The Nemesis 813 PP Amplifier

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IslandPink
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#271 Re: The Nemesis 813 PP Amplifier

Post by IslandPink »

Good effort !
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#272 Re: The Nemesis 813 PP Amplifier

Post by Cressy Snr »

All good stuff! :lol:
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#273 Re: The Nemesis 813 PP Amplifier

Post by Mike H »

Shoddy. :D

But no congrats. Image

izzy wizzy wrote: Sun May 05, 2019 12:06 pm It was only natural when testing, something happened and I lost a BC184
Natch. Image
 
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#274 Re: The Nemesis 813 PP Amplifier

Post by Ali Tait »

Well done! :D
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izzy wizzy
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#275 Re: The Nemesis 813 PP Amplifier

Post by izzy wizzy »

Thanks everyone. I now have two quiet amps. They sound lovely to my ears. Feel I can move forward now without fighting them. Hope I don't live to regret that statement. It's only taken 15 years to get to this point. Mercury next.

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

Post by Nick »

All I can add to the mercury development is when in use, let them warm up for 30 sec at least before applying HT (its fun to watch the mercury vaporise, and then trying not to jump when they pop into life when the HT comes on. Also, before using them for the first time, run them just on heaters for 30 minutes or so to clear all the liquid up and let it find it way to the bottom on the valve and not on any of the electrodes.

Though you probably know all that.
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izzy wizzy
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#277 Re: The Nemesis 813 PP Amplifier

Post by izzy wizzy »

Thanks Nick. I'm a regular MV user (have them in the phono) but that still didn't stop me having some hairy moments last time with these amps but then they weren't playing nicely at all. Had fireworks in the bottle that looked like they were undercooked. They weren't. Mains fuses blowing. Groaning transformers. It got scary. But I think it was coz the amps were oscillators.

Anyway hopefully we live in different times. Here's some Mercury I have at hand from the ridiculous GU20, 866 in the middle which will probably be the right one to use and the little RG1-250 which is right on the limit for this application. I don't fancy being on the limit with Mercury. That GU20 is 250mm long.

IMG_20190506_090708722_HDR_compress_78~2_compress_63.jpg

As the 46s were using the 866 transformers I have the GU20 wired up ready to go from a while back on one channel but first there's work to do around the house before I'm allowed to play.
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#278 Re: The Nemesis 813 PP Amplifier

Post by izzy wizzy »

That didn't go well. Cooked the GU20s 1/2 the day and on turn on, big groan from the MVs, a flash and the plug fuse blew. I've had them going before, as in 15 years ago. Maybe there's a dodgy one I'd forgotten about. Maybe I should just play with 866s.

This might have to wait a few weeks. My wife is in the final throws of her masters and doing a lot of graphics rendering for her portfolio which can take hours per drawing. If I blew a circuit breaker taking out the power mid one of those, my life wouldn't be tenable. Reckon I can live without MVs for a bit and maybe fettle something else less risky.

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

Post by izzy wizzy »

Couldn't leave it alone. Remembered I have a variac. Cooked up another used GU20 to replace the one that didn't quite look right. This time it worked when brought up slow. It's got the sound I'm after compared to the silicon; effortlessly easy.

Down side is there isn't much blue glow, only a bit under the bin lid anode. Not too surprising as they could take 2.5A and the amp only draws 230mA. 88W to heat the pair is a bit silly.

gu20glow.jpg

Time for something more "sensible" :) 866s in the other one.
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#280 Re: The Nemesis 813 PP Amplifier

Post by IslandPink »

They are very cool indeed - love the screw-fit socket !
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#281 Re: The Nemesis 813 PP Amplifier

Post by Cressy Snr »

Pure Frankenstein :D
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#282 Re: The Nemesis 813 PP Amplifier

Post by izzy wizzy »

This is all going a bit too well at the moment. 866s cooked, brought up on the variac all good. Variac out and it all goes properly.

And the amps are quieter. The slight buzz that was there with your ear in the speaker before isn't there now. And way more blue glow though in reality, not as much as the pic shows. The 813s aren't that white either. I'll see if there's any difference between them tomorrow.

866glow.jpg
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#283 Re: The Nemesis 813 PP Amplifier

Post by Cressy Snr »

Hi Stephen

A thought from a chronic worrier:
Don’t want to be a party pooper but if these are going to Owston, then there is a health and safety issue re the use of MV rectifiers.

I’m sure MV rects sound nice and I have to admit, they do look lovely, but break one at the venue and you’ve got a major incident, requiring deep cleaning of the room by specialist contractors.

OK, so I suffer from anxiety and maybe I’m worrying unduly, but it’s one thing having exposed high voltages (and none of us are daft enough to touch something nasty) but quite another having poisonous substances escaping into the environment if somebody gets clumsy after a few beers.

Can you use alternative rectification for Owston?

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izzy wizzy
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#284 Re: The Nemesis 813 PP Amplifier

Post by izzy wizzy »

Cressy Snr wrote: Tue May 07, 2019 11:07 am Hi Stephen

A thought from a chronic worrier:
Don’t want to be a party pooper but if these are going to Owston, then there is a health and safety issue re the use of MV rectifiers.

I’m sure MV rects sound nice and I have to admit, they do look lovely, but break one at the venue and you’ve got a major incident, requiring deep cleaning of the room by specialist contractors.

OK, so I suffer from anxiety and maybe I’m worrying unduly, but it’s one thing having exposed high voltages (and none of us are daft enough to touch something nasty) but quite another having poisonous substances escaping into the environment if somebody gets clumsy after a few beers.

Can you use alternative rectification for Owston?

I’ll get me coat...
Questions that come to mind are;

Do a lot of valves get broken at Owston?

Is it the mercury that raises your worry levels or just the breakage?

My phono preamp uses MVs but they're in a box. Is that OK?

If the power amp MVs were enclosed, is that OK?


Reassurances ... maybe ...

Been using MVs for 20 years no problem in a house of kids and pets (that did motivate me to put them inside the box), moved house with them and I try to refrain from juggling them.

I had hoped to sleeve the amps in a rudimentary fashion anyway so I can use them without having to lock the door here at home while they're on; safety and all that, pets, people who don't always do as they are told etc

ETF often has exposed MV rectifiers on show along with the aforementioned dangerous voltages.


Way forward:-

The simple answer to your question is, if the MVs themselves are the issue, then I'd have to change the rectification in my phono and the amplifiers. Sure, they could be changed is the obvious answer. As you bring up a point many voice on forums relating to MVs, maybe I could voice your concern on the "what are you bringing to Owston" thread to see if I'm being reckless bringing these things i.e. there might be other people with the same concerns. I don't want to impose on people or make anyone uncomfortable so if this is an issue greater than I perceive it, I would just bow out and watch from a distance.

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

Post by pre65 »

The "modern" way would be to do a risk assessment.

If the MV rectifiers are enclosed I'd say the potential problems are minimal.
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