Next Amp Considerations

First, the 5F6A / JTM that I recently completed building, includes a two-tube power/output section that is a class AB "push-pull" design, known for stability and power efficiency. A class A power section is a simpler design that can work with just one tube (and therefore doesn't require a phase inverter stage driving it), and although it is less efficient, this circuit is known to produce different audio/tonal characteristics than AB designs. So I'm interested in building something that uses a class A power section design, which would be lower power/volume than the 5F6A / JTM, but perfectly fine for my purposes. 

Next, I've always liked the depth of a stereo guitar sound, I used a Roland JC-120 (head version) for years, then later, a Fender Princeton Chorus, both stereo amps that allowed for time-based and textural effects - reverb, delay, tremolo, vibrato, chorus, etc. - that sound so much better in stereo. I've been intrigued by vintage Magnatone amps (especially the 96-10041 from the early 60's), and the recently resurrected company does have a new-ish stereo amp that utilizes their special versions of tremolo and vibrato. I considered building an imitation of that, but I think the analog tremolo, vibrato and reverb circuits would not be worth the trouble, considering the variety of great sounding digital versions of those and other effects (as external floor boxes or rack mounted gear) that one could just plug into an effects loop (like on my pervious amps). 

Finally, I've been intrigued by the Alexander Dumble sound, and have read a lot about the architecture of his original amps and amp mods (probably won't be buying one anytime soon), and the many designs that folks have created (Sebago Sound, Custom) to imitate the tone, so am interested in implementing some of that in the preamp section of my next amp. 

So that's the general idea: 

• Class A power section.
• Stereo for richer effects, which means:
• two-channel effects loop (buffered) between the preamp and power sections
• two single-tube output sections in parallel, to drive two speakers independently.

• Dumble-inspired preamp design.

Considering it will be a stereo amp, I also plan to build a 2-speaker cabinet to match, that can be run as stereo, with the new amp, or mono with the first amp. 

Calling the modded 5F6A done

I've spent a lot of time joyously playing this amp in the past 2 months, exploring the wide array of cleans, crunchy and overdriven sounds. The amp works well for the variety of styles from which I draw to get my own sound, from jazz, to roots-country, to pop and funk. I'm still trying to figure out whether there is anything for me in the the "stock" channel dirty sounds of the Tweed Bassman - it's just a bit ragged sounding for my tastes when cranked up. For output tubes I've tried 5881's, 6L6's and KT66's and so far prefer the 6L6's, but I have some other sets of 5881's and 6L6's still to try. 

Link to final schematic and layout.

For the past few weeks I have focused exclusively on better understanding the cascaded input mode and Cold Clipper bias setting of the V1A triode. With the MC5, I located the sweet spot where the amp maintains a full dynamic range, single notes ring and shimmer, double-stops crunch a bit but aren't fizzy, and when I switch the pickup from single coil to humbucker, the guitar output pushes the whole pre amp section into a nice, heavier but still articulate, fairly smooth overdrive. 

In the cascaded input mode, the Telecaster (both guitars picture below) with its slightly lower output single coil pickups also has its own sweet spot, where it maintains its Tele voice, but has a thickness and shimmeriness I like. To get a thicker overdriven sound here I use the ChaseTone Secret Pre pedal to boost the signal from guitar to amp input. 

To control overall volume, the amp's speaker output is routed to a Fryette Power Station, which drives a single Celestion G12H speaker, mic'd with a Shure SM57. The Dirty Tele and MC5 clips were recorded dry and a little reverb applied in the rough mix down, and the High Gain clip utilized the Fryette effects loop into a Line 6 effects unit for reverb and delay during recording. 

This short clip of the Tele uses cascaded mode, and progresses through light comping and a little lead playing on both pickups, then I switch to a clean boost and bridge pickup for the third half of the clip.  

Dirty Tele Clip on Soundcloud

This short clip of the MC5 uses the same amp settings, though I dialed the gain back slightly just to clean it up a bit; it also progresses through comping and lead playing just on the neck SC pickup, then switched over to humbucker, then through the boost pedal, and finally a few seconds playing just through the bridge humbucker.  

Dirty MC5 Clip on Soundcloud

I can get higher gain out of it, but the character of the guitar and amp both tend to diminish as gain increases, so I haven't spent a lot of time yet in that realm... but here's a sample of a high gain sound, using the Tele with boost peal and/or DOD 250 (I don't remember). 

High Gain Tele on SoundCloud

So, tone-wise I think I have a grasp on it and am usually able to dial up a specific sound for a specific application. A lot of folks-in-the-know say good amps are usually just really good at doing one thing, and don't expect it sound great at a clean setting as well as overdriven...but I'm pretty delighted with the versatility of this amp.

The tolex finally arrived and I spent the better part of a day learning and doing that bit.  

Left - Fender Telecaster (American Elite, 2014)
Right - Ibanez Musician (MC500, 1980)