The Nemesis 813 PP Amplifier

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IslandPink
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#256 Re: The Nemesis 813 PP Amplifier

Post by IslandPink »

Remind me Stephen, are you using a shared cathode resistor a la Amity in this ? - if so can you not share the supply for two 4P1L's ?
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#257 Re: The Nemesis 813 PP Amplifier

Post by izzy wizzy »

Paul Barker wrote: Fri May 03, 2019 2:03 pm “Options I've seen are parallel with the tail taken from the centre tap of the fils but have also seen series with the tail taken from the centre join of the two fils. Not sure of which is technically better.“

2nd way not an option in direct heated 4p1l as bias affected.
I'll have to have a think about this as maybe I don't understand things very well. It was going to be my first option. Idea taken from here http://www.bartola.co.uk/valves/dht-push-pull/ either option 4 or 5.
IslandPink wrote: Fri May 03, 2019 3:11 pm Remind me Stephen, are you using a shared cathode resistor a la Amity in this ? - if so can you not share the supply for two 4P1L's ?
Yes a common tail resistor as in the 46 driver. Cct shown on page 11 but now with SMPS for the 813s. I should update the circuit but it hasn't changed much.

So unless I get to find out what Paul means as to why it's not a great idea, that's what I was going to try. I can't wait to try a VCCS thingy for the fils. Having looked at the Coleman reg cct, an old version, I think I may have enough parts to replicate something like it in the shed to test the merit of it and to get the amp quiet. I'll need to series the fils to keep the current low so I can use MJE340 or 350 which have a 0.5A limit hence option 4 or 5 from the above. It won't be optimum but close enough to see how it goes. It will either be a NPN version or an upside down PNP version if that makes any sense.

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Stephen
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#258 Re: The Nemesis 813 PP Amplifier

Post by Paul Barker »

in 4 and 5 If F1 represents a dc supply then u1 and u2 are differently biased. Presumably compensated in the active bias, crazy.
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#259 Re: The Nemesis 813 PP Amplifier

Post by izzy wizzy »

Paul Barker wrote: Sat May 04, 2019 8:39 am in 4 and 5 If F1 represents a dc supply then u1 and u2 are differently biased. Presumably compensated in the active bias, crazy.
Yes Paul. Thanks. I've used the time between last post yesterday and this morning to read up the diyaudio thread that was the gestation of Rod Coleman's regulator. In there I got what you were talking about.

And in that thread is his ideas that didn't make it to product for a PP version. It didn't fly any further due to lack of demand coz SE rules and PP doesn't for many peeps I guess. His idea is the cct below which I nicked of diyaudio; hope he doesn't mind.

PP_ovu1.jpeg

I'm hoping this will be much easier so I don't have to build the gyrator bit which is inthe positive leg feeding the filamant. He reckons PP cancels out it's effect. He does present a PP idea earlier in that thread that does have a single gyrator feeding the positive leg but later dispensed with it in the developed design. Won't be using the CCS in the tail either; just a resistor. The shed rumage last night located all the parts I need so hopefully some time will present itself over the weekend to build it.

Cheers,
Stephen
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#260 Re: The Nemesis 813 PP Amplifier

Post by Nick »

Not sure how that’s really any different to two filament supplies other than you only need the one first part of the supply, and it will save a transformer winding I guess. But in terms of heating two of Andrews supplies (for example) will work the same.
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#261 Re: The Nemesis 813 PP Amplifier

Post by izzy wizzy »

Nick wrote: Sat May 04, 2019 10:24 am Not sure how that’s really any different to two filament supplies other than you only need the one first part of the supply, and it will save a transformer winding I guess. But in terms of heating two of Andrews supplies (for example) will work the same.
All I'm trying to do at the moment is get a quiet amplifier the simplest way possible and see if this will work with parts to hand. If Andrew's supplies were available to me this weekend, I'd do it.

I reckon my end goal will be two of Andrew's supplies/channel if they are still available which I'm waiting a response on. I posted in his thread if that's the way it's done?

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Stephen
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#262 Re: The Nemesis 813 PP Amplifier

Post by Nick »

I am sure he will see the post.
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#263 Re: The Nemesis 813 PP Amplifier

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izzy wizzy wrote: Fri May 03, 2019 7:06 pm
IslandPink wrote: Fri May 03, 2019 3:11 pm Remind me Stephen, are you using a shared cathode resistor a la Amity in this ? - if so can you not share the supply for two 4P1L's ?
Yes a common tail resistor as in the 46 driver. Cct shown on page 11 but now with SMPS for the 813s. I should update the circuit but it hasn't changed much.
OK, so one side ( 'E' ) is connected to the 440R resistor ( or a suitable value for 4P1L's ) and you can connect one Lehane supply across E-F ?
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#264 Re: The Nemesis 813 PP Amplifier

Post by izzy wizzy »

IslandPink wrote: Sat May 04, 2019 11:56 am OK, so one side ( 'E' ) is connected to the 440R resistor ( or a suitable value for 4P1L's ) and you can connect one Lehane supply across E-F ?
I think things have moved on a bit from that post due to Paul's comments. I will need 2 Lehane regs but quite how I use them is up for grabs at the moment. See Rod's drg further up and Nick's comments.

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Stephen
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#265 Re: The Nemesis 813 PP Amplifier

Post by IslandPink »

OK, I understand you can't run them in series ( as Paul said ) but why the change from your circuit on page 11 to one of Bartola's circuits where he has twin CCS's which both return to ground ? I can't see any of the 6 circuits on his page that looks like what I was assuming, and what you have on p.11
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#266 Re: The Nemesis 813 PP Amplifier

Post by izzy wizzy »

IslandPink wrote: Sat May 04, 2019 12:22 pm OK, I understand you can't run them in series ( as Paul said ) but why the change from your circuit on page 11 to one of Bartola's circuits where he has twin CCS's which both return to ground ? I can't see any of the 6 circuits on his page that looks like what I was assuming, and what you have on p.11
After Paul's comments, I've ditched Ale's ideas and gone with Rod's as in the pic above. Difference being, I'll be using a tail resistor not a CCS. So it will be similar to p11 circuit ... well in my head anyway ... just with a floating dual current source thingy fil power supply.

Obviously a complete circuit posted with the new ideas would be helpful so sorry, you'll have to struggle on with my rambling :) Closest is that pic of Rod's.

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Stephen
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#267 Re: The Nemesis 813 PP Amplifier

Post by izzy wizzy »

I've cobbled together one of these from stuff I had lying about and it's burning away in the shed a while on a resistor before I try it on a filament. If all goes according to plan, I'll make the other half and then pop it in the amp. So far it seems stable enough after a warm up. Cold to hot it drifts about 3% but there's not a lot about it that's ideal. Fingers crossed.

4p1lfil.jpg
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#268 Re: The Nemesis 813 PP Amplifier

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Andrew is away ATM, says he will look in ASAP.
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#269 Re: The Nemesis 813 PP Amplifier

Post by Mike H »

Couldn't quite see what was going on there at first but now I see it's a floating filament supply and only the centre resistor goes to earth rail.
 
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#270 Re: The Nemesis 813 PP Amplifier

Post by izzy wizzy »

It was only natural when testing, something happened and I lost a BC184 but anyway the testing proved it worked. It's great that it brings the valve fils up nice and slow taking about 3 sesconds to get to full voltage.

Bunged it in the amplifier and it works. I'm amazed how quiet it is now. Did a comparison to the AC channel which was a bit unfair on the quiet one as I have a changeover switch to go between and of course the AC channel is humming away while the quiet channel is going. I don't think the quiet one loses out to the AC overall plus it's quiet. The two are different but I think I prefer the quiet one. The AC one certainly sounds busier but I think there's some music related distortion that makes it sound a bit more exciting in a dirty kind of way ... if that makes any sense.

I could make the CCSs with MJE340s only which I might try for the next channel mainly coz I've run out of BC184s and would have to use something else anyway. A better implementaion surely must improve on what I have got here.

This is very exciting :D

Cheers,
Stephen
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