Little Walter Amps?

[randalp3000]

I built one also with a choke. Later changed it to a LTP. Liked it better the way it's supposed to be and will someday put it back.

Fun amp for sure.

do it, do it, do it

[talbany]

I recently built the 5B6 version (Thanks Mark)..I use 2 KT-88 (60% max plate about 25w per 8 and huge Iron (a Bass amp now!..Lol) FWIW.Here is my review

This is a fun amp to play for sure!!.. I play in several different type bands, everything from Rock to Blues, Jazz and Rock Jazz.. I own over 15 amps now of all different styles and built them all myself...bla.bla...The one tool I needed was an amp to do the Blues/Jazz thing at fairly low volume Dinner club type gig..Also something that wasn't to aggressive in the mids and treble EQ range..The 5B6 circuit seems to be (so far) a good tool for delivering this kind of tonal vibe and takes pedals like a champ..Depending on how you set it up it can still move some air and still stay tight ( a product of the Big iron)..These amps don't seem to have much preamp headroom,(which is why Vince Gill uses 4 at the same time,see pic) if you like an amp that breaks up a 6SL/SC into a cathode biased output section is what these amps are known (Smooth)..Being an octal CB amp, they have there own character and feel very different from the 5F6-Bassman, much softer feel and slower with plenty of sag,and scooped in the mids (which is why Tele players really like them)The main problem I have with mine is a lack of control over the tone control,this is no real surprise since it's a bass amp..I tried several different ways voice it more for guitar even tried the later 5c5/Deluxe tone control but all these mods changed the character of the amp so I went back to the original tone control and added in a few bright caps (on a switch) to give me some control at different vol levels.. It's not perfect but better than nothing..IMO
Overall I think it's a nitche amp that for me fills the void of a small club/studio Jazz/Blues, Country, type gigs where vol is of concern and can see the appeal with the Nashville Studio low volume guys and you don't necessarily need the aggressive tone of the later AX style amps..It certainly doesn't replace any of my other amps but just adds to my options..Oh and did I say it was a blast to play

2XKT88 (Running a healthy 45w) 5B6 with a Fuzz Face and an R9.. Hand me a Beer I may be here a while!

Good Luck with your builds!!

Tony

[M Fowler]

I'm currently building another 5b6 cage amp to replace the one I sold to steel player and it will be just like my first one PTP and using the same Weber transformers.

Fun to play is right.

[David Root]

I have an original cone Altec 417B in an Avatar open back 1x12. Since it's 8 ohm and so is the OT I'm using I kinda think it might be a good match for the 5B6. A bit more volume if you need it too, the Altec is very efficient.

It sounded very good with my 6G3 De Luxe.

I'm still at the WIP stage with my amp but I tried to make it more suitable for guitar by cutting the coupling caps from .1uF to .05uF.

Has anyone tried a 417 with the 5B6?

PS I also have a 2x12 Avatar with a pair of 16 ohm Altec 417Bs in it, but it's a bit heavy to lug around.

[telentubes]

I've shelved mine for the time being as there is some funny, barely discernible distortion in the mix I haven't been able to track down. This is even after rebuilding from circuit board to point to point. I will try different trannys at some point. I went on to build the 2 Small Specials which are completely satisfying amps with only the slightest amount of tweaking to get the voltages in line. Great right out of the box. Haven't given up on the 5b6 though.

[M Fowler]

I'm going to elevate the filament and see if that takes some of that octal preamp tube noise out of the equation.

You do have to go through a stash of tubes before you find a non microphonic one or lower noise.

Once you turn the volume up, they do get noisy.

I also use a dpdt bright switch with 250pf and 500pf but I have kept the coupling caps at .1uf/600v on all my builds.

[EtherealWidow]

I noticed while trying the LW turned up there was quite a bit of swirl going on. Is this inherent to the circuit design? What structure in the amp is responsible? PI?

[talbany]

I noticed while trying the LW turned up there was quite a bit of swirl going on. Is this inherent to the circuit design? What structure in the amp is responsible? PI?

What happens is that first the phase inverter or output stage clips and produces a flat square wave. As the note decays, the signal level decreases, and the midrange frequencies start getting "unclipped" (either by the fact that their frequency band level is lower, or by phase cancellations due to the unequal phase shift with respect to frequency caused by tone controls and other RC phase shifts that occur in a gain stage) and show up as a "dip" in the top of the square wave, which will move back and forth along the top as the fundamental and other harmonics shift the operating point. Even if the clipping ratio isn't extreme enough to show the "dip" on the scope, the duty-cycle of the square wave will usually be dynamically changing as well.

Since the preamp stages are all AC-coupled to each other, the operating point shifts as the signal gets smaller, due to slight "blocking" distortion, where the gain stage clamps the top peak to a point slightly above it's cathode voltage, while allowing the wave to still increase in the negative direction. As the signal decays, it shifts upward and changes the duty-cycle of the clipping. It is this ever-changing shifting of the operating point that causes the "swirl" effect. The trick to good "swirl" is in the correct staging of the gain and frequency breakpoints of each gain stage in the amp, particularly in the phase inverter and output stage.

A similar effect can be caused by too much drive from the phase inverter to the output tubes. As the note decays, a riding "buzz" can be heard coming in and out. This is crossover distortion aggravated by too much signal swing to the output tube grids. Reducing the signal levels at the output of the phase inverter will cure this. Another cause of a "swirly" sound is a parasitic oscillation that is riding on the output signal, causing intermodulation distortion.


Tony