5f6a Clone: Adding Reverb and Moving Tone Circuit

[The New Steve H]

I've been watching Gerald Weber's video about understanding tube amps, and of course, it's giving me ideas about modifying the Bassman clone I'm building, BEFORE I EVEN FINISH.

Arrgh.

1. Reverb. I don't know much about it. The Bassman circuit doesn't have it. I have a Holy Grail pedal for my small amps. I have a Blues Jr. with built-in reverb. The Blues Jr. reverb sounds 1 x 10^9 times as good as the Holy Grail, so I am guessing a real spring reverb is better than whatever is in a pedal. Correct me if I'm wrong. The Holy Grail sounds like crap to me, even though the kid at Guitar Center said it was a great pedal.

Should I go ahead and try to cram a reverb circuit into the Bassman, or is there a pedal or DIY project I should consider instead? I don't know if I have the brains to figure out how to put the circuit in there, but it might at least make the amp sound better when it explodes.

2. Gerald Weber says the tone controls on a Bassman don't actually do anything because Leo Fender put them in the wrong place. I exaggerate, but that's not far from what he said. I am wondering if it's possible to simply move them farther upstream in the signal chain. He says they should be after the 1st gain stage.

If you look at the schematic, it appears to be possible to simply move the wires so the tone circuit comes before the second stage, but I have no idea whether this will work, or if there is some kind of impedance problem that will cause the amp to go nova and saturate the entire neighborhood with gamma rays.

I don't know if I really need a tone circuit, since every single pedal I have has a tone knob, and my guitars do, too. Maybe I should just omit it and use the extra space on the amp's panel for a clever LED display that doesn't actually do anything.

This stuff is a blast. I wish I had started making amps 30 years ago.

Edit: forgot schematic.

[The New Steve H]

I guess I must be smoking the wrong brand of crack again, because I just checked the Blues Jr. reverb against the Holy Grail, and this time, I liked the Holy Grail a lot better. Can't figure that out.

Still, I could use info on the tone thing.

[tubeswell]

I persisted with getting reverb into a 5F6A for 18 months or so (of tweaking and changing after I'd actually built the amp). I ended up going with something akin to the Allen Old Flame and it sounds great. (Just thought you might like to save the bother of a protracted experiment)

soundbyte through 2 x G12 greenbacks with my strat (please xcuse my crappy playing)

[tubeswell]

some different bytes (but still more crappy playing

[statorvane]

Having built one, I'd finish the stock 5F6-A first, then contemplate tone stack changes or adding reverb.

If you are pretty sure you want to add reverb, leave room for a reverb x-frmr and two noval tubes (12AT7 and 12AX7) for a Fender style reverb. Or think abotu building oen of the stand alone Fender Reverb units. You can use in on different amps.

I don't know what the Weber guy means by the tonestack not working where Leo placed it - I think that is characteristic of the tweed era amps before Fender transitioned to plate driven stacks after the first gain stage in the blackface era. I am guessing that guy prefers the Blackface Bassman over the Tweed. That is, that is one guy's opinion. There are a lot of opinions out there....

[M Fowler]

Pete nice sounding amp

I would build one of Allen Amps versions with reverb from the various layouts floating around, they sound very good.

[Jana]

Whenever I hear, "Gerald Weber says..." I turn on the BS meter.

For what it's worth there are a lot of classic Marshalls that have the tone stack in the same place as the 5F6A. The 5F6A is the amp that Marshall copied and the rest, as they say, is rock and roll history.

[The New Steve H]

Weber had a schematic for a Bassman, and he went through it. Someone in the audience asked why the Bassman tone stack didn't do much. He pointed to the location, which you can see in the schematic, and he said the signal was too strong at that point. He put up a Super Reverb schematic later and pointed at a much earlier place in the signal path. He said that was where the tone stack was attached, and that it explained why the Super Reverb tone stack had a greater effect.

Whether this is right or not, I can't say. I have a feeling I'm going to reach a point soon where I've built about as many amps as I've played, so I don't know a whole lot about how this or that amp actually sounds.

He also suggested some protective changes in the power chain, such as putting diodes on the rectifier tube.

[tubeswell]

He also suggested some protective changes in the power chain, such as putting diodes on the rectifier tube.

Probably copied R.G. Keen's articles on immortal amp mods

http://www.premierguitar.com/Magazine/I ... r_Mod.aspx

http://www.premierguitar.com/Magazine/I ... _Pt_2.aspx

http://www.premierguitar.com/Magazine/I ... _Pt_3.aspx

http://www.premierguitar.com/Magazine/I ... _Pt_4.aspx

[topbrent]

Here is Doug Hoffman's version of adding reverb to the bassman/plexi framework.
http://www.el34world.com/charts/reverbmod.htm

[img:459:359]http://www.el34world.com/charts/images/Cmbopre.gif[/img]

[The New Steve H]

I decided to look up Super Reverb schematics to find out where the tone stack goes. I found several different schematics. I picked a silverface version, purely because it seems like all the people I've seen imitating SRV have amps with silver cloth on them! I'll post it here.

It looks like it has two tone stacks, and each one goes to a plate in the first amplification stage. I am wondering if I can wire a 5f6a up this way without causing an electronic catastrophe.

I'm enjoying Gerald Weber's videos, but I can see that I need to go back and re-learn how to calculate impedances and what I have to do to make circuits work together. Otherwise it's just monkey-see, monkey- do.

[diagrammatiks]

putting the tone stack after the first stage allows more shaping of the initial signal.

putting it before the master volume makes it act as a 4 band master volume for the amp.

the best type of tone stack really depends on the amp more then anything.

[The New Steve H]

I don't know how much this matters, since there are like 50 other tone controls between the strings and the speaker. But if the 5f6a tone stack really IS lame, it seems like a mistake to use it without some good reason.

I could just get rid of it.

[Jana]

I guess the only way you will know is to try it. I personally don't think the Marshall JTM 45, the Plexi series and all the 4-holers, the 2203/2204, and the countless variants that have evolved from those amps are lame. What I do find lame is GW's predisposition to parroting lame rumors.

It really boils down to what you want in an amp. If you're going for the fender vibe then move the tone stack up front, if you're going for a more british vibe than put it behind the cathode follower. Neither is lame, just different. Oh, I forgot to add Vox to the above list. There is a Trainwreck in that list too.

[The New Steve H]

It's ALL good!