The Nemesis 813 PP Amplifier
- IslandPink
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#16 Re: The Nemesis 813 PP Amplifier
I applaud -
(I) no interstage from st.1 to st. 2
(ii) 46's as drivers
(I) no interstage from st.1 to st. 2
(ii) 46's as drivers
"Once you find out ... the Circumstances ; then you can go out"
- izzy wizzy
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#17 Re: The Nemesis 813 PP Amplifier
I'm interested to hear the 46. These are the only directly heated valves I've played with but still no pure triodes. As an experiment along the way, I'd like to try the thing as just 46 - 813. Previously it went damn loud without the line stage I have now. Maybe the input transformer could be a slight step up to help a bit. Be brilliant if I didn't need stage 1.IslandPink wrote: ↑Sun Nov 04, 2018 11:22 pm I applaud -
(I) no interstage from st.1 to st. 2
(ii) 46's as drivers
Cheers,
Stephen
#18 Re: The Nemesis 813 PP Amplifier
Either a simple bead on the wire (useful for heaters in ID valves as well)
https://www.rapidonline.com/rvfm-k5b-rh ... ad-23-0730
or larger ones with a few turns around
https://www.rapidonline.com/w-rth-elekt ... te-54-8636
https://www.rapidonline.com/rvfm-k5b-rh ... ad-23-0730
or larger ones with a few turns around
https://www.rapidonline.com/w-rth-elekt ... te-54-8636
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
- izzy wizzy
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#19 Re: The Nemesis 813 PP Amplifier
Thanks Nick. Should I use the small single lead through on G1, G2, G3 and do away with the stoppers. The larger one with a few turns on the filaments?Nick wrote: ↑Mon Nov 05, 2018 8:54 am Either a simple bead on the wire (useful for heaters in ID valves as well)
https://www.rapidonline.com/rvfm-k5b-rh ... ad-23-0730
or larger ones with a few turns around
https://www.rapidonline.com/w-rth-elekt ... te-54-8636
Cheers,
Stephen
- pre65
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#20 Re: The Nemesis 813 PP Amplifier
The only thing necessary for the triumph of evil is for good men to do nothing.
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
Edmund Burke
G-Popz THE easy listening connoisseur. (Philip)
- izzy wizzy
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#21 Re: The Nemesis 813 PP Amplifier
That's what got me started on 813s. I know Paul and heard that amp a long while back. Must have made an impessionpre65 wrote: ↑Mon Nov 05, 2018 10:56 am Is this of any interest Stephen ?
http://mackiefamily.unospace.net/audioc ... 13main.htm
Cheers,
Stephen
#22 Re: The Nemesis 813 PP Amplifier
I would start with small ones on all the wires (they are available with different internal dia) and add the multi turns as needed. You can also make a common mode for the heaters by winding both wires around a core. Like many things there is no single answer, but they are useful things to have in the box when needed. Some will need grid stoppers as well, but you need to find the instability and address the frequency its oscillating at.izzy wizzy wrote: ↑Mon Nov 05, 2018 10:40 amThanks Nick. Should I use the small single lead through on G1, G2, G3 and do away with the stoppers. The larger one with a few turns on the filaments?Nick wrote: ↑Mon Nov 05, 2018 8:54 am Either a simple bead on the wire (useful for heaters in ID valves as well)
https://www.rapidonline.com/rvfm-k5b-rh ... ad-23-0730
or larger ones with a few turns around
https://www.rapidonline.com/w-rth-elekt ... te-54-8636
Cheers,
Stephen
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
- Mike H
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#23 Re: The Nemesis 813 PP Amplifier
The Thing that covered half the floor at Owston?Cressy Snr wrote: ↑Sun Nov 04, 2018 6:06 pm Look forward to following this Stephen.
At last, after all these years, a boatanchor build to follow. I think the last one was Simon's "Madness" amplifier , and that's a looong time ago now.
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
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#24 Re: The Nemesis 813 PP Amplifier
You referring to me or the amp Mike?
#25 Re: The Nemesis 813 PP Amplifier
I recall you mentioning that with the bits for the static amp?Nick wrote: ↑Sun Nov 04, 2018 9:44 pmIt all looks pleasantly similar to the 211 I made years ago. You have to love MV rectifiersizzy wizzy wrote: ↑Sun Nov 04, 2018 7:14 pmDid you mean I should/could use them instead for a better result? If so, I guess that is an option further down the road.
Cheers,
Stephen
I meant that GM70 should be a simple replacement for the 813's and the true triode nature may make them less prone to RF oscillation. I also mean that I must one day build the PP gm70 amp I have the audio transformers for.
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#26 Re: The Nemesis 813 PP Amplifier
Just a thought - the circuit looks very like what I was first trying to do with my EL84 p-p amp, circa 2016 (?)
Viz, p-p interstage transformers or centre-tapped choke, but in any case some kind of balanced p-p input / driver stages, using two EF86.
I first simulated in LTspice. Just as well! I could do the p-p input / driver stages and the p-p output stage separately, and by themselves they worked beautifully in simulation.
But soon as I plugged them together it oscillated like buggery and the sim totally crapped out. Absolutely hopeless. Didn't matter what I did. Finally it went to bog-standard cooking pentode + concertina phase splitter, just to get something that worked. No p-p input / drivers, no interstage transformers or chokes (CT or otherwise). That works fine. There was still a bit of a problem with low frequency instability, such that I had to reduce the input pentodes' gain to stop it. This also showed up in simulation, but only if I extended the sim time to several seconds, as it took that long to start up. Oops.
Anyway it's a lovely amplifier and works very well, altho not at the moment cos the mains on-off switch has disintegrated.
I think the problem with the original idea, p-p input with TX's or chokes, was too much open-loop gain.
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
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#27 Re: The Nemesis 813 PP Amplifier
PS: do you have an oscilloscope? Your hum / noise could be an audible manifestation of radio frequency oscillations and suchlike.
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
- izzy wizzy
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#28 Re: The Nemesis 813 PP Amplifier
I kinda have a scope; 2 in fact. A basic USB scope and a Tek that's sat around for ages and doesn't seem to go very well. The main issue is the scale of the voltages which renders fault finding very difficult.
Anyhoo, I'm trying to come at this from a safer angle this time given the problems of the past. Ian built pretty much my first design http://izzy-wizzy.com/audio/powamp813.html (bottom of page) and his worked. I've seen some other PP813s and they've worked. With some more attention to detail, I'm hoping I can make this work.
Plan is to make output stage and hook it up as is to see if it works and is silent. Then move 1 stage back, the 46s and see if that can be made to work. If I'm lucky, that's all I need do. If not, I may need the 12B4 stage. The PSU will be simpler than the past and so I'm hoping I won't need the scope.
I hate fault finding so much, I tend to pull something apart and build another except this time, I may be at the end of the road for that approach.
Cheers,
Stephen
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#29 Re: The Nemesis 813 PP Amplifier
Yep sounds like a plan.
"No matter how fast light travels it finds that the darkness has always got there first, and is waiting for it."
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#30 Re: The Nemesis 813 PP Amplifier
Wired up a power supply. Decided I had enough diodes for 5 per leg so why not with these delicate things. I like the external link cable so will use only one RG214 coax for HT. It's got 3kV rating and the N series connector is rated above 1kV RMS. Bit late tonight to power something like this up.
Cheers,
Stephen
Cheers,
Stephen