Suggestions for 15w cathode bias/SE build - parallel 6V6s?

[rogb]

Hi all,
Ok here's the deal, I have just completed my first complex scratch build - the TAG inspired 86 Special - single EL84 or 6V6, OD/clean, VVR, loads of controls and switches, all in a 12 x 8 x 2 chassis with 10" Emi Delta Lite combo at 20lbs all up.

I love it and it sounds great, perfect for recording, but..........
when I play at jams all I really need is a good big touch sensitive clean sound with my Keeley TS9 providing drive as needed. The 86 Special has a little trouble staying clean with drums, bass and the odd sax player.

I am really digging the cathode bias vibe, so thought about building another complete chassis the same size that I can slot into the combo cab as needed - one cab, one speaker, 2 amps! All that cab work saved!

I would really like to hear from the cathode fans on here with some ideas for a 15w- ish Fender-type clean with maybe a touch of grit at the top, so it can be cleaned up with the guitar volume.

I really like the 6V6s (but not crazy about EL34s), so a parallel 2 tube rig should give me the power for small jams, and enough clean headroom, until the TS9 goes on.

Ideas please, something with TMB pots which I like to lift with a switch as needed.

Effects loop jacks are a must for a Nanoverb in the cab base.
PT/ OT (Edcor?) and other hardware ideas too!

Many thanks

Rog

[martin manning]

Just to be clear, is it the cathode bias or the single-ended architecture that you are liking?

[rogb]

Just to be clear, is it the cathode bias or the single-ended architecture that you are liking?

Yes, somehow in my excitement over a new project I forgot to even mention the SE thing, I like the cathode bias and SE rather than PP, I like the whole AX84 mojo.
Sorry about the vagueness, Martin.
Please suggest away!

[brewdude]

I'm not sure you should expect a pair of 6V6's paralleled SE, at ~10 watts, to have that much more headroom than a single 6V6, at ~5 watts.

You might try a single ended KT88 for ~20 watts. The problem I see with a higher power in an SE amp is OT needs to be big and heavy and they are expensive.

[xtian]

So, I built a KT88 SEL based on the AX84 design: https://tubeamparchive.com/viewtopic.php?t=11485

It was a great amp (sold it), and fit well with a quiet drums/bass/guitar ensemble, but did not have enough headroom to stay clean at band volume.

[tubeswell]

Earlier this year I built a parallel SE for 6V6s with an EF86 in V1 and tremolo. (see attachment)

Initially I had a 5F2A tonestack (which sounded good). Then I switched to a big muff tonestack - which also was good, but was configured for better mid-scoop, albeit with less overall gain than the 5F2A tonestack)

Soundbyte links in this thread:

https://tubeamparchive.com/viewtopic.ph ... light=ef86

I was going to experiment some more with gain in the amp, but someone desperately wanted to buy it so I sold it to him before I got the chance to tweak it some more. (Now I am building something similar but in front of a PP amp)

[RJ Guitars]

Rogb,

A few of us collaborated and built a few large sized SE amps based on the 5F1 schematic. I used a single KT88 in mine and in fact have tried: KT90, EL34, 6V6GT, KT66, and 5881 tubes... cathode biasing allows a lot of flexibility in tube jockeying. Here is the link:
https://tubeamparchive.com/viewtopic.php?t=14349

This build collaboration produced a really cool amp, not exactly to your specifications but add that 2nd output tube and you have most of it. We did use Edcor transformers and a tonestack removal switch - this is a cool addition!

The one thing that I did not find with this amp was an excess of headroom. The KT88 and KT90 gave it plenty of loud, but not an excess of clean headroom. You might run the voltages up with a hotter power tranny and add more clarity to the amp.

I'll watch with some interest to see what you build, I love the simplicity of the SE amps.

rj

[rogb]

Wow, plenty of good ideas here, thanks guys

I'm liking the simplicity of the RJ Supre, could be fine in a 12x8x2 chassis.
I see Edcor have no UK outlet, so I may go Hammond. The 125 ESE may be good
as an OT

Do you think the 270 Hammond will take the extra 6V6?
What about an extra gain stage, with a 12AT7 in v1 then 12ax7 in v2,
do you think this will help with clean headroom?

[tubeswell]

What about an extra gain stage, with a 12AT7 in v1 then 12ax7 in v2, do you think this will help with clean headroom?

Even a single 12AX7 with both of its triodes cascaded (like in a 5F1 or 5F2) has enough gain to push a 6V6 grid into clipping. So no, 2 x 12A_7 tubes will not make it any cleaner. But if you took a 12AU7 and made both of its triodes into a cascode stage and used that (on its own) to drive the 6V6(s), it would be cleaner.

[rogb]

OK I could go with the single 12AX and work down through the AT and AU if want less gain, sounds good, there are some nice NOS available here in the UK

With regard to a higher power PT, Hammond do a 325-0-325 so that could give the extra clean headroom.

I'm going up a few pounds in total weight here for the larger PT/OT combo, but it seems worth it