6n7 dual triode output

[ArcticBreaze]

Any one have any experience using the 6n7gt as a pp output driver.


from what i have found on the net it should make almost 10 watts but all the circuits i have found use it to drive 6l6's.

am looking to build one of Rob Robinette's bassman micro's, but with octal tubes thought this may give me a 10 watt option

 

[jeff5may]

Nope, won't sound good in that circuit at all. At the ten-watt range, the fidelity will compare to a helicopter radio transmission or a really old space mission: "The eagle has landed...". Maybe the same fidelity as a 5 dollar walkie-talkie. Any amount of bias applied to reduce distortion will reduce power output fast. The grid presents a huge load to the driver before it if not isolated with a step-down transformer. Trying to drive one without a transformer will get you zilch before the PI tube distorts. Not in a good way, either.

Another application these were used in (as well as the 6a6, its predecessor) is very old car radios that only put out a couple of watts at barely tolerable levels of fidelity. Customers complained, so the "premium sound" radio was born.

For that circuit to do around 10 watts, I would throw some 6k6 or 6v6 or kt66 tubes in as outputs. Wire the valves up like the print, plus pin 4. You can tie pin 4 to pin 3 with a 100 ohm resistor for triode strapping mode, or tie both pin 4's together, then run a source resistor from there to the center tap of your output transformer. Maybe 4.7K ohms, as big as you want. Stick a small electrolytic on pin 4 to ground in case bad noises happen.

 

[ArcticBreaze]

thanks for the heads up on the 6n7, will probably hav to drop back to about one watt as designed and use 6sn7 as output, whole idea of the micro is not to use output tubes like 6v6 or kt66

cheers

 

[Printer2]

thanks for the heads up on the 6n7, will probably hav to drop back to about one watt as designed and use 6sn7 as output, whole idea of the micro is not to use output tubes like 6v6 or kt66

cheers

If you want to do up to 10W then there are other tubes that can be used that are not 6V6 (although I think the 6K6 is a good choice). The question is what do you want? A 10W amp or 1W amp? Personally I think a pentode should have been used instead of the 12AU7 in that schematic. Mind you, what else would you do with all the 12AU7's out there?

 

[ArcticBreaze]

hi there P2. you,d need 2 pentodes in there, but i am trying to stay with dual triode the original amp is 1 watt or 3-4 watts with a 12bh7 i just got a bit excited after looking up the 6n7's in my old Supertone (where they are preamp driving 6f6 outputs)

is there an octal that's close to spec of the 12bh7 (hav tried google but....) pin compatible with the 6sn7 would be good.

 

[Printer2]

12SN7 also.

 

[jeff5may]

12au7 in a "bassman" is self-sabotage. Go audition a tiny terror somewhere and you'll see what I mean. Even running a decent half-stack at apartment-friendly levels, the 12au7 runs out of growl and punch before the neighbors start getting upset. Yes, the darkness/brightness of individual tubes or different manufacturers, but in general they all run out of bottom end fast.

In the same pinout as 12au7, you have some good choices: 6FQ7, 6CG7, 6N1P, ECC99, 6H30. In octal, you have 6SN7, 6N6P, 12SN7 and a gazillion more obscure numbers. The combo tubes that were used in radios and TV sets(1 preamp + 1 power amp) for decades include 6BH7, 6BL7, 6BX7, 6DN7 plus a whole lot more.

 

[ArcticBreaze]

sorry jeff should hav said this is for harmonica not guitar terror is to gainy (<--- apparently not a real word lol) feeds back with mic

i like the tone i get from octals and the 69 bassman is the most sort after harp amp. so i thought id give this one go, also build a mic right into the speaker cab so it can be Di'ed on stage.
probably the whole idea is nuts and wont work but that never stopped me before.

 

[jeff5may]

Oops, I made a boo-boo. The tiny terror has a 12au7 as the PI that feeds a pentode output stage. My bad. So the tiny terror is like 5 times louder than what you propose (watts not dB). The bass response of the tiny terror is still rather thin.

Either way, with a mini tube - socket output the 12au7 and 12bh7 sound close to the same as far as tone, the bh7 gives an extra watt of clean output if you bias it up. The ECC99 has a fatter sound to it and gives you another extra watt. Doubling any of them up in parallel pairs works well if you have an extra tube and socket. As always, make sure you have enough iron.

My son is right in the midst of a project like you're thinking about. It has evolved from basically the schematic you posted to something much meaner. Originally, we ran a 12AU7 as the output, and having a layout so simple proved easy to fine tune the gain stages and tone stack to his liking. The TMB stack got a "mid sweep" control, and the bright caps got taken out. The Eq buffer got deleted. Then he figured out the amp wasn't loud enough for his room.

We turned the 12AU7 into a long tail pair that drives a pair of octal sockets. Feeding upon his ever-changing intentions, we changed the feedback path so now it feeds into the PI, and has presence and resonance knobs. We tried triodes and pentodes and tetrodes as outputs, as well as a dozen or so preamp tubes. He settled on 2 x Sovtek 12AX7 (1-preamp, 1-PI) and a power stage layout that will accept 6K6 or 6V6 output tubes without adjustment. The 6K6 are loud enough for the bedroom, and the 6V6 are loud enough to practice with the band. He voiced the amp much less "gainy" than I expected, deciding on a clean "shiny/tweedy" structure that is more like what you are after than I thought he was. If he wants super distortion or overdrive, he stomps on a pedal for it.

Now when he goes to the music shops to audition amps, he goes straight to the tube amp and half stack section. The modeling and solid state amps have lost their novelty. Some of the pricey tube heads don't even sound as good as his little "lunchbox".

 

[ArcticBreaze]

well i started with a Chinese 5e3 clone kit from mableaudio.com it was my first venture into valves or "tubes" as you call em in the states, came with no instructions and some of the parts were plain wrong. luckily my father (now in his seventy's so he has forgotten more than i will ever know) was an electrical engineer and did his time on tube radios,tv's etc. so when it didn't go I took it to him and he showed my how to fix it. gave me a bunch of books and box's of valves that he no doubt was glad to see the back of lol.

this has been my mod platform and has seen so many incarnations (someone else on this form claimed to have the worlds most soldiered 5e3 but mine can't be far behind)

what i learned from the 5e3 Iput into Big Red 50 watt tube amp 6sl7 pre and pi into 6l6 pp and a 15" speaker no kits here scratch built from ground up but I made the mistake of making a combo cab, its too heavy and tall for a short *** like me to lug round. just made it worse last week it's now a head with a 2x12 lol sounds soooo good thou.

this IS the sound I'm after but with out the blood trickling from ma ears.

so looking to build a small amp that can be miced for the small gigs.

 

[jeff5may]

Haha how true! As I type this reply, my son is playing his little micro-head through the speakers in his 2x12 combo head (SS Randall RG100 something). He loves the sound of the celestions, but not the weight factor.

If you have a free mystery box full of working valves, pilfer through them and figure out what you have. There are lots of TV sweep tubes that make good PI and output stages. The 6N7 will do phase inverter duty if you put it in the right circuit. How well it is suited for use in your amp, I sure don't know! I would rather encourage you to try it and decide for yourself than tell you it can't be done. I do know that they are not good as outputs, though, unless you are building something like an AM radio.

Here's a schematic of an audio amp that uses a 6N7 as a phase inverter:

And another:

The preamp and PI stages in the first amp aren't much different in layout than the previous versions of tweeds than the 5E3. The second amp shares fendery PI and output stages.