Re: The modified circuit:
Well, this looks like more than a little tweaking of resistors
You seem to have picked up on tube amp design skills really fast and re-done the whole driver/phase-splitter topology.
A couple of questions out of my own curiosity:
The connection of the concertina phase splitter's cathode resistor seem a little unorthodox, could you explain?
Why did you add the input cap?
SveinB
Cobra2 said:
Well, this looks like more than a little tweaking of resistors
You seem to have picked up on tube amp design skills really fast and re-done the whole driver/phase-splitter topology.
A couple of questions out of my own curiosity:
The connection of the concertina phase splitter's cathode resistor seem a little unorthodox, could you explain?
Why did you add the input cap?
SveinB
I wish...
The credit for circuit change and drawing should go to mississippi...
(but I skipped that cap ;-) - and gave the input-stage slightly more bias...compared to last drawing.
Phase-splitter is very similar to last figure here:
http://www.arrakis.es/~igapop/russianotes.htm#6N1P /6N2P How to use them
Arne K
The credit for circuit change and drawing should go to mississippi...
(but I skipped that cap ;-) - and gave the input-stage slightly more bias...compared to last drawing.
Phase-splitter is very similar to last figure here:
http://www.arrakis.es/~igapop/russianotes.htm#6N1P /6N2P How to use them
Arne K
Cobra2 - from our discussions on the other, more tranformer based thread.
I got curious and plugged the Numbers here into the TCJ p-p calculator (so all this is for operation as Triodes IMO the most musical use for an EL34 anyway
)
9k2 opt? Oh well here goes....
"Should" (as a triode) get you 11w output but leave class A at 4.24 watts
reducing the cathode bias resistors on the output stage to say 350R (in total) makes it Class A all the way, but power drops to 9.88w
Not so bad as a loss. Also check the bypass caps, I have 1000u in mine, needed 600 odd on paper so 330U is a bit light? (the parts bin could only supply 1000u so thats what I used.)
incidentally your higher than expected trafo impedance is the second time I've seen that done. Ok for a Triode its lower distortion at the expense of power but not for a pentode... where it should, er, suck. (more distortion & less power) Hmmm odd
Actually looking at your circuit, have you tried triode mode? Its easy to do. Add a screen resistor though, maybe a couple hundred ohms
Lastly try messing with the feedback loop, Ok I have an SE amp but it REALLY worked once I got it somewhere close. Only a question of clipping in resistors. BTW adding a cap in parallel with the feedback resistor didn't help in my case. I tried a range of values hoping for a subjective bass boost - nope!
Andy
I got curious and plugged the Numbers here into the TCJ p-p calculator (so all this is for operation as Triodes IMO the most musical use for an EL34 anyway
)9k2 opt? Oh well here goes....
"Should" (as a triode) get you 11w output but leave class A at 4.24 watts
reducing the cathode bias resistors on the output stage to say 350R (in total) makes it Class A all the way, but power drops to 9.88w
Not so bad as a loss. Also check the bypass caps, I have 1000u in mine, needed 600 odd on paper so 330U is a bit light? (the parts bin could only supply 1000u so thats what I used.)
incidentally your higher than expected trafo impedance is the second time I've seen that done. Ok for a Triode its lower distortion at the expense of power but not for a pentode... where it should, er, suck. (more distortion & less power) Hmmm odd
Actually looking at your circuit, have you tried triode mode? Its easy to do. Add a screen resistor though, maybe a couple hundred ohms
Lastly try messing with the feedback loop, Ok I have an SE amp but it REALLY worked once I got it somewhere close. Only a question of clipping in resistors. BTW adding a cap in parallel with the feedback resistor didn't help in my case. I tried a range of values hoping for a subjective bass boost - nope!
Andy
No wonder it lacked power...
I did not try triode-mode, (was looking in to it, but I needed all the power it had, and more, for my use/speakers).
I was however tempted to see if I could use 2 more EL34(in paralell) and in triode-mode, to get some more power.
But then again, the power-trafo will need an upgrade.
Maybe cheaper than 2 new op trafos...
Will this idea work with the op trafos I have?
Arne K
I did not try triode-mode, (was looking in to it, but I needed all the power it had, and more, for my use/speakers).
I was however tempted to see if I could use 2 more EL34(in paralell) and in triode-mode, to get some more power.
But then again, the power-trafo will need an upgrade.
Maybe cheaper than 2 new op trafos...
Will this idea work with the op trafos I have?
Arne K
feedback
OH hang on
I have a question! whats going on with the feedback loop fed into the gain tube's cathode. Ok with it so far, but what appears to be a concerina phase splitter is sat on top of that. is this a different phase splitter or shoud the 33k resistor teminate at ground not the hot end of the 180ohms?
(and does it matter anyway?)
If anyone can clear that up I'd appreciate it - It just looks asymmetrical to me, probably nothing and blindingly obvious but still...
Andy
OH hang on
I have a question! whats going on with the feedback loop fed into the gain tube's cathode. Ok with it so far, but what appears to be a concerina phase splitter is sat on top of that. is this a different phase splitter or shoud the 33k resistor teminate at ground not the hot end of the 180ohms?
(and does it matter anyway?)
If anyone can clear that up I'd appreciate it - It just looks asymmetrical to me, probably nothing and blindingly obvious but still...
Andy
Cobra2 said:
you get waaay more power in Pentode mode as shown than with triodes.
You might be surprised how little power you need. After a diet of 50w transistor amps with the attenuator at 9 oclock I was surpised to learn that didn't mean 25% power (log pot!) I measured this, and found that at my most comfortable listening level I was using only 3-5 watts even if the amp could go MUCH louder
I reckon on about 3w from my SE amp - it goes loud enough. OK not as loud as the prodigy in my lounge but loud enough - 10w of triode ought to be do-able. I have 89dB Castle Harlech's But I don't tend to listen at ear crushing volume either
going to parallel tubes is a nightmare! All trafos need to be comfortable with 2x the current and the requirement for the impedance is halved - your 9.2k OPTS are really in the wrong direction then.
Not saying dont though" Until recenly I was planning on an Octet of KT88's then one day I sat myself down and said, "now come on be serious"
Andy
Cobra2 said:
Ok I see you need Juice! All I can suggest then is UL (which I *think* you can do with a MOSFET if your OPT's dont have the tapping? anyone? I have seen this I'm sure, but I cant remember where!
course its open to debate, but yes parallel push pull would seem to be the way to go (anticipated or not ;-)) Parallel PP KT88's should get you three figure numbers! Outside my expertise to
even start to comment on though.
Andy
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