Contemplating a 5b6 build. I'm looking for power, and advice

[telentubes]

Ok Ok, your right. I'm going back in and getting this thing running right. I think I will try some different iron since the rest is built.

[KellyBass]

While checking out some Little Walter clips and pics, I was a little surprised to see that Little Walter has, or had, an 80 watt 2 KT120 offering. LW says that the KT's are "impervious to distortion"!? I don't know...I've got a KT88 amp that shreds with the best of 'em.


By the time I read this, I had already planned on using 100 watt iron and some KT100's or 120's. I really need the headroom in this amp...but I don't want to lose that tiny bit of "bite" that I hear when I listen to clips of the 2 6l6 amp. This amp will be used for some wicked Tele chicken pickin'. Besides, From what I gather, these amps are a pretty great pedal platform for distortion pedals, etc.

Any thoughts on those impervious KT's?

[rp]

His criteria is: (his words)
50-60 watts...enough to compete with super's
Steel guitar type cleans and a bit of fur when he needs it
Strong low end
A beautiful, warm full bodied tone
Something different. Not the typical Fender tone.
Simplicity!!! Volume and tone knobs
Well, the 5b6 came to mind very quickly. Besides, I can't wait to build one!

Haven't built a 5B6, but have built a 5C1 and 5C8. Early octal pre tweeds are more cult amps and around the house, coffee house, recording amps, from my limited experience. But I been around a lot of vintage gear and never seen anyone gigging with very early tweeds and it's not vintage value restraining them as I know people gigging w/ valuable later tweeds.

Cathode bias above 25Ws is iffy IMO, if you plan on leaving plenty of headroom and want a bouncy clean sound I guess 50-60 CB could work for that otherwise I'd take fixed bias any day at that power. The lower filtering in those early tweeds isn't best for 50-60 watts either. Louder amp, louder hum. Low filtering isn't the best for modern playing, terrible for gigging, but it's part of the warm organic mojo of the old amps.

I'd worry the octal pre's would make just too much noise with 50-60 watts, both inherent hum and from the bigger vibration coming at them.

IME cctal pre's aren't the most pedal friendly but that might be only for grid leak biased input ones which the 5B6 isn't, my 5C8 has both but I haven't hit it hard w/ pedals at volume yet. It's built as a hifi chassis and not travel friendly. The speed, immediacy and rich tone have so far made me ignore pedals. It does the clean/hair thing by just digging in so well I don't want overdrive. I think those feel and tone qualities are not just from the pre's but are holistic and from the preamp, lower power, low filtering, lower voltages, and cathode bias all together. Change too much and not sure what you'd get. Though others report happiness w/ such mods and LW seems to be selling them.

Anyway, my thoughts are I'm not sure I would just hit a customer looking for a band/gigging amp cold w/ an early tweed clone. I'd be even more worried to hit them with a heavily up-graded 5B6 circuit w/o first having lived with one myself. If they knew what too expect from their experience then that might be different.

That said, long live all-octal tweeds.

[KellyBass]

You've made some great points, RP...thanks!

In the past, I've built some wacky 20-50 watt cathode biased amps and I recall using a rather high uf value CB capacitor (1000uf) to "move the valves more toward fixed bias state". I wonder if this, to some degree, would be an option with this circuit. For the life of me, I can't remember the exact technical reasoning here. It's possible that I read this in one of Merlin's books....and I do recall the amps being a bit stiffer. Not good for the 5b6.

Anyone care to elaborate?...and educate?

[rp]

I read that too, that a very large cap makes cb react more like fixed. I also read you can use a diode like some do on preamp tubes. I can see this as a kluge or quick mod to an already built amp, but in a new build if mimicking fixed bias why not just use fixed bias? Or a fixed/cb switch? The LW amp uses Hammonds IIRC, the PTs used likely has a 50V tap anyway. My 5F6A is set up that way, lots of fun, cb nice for lower volumes, twangy and bouncy, fixed when you turn it up and rock. I hate lots of options but that one is pretty useful.

[RWood]

I concur with that last statement^^^

Although playing a nicely sagging colorful octal 30w through a high sensitivity speaker like the Swamp Thang really gives it a nice punch without loosing the octal mojo.

[M Fowler]

Two steel guitar players I know are running stock 5b6 my cage amp and the other a 50w LW amp. The 5b6 cage has NOS 6L6's and the LW was running KT120. You get a fuller tone with KT120 but not a huge increase of power because it's a stock circuit/transformers etc.

I've tried both NOS and new Tungsol 6SC7 and 6SL7 tubes using o'rings just for save measure. I like the 5b6 cage amp with 5u4 rectifier tube the best just gives it that warmth I like.

Once I started increasing transformer size and voltage the amp does get noisier probably due to the octal preamp tubes but I haven't tried DC filament yet. Lot of experimenting to do yet. However, I did get a huge increase of volume with 50w bassman iron with 6550 tubes. Next will be 100w iron and try KT88 or KT120 tubes.

[KellyBass]

Well, I finally pulled the trigger and ordered some parts from Ken Watts today. I really like his chassis' and he has one that is 12.5 x 8.5 x 2.5. It's an inward lip, so the extra .5 is great. The Tino book finally came in and the layout seems VERY specific! I'm gonna follow it to the letter on the tubes, cinched, wire runs, etc.

As far as the transformers are concerned, would it be wise to stick with a horizontal laydown PT? I'm looking at getting a basically stock PT. The one I've picked out is a bit extra beefy in case of the bigger power tubes... 700v ct @ 200ma and 5a for the filaments.

As far as the OT goes, I found a new triode Dynaco a431 in my stash! Transformer specs are: 4300 ohms CT primary with screen taps, 4,8 and 16 ohm secondary. 20 Hz to 20 KHz response at 60W, within 1 db, 30 Hz to 15 KHz at 120 watts. Nice! Too much? Thoughts?

[M Fowler]

Laydown verses standup PT depends on your design if you need more room in the chassis for filter caps. My 1st 5b6 cage amp used a Weber can cap. The 2nd cage amp I put the filter caps located in the circuit positions rather then a cap board style all in a row like Little Walter amps does it.

I follow the Tino build guide but spaced my power tube sockets to allow for KT88's and KT120's.

That Dynaco OT is a great transformer.

I think, for me anyway, keeping the chassis small like the Watt's chassis you are using and short PTP wiring really keeps the noise down. I have hit and miss issue using NOS preamp tubes so the fact that we can buy both new 6SC7 and 6SL7 is a big plus.

[RWood]

My supposedly NOS 6sc7 went microphonic after a day or so.
I put new Russian in and have been playing 3 or 4 times a week for 3 months with no problem.

Both of my Tino builds are dead quiet following his layouts!

[pops]

I have used a small bridge rectifier after the power tube filaments and and filtered the filaments for the pre just like a power supply with caps and resistors. Did this in a 5f8a and it was dead quiet. Might try this to keep a higher power amp quiet.