I had been endlessly trying to get a scrapheap amp back working and sounding somewhat good, but just could not get her working. See the thread over here.
Anyway, in the end I just gave up and in an effort to salvage something, anything, I hit upon this schematic, courtesy of tubecad:
The thing is, this one sounds absolutely fantastic. Nothing special on any of the parts, all are stuff I had lying around, although I think my transformers are sowters. Anyway, after sorting a few issues with hum etc (thanks again trobbins), this amp is sounding just great. Its easily on a par with the F5s that I've built, and having compared with other amps I've heard, it stands up very well. Soundstage is wide and deep, treble is sparkly and clear with no harshness, bass is tight - although I have heard it in bigger quantities. It really is well worth a mention here as a nice amp to build, lowish to medium gain, and about 8W so good enough for horns.
Its simple enough to build with a low enough parts count. From the tubecad site:
Fran
Anyway, in the end I just gave up and in an effort to salvage something, anything, I hit upon this schematic, courtesy of tubecad:
An externally hosted image should be here but it was not working when we last tested it.
The thing is, this one sounds absolutely fantastic. Nothing special on any of the parts, all are stuff I had lying around, although I think my transformers are sowters. Anyway, after sorting a few issues with hum etc (thanks again trobbins), this amp is sounding just great. Its easily on a par with the F5s that I've built, and having compared with other amps I've heard, it stands up very well. Soundstage is wide and deep, treble is sparkly and clear with no harshness, bass is tight - although I have heard it in bigger quantities. It really is well worth a mention here as a nice amp to build, lowish to medium gain, and about 8W so good enough for horns.
Its simple enough to build with a low enough parts count. From the tubecad site:
Fran
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The EL84 is a great tube - difficult to mess up.
However I think in this circuits case it is the differential output stage which is bringing most of the benefits. Everything I have built with differential outputs has had excellent soundstage and imaging, and crisp delivery.
Good work Fran.
A shoot out some time in the summer seems in order😀
Shoog
However I think in this circuits case it is the differential output stage which is bringing most of the benefits. Everything I have built with differential outputs has had excellent soundstage and imaging, and crisp delivery.
Good work Fran.
A shoot out some time in the summer seems in order😀
Shoog
Seems like a couple of minor tweaks could improve it still further. The operating point of the phase inverter is not really optimum IMHO. I'd aim for something like 100V on the cathode of the split load inverter by adjusting the value of the lower 1M to something like 1.5M and I would probably decrease the load resistors to 20K or less in order to get the plate current up.
A red led on the cathode of the first section of the 6N1P would give you a little more gain, and possibly somewhat better linearity as well, but might make the design more sensitive to variations in transconductance from tube to tube.
Looks like a good, simple and tweakable design..
A red led on the cathode of the first section of the 6N1P would give you a little more gain, and possibly somewhat better linearity as well, but might make the design more sensitive to variations in transconductance from tube to tube.
Looks like a good, simple and tweakable design..
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... and a BBQ maybe?
It sounds lovely, really does.
EDIt: Sorry Kevin, simulpost! Might look at those numbers. I also wondered about using a CCS but want to listen for a while and get a handle on it.
It sounds lovely, really does.
EDIt: Sorry Kevin, simulpost! Might look at those numbers. I also wondered about using a CCS but want to listen for a while and get a handle on it.
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When my studies are over for the year - at the end of May - I would love to come over. No meat on that BBQ for me though.
Currently trying to get my hands on some old Gaertz field coil drivers for another OB build. Lots of new ideas.
Sorry looking at it again its not differential - just a nice simple circuit.
Shoog
Currently trying to get my hands on some old Gaertz field coil drivers for another OB build. Lots of new ideas.
Sorry looking at it again its not differential - just a nice simple circuit.
Shoog
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You know, I'd love to have a go at some open baffles. You bring the drivers, I'll cut the ply....
I'll keep the veggies separate!
I'll keep the veggies separate!
I would think power O/P is less than 8 WPC. Look at page 3 of the GE 6BQ5 data sheet, where some PP AB1 triode mode conditions are given.
The 6Н1П (6n1p) is an excellent driver, thanks in part to its large cathodes.
There's lots of sonic mojo in "12" W. multi-grid power O/P types, in pentode, UL, and triode modes. Poindexter's "Musical Machine" uses a very similar O/P stage constructed around 6V6 "finals".
The 6Н1П (6n1p) is an excellent driver, thanks in part to its large cathodes.
There's lots of sonic mojo in "12" W. multi-grid power O/P types, in pentode, UL, and triode modes. Poindexter's "Musical Machine" uses a very similar O/P stage constructed around 6V6 "finals".
Eli - haven't tested the power output myself (don't even think I have the gear to do it), just quoting broskie from his post.
Sounds plenty loud with the horns - and all my sources put out 1v rather than the customary 2. Using a dcb1 buffer up front.
Fran
Sounds plenty loud with the horns - and all my sources put out 1v rather than the customary 2. Using a dcb1 buffer up front.
Fran
No global feedback I see. I did much prefer my EL84 amp without.
I originally tried UL with no global feedback. It was better than with feedback but I felt that there was a hint of sharpness so didn't pursue it
Andy.
I originally tried UL with no global feedback. It was better than with feedback but I felt that there was a hint of sharpness so didn't pursue it
Andy.
Whut Eli sez. You are going to get four watts, maybe five max, from this circuit. If you load down the outputs with a lo-Z output transformer in the attempt to get a little more power, you'll get that late tube soft sound.
That said, you'd be surprised what five watts can do, as long as you're not trying to drive Acoustats with 'em.
Aloha,
Poinz
I really would be inclined to try an experiment of disconnecting the bypass cap on the outputs and seeing how it sounds. It shouldn't make much difference to the output power.
Shoog
Shoog
I have built this one too!
I made a couple tweaks so far...I implemented a CCS for the EL84 cathodes using an LM317 to hit 80mA total per channel.
I also implemented some red LEDs for the front cathodes of the 6n1p's in lieu of the resitors.
This amp really rocks! and is very tweakable...
I made a couple tweaks so far...I implemented a CCS for the EL84 cathodes using an LM317 to hit 80mA total per channel.
I also implemented some red LEDs for the front cathodes of the 6n1p's in lieu of the resitors.
This amp really rocks! and is very tweakable...
Shoog - you mean the 1000uf on the cathodes of the 84s?
Cjkpkg : would you post some schematics?
Fran
Cjkpkg : would you post some schematics?
Fran
Yes that one. It would become semi-differential. If it worked then replace the 400R with a LM317 CCS.
Shoog
Shoog
I've built this amp up, but with 6CG7 drivers and Sy's led output stage biasing scheme. Very nice amp, and plenty of volume from every speaker I've tred, even low efficiency types. Very nice sound, tryed a led on the 6cg7's cathode, and it seems like slightly more usable volume before breakup. All in all, a great amplifier.
