First 5f6a build

[duke of earl]

Hey guys,
 
Been a while since I posted on here but I am back in the saddle and have a board all laid out which is pure stock or as close to the 59 as possible. Do you fellas have any improvements to this circuit that will make it more stable or sound better than the original? I don't want to drop any solder until I get some feedback (pun intended) from the expert panel. Your thoughts will be much appreciated.

[DummyLoad]

Never cared for that circuit. Build a jtm45 instead. Yes I know they similar. The minor differences make all the difference.

Whatever you decide, good luck to you!

--Pete

[labb]

Fender 5F6-A, the Godfather of electric guitar amps...Some liberties I took with a build: Solid state rectifier, 6L6 power tubes, #1 bright and bass inputs only, different grounding from original, Power tube grid resistors, larger power tube screen resistors, shielded cable to the grids of all preamp tubes, different OT so I could use 4,8 or 16 ohm speaker,  built as a head. You can't go wrong with this amp if you can handle the volume of a 40 watt amp. It is going to be loud, and I mean really loud.

[Willabe]

Some guys leave out the 47pF suppressor cap that's across the PI plates.

Fender probably used it to kill parasitic oscillation because of lead dress. If so most likely only some units came off the line with the problem. So they nipped it in the bud by putting in that cap. For bass (which is what that amp was designed for) you probably wouldn't even hear it in the circuit.

Some say leaving it out opens up the top end others prefer to leave it in, beauty is in the eyes or in this case in the ears of the beholder.


              Brad        

[Platefire]

Mine became way more useable when I installed a master volume. It's a converted Dukane PA but it works great for me. Platefire

[printer2]

Agree on the master volume. I built a single channel amp loosly based on the Bassman and the MV means it does not have to stay cranked to get in the crunchier zone.

[tubenit]

IF I were going to build one, I'd probably do this.  The FX level makes a superb master volume.

with respect, Tubenit

[duke of earl]

Great input. I will look at all of this when my work (HVAC Service) slows down and I can absorb it all. I appreciate it fellas.

[Platefire]

Tubenit's schematic makes great use of the unused V1b. You get an effects loop and a master volume. I think the 250K pot works as a MV only if your not using the effects loop--if I read it right? Platefire

[tubenit]

I think the 250K pot works as a MV only if your not using the effects loop--if I read it right?

It works as a master volume whether you have a delay or reverb in the effects loop or not.

With respect, Tubenit

[Mike_J]

My first build was a 5f6a Bassman clone.  I also own a Fender Reissue LTD 1959 Bassman.  They pretty much sound identical so if you have access to a guitar store that sells the LTDs I would try one out before I built one to see if you like it because based on my experience your amp when it is done is going to sound like the LTD does.  In my opinion that is a good thing as it is pedal friendly and is a great amp.  The suggestions concerning insertion of a master volume are good as the amp is very loud.

The biggest difference between the 5f6a and the jtm 45 is four 10 inch Alnico speakers versus two 12 inch ceramics.  The 5f6a has the feedback tied to its 2 ohm load and the jtm 45 has its feedback tied to its 16 ohm load.  That will also make a little difference in the tone of the amp.

I personally am very fond of the 12 inch Celestion Greenbacks they have the British sound of the late sixties and seventies that I grew up with.  The 5f6a will not too surprisingly sound more Fendery and will have less of the Marshall crunch probably due to the speaker difference.

When I built mine it had a motorboating issue which was quickly eliminated with 1.5K grid resistors on pin five of each power tube like the Fender blackfaced amps used.  I also put an extra 8 uF @ 450 volt electrolytic cap on the first preamp tube.  The original 5f6a schematic had the first two preamp tubes share a single 8 uF @ 450 volt cap.   I also ran a bare copper ground wire on the back of the pots and tied each tubes grounds to the ground of the electrolytic for that tube before running it to the bare ground wire corresponding to that tube.  I made mine on the same kind of board material the original amps were made with.  If I had to do it over again I would have done it differently.

If I started from scratch now I would buy some G-10 from Doug.  I would use Doug's layout for tubes one and two.  I would do the PI tube like Fender did it in their layout.  I think it flows better that way and results in shorter wire runs which makes for a quieter and more stable amp design.  Secondly,  I would then put in an adjustable pot and wire my bias like Fender did in their AB763 amps.  It will make biasing tubes much easier.  You may or may not need the grid resistors I mentioned earlier and again insertion of a master volume will make the amp more useable, my suggestion would be a PPIMV as when you max the dual pot you have essentially a stock 5f6a.

From my experience and a lot of tinkering it will still sound like the LTD reissue though when done which like I said is not a bad thing in my opinion.

Good Luck
Mike

[Ed_Chambley]

I have one I have been tinkering with.  I cannot and have not ever been able to get much response from the tone stack.  I installed a Master and added a bypass cap to increase gain and just tweaked the amp to have a good tone with a single 12" Weber.


I prefer a plate driven tone stack I guess.

[Platefire]

Duke of Earl

  I know this is a busy season for HVAC. If a unit going to die it's usually in the heat of summer. I thought my condenser unit had died a couple of summers ago with the compressor going bad but my HVAC man put a "hot start" kit on it and it's still going on borrowed time. Some times when the compressor kicks in it makes such a noise that I think, surely this is it! but not yet. Just a few months ago the condenser unit fan went out and I just noticed it was sounding different when it turned on, went out and checked and noticed the fan not turning. so it got a new fan. It's a RUDD and how it's still going I don't know.
  Maybe you can start on the 5F6A in fall? Then it will dead winter and all the HV units will be going bad. Just think of it as job security! Platefire

[billcreller]

I had thought about building one of those, since I have a base that I don't know how to play ! Can I assume that those 5881 tubes can be replaced with the 6L6 types ?