I had a laugh at the 7.5w output... But yes I have to start playing with the software. 25w dissipated on the cathode resistor! Ha silly.
Hmm so 120w filament, about 100w on the plate, 25w on the cathode. 300w of heat for nearly 10w out. Did I miss something? 3% efficiency.
Now back on track for the test bench setup: I'm going to seriously consider parafeed, and diy chokes/opts. I'll try pentode configuration/ triode switching and keeping the cathode bias resistor. I'm close to winding the power transformer. (I will chuck in a bias winding for the future) I think the easiest way to do filaments is a switchmode supply, they appear popular for huge filament currents.
I have been thinking in with keeping top caps and using a 807 as a driver stage.
And when all else fails a giant Hammond se opts will be used as they're infinitely re-usable.
Tim
Hmm so 120w filament, about 100w on the plate, 25w on the cathode. 300w of heat for nearly 10w out. Did I miss something? 3% efficiency.
Now back on track for the test bench setup: I'm going to seriously consider parafeed, and diy chokes/opts. I'll try pentode configuration/ triode switching and keeping the cathode bias resistor. I'm close to winding the power transformer. (I will chuck in a bias winding for the future) I think the easiest way to do filaments is a switchmode supply, they appear popular for huge filament currents.
I have been thinking in with keeping top caps and using a 807 as a driver stage.
And when all else fails a giant Hammond se opts will be used as they're infinitely re-usable.
Tim
Good news!
The plan B GU81's are in my country, the first parcel and sockets are somewhere on a train then a boat I believe, my seller for those items had been great in chasing up the freight. He has told me that from March 10 nothing is getting out of Russia any more 🙁
As for gu81 sockets well I may be building some. I think it's doable and if I fail look out for a wanted post coming up sockets are top priority.
Filament supply: there are plenty of 12v SMPS available infact I have a few In the junk bin. As Ill build the whole amp in one chassis I'm thinking a single 12v psu is the go. As size is not a big problem I'm leaning towards a bigger SMPS for headroom and hopefully no fan noise. (800w) From all reports there is a small under volt margin to extend tube life but go a fraction lower and the tube doesn't last long. I think don't exceed 12.6v aim for 12.3v. The SMPS I could buy suggests +-3% output adjustment.
HT supply: I have been looking At 600v for the plates to keep it sensible. One idea I have with winding this transformer is a pair of 450v windings, that's around 640v DC after a bridge. Or if I am happy to raise the voltage in the future (series the windings) 1250v dc...
I have used bridge rectifiers and smoothing caps on all my builds but should I try a choke/fullwave style HT?
For me chokes are easy to wind and big high voltage caps get price prohibitive. Maybie I go this way it does mean that the transformer will have 750+750 windings though and that's getting up there!
Or compromise with a bridge rectifier into a choke/capacitor filter?
Now for the subjective part. What psu sounds better?
Cheers,
Tim
The plan B GU81's are in my country, the first parcel and sockets are somewhere on a train then a boat I believe, my seller for those items had been great in chasing up the freight. He has told me that from March 10 nothing is getting out of Russia any more 🙁
As for gu81 sockets well I may be building some. I think it's doable and if I fail look out for a wanted post coming up sockets are top priority.
Filament supply: there are plenty of 12v SMPS available infact I have a few In the junk bin. As Ill build the whole amp in one chassis I'm thinking a single 12v psu is the go. As size is not a big problem I'm leaning towards a bigger SMPS for headroom and hopefully no fan noise. (800w) From all reports there is a small under volt margin to extend tube life but go a fraction lower and the tube doesn't last long. I think don't exceed 12.6v aim for 12.3v. The SMPS I could buy suggests +-3% output adjustment.
HT supply: I have been looking At 600v for the plates to keep it sensible. One idea I have with winding this transformer is a pair of 450v windings, that's around 640v DC after a bridge. Or if I am happy to raise the voltage in the future (series the windings) 1250v dc...
I have used bridge rectifiers and smoothing caps on all my builds but should I try a choke/fullwave style HT?
For me chokes are easy to wind and big high voltage caps get price prohibitive. Maybie I go this way it does mean that the transformer will have 750+750 windings though and that's getting up there!
Or compromise with a bridge rectifier into a choke/capacitor filter?
Now for the subjective part. What psu sounds better?
Cheers,
Tim
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Here is sharing on diy chassis, tube socket, psu choke and schematic:
http://bbs.hifidiy.net/forum.php?mod=viewthread&tid=1344485&extra=&highlight=fu80&page=6
http://bbs.hifidiy.net/forum.php?mod=viewthread&tid=1344485&highlight=fu80
In Chinese, but you can translate with Google.
http://bbs.hifidiy.net/forum.php?mod=viewthread&tid=1344485&extra=&highlight=fu80&page=6
http://bbs.hifidiy.net/forum.php?mod=viewthread&tid=1344485&highlight=fu80
In Chinese, but you can translate with Google.
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The spring contacts seem like the most difficult part to source. Maybe contacts used for a large blade fuse?
Wow I never found those threads, the socket build is exactly like I was going to undertake. It appears that every build on this tube heads along a similar path.
Lucky its a day off for some reading.
Thanks
Yes I was going to scrap some automotive relay sockets. I'll have the tubes to measure up next week.
They are here!
Untill they're Infront of you it's hard to gauge their size...
Thoughts of bailing out are coming to mind. I won't use them in the house, they'd cook anything within 2 feet of them! I'd imagine putting the record player to one side would end in a melt down☹️ Infact the IR thermal output was not too close on my radar and that's a bad one on my behalf. I knew they'd get hot but from a few ham radio sites word is that they really heat up objects next to them. I will test this.
Building sockets will be a challenge. The actual socket spade pins are linked via braid to the tube pins.
It's going to be a monoblock conversation piece/shed warmer I think. Home hifi is out of the question for me.
Another concern is the batch of GU81's that arrived may not be new and are all from various batch numbers even the envelopes are different in height etc...
Any ideas how to test if they're used, I'm thinking cold filament resistance may be clue. If they're all very close in value maybie they are all new or pulled from equipment at 500 hours etc.
Somebody very wise somewhere wrote in a Post "Don't touch the gu81 for audio"
They may be onto it.
Untill they're Infront of you it's hard to gauge their size...
Thoughts of bailing out are coming to mind. I won't use them in the house, they'd cook anything within 2 feet of them! I'd imagine putting the record player to one side would end in a melt down☹️ Infact the IR thermal output was not too close on my radar and that's a bad one on my behalf. I knew they'd get hot but from a few ham radio sites word is that they really heat up objects next to them. I will test this.
Building sockets will be a challenge. The actual socket spade pins are linked via braid to the tube pins.
It's going to be a monoblock conversation piece/shed warmer I think. Home hifi is out of the question for me.
Another concern is the batch of GU81's that arrived may not be new and are all from various batch numbers even the envelopes are different in height etc...
Any ideas how to test if they're used, I'm thinking cold filament resistance may be clue. If they're all very close in value maybie they are all new or pulled from equipment at 500 hours etc.
Somebody very wise somewhere wrote in a Post "Don't touch the gu81 for audio"
They may be onto it.
For a test I would set up a few power supplies and pick a grid bias voltage and see how much plate current each of your tubes draw. See how close each tube falls to a fixed operating point. Some burn in time might be worthwhile too.
Any ideas how to test if they're used
Heat up the filament only (no HT) then measure the voltage between grid and heater (cathode), see how they compared.
https://www.diyaudio.com/community/...increased-screen-current.363579/#post-6426650
Heat up the filament only (no HT) then measure the voltage between grid and heater (cathode), see how they compared.
https://www.diyaudio.com/community/...increased-screen-current.363579/#post-6426650
What about this low power headphone amp and several higher impedance speakers in series?
https://www.diyaudio.com/community/threads/gz34-otl-6n23p.156789/
40 ohm output impedance sounds very achievable. Even though its low power, Idk but im thinking 250-500mw per channel, it can still get to listening levels, and even louder...
Say 6 in a linear enclosure, with perfect alignment and spacing, 1 box ported, left and right chamber t line ports or something like that?
It would help with directionality having it as a sound bar, I think imaging could be unreal.
Also power consumption would be low, and sensitivity high, super minute details, probably can still eek out bass with proper driver surface area, and a light and rigid cone,
https://www.diyaudio.com/community/threads/gz34-otl-6n23p.156789/
40 ohm output impedance sounds very achievable. Even though its low power, Idk but im thinking 250-500mw per channel, it can still get to listening levels, and even louder...
Say 6 in a linear enclosure, with perfect alignment and spacing, 1 box ported, left and right chamber t line ports or something like that?
It would help with directionality having it as a sound bar, I think imaging could be unreal.
Also power consumption would be low, and sensitivity high, super minute details, probably can still eek out bass with proper driver surface area, and a light and rigid cone,