I'm going to try to build this soon. I'd appreciate it if anybody had some suggestions or insight. I know a good amount about tube amps, but I could sure use help.

for the speaker, I got a 15" 75W blue dog ceramic speaker from ted weber. Similar to the vox blue speakers but much more power handling and lows.

The circuit is mainly based off of two amps right now, a vox AC50 and blackface bassmans.

The first channel Is very similar to an AC50 preamp, with a couple of differences. It starts with a common cathode amplifier with a 820 ohm resistor. This has less gain than a normal fully bypassed stage, however I did that so I could add a treble boost switch which adds a small capacitor in parallel with the resistor boosting frequencies above about 500hz an extra little bit. The 820 ohm resistor has a slightly smaller effect (gain difference) than a 1.5K resistor would.

Next is a cathode follower into a Vox AC50 Tone stack. However, at the end I added a 1M volume pot, this shouldn't signifcantly change the impedance of the circuit too much. I probably won't add a bright cap.
The next stage is a recovery stage. I might move the volume pot after this if I think I need it instead there. This is then coupled with a .022uf cap into a 220K resistor, than to an additional gain stage. I might make the tonestack more like the classic plexi if this doesn't work out too well.

The other channel is straight off of most blackface fenders "normal" channel, with the addition of a rotary switch which selects 3 different values of capacitors on the tone control, switching between .022, .047, and .1uf. These change the bass response of the circuit. In a blackface AA864 bassman amp, the value is .1uf w/ a switch to make it .2uf. In a super reverb, it's .022, in a twin, it's .047. I'm not sure exactly how much this will change the response overall, but I think it's an easy thing to do so I might as well. I have a fixed 6800K resistor in there right now, I might turn that into a mid control instead.

This is coupled with a .022uf cap into a 220K mix resistor into the same third stage as above.

This third stage is just like the common third stage on the ab165. I think I am going to keep the 470K feedback resistor, but I'm going to change the input resistor to 1M, giving a little less feedback, but I'm not sure.

Finally, this is all fed into a long tailed phase inverter (12at7 or 12ax7) configured with a presence control, like the classic bassman. The feedback resistor will be increased to 56K. Coupling capacitors after will be .047uf into the power stage.

The power stage will be 6l6s probably, but kt66s or el34s are an option. The output transformer will be a hammond 1650N, rated for 60W output. I might go with something a closer to 50 as I should be able to put out 60W or more with the voltages on this weber power transformer, and saturating an output transformer. The weber power transformer should be fine with this given the specs and solid state rectification.

fuckin' sweet.

i hear amp builds are not very cost effective but i hear this from the douchebag bassists at talkbass.com.

All good info... have you drawn the circuit out? Are you trying to keep it clean?

I'm going to have Ted make me some Alnicos with the 55hz cove and a aluminum dust cap to "widen" the bandwidth of the speaker to be more "full-range"

as for an amp... I'm pretty happy with the standard Ampeg curcuits for baritone (V2, V4, B25, jupiter etc.)

I don't like to much gain for my Fender Bass VI... but I'm curious about the vox tone stack in a cleaner amp with more headroom. Say a AC30 front end with a Ultra-linear 6550 output

that damned fly wrote:fuckin' sweet.

i hear amp builds are not very cost effective but i hear this from the douchebag bassists at talkbass.com.

It's kind of expensive. I'm going to do everything myself though, building the cab, punching the chassis, all of it. I might sell my main amp afterwards too, so end up even or so.

rough estimates (for me)
180 for transformers
20 for chassic
110 for speaker
50 for small components
15 for cabinet
30 for covering/grill cloth
60 for tubes
+time

so about 450 or so

You can pick up transformers pretty cheap out of old radios and stereo equipment if you know what you're looking for. When you do this, you can build 5-20W amps pretty damn cheap that sound great. Say you did that:

20 Transformers
20 chassis
50 speaker
40 for components
40 for cabinet/grill cloth
40 for tubes

so that's just about 200 bucks if you build it all yourself.

TheMilford wrote:All good info... have you drawn the circuit out? Are you trying to keep it clean?

I'm going to have Ted make me some Alnicos with the 55hz cove and a aluminum dust cap to "widen" the bandwidth of the speaker to be more "full-range"

as for an amp... I'm pretty happy with the standard Ampeg curcuits for baritone (V2, V4, B25, jupiter etc.)

I don't like to much gain for my Fender Bass VI... but I'm curious about the vox tone stack in a cleaner amp with more headroom. Say a AC30 front end with a Ultra-linear 6550 output

yeah, I just drew out the preamp today. I kind of want it clean, I think the AC50 side might have a bit too much gain, but I don't know. Originally they had a 12au7 into the plate/cathode follower and then directly to the PI for that amp. I could skip the last gain stage too, but then I wouldn't be able to bridge inputs, although I might find out that's better anyways. The 12at7 in the PI should give a tad bit lower gain than a 12ax7. I want to play around with some 12ay7s too, that might be the ticket.

if you were to play a baritone into a bass amp but with a guitar cabinet, would that be allright for the cab?
playing bass with a guitar cab isnt so good, but could a 4x12 handle a baritone through a bass amp?

danken wrote:if you were to play a baritone into a bass amp but with a guitar cabinet, would that be allright for the cab?
playing bass with a guitar cab isnt so good, but could a 4x12 handle a baritone through a bass amp?

A sealed 4x12 theoretically will be ok... again loading it with driver that can handle the low-end and higher spl would be good.

a friend of mine loaded his Ampeg V4 cab with Eminnece Beta 12s. he uses it with a Juno 60 which has a lot of low-end.

I know a local guy who actually plays an amplified stand up bass through a marshall alant and it sounds pretty good, but he didn't really crank it.