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Single-ended 6L6 amps


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6/7/1999 8:22 AM
Steve Jones
Single-ended 6L6 amps
There are lots of SE amps that use a single 6V6 such as the Champ, Princeton, Harvard, Supros, etc. I have only seen one (Champ 12 I think) that uses a single 6L6. Is there a reason for this? I am considering a single 6L6 amp as a project (because of a power trannie I have that is too high a voltage for a 6V6) and am wondering if there are tonal, performance, or other reasons that make a 6L6 a bad choice for this.  
 
Opinions?  
 
If someonce can point me in the direction of some schems for SE 6L6 guitar amps that would be appreciated!  
 
Thanks!  
 
Steve
 
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6/7/1999 1:05 PM
John Martin

I have a fifties Epiphone, and a Premier "Twin Eight" that use a SE 6L6 output. Have also seen a few phono amps with SE 6L6. They can draw a lot more current than the 6V6 and can possibly overload those tiny 6V6 type SE output transformers. Both of the amps mentioned above have 10K screen resistors if that gives you any indication.  
 
JM
 
6/7/1999 1:13 PM
Steve Jones

Thanks John!  
 
Do you like the sound of these two amps?  
How would you compare the sound to a Champ?  
 
Thanks!  
 
Steve
 
6/7/1999 1:07 PM
Steve M.

Steve,  
 
Check out this link:  
 
http://www.infomaniak.ch/~bonavolt/audioel.htm#Amps  
 
These are all hifi amps, but there are a few SE schematics (including an SE 6L6) that might give you some ideas.  
 
You also might check out this link:  
 
http://www.servtech.com/~piazza/joepage/Amps/prem50.gif  
 
This amp uses the 7591A tube in SE configuration and is a guitar amp. It has similar ratings to a 6L6GB in that they both have 19 watts max plate dissipation.  
 
BTW, Glass Audio published an article several years back called "The Remaking of a Champ." The author basically gutted a BF Champ, installed a Champ 12 OT so that he could use a 6L6 instead of a 6V6. He also added a high gain preamp, and regulated the voltage on the tubes' heaters.  
 
Hope this helps,  
 
Steve M.
 
6/8/1999 6:16 AM
MKB

Hi, Steve. I just recently completed a tweaked tweed 5F2-A Princeton that was built for one 6L6 SE. The amp has three pots; volume, tone, and power amp feedback per the suggestion of Bruce at Mission Amps (recent posts here). These pots give the amp a wide range of tones. The amp has a triodepentode switch also. I used the 6L6 because the OT was from a 6L6 SE PA amp and the PT would supply the current. With a 5Y3 rectifier, I got a B+ of around 300V, and with the 6L6 running at 60mA, I had around 5W out at 8ohms. In retrospect I should have used a higher voltage transformer, maybe for around 400V.  
 
I have a wirewound pot in parallel with a 470 ohm resistor as the cathode resistor for the 6L6. The thought here was I could use a 6L6, 6V6, EL34, etc. and check the tonal differences. I have only tried a Sovtek 6L6, Sovtek 5881, and Mullard EL34 so far. Frankly, the EL34 sounded so good that I haven't tried anything else yet as I am too busy playing the thing. The 6L6 sounded fine however, more full range tone with crunchy highs; the EL34 was smoother and brighter. Since the circuit is so simple, the power tube choice makes a huge difference. I plan to try a 6V6 soon and I will report back with my impressions.  
 
I can't see any reason why one 6L6 is not a great idea for a SE amp. In fact, it is really easy to design the amp to use many different eight pin octal types, you can possibly use a 6L6, 6V6, EL34, 6CA7, 5881, 6550, etc. The simplicity of the circuit really allows the power tube tone to shine. The only problem I had was using the Sovtek 6L6 in triode mode, I got some arcing (maybe a bad tube). Everything else worked fine.  
 
Good luck!
 
6/8/1999 6:34 AM
Steve Jones

Thanks MKB!  
 
Your post is fascinating. This is just the sort of thing I'm looking for. The flexibility of wiring to use different power tubes is interesting. By any chance do you have the schematic worked up for your amp, and would you be willing to share it? If so, please email to sjones@fgm.com. Thanks for your post!  
 
Steve
 

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