What Blackface Bassman should I build?

CrazyFrankSD

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I know as I type the title this is will not end with a resounding and unified opinion, yet I still ask because I've not paid any attention to the subject in 20 years.

So back in the late 90's I had a Blackface 1967 Fender Bassman head that I absolutely loved. As I recall the channel was clean even at reasonably high volume and it was DEEEEEEEEP luscious Fender nirvana. Floor rattling lows and chimey highs that LOVED any pedal you ran into the front end of it. I loved that amp. If I was going to compare it to anything it would be if you had a 50 watt Twin without the reverb and vibrowhatever. The sound was immersive and I loved spending hours bathed in its deep glorious waters.

My Twin largely scratches this itch today, but I'd like something a bit easier to move around and maybe not as loud.. and I see these modified Bassmans with a Marshall-esque #1 channel that sounds awesome.. so I've decided that's my next amp build.

The question is.. what way to go?

Originally I'd thought I'd build an AB165 since that's likely the circuit that was in my beloved '67 Bassman and then after that was built essentially "stock" then I'd try different mods on the first channel.. but now I read all these people swear by the AA165 - which really doesn't sway me much other than having a bias pot seems like a good thing to have.

So that brings me to today. I have some vintage Schumacher iron (1965) out of a mid 60's Epiphone Futura EA-12 (along with whatever 1/4" jacks, sockets, and odds n ends worth salvaging from that circuit.. obviously no electrolytics lol) and I have a Fleabay sourced Blackface Bassman chassis en route... the real question is what circuit do I build for it?

Knowing that I'd love to have "45-50 watt Twin-ish sans effects" in one channel and "Fire breathing Marshall" in the other channel is there a "from the ground up" circuit design floating around that would cover those bases?

Thoughts, suggestions, criticism, etc is greatly appreciated!
 

72_Custom

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I'm not sure there is a stock Bassman circuit that matches your description. I think the path of least resistance would be to build something based on the AA864 circuit, but change the Bass channel's tone stack to be the same as the normal channel (you may want to try playing around with the value of those 220k voltage dividing resistors before the third gain stage too). Then this channel would be your overdrive channel (with 3 gain stages) and the normal channel would be your cleaner channel (with only 2 gain stages).


To me, the perfect BF Bassman never existed. It seems like the AB165 preamp with the AA864 power amp would be the perfect combo. That's essentially what you'd be getting here on channel 1, while preserving the stock AA864 sound on channel two. The AA165 and the AA864 are very similar, so I don't think you really benefit much by going that route. I too have an AB165 and I agree that it's pretty darn lovely. Definitely a lot more gain on tap than a Deluxe Reverb or a Princeton Reverb.
 

schmee

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The Bassman will be lighter, but it will still be very loud, and you already have a Twin, so that's something to ponder.
How about a simple Brown 1 x 12 Vibrolux?
There isn't much difference in the AA and AB165 is there?
 

Phrygian77

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@schmee the biggest difference between the AA165 and the AB165 is that both channels feed into the third gain stage, which has local feedback. The global NFB scheme is different also.
 

Phrygian77

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There are enough triode sections to get more gain than anyone needs. The problems are that you have limited control space/options on the front panel, and you have to mix the channels together which usually results in compromising one or the other.

I suggest building the AB165 preamp with the AA864 power amp. Make the bass channel a moddified blackface channel. Use 1uF cathode bypass caps, use a 15k or higher fixed mid resistor, maybe use a 330p treble cap, etc. You get to experiment. Lastly, add a PPIMV (250k stacked) to the rear panel. Both channels will be in phase so you can combine them.
 

Paul G.

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Yup, AB165 preamp (also used as the basis for Dumble and Trainwreck amps), AA864 power amp. You might use Marshall (or Trainwreck) tone cap values, and a bright switch on the bass channel to make it more usable for guitar.
 

ce24

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Traynor YBA1.....SChematic READILY.AVAILABLE. can go either way Marshall or Bassman....two channels...
 

gabasa

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What I like about the AA864 over the AB165 is that you can have a beautiful, standard blackface circuit in the Normal channel, as well as a hotter Bass channel with an extra gain stage. I just finished one of these, built pretty much exactly how @72_Custom described it above. It’s an AA864 with a more guitar friendly Bass channel and so far I love it.
 

gabasa

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I don't know if this helps, but after I put mine together recently, I had a bit of troubleshooting to do, but now it works perfectly fine. If you're interested in the '64 version, with the bass channel more guitar-friendly, here's the schematic I used. It's the original AA864 schematic, tweaked:

 

MatchlessMan

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Subscribed!

I’m contemplating building a 50W Bassman as a single channel head to use for - wait for it! - bass guitar. I had good success last year with an Ampeg B15-ish head that I now use in my home studio / practice room.

So as a supplementary question (thread hijack), which circuit do we think makes the best bass amp?
 

Phrygian77

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Subscribed!

I’m contemplating building a 50W Bassman as a single channel head to use for - wait for it! - bass guitar. I had good success last year with an Ampeg B15-ish head that I now use in my home studio / practice room.

So as a supplementary question (thread hijack), which circuit do we think makes the best bass amp?

The Ampeg B15. :D
 




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