6l6 in VHT Special 6

[Walking Eagle]

Other policies

kev1n, I would like to ask you a question. Would you be satisfied with a single ended amp with a triode connected 6550? The output power would be about 15W RMS...

[timrichter9]

Speakers make the amp

I ran it stock through a birch ply Vox 4x12 with Wharfdales and it seemed to open up....
Speaker first, then mods, I say.

Hi,
I was wondering what mods i would have to do to run a 6l6 in my vht special 6 and get the full 20 some watts from it. OT replacement? Bias? ect..
http://www.vhtamp.com/pdf/VHT_Specia...ic_5-17-10.pdf schematic

[kleuck]

You're right, but the question was about running a 6L6 at its best, speaker has nothing to do with that.

BTW my last mods, mostly : back to the stock value for R4, R18 (6V6 grid) >> 470K for more crunch and brightness, non polarized cap on the 6V6 cathode (makes no difference actually though this trick slightly improved precision and articulation when used on the preamp tube)
Last mods : orange

[kleuck]

Last : dark purple, the low level input is now a bright channel (cut lows under 500 hz)

[kleuck]

My "Tweedy" SP6 Ultra schematic (page 2) was crappy, so here is a better picture :

[kleuck]

Measures and calculation with NOS tubes (int my SP6, not the Ultra)

[kleuck]

http://farm9.staticflickr.com/8347/8...b1eb61dd_o.png

[kleuck]

Added a snubbing diode across the choke, a simple UF4007, not sure it will survive
I tried -as i use now a 12BZ7 in the preamp- to isolate the noval support with pieces of heat-shrink tube, sounds to work fine.

[kleuck]

Great crunch machine, lots of gain, not too much lows, "Barking amp" said a friend With these values for the triodes, 12AX7 and 12BZ7 sound good, but i prefer (more gain and dynamic) the 12BZ7. The amp sounds louder, and even louder with a 12BZ7. Video asap.

[kleuck]

Error :

[kleuck]

FYI, a TDPRI member just made a page about the SP6 Ultra mods : Amp Mods

[kleuck]

A friend tries my VHT SP6 with a 6L6 :

<a href="http://youtu.be/0goQd8S8QLQ" target="_blank">

He plays a Tokaļ (alder) with cheap mini-humbuckers (non-stock)
At the beginning with an attenuator (~1,5 watts) then without (~7watts)

[kleuck]

I had an issue after removing the Zobel : high frequency oscillation on a given combination of volume and tone, only with 6V6.
No way to get rid of it without killing the tone too, so, the Zobel is back, BUT with a lower value cap, no action on the guitar bandpass, but no more oscillation.
So the idea of using a Zobel in the cab is no more really sensible, an internal conjunctive filter would do the same.
I fine tuned the lows too (1,5 µf instead of 2,2 µf on the second triode) , and i forgot to modify the text, but the "bright" input should be called "Twang" input actually.

[kleuck]

Modified the Princeton Tone with a 10nf cap instead of the stock 4,7 for a wider sweep.

[kleuck]

Clearly here, the amp is more "tubey" with a CC on the plate of the second triode, slightly more "tube compression/expansion" and mids, a more organic feeling. Not night and day, but definitely noticeable when you are the player at least.