Blonde Bassman 6G6-B build

[JohnnyCrash]

I started this a long time ago. Finally got around to assembling and building it.

Pull the Bass channel’s volume pot and it swaps the stock cathode bypass for a 0.68uF “Marshall” setup (the schematic for the Bassman’s first cathode shows a Marshally 2.7k here, to boot).

Pull the Normal channel’s Bass control and there is a modest (midrange resistor from stock 6.8k to 15k) midrange boost.

And the Presence was omitted, I simply hardwired in the stock negative feedback circuit, albeit on a three-way Negative Feedback switch (stock 56k, no NFB/raw, and a good bit of cleaning and tightening feedback with 22k — all off the 4ohm tap).

In the Presence’s place is a dual-gang 250k Post-Phase Inverter Master Volume (PPIMV).

I also shrunk the capacitor across the Bass channel’s Treble control’s (it looks like a… Gain control?! Wow, Leo!) plate resistor from 2200pF to 680pF. I thought I’d need to open up the top end for guitar use, but IDK, it sounds pretty dang bright.

I also put bias test probe points on the back, using the unused Ground switch hole for the 10k bias pot.

I haven’t had a chance to play it, yet. My two year old son is asleep. I have, however, fired it up, biased it, plugged my Tele into it, and confirmed it made sound and each control did what it was supposed to do. Except the NFB switch in the back, but I’m sure it probably works, I took my time on this one, chipping five minutes here, ten minutes there.

More to follow. I hope I can really play it tomorrow…

 

[micadoo]

Nice looking build mate, let us know how it sounds when the little tacker wakes up

 

[symbiotic]

I'll be super interested to hear your take on the bass channel, as I have a broken old Blues Deville that is dying to be turned into some sort of Bassman, and the unusual topology of the 6G6 bass channel has always intrigued me. Never had the chance to play one but was acutely aware of how good it sounded when Dallas Good of The Sadies (RIP) played through it.

 

[JohnnyCrash]

Gave it only about twenty minutes of playing. So far, I like it. The master volume helps control volume, but it still sounds better loud.

Symbiotic, the Bass channel is interesting. It didn’t feel like the bass control actually did a whole lot to the guitar’s low frequencies (at zero it was noticeable, above that it was “not zero” setting. A smidge more bottom, but not much.

Perhaps it was designed to only get the low-low frequencies, not those of a guitar’s. IDK.

The treble control is wild. It’s not exactly a typical high frequency brightness kinda thing… it was more like an upper midrange control on a gain knob. The treble does indeed get its own triode, all to itself. So it kind of is a gain control. With my Tele, I had to lower the treble, which also reduced gain and bite. There are some tips I could suggest here, if you’re worried about taming treble. Still, it sounds great, it’s just a different animal. You gotta get used to how it responds.

The volume control on mine has a pullswitch on it to swap the first cathode to a smaller Marshallesqe 0.68uF. It responds like a typical volume control, except it’s on a hot and gainy channel, so it goes from beautiful cleans, to warm and thick cleans, to early rock overdrive, to classic rock, to h*ly sh*t! in about a half a twist of the knob.

The Bass channel likes to rock and roll, but it takes getting used to, and I’ve only just met this blonde beast.

I plan on using it to record a wide array of genres, it can be used for many, but it especially seems to have an old greasy ‘50s almost-nasal Tele voice kinda midrange meat that your ears kinda guide the knobs to subconsciously. My Tele sounded ridiculously better than I could play it on both channels (but especially the Bass channel).

It’s a musical amp.

The Normal channel surprised me. Everyone told me the brownface tonestacks, even with the odd 350k/70k tapped Treble pots, line up the same in tonestack calculators.

This Normal channel did not sound like the black faceplate era Bassman I built (and plan on rebuilding soon). It sounded more middy, more forward, like most brown faceplate era amps sound.

Could be a few things. In any case, I was actually equally fascinated by the Normal channel. It sounded bigger and fuller, and it looked very BF, but it reacted differently. It felt gainier when I turned up the treble. It had that BF sparkle, but with a little meat.

Could be the 220k plate on the end that people might forget to plug into the TS calculators. Could be the difference in PI tubes (a 12AX7 in the 6G6-B’s case). Could be the odd negative feedback circuit. A very light negative feedback from a 4 ohm output transformer tap probably sounds more gainy and lively, but the tail resistor is 4.7k. That bumps up the NF, if I’m recalling correctly. The blonde Twin I think used a resistor half that size on that tail’s end. Could be different larger coupling cap values. IDK. But it sounds like a BF on a very light dose of steroids.

In any case, awesome amp so far.

 

[JohnnyCrash]

Here’s my ghettofabulous back panel.

 

[jsnwhite619]

Congratulations! I got to play an original one time with a Strat, and it was definitely the absolute best overdrive tone I've ever heard myself play - fantastic amp.

 

[symbiotic]

Thanks JohnnyCrash, that's a lot of food for thought. Might even have to pop another preamp tube hole in the chassis and find a way to cram both channels into the Deville. Rock on!