Mod to SE 6SN7 - 6V6 amp

[brucetassin]

Hello Everyone,

I have a SE 6SN7 - 6V6 amp (boozhound Labs) that works very well as it is, but now I would like to get a little more out of it. I reworked the schematic as to how I think it should be changed (just guessing) but choosing the values is well beyound me. Would anyone like to make suggestions for the missing values and comment on the changes? I already have a push/pull amp so I dont want to go there, and I want to keep the mod as simple as possible. My power supply can handle the extra tube just fine.

[aardvarkash10]

what is it currently delivering for you that you like?

what little more are you wanting to get out of it?

[kevinkr]

I'm assuming that the second (lower) schematic is yours?

If so this will just add a lot additional gain and probably reduce resolution in so doing. It's not an improvement in any meaningful sense that I can see..

At the minimum a cathode bypass cap on the output stage would be a good idea..(existing design) A 100uF/35V part should suffice..

Selecting a hotter operating point in the first stage and implementing fixed bias in the second stage might bring some improvement as would the fitting of a higher quality OPT.

I reinterpreted an old 6J7/6V6 all pentode design about a year ago (here on diyAudio) and used a small 12V camera battery to provide grid bias to the output stage..

More than likely you need to build a more powerful amp to achieve the improvement you are looking for. Check out tubelab's simple single ended amplifier. Great project and learning opportunity and at the end of it all a good, solid amplifier.

[brucetassin]

I'm using a CD player (Pioneer) from the 70's or 80's. I have not measured it's output but I think it's less than 1 volt. I also have 12 inch, three way speakers from that same era. I get good sound and volume from that setup but I would like a little bit more volume (power). I already have a 6V6 push/pull and a 6BQ5 push/pull, so I dont want to build a whole new amp, just improve this one if I can.

[kevinkr]

Originally Posted by brucetassin

I'm using a CD player (Pioneer) from the 70's or 80's. I have not measured it's output but I think it's less than 1 volt. I also have 12 inch, three way speakers from that same era. I get good sound and volume from that setup but I would like a little bit more volume (power). I already have a 6V6 push/pull and a 6BQ5 push/pull, so I dont want to build a whole new amp, just improve this one if I can.

Post 1983 as that is when CD was introduced.. Standard is 2Vrms.. You just need a more powerful amplifier or more efficient speakers I would guess, the gain is probably more sufficient to drive the power stage to full output.. A 6V6 is good for about 1.5W in triode IMLE, and about 5W in pentode. Do you hear obvious clipping on loud music as things now stand? - If not then additional gain might be what you need, otherwise not..

[brucetassin]

Like my equipment (except amp) I am old (67 years old) and just damn glad I can hear the thing play. I can turn full volumn and not hear clipping and it's almost uncomfortable to be near. I would not listen at that level for long, if at all. Except to hear what it can do. I'm not prepaired to do any meaningful testing, just listening to it. I'm retired and just amusing myself with this stuff.

[kevinkr]

Totally cool.. Take a look and see if there is a bypass capacitor on the cathode resistor of the 6V6 - if not present installing one will give you a little more gain, and better bass performance. Possibly even better would be battery derived grid bias.. (Measure the voltage across the cathode resistor and then figure out if you can get there with some combination of available batteries.. 1.5V, 9V, 12V alkalines) The grid bias gets rid of the cathode bias cap and resistor..

[brucetassin]

I built this amp about 6 months ago. Yes, there is a bypass capacitor on the cathode resistor of the 6V6. I forgot to add it to the schematic after I built the amp. This design is from Boozhound Labs. My other two amps (6V6 PP and 6BQ5 PP) could blow the walls down if I turn them up using the same CD player and speakers. I have a set-up where I can choose which amp gets switched onto the CD and Speakers so I can listen to anyone whenever I want to. My gut feeling is that the amp could put out "just a little more" if I would drive the drivers just a little more. Updated schematic.....

[aardvarkash10]

just a little more (in the context of keeping this topology and these parts) is not going to make an appreciable difference in the power you hear.

There are some simple things you could do to fettle the amp - I'd go with a LED bias on the 6SN7 and a LM317 under the 6V6 as a start.

[brucetassin]

Thanks aardvarkash10 . I will research the 2 suggestions.