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I am attempting to bread board my first pp amp, so of course I run into something I don't understand right out of the chute.
In the schem below I believe the plates of the 6v6s are connected to the primary leads of the output trannies, but what is grid #2 from each tube connected to?
Thanks
Edits: 11/19/14Follow Ups:
It looks simple and straight forward. It's not 6v6, but I have a nice collection of el84s as well.
Edits: 11/19/14
that circuit also uses UL taps.
connect the screen of the output tube to the plate of the output tube with a 100 ohm resistor. remove feedback. everything else stays the same.
I'd actually use a different phase splitter. the phase splitter in both of those amps is a "floating paraphase".
some people like em.
I like an LTP/differential pair. LM334 in the tail. 68 ohm resistor for the 12ax7. probably would work for the 6sl7 too. 68 ohm resistor sets the CCS in the tail to 1ma. both halfs of the driver tube are tied together, the LM334 is a constant current sink to ground. gives better balance than floating paraphase.
Do you mean connect G2 to the plate with a 100 ohm resistor? What is the feedback I need to remove? I have never built an amp that used feedback so I don't know what it looks like. Is it G3 back to the cathode?
yes g2.
for the feedback, global feedback loop is from the secondary of the output transformer to the cathode of the 6sl7.
might want to try it both ways, with and without feedback. it's not needed in "triode mode" but will reduce gain and change the sound a bit.
I see. Great, I will give it a try.
Thanks!
Dang, you're right. I missed that. Well if I am going with triode mode I might as well try the 6v6.
Thanks
The link below has the data sheet for the hammond 125e, the opt I was intending to use. Do I need to use a different amp design if I want to use these opts?
Just pointing out that 2.9 henries is mighty low inductance for an 8K primary impedance - bass power fades below 400Hz.
I understand. Just running a comparison test to see if the 125 series has any of the nice properties of the 125 ese series. These will be used for quick bread boards if they don't.
Yes.
Got any suggestions? I want something simple using 6v6s as the output tubes.
This amp was designed by Poindexter who used to be a regular here.
I built this amp several years ago and it sounds very good.
By the way does anyone know what Poindexter is doing these days?
His website hasn't been updated for nearly 12 years now.
Cal
Interesting. Not sure if I have any 5965s though. I will have to check.
Thannks
Poindexter used 6GK5 as driver in later versions of this amp. He thought it was mo' better.
His website seems to be gone but if you google "musical machine" you should be able to find details. I can also probably dig it up in my files if needed.
The dude was a real asset to the Asylum.
.
Freak out...Far out...In out....
Thanks, I will see if I can find it.
Less than 20 bucks will get you 5 of them.
The 5965 and the 5965a are military grade tubes, more expensive.
But the 12AV7 will give you an idea if this is the amp you are
looking for.
Plus, you will get to hone your skills at designing and
building negative power supplies, this is the amp that
I learned those skills on.
Cal
I am going to try a triode mode 6v6 with a 6swl7 driver first and see how that goes because I have all the parts for it. May send off for some 5965s while I am doing that.
Thanks
edcor iron is cheaper. sometimes better.
~ $60 shipped ish for 15w PP iron.
I've used it, not bad at all.
I'd probably buy Dynaco ST35 iron if I was going to build a nice 6v6 or EL84 varient PP amp. I'd run em in UL mode too.
I will probably try them one of these days as money and time allows.
You'll need push-pull OPTs, so 5965s aren't the only thing you don't have on hand.
Dave
The 125e is a push pull opt.
My apologies, I read "se". With a low frequency rolloff at 150hz, it's pretty limited, good luck.
Dave
Ultralinear taps on the transformer.
That's nice. What are those? : )
I have heard of them but have no idea what they do. I have always built SE amps. What if my opt doesn't have them?
If the taps are set up correctly the linearity of the output section will be similar to that of a triode.
Many older UL taps are not set up correctly as they were bypassing a patent. This has gone on so long that many people think that UL does not give the same linearity as a triode.
There is of course a slight loss of power...
Somebody did a bunch of math and determined that connecting the screens to taps at 43% of the plate winding results in minimum distortion. That's ultralinear in a nutshell, which is as deeply as I know it.
If your output transformers don't have ultralinear taps you've got a couple of choices: Run them as pentodes/beam power tubes or as triodes.
To wire as pentodes connect the screens to a well-filtered supply typically about 40 volts less than the plates.
To wire as triodes (less power, better sound) wire the screens to the plates through current limiting resistors (about 100 Ohms is common, and use calculated power resistors).
You could also install a switch to go back and forth between triode and pentode mode.
Well you have two options if your transformer has no UL taps: 1. Regulate the screen voltage with a series regulator as in RCA tube manual 50 watt power smplifier, 2. Hook the 6v6 pentode up as a triode (this will reduce power output).
"...the fool doth think he is wise but the wise man knows himself to be nothing but a fool." Will Shakespeare
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