Please check my layout!

[fdesalvo]

Sorry- posted this in the wrong forum earlier.

This will hopefully be a single channel ab763! Any comments- please excuse the power section's lead dress- this is the first revision.

I am still learning as I go along and as you can see this is a modified version of Hoffman's amazing layout diagram, where I deleted the vibrato and reverb circuitry and added two more power tubes. I still need to add in a ss rectifier and delete the GZ. What I am after is an amp with a beautiful clean that takes pedals well.



Peace and chicken grease!

[bnwitt]

You're going to need an additional triode to recover the loss in the tone stack before you go to the phase inverter.

[loudthud]

As noted by bnwitt, you don't have a whole lot of gain. Thinking ahead, it wouldn't be a bad idea to leave room for another tube and a little space on the eyelet board just incase you want to add things later. The most important thing to me would be how all the grounds are connected. Opinions will vary. Study what you can find on the Hoffman site and that will work fairly well. If you want something that is dead quiet, like you can't tell if it's on or not, Kevin O'Conner's Tut books can show you the way. You'll need phone jacks that don't ground to the chassis.

[fdesalvo]

Thanks, guys. Would copying the first stage and adding it after the tone stack do the trick in getting me to the clean tone and headroom of the twin? Thanks for the critique and I will definitely get that book asap.

[bnwitt]

Thanks, guys. Would copying the first stage and adding it after the tone stack do the trick in getting me to the clean tone and headroom of the twin? Thanks for the critique and I will definitely get that book asap.

If I were you, I would follow the original Fender Twin layout for grounding and everything else. The blackface Twin amps were dead quiet to begin with. Now believe me, I am a Hoffman grounding scheme fanatic as I use it with a few changes to build very quiet on idle amplifiers but the original Fender BF twin layout is a great one. I just had a 66 model in for service and it had zero hum or hiss and the only changes from when it left the factory was a cap job.

Help me understand why you are going in this bare bones direction. I can see dropping the normal channel as it is seldomed used but I'm not sure why you wouldn't want the tremolo (really vibrato) and the reverb in your amp. They really add some diversity to your tone. Also, do you really need 80 watts? The twin is very very loud. Are you a jazz player or gigging in large halls?

[fdesalvo]

If I were you, I would follow the original Fender Twin layout for grounding and everything else. The blackface Twin amps were dead quiet to begin with. Now believe me, I am a Hoffman grounding scheme fanatic as I use it with a few changes to build very quiet on idle amplifiers but the original Fender BF twin layout is a great one. I just had a 66 model in for service and it had zero hum or hiss and the only changes from when it left the factory was a cap job.

Help me understand why you are going in this bare bones direction. I can see dropping the normal channel as it is seldomed used but I'm not sure why you wouldn't want the tremolo (really vibrato) and the reverb in your amp. They really add some diversity to your tone. Also, do you really need 80 watts? The twin is very very loud. Are you a jazz player or gigging in large halls?

Hey, man. I play in large venues and outdoors often times and I need the headroom. I play in a modern rock band and I need the tight bottom end that a quad of 6l6s gives me- at the same time, I looove the blues and love the sound of cranking a twin and backing off my guitar volume! Tasty!

I have an incredible pedal board and use that to create the ambience. If this was going to be a bedroom amp, then reverb would be a must and I would follow the layout to the t! Thanks for your insight, my man.
~F

[tubeswell]

For my 2 cents, further to what the others said (besides the bit about not enough pre-amp gain), I would keep the 'verb myself - lots of people think that reverb 'hides' inadequate playing skill - but that's just plain wrong. Proper tube driven reverb is the sweetest thing. Now if I was going to change the BF, I'd add brown (concert or vibrasonic style) vibrato or tweed (tremolux) bias-vary trem to it and get more of those hypnotic tube-driven effects.

80W won't get you much more vol than 40W for the outlay (including bigger OT) of the extra two tubes. 40W is 81% as loud as 80W, all other things (including speaker efficiency) being equal. You will have a louder amp for sure, but this will probably only be an advantage if you need to play loud and clean, or if you keep at least the reverb, where there will more definition using the reverb at higher volumes.

[fdesalvo]

For my 2 cents, further to what the others said (besides the bit about not enough pre-amp gain), I would keep the 'verb myself - lots of people think that reverb 'hides' inadequate playing skill - but that's just plain wrong. Proper tube driven reverb is the sweetest thing. Now if I was going to change the BF, I'd add brown (concert or vibrasonic style) vibrato or tweed (tremolux) bias-vary trem to it and get more of those hypnotic tube-driven effects.

80W won't get you much more vol than 40W for the outlay (including bigger OT) of the extra two tubes. 40W is 81% as loud as 80W, all other things (including speaker efficiency) being equal. You will have a louder amp for sure, but this will probably only be an advantage if you need to play loud and clean, or if you keep at least the reverb, where there will more definition using the reverb at higher volumes.

Thanks for the input, man. While there may not be much perceivable difference in voume, I am aware of a huge difference in headroom between
40w and 80w. For my style of music, that difference on the lower side translates into mushy lower end and clean breakup where I don't want it. I need a solid bottom end and the stock twin power section gives that in spades.

All I am after is an 80-100w single channel ab763 with no frills. Like I said if this were going to be a bedroom amp, I'd keep the reverb and only make the amp around 40w.

[fdesalvo]

Hi, fellas.

I've added another gain stage and will post the pic tonight when I get home. I basically grafted in a copy of V1 minus the tonestack. Is this the idea? Thanks again for the opinions.

[fdesalvo]

Updated

Ok. Here's the latest and greatest revision. Can anyone tell me where I'm going wrong here?



~F

[tubeswell]

Well (without having a really good look at everything else,) on that 2nd tube you probably will only need one triode at the most, so I wouldn't bother with wiring up the other plate and cathode. (and besides that the way you have the plates wired looks wrong - you have don't have the signal wire coming off the first plate going to the next stage - you only have one coming off the 2nd triode plate, (where the grid isn't wired up - were you intending to have a parallel triode?)). Besides that, even with one extra triode I believe you may want to consider more inter-stage attenuation, either before or after that triode.

And the other thing I've noticed is that you have the PI grounded with the heater etc. The PI is a low-current tube, so I would ground that with the other pre-amp tubes, otherwise you are likely to get hum issues (IMHO).