Poundland 45
- IslandPink
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#76 Re: Poundland 45
Yes. Noise levels are fine at the level of a driver stage. As Nick says, a Zobel will help a little, I found it cleaned up the HF slightly on my phono stage. So this is a C+R across the pair of VR tubes instead of using the single capacitor. There is no formula for finding the optimum values ( as Gary Pimm found ) but try 0.1u & 390R as a starting point.
"Once you find out ... the Circumstances ; then you can go out"
- Cressy Snr
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#77 Re: Poundland 45
It’s the LibreOffice suite. https://www.libreoffice.org/
I use a ‘Draw’ document to do the diagrams. Over the years I’ve built up a little library of objects that represent circuit symbols, such as resistors, electrolytics, film caps, pentodes triodes, rectifiers, VR tubes, diodes, zeners, DHTs, DHPs ad infinitum. I just drag and drop them out of the gallery and join them up with lines.
Neal put me onto LibreOffice years ago after Apple had ceased making their AppleWorks software, and replaced it with iLife, which was frankly a pile of shite.
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#78 Re: Poundland 45
Cheers Mark,IslandPink wrote: ↑Wed Sep 08, 2021 11:14 am Yes. Noise levels are fine at the level of a driver stage. As Nick says, a Zobel will help a little, I found it cleaned up the HF slightly on my phono stage. So this is a C+R across the pair of VR tubes instead of using the single capacitor. There is no formula for finding the optimum values ( as Gary Pimm found ) but try 0.1u & 390R as a starting point.
I’ll look into that this afternoon, if I can find the right resistors. I know I’ve got some 390s knocking about somewhere.
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#79 Re: Poundland 45
OK,
I changed the cap to a Zobel with the aid of a 390R resistor. It was pretty subtle, but there was a slight increase in the clarity of the treble. Every little helps as they say.
I also added a heatsink to the first transistor in the CCS cascode. I prefer the belt and braces approach when valve electronics and solid state cross paths. Instead of being a bit hot, the first transistor is now quite warm, if you know what I mean.
Updated schematic:
I changed the cap to a Zobel with the aid of a 390R resistor. It was pretty subtle, but there was a slight increase in the clarity of the treble. Every little helps as they say.
I also added a heatsink to the first transistor in the CCS cascode. I prefer the belt and braces approach when valve electronics and solid state cross paths. Instead of being a bit hot, the first transistor is now quite warm, if you know what I mean.
Updated schematic:
Sgt. Baker started talkin’ with a Bullhorn in his hand.
#80 Re: Poundland 45
Yep, heatsinks are good mkay
BTW, careful with DN2540 they are easy to kill (or degrade) with static.
BTW, careful with DN2540 they are easy to kill (or degrade) with static.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
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#81 Re: Poundland 45
Thanks Nick,
Better dig out a zap strap for any future work then.
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#82 Re: Poundland 45
Fed up with the loud crack through the speakers every time the shunt VR tubes strike when the valve rectifier has ramped up, I’ve changed the rectification to a pair of solid state SiC 1200V 3A Schottky diodes. Now the VR tubes ignite before there is any amplification happening, meaning that startup is completely without incident.
I’ve also put a 1nF/1k Zobel network across the power transformer HT secondary winding to snub any residual spiky bits. The Black Gate WKz, 2 x 220uF capacitor has been welcomed back to the fold and sticks up through the hole where the rectifier valve used to plug in.
It’s all worked out very well and sounds great. No sonic ill-effects at all from the rectifier heresy, in fact it’s all very quick, dynamic and tonally neutral. One transformer less and 15 fewer Watts drawn from the wall too, as there is no 5V 3A rectifier heater to contend with. It’s win, win as far as I’m concerned. I was a bit loath to throw solid state bits at this amp, but I must say the DN2540 CCS fed shunt reg on the input stage, and the SS rectification have both worked beautifully.
I’ve also put a 1nF/1k Zobel network across the power transformer HT secondary winding to snub any residual spiky bits. The Black Gate WKz, 2 x 220uF capacitor has been welcomed back to the fold and sticks up through the hole where the rectifier valve used to plug in.
It’s all worked out very well and sounds great. No sonic ill-effects at all from the rectifier heresy, in fact it’s all very quick, dynamic and tonally neutral. One transformer less and 15 fewer Watts drawn from the wall too, as there is no 5V 3A rectifier heater to contend with. It’s win, win as far as I’m concerned. I was a bit loath to throw solid state bits at this amp, but I must say the DN2540 CCS fed shunt reg on the input stage, and the SS rectification have both worked beautifully.
Sgt. Baker started talkin’ with a Bullhorn in his hand.
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#83 Re: Poundland 45
Nice
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
- Cressy Snr
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- Cressy Snr
- Amstrad Tower of Power
- Posts: 10579
- Joined: Wed May 30, 2007 12:25 am
- Location: South Yorks.
- Cressy Snr
- Amstrad Tower of Power
- Posts: 10579
- Joined: Wed May 30, 2007 12:25 am
- Location: South Yorks.
#86 Re: Poundland 45
I’ve at last got around to ripping out the temporary lash-up of the DN2540, cascode CCS that feeds the VR tubes that regulate the input stage HT.
I built a new one up on a piece of prototyping board, using electrostatic protection protocols to prevent any possible degradation of the pair of MOSFETs. Of course there was no guarantee that the MOSFETs were perfect in the first place but you have to start somewhere.
Anyway it all worked first time, once it was adjusted up, so the amp is now Owston ready and sounding good.
Solid state rectifier and first cap can be seen on the far right. CCS board to the left of the VR tubes.
I built a new one up on a piece of prototyping board, using electrostatic protection protocols to prevent any possible degradation of the pair of MOSFETs. Of course there was no guarantee that the MOSFETs were perfect in the first place but you have to start somewhere.
Anyway it all worked first time, once it was adjusted up, so the amp is now Owston ready and sounding good.
Solid state rectifier and first cap can be seen on the far right. CCS board to the left of the VR tubes.
Sgt. Baker started talkin’ with a Bullhorn in his hand.
#87 Re: Poundland 45
Owston ready... I'm impressed Steve
The tube manual is quite like a telephone book. The number of it perfect. It is useful to make it possible to speak with a girl. But we can't see her beautiful face from the telephone number
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#88 Re: Poundland 45
Well you have to make the effort.
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#89 Re: Poundland 45
nice
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
- andrew Ivimey
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#90 Re: Poundland 45
I'd put the vr tubes out on top and if they eeren't glowing I'd get them to draw current so they do. What's the point if valves if you can't make'em look spectaculeer or even dangerous.
Philosophers have only interpreted the world - the point, however, is to change it. No it isn't ... maybe we should leave it alone for a while.