12 and 13 watts and 6P3S between 20 and 21 watts. I would prefer 14 and 22 so will try to lower the resistors a little more.

[J M Fahey]

Just curious: what does "center biased" mean in this case?
Thanks.

[kleuck]

The OT is 9K a so center bias ("max power") with the anode voltage i measured (342 volts if i remember well) would be around 14 watts static for a 6V6, for a 4K5 OT and with the 6P3S, it would be 22 watts (310 volts on the anode) so i try to nail that, not really for the tiny difference in power (not sure to hear one) but to try to have a better sound when using 6L6 or 6P3S-E, which doesn't sound really good with the cathode resistor meant for the 6P3S.
I try to find the best accomodation between the two bias resistors, for all my tubes (EL84 with the socket are runnnig pretty cold too, 9 watts)
Did not try yet with, but i found the 6V6 and 6P3S to sound better ("rounder") and slightly more powerful, but it can be a placebo effect, i did not have time to really play, just a few minutes to be sure nothing was burning or redplating

[kleuck]

Tested the 6P3S-E and a vintage 6L6 this morning, indeed the 6P3S-E sounds way better now.

[kleuck]

http://youtu.be/DBodXr4docc

My friend Marc is playing an alder Telecaster, with Tonerider pickups (alnico III) and a custom electronic : 1M pots and 5 nf tone cap.
The VHT is (obviously) modded, bias is a little higher than on my last schematic (430 ohms for the 6V6 and 235 for the 6L6-like) R5 is lowered to 22K.
At the beginning of the video, the SP6 is fitted with a 6P3S-E, at the end (Hendrix) it's a 6P3S (slightly less powerful, but much more musical imo).
Preamp tube is a Telefunken smooth plate.
Cab is fitted with an Eminence Ramrod (awesome speaker) which is a 10".
Video recorded with a Sony HxV7 (or H7Xv ?) well, a good APN, on YT you can hear in HD, it's really better, but 8-10 watts in a small room was too much, the sound is squashy.

[Bruce / Mission Amps]

Yikes that tone in first part hurts my ears....