Favorite PP 6L6 amp circuit

[Paul1453]

OK guys, I need your expertise here.

I have very little experience with playing guitar tube amps.
I started playing guitar as a kid in the 70's.
Back then, if you were some kind of Rock Star you needed a 100 Watt Marshal stack.
As a kid, I obviously could never afford anything like that.
So I played whatever was available.

At school "Learning Center" we had access to some decent Fender amps if I recall correctly.
I had a great time for a semester for 3 hours a day we were a Rock Band.
We learned hit songs from the time like VH "Jamie's Crying", Toto "Hold the line" and George Benson's "On Broadway".
We had music instructors that taught us the basic structure of these songs.
When we could manage to play the tunes, the instructors would go into extended jam sessions on lead.
It was a magical time in my childhood.  We were a Rock Band.

If I had my own amp at home it was most likely a very cheap SS amp.
All that to say, I don't know squat about all the different great sounding tube amps.

I recently got into tube amps to revive my old Army electronics training.
Thing are coming back to me slowly, and I've made a number of low watt amps now.
I've got a 6L6 PP OT from a Hammond organ amp, and have managed to make a Wards Airline GIM-9111A amp on my BB.
It might not look great, but it does sound good even with the haywire setup.
It only uses half of one of the two 12AX7 tubes.
Before I commit to building this in a chassis, I'd like to try at least 1 or 2 more designs on my BB.
I want to maximize the potential number of buyers for this amp when I do finally build it.

What kind of not too terribly complicated PP 6L6 amp circuits do you much more experienced players like?

[labb]

Fender 1959 Bassman, 5F6-A. The granddaddy of all.

[Paul1453]

Fender 1959 Bassman, 5F6-A. The granddaddy of all.

Is there something I can do if I don't have a PT with that negative bias tap?

[DummyLoad]

68 AB763 twin reverb or 68 AB763 super reverb.


--pete

[DummyLoad]

Fender 1959 Bassman, 5F6-A. The granddaddy of all.

Is there something I can do if I don't have a PT with that negative bias tap?

go to link below and download sluckey's scrapbook. ref.: pg. 5 - typical marshall schematic.

http://sluckeyamps.com/misc/Amp_Scrapbook.pdf

--pete

[eleventeen]

You can easily steal bias from one of the HV leads, look at the schematic for a 6G3 Deluxe.


http://el34world.com/charts/Schematics/files/fender/Fender_DELUXE_6G3.pdf


Note the reversed direction for the single diode, half-wave config. You just have to smack down the voltage with a series resistor. Small filter on the output of the rectifier, then usually we see a stack of 3 resistors, the middle one is a pot, and that's where we grab our bias. Or it can be done with 2 series resistors.


You just have to fiddle with the voltage divider resistors to get them where you want them. You want 1: NOT to be able to dial bias so hot your output tube glow red 2: to have the bias pot be happy sort of in the middle of its rage, 3: Want to wire the circuit so that if the wiper of the pot fails for some odd reason, your bias voltage swings way NEGATIVE, shutting off the output tubes, versus POSITIVE which would quickly scorch them.

[Paul1453]

Thanks guys!

I think I can do the Bassman on my bench power supply.

about +440 is the max it will do, and it has an adjustable negative.

If it is a great sounding classic, I could spring for the proper PT.

I'd like to hear a number of the classic circuits before committing to the build. 

[SILVERGUN]

If you haven't built anything with the classic Fender reverb circuit in it, I would HIGHLY suggest you try it.
For me, it's a must in a clean amp and makes the amp much more enjoyable to play.
 
It's not really about the amount of reverb, but more just about how it adds to the depth of the tone. I get bored pretty quickly with just a straight clean amp, but just the inclusion of reverb has me playing for hours.
 
Check out sluckey's Tweed Deluxe Reverb project and make sure you make it all the way to the bottom of the page where he decides to go with a different PT, OT and 6L6...I built something similar and just couldn't stop playing it,,, still one my favorite amps of everything I've built.
http://sluckeyamps.com/tdr/tdr.htm
 
As DL suggested above, AB763 is a must try, and is considered by most here as the holy grail circuit.

[Paul1453]

If you haven't built anything with the classic Fender reverb circuit in it, I would HIGHLY suggest you try it.
For me, it's a must in a clean amp and makes the amp much more enjoyable to play.
 
As DL suggested above, AB763 is a must try, and is considered by most here as the holy grail circuit.

Well I'm glad my last junk gear purchase included a reverb tank then.   

Yes, the 6L6s seem like a very clean amp compared to the little 6V6, 6BQ5/6AQ5 circuits I've been playing with.

So the 6G3 shows a tremolo circuit added to the bias, but the main idea is just a reversed diode tap with a few RC filter and dropping stages to get the proper - bias voltage range.  This bias voltage uses little to no current, except in those dropping resistors, correct?
A ballpark guestimate of the mA of current draw this adds to the HT tap?  I suppose this is dependent on the B+ voltage.

It seems as most GC circuits run at around +450, and my older G or metal 6L6 circuits at +380 or less.
The Airline design, with it's +380 B+, worked for all my metal 6L6s, of which I have the most, and 6L6G tubes.
And when I put my only 2 6L6GCs in there I couldn't hear any difference between all 3.  Clean but not quite as powerful as I was expecting for this output wattage.
Is the higher B+ desired more for output power or as I had read a decrease in odd order harmonics generated?

I have a number of PT's that could work.  A few that could do +500 or more with SS rectification. 
Some with 5 VAC taps and some without, but none with that specific - bias tap.
Then the other decision tube or SS.  To get a true representation of a circuit's sound, I supposed it is necessary to follow the PS design exactly.
Or is this sag and other effects of tube rectification barely noticeable to newbies like me?   

[eleventeen]

Once you understand how to overcome the apparent "problem" of not having a bias tap, the bias tap is a complete nothing. You can always make that reversed diode half wave rectifier. But it will have biggish volts without a voltage divider on its DC side. So you have to whittle its output down, WAY down. Takes a few resistors, that's all. One of them is a pot whose wiper lets you dial in a particular voltage level for your bias. The only thing a bias tap does is to set up the same reversed HW diode with 70 or 80 volts (no load) instead of the 300 or 350 you'll have. You don't need any more parts than if you had a bias tap, just different values.


Bias uses almost no current at all. 1 mil, 2 mils. Nothing, negligable. Your PT will not even know it's there.


Incidentally; if you want to do this (steal bias off one of the HV feeds) where the main B+ rectifier is a voltage doubler; you have to add a (fat, like .22 or .47) capacitor in series with the rev diode. Go look at Bogens for this aspect, if you are interested.