Low Wattage 6L6 amp

[macula56]

I like 6L6's more than any other power tube that i have used. Are there any good low wattage 6L6 designs that i could build on? by low wattage i mean 10 - 15 ideally. Most amps that i have seen that are that low are 6V6 or EL84 designs. Anyone have any suggestions? Thanks in advance as always, JMac.

[birt]

make an SE 6L6 amp. don't go too high with the B+. try power scaling. there are lots of possibilities.

[DummyLoad]

http://www.el34world.com/Forum/index.php?topic=14383.0

[Willabe]

You can always get less out of a tube/pair of tubes, but it might not sound the same/play the same to you.

Amp companies used smaller, less expensive tubes when less output was needed. Why use a tube/s that cost more when you don't need the extra output? Not only the cost of the tubes themselves but the cost of extra heater current/bigger PT and extra heat penalty from the bigger heaters. So if you want a low output amp with 6L6's might be best to look for real early/old amps from the earliest days of guitar amps?

What do you like about the sound of 6L6's?  Is it their clean sound, more head room? Tighter bass? Or do you like their breakup better? Do you want a SE or PP amp? What sound are you after at a lower volume? Clean, dirty?

10 to 15 watts from a pair of 6V6's might sound really close to a pair of 6L6's at that output level? At 10w you will not be pushing the 6V6's hard and the tubes will have more head room than if you drove them harder to their limits.

OTOH, you could run a pair of 6L6's very conservatively and you might really love it.

Plus, Kevin O'Connor's Power Scaling when done right is about keeping the tubes transfer curve intact across the entire volume range so as you tune down the PS (output volume) it retains the same tones. This might be an option too.


                 Brad      

[macula56]

cool schematic Dummyload. i don't get on with single ended stuff all that well. sounds ok to me but lacking. at least the ones i have played. i like the smooth bass response i get from PP 6L6's. i can never seem to get a good enough bass response out of 6V6's. plus i have like 30 or so 6L6's laying around the house. appreciate the replies.

[Ed_Chambley]

I converted an old Stromburg Carlson PA.  Picked it up at a flea market.  Dummyload gave me what he called a hack for it.  Runs 2 6l6, cathode bias.  Does good to reach 30 watts and at 30 watts high on crunch and sustain.

Other than removing the old caps, it was easy.  Solder joints on the PTP and leads were mechanical wrapped.  Very old school.  It will play clean at lower volumes.  It sounds surprising like an old Supro.

Total cost-$185, sound-priceless.

[macula56]

i thought about cathode bias 6L6s. i have never tried that. do they sound good with cathode bias?  or maybe 6L6s in triode mode. anybody do that?

[tubeswell]

i thought about cathode bias 6L6s. i have never tried that. do they sound good with cathode bias?

Here's some clips of a SE 6L6 (with a celestion G10) that I made a while back

http://www.nzguitars.com/forum/download/file.php?id=8343

http://www.nzguitars.com/forum/download/file.php?id=8344

http://www.nzguitars.com/forum/download/file.php?id=8346

http://www.nzguitars.com/forum/download/file.php?id=8347

[printer2]

From a spec sheet 6L6's running at 250V, 5k in Push Pull will put out about 15W in Class A, mind you at 2% distortion. I have a Bogan with a pair that is 15W.

[Willabe]

Is that from a spec sheet for 6L6, 6L6GB or 6L6GC ?


              Brad     

[Willabe]

Hey Pete, I can't open up those sound clips?


              Brad     

[DummyLoad]

Hey Pete, I can't open up those sound clips?


              Brad     

they should download then click to play them. they're mp3

--DL

[Willabe]

I get a"General Error" page.


              Brad     

[DummyLoad]

Is that from a spec sheet for 6L6, 6L6GB or 6L6GC ?


              Brad     

RCA 6L6GB datasheet.

http://scottbecker.net/tube/sheets/049/6/6L6GB.pdf

third page P-P class A1 - 13.8W w/ 250V B+ in cathode bias.

--DL

[DummyLoad]

I get a"General Error" page.


              Brad     

right-click on links - save as may work?

--DL

[Willabe]

Thanks DL, they opened up for me.

I like it Pete.


                Brad     

[tubeswell]

FWIW here's the schematic and my voltage notes with the 6L6 and 5U4G



Loaded with 5U4GB, 6L6 (4K Pr Z), 12AX7, EF86

Contrary to the schematic - the following voltages were taken with the 280-0-280VAC HT taps

Supply nodes
B+ = 333 VDC at reservoir cap
10k node = 285 VDC
27k node = 222 VDC

6L6G
Plate = 326 VDC
Screen = 283 VDC 560R g2 resistor dropping 2V = 0.004A
Cathode = 20.4 VDC (across 472R measured) = .0432A
.0432A Ia+Ig2 x 305.6V a-k = 13.2W (minus 4mA Ig2 = 13.0W plate dissipation)

12AX7
Driver Stage (222 HT)
Plate = 134 VDC
Cathode = 1.21 VDC
LFO Stage (285 HT)
Plate = 166 VDC
Cathode = 1.78 VDC

EF86
(222 HT)
Plate = 98 VDC
Screen = 73 VDC
Cathode = 1.02 VDC

Comment: Best sounding trem with this configuration

[macula56]

those clips sounded very nice for sure. i especially liked the whole lotta love tone. but getting back to my previous post, what are some examples of cathode bias push/pull 6L6 amps?  and does anyone have any experience with 6L6's in triode mode?

[PRR]

Simply getting 10W-15W from a pair of 6L6 is trivial. Read the 6L6 data-sheets, or use the 6V6 conditions (300V 8K).

But with all your questions, I think you need to:





Try different conditions until you find one you like.

[macula56]

i have often thought of building something like that for playing with different preamp circuits.

but i'd still like to know if anyone has experience with 6L6's in triode mode.

[Ed_Chambley]

Yes, I have an old Giant Zeneth AM.  Called a 9 tube.  Field coil speaker was trash, so I added a OT and tried different methods.  Mind you it has ST bottle 6L6G and a full range speaker.  Ended up using what is basically a 5C8 Fender.  After 2 days of trying different things, and not having very good bass response, I did what the guys here say all the time.  Build on a proven schematic.

Forgot to mention I have a AB763 preamp I use to test any power section.  This is where your objective lies.  It is all in what sound you are going for and what you like.  For me, if an amp will not play sparkly clean I am not a fan.  OTOH, there are many who swear by a 5e3 and it is easy enough to build a 5e3 with 6L6's.
 

[crashtm1]

This one is worth taking a look at... 15 watts with 2x6L6... She's got great tone..

[printer2]

How about a Gibson BR-1, 6L6 at 18 watts.

http://www.superiormusic.com/page199.htm

http://www.prowessamplifiers.com/schematics/Gibson/br1.pdf

1946 Gibson BR-1 Amp demo - with Tokai Les Paul & Stratocaster


Maybe skip the field coil speaker. Wonder what the plate voltage is.

[PRR]

> triode mode

Not counting flea-watt amps: there are "NO" triode guitar amps.

(Yes, a few with pentode/triode switching.)

Going back to the dawn of electric guitar, the first good/useful guitar amps come about the time of the first good power pentodes.

I suspect "the sound of electric guitar" is "the pentode sound".

But.... it would be simple to go ahead and _build_ something and try it both ways.

[tubeswell]

You could try a variation of Merlin Blencowe's morph control. Here's an (untested) schematic I came up with a while back (based on Merlin's idea for a small signal pentode). You could either use a double-ganged morph pot, or even try 2 separate morph pots for a range of effects.

For full screen bypass bandwidth, the caps need to be big enough to fully bypass the screens when the pot is cut to the 'pentode' mode.  This means that the screen bypass cap will ideally have be large enough for full bypass bandwidth on its own, or not - depending on whether you want full bypass bandwidth or not.  Any 'unbypassed' bandwidth will end up with more screen compression.

The other cap (the 'plate blocking' cap that connects the screen to the Plate at AC when in 'triode' mode) needs to be about 5 x bigger than the screen bypass cap (because the two caps end up in series in 'triode' mode) to ensure sufficient coupling bandwidth with the plate.   This plate-blocking cap should also be rated for 1kV minimum. The pots themselves should be as large a resistance as possible (say 1M each), so that they effectively block any AC at the plate interacting with the plate blocking cap. 1M pots can probably gotten away with being 1/2W rating. Those are my musings

(NB the choke is 'wrong' in this schematic)

[macula56]

that's what i was refering to PRR. i have seen amps with a switch for triode/pentode but i have never played thru one. other than volume drop i don't really know what they sound like. i may just make a stereo power amp with EL84's and 6V6's. i can never seem to get a good enough bass response out of 6V6's lkike i can with 6L6's but i like the way they sound overall.
thanks for the schematic tubeswell. i really need to get Merlin's book.

[HotBluePlates]

... i have seen amps with a switch for triode/pentode but i have never played thru one. other than volume drop i don't really know what they sound like. ...

Triode mode sounds a little quieter, and a little darker. Not "more bass" draker, but "less treble" darker.

I have read (but not tested) that triode mode's lower internal impedance leads to less distortion of the output stage, along with the reduced volume. The lower distortion takes the bright edge of the tube's sound, even before it gets noticeably distorted.

Testing it would involved measuring the output of both setups with a distortion meter of some form, while checking for similar input and/or output signal levels.

[macula56]

thanks for all the great ideas guys. i'm gonna let them percolate in my brain and see what pops out. i think i am gonna go with a stereo power amp with EL84's and 6V6's and mess with preamp values til i can get the 6V6's to give me the bass response that i want. i have a Randall RM20 modular head that has a master presence and a master density control on it. these 2 tailor the overall sound pretty well. the density adds a lot of low end. i wonder if it's like a resonance control maybe. does anyone here have any experience with the Randall Modular amp heads?