Impressive. Very nice.
I'd bet the bass shake your bones ? 🙂
How can you get suck low THD when the 6AU6 alone gives more?
I am working ATM on a PPP 6L6 with a 6AU6 triode strapped biased @ 2 mA and I am getting 0.116% THD at the first stage alone.
I'd bet the bass shake your bones ? 🙂
How can you get suck low THD when the 6AU6 alone gives more?
I am working ATM on a PPP 6L6 with a 6AU6 triode strapped biased @ 2 mA and I am getting 0.116% THD at the first stage alone.
Also 0.116% THD from a 6AU6 driver stage could be excellent, what is the signal level where you are getting that THD?
0.1V input, 3V swing.
B+ 304, 82K plate, 1k5 cathode with 40uF electrolytic + 10u film cap, 10K grid stopped, 470K input load resistor.
Simple circuit.
B+ 304, 82K plate, 1k5 cathode with 40uF electrolytic + 10u film cap, 10K grid stopped, 470K input load resistor.
Simple circuit.
"you said "Talking of loud amps I have a box of 813's under the bed, a PP 400w is on the cards"... I bought two identical 650VA mains tfmr's which I will rewindmyself. I'm in the process of winding the mains tfmr for the PSU using a 1000VA toroid, so I'm getting there.
I'm just designing a class AB2 amp using 807's, only 50w but the driver stage shows promise. I'm using 6H8C's paralled set at 15mA at present but they can drive over 1000p without distortion, good F response etc. Obviously driving 813's would be a bit trickier, however see attached. He's using two 12BH7's to drive four 813's, a 1000w amp.
Andy.
I'm just designing a class AB2 amp using 807's, only 50w but the driver stage shows promise. I'm using 6H8C's paralled set at 15mA at present but they can drive over 1000p without distortion, good F response etc. Obviously driving 813's would be a bit trickier, however see attached. He's using two 12BH7's to drive four 813's, a 1000w amp.
Andy.
Attachments
"Impressive. Very nice.
I'd bet the bass shake your bones ? 🙂" Thanks, yes, it does have excellent bass but also V good F response. "Cancellation and feedback." Correct. "Also 0.116% THD from a 6AU6 driver stage could be excellent" It is, that sort of THD for an IP stage is fine, I have the 6AU6 triode strapped as you do but am using CCS as anode load. no grid stopper, no cathode bypass cap from memory.
I'll draw the schematic if you interested, I aslo have some NOS 6AU6's if you want a couple to experiment, yours FOC just pay the postage.
Andy.
I'd bet the bass shake your bones ? 🙂" Thanks, yes, it does have excellent bass but also V good F response. "Cancellation and feedback." Correct. "Also 0.116% THD from a 6AU6 driver stage could be excellent" It is, that sort of THD for an IP stage is fine, I have the 6AU6 triode strapped as you do but am using CCS as anode load. no grid stopper, no cathode bypass cap from memory.
I'll draw the schematic if you interested, I aslo have some NOS 6AU6's if you want a couple to experiment, yours FOC just pay the postage.
Andy.
Hello Andy.
Yes I would be very interested in your input stage with CSS, as I think I can improve my amplifier response even further.
Thanks you for your generous offer for the 6AU6. I have purchased many, different brands and put them to test.
I haven't finished my rolling but so far, by far, I prefer the French military 6AU6WB made by Thomson CSF.
You might want to try them on your beautiful amp.
Thank you,
Brice.
Yes I would be very interested in your input stage with CSS, as I think I can improve my amplifier response even further.
Thanks you for your generous offer for the 6AU6. I have purchased many, different brands and put them to test.
I haven't finished my rolling but so far, by far, I prefer the French military 6AU6WB made by Thomson CSF.
You might want to try them on your beautiful amp.
Thank you,
Brice.
Thanks for all your kind words, much appreciated. I'll draw that up for you today.
"Altec 260 use 6au6 to drive the 813 PP" interesting, not seen that, will have a butchers.
The meter has a proper VU meter driver, however the two beautiful 500uA vintage panel meters I bought, one was OC, luckily I had two 1mA FSD identical meters, but this changes the balistics. Also after trying my best to transfer a VU scale onto the meter faces I gave up and painted them black, then covered the needles in gold leaf, so now they're just something to look at, a visual accompniment to the music.
Andy
"Altec 260 use 6au6 to drive the 813 PP" interesting, not seen that, will have a butchers.
The meter has a proper VU meter driver, however the two beautiful 500uA vintage panel meters I bought, one was OC, luckily I had two 1mA FSD identical meters, but this changes the balistics. Also after trying my best to transfer a VU scale onto the meter faces I gave up and painted them black, then covered the needles in gold leaf, so now they're just something to look at, a visual accompniment to the music.
Andy
Here's the schematic of the front end of these amps, it could probably be be better implemented but it works, you have to stop tweaking at some point.
One thing I might change is the gain, which is low, sensitivity is 1.5v, not ideal. The CCS I've used extensively on other amps, it's simple and works, but you could probably get far better OP Z by using another higher hfe tranny. I prefer to use a preset and fixed resistor as the Re as you can then adjust it to get operating conditions bang on.
The magubbins after the anode helps keep the amp stable, I lifted these value's from Pat Turner's various amps designs.
One last point if anyone is going to build such an amp, I'd highly recommend some sort of protection circuitry, I'm glad I did, saved my **** on numerous occasions when tweaking and testing the amp; very easy to leave a wire off on the prototype and lose bias or make a change resulting in HF oscillation. If these amps pull too much current the protection kicks in far quicker than a fuse.
Andy.
One thing I might change is the gain, which is low, sensitivity is 1.5v, not ideal. The CCS I've used extensively on other amps, it's simple and works, but you could probably get far better OP Z by using another higher hfe tranny. I prefer to use a preset and fixed resistor as the Re as you can then adjust it to get operating conditions bang on.
The magubbins after the anode helps keep the amp stable, I lifted these value's from Pat Turner's various amps designs.
One last point if anyone is going to build such an amp, I'd highly recommend some sort of protection circuitry, I'm glad I did, saved my **** on numerous occasions when tweaking and testing the amp; very easy to leave a wire off on the prototype and lose bias or make a change resulting in HF oscillation. If these amps pull too much current the protection kicks in far quicker than a fuse.
Andy.
Attachments
I use octocouplers and mosfet to protect the 'heating filaments' and valves (cut the 12,6v and the HT supply)
FYI : Altec 260a = 260w RMS, PP 813, drive 6au6 ...
260A Ampl/Mixer Altec Lansing Corp.; Oklahoma City OK, buildSchematic - Altec Lansing 260A Tube Amplifier @ AmpsLab.com
260A Ampl/Mixer Altec Lansing Corp.; Oklahoma City OK, buildSchematic - Altec Lansing 260A Tube Amplifier @ AmpsLab.com