JoshK said:
Even if it were the larger output iron you need will mask it, and lower efficiency speakers with their inherently higher distortion will further mask it.
I run my 805 SET amp on high sensitivity speakers near 100dB 1W/1m.
I have plenty of headroom and spend all my time where the amp has the lowest distortion.
JoshK said:
I was just repeating what I thought was the general consensus. Lower thermal compression will certainly play a noticeable part of the improvement. There may be other factors that help the reproduction as well. Perhaps someone else with the engineering knowledge will chime in here.
Hi efficiency spkr
Check me out, but efficiency is related to(dB)@2.87Vrms/1Watt/Ft:
yes?
and then, anything over (95dB) is hi efficiency, I believe...
check out tubelab's sitetubelab.com for some impressive transmitter amps
Check me out, but efficiency is related to(dB)@2.87Vrms/1Watt/Ft:
yes?
and then, anything over (95dB) is hi efficiency, I believe...
check out tubelab's sitetubelab.com for some impressive transmitter amps
Operating Point of 805 SE Amp.
Hi RCAVICITIM,
I have a pair of United 805 (I think it is similar to RCA) and want to make a se power amp.
What's the operating point of your 805 amp such as plate voltage, plate current and grid bias? I understand that 805 is very difficult to drive (A2, grid current). I will use a 2A3 or 25 with interstage transformer to drive it. What's the peak to peak voltage swing that I should design for?
Any advice is greatly appreciated.
Thanks.
Regards,
T.C. MA
rcavictim said:
Hi RCAVICITIM,
I have a pair of United 805 (I think it is similar to RCA) and want to make a se power amp.
What's the operating point of your 805 amp such as plate voltage, plate current and grid bias? I understand that 805 is very difficult to drive (A2, grid current). I will use a 2A3 or 25 with interstage transformer to drive it. What's the peak to peak voltage swing that I should design for?
Any advice is greatly appreciated.
Thanks.
Regards,
T.C. MA
The 805 is now offered from China (has been for a few years) with the plate cap missing and the plate connected to the previously unused 4th pin in the base. This compromises the 805 for full blown transmitter and RF applications but I cannot see where it is anything but better for audio applications as it gets a potentially dangerous HV above chassis connection done away with.
The downside is that an 805 amp built without the flexible top anode connector option won`t be able to play the very good original vintage 805`s like from RCA, GE and Westinghouse as I do in my own amp.
The downside is that an 805 amp built without the flexible top anode connector option won`t be able to play the very good original vintage 805`s like from RCA, GE and Westinghouse as I do in my own amp.
Re: Operating Point of 805 SE Amp.
TC,
My 805 SET amp began life as a NIB MingDa MC3008AB. It did a serious power supply meltdown after just 5 hour`s use caused by overheated, increasingly leaky, superheated, then shorted voltage doubler electrolytic caps in the HV power supply that were not spec`d to handle the high ripple current. The mains fuse had been purposely oversized by some 600% at the factory to stop it from popping frequently on the turn on transient. The amp I bought (sn 12) was not quite ready for the marketplace. The failure took out the 12 winding custom potted power xfmer as well. I spent several months building the remains into a custom hard maple, copper lined cabinet of my own design with an all new and much improved power supply and cooling system (another serious shortcoming in the original amp). I had to wind a couple of custom xfmers as well. I did not get into modifying the audio circuitry however and actually do not have the info you wish written down. I know that I am running 1050 volts anode supply and am dissipating ~120 watts per 805 anode.
Since remanufacturing this beast into a fine amplifier I have put two plus years of daily use on it with no troubles.
I have no complaints at all with the audio circuit as designed at the factory and their output iron is good. I love the sound and command this amplifier has due to it`s enormous power reserve. Drivers are direct cathode coupled 300B`s.
With the 12 tranformers now inside it is pretty heavy at about 130 lbs. Here is my handiwork. 18 coats of hand polished black and clear lacquer. What`s it like to own the only amp of it`s kind in the world? Priceless!
snoopyma said:
TC,
My 805 SET amp began life as a NIB MingDa MC3008AB. It did a serious power supply meltdown after just 5 hour`s use caused by overheated, increasingly leaky, superheated, then shorted voltage doubler electrolytic caps in the HV power supply that were not spec`d to handle the high ripple current. The mains fuse had been purposely oversized by some 600% at the factory to stop it from popping frequently on the turn on transient. The amp I bought (sn 12) was not quite ready for the marketplace. The failure took out the 12 winding custom potted power xfmer as well. I spent several months building the remains into a custom hard maple, copper lined cabinet of my own design with an all new and much improved power supply and cooling system (another serious shortcoming in the original amp). I had to wind a couple of custom xfmers as well. I did not get into modifying the audio circuitry however and actually do not have the info you wish written down. I know that I am running 1050 volts anode supply and am dissipating ~120 watts per 805 anode.
Since remanufacturing this beast into a fine amplifier I have put two plus years of daily use on it with no troubles.
I have no complaints at all with the audio circuit as designed at the factory and their output iron is good. I love the sound and command this amplifier has due to it`s enormous power reserve. Drivers are direct cathode coupled 300B`s.
With the 12 tranformers now inside it is pretty heavy at about 130 lbs. Here is my handiwork. 18 coats of hand polished black and clear lacquer. What`s it like to own the only amp of it`s kind in the world? Priceless!
Attachments
Julien said:
Julien,
Let`s review some facts of physics. In a RF power tube the lead connecting the anode to the external anode connection, and the materials in it`s vicinity become hot from radio frequency heating and a source of power loss as well as introducing extra inductance that can limit the high frequency operation of the tube. By running as short a lead from the anode to the top plate cap the original design of the 805, a tube designed for RF power use in broadcast transmitters, deals with these issues. Placing the anode connection on top also raises the anode circuit flashover voltage (the same reason a 6L6 cannot be run reliably at 750 volts whereas an 807 can). By lengthening the anode lead and placing it in the same bundle as the other electrode leads one reduces the high frequency power capabilities of the tube design for the reasons just explained.
If you re-read my post I actually compliment the plate cap-less design, pointing out it`s attributes for audio use.
I made no comment about interstage xfmers used to drive the 805 grid.
Re: Re: Operating Point of 805 SE Amp.
You did compliment the change from top cap to pin connection. But your syntax may be a bit complex for an international forum. Better to say it simply: "for audio applications, the pin connection is better as it gets etc...."
Sheldon
rcavictim said:
rcavictim said:
You did compliment the change from top cap to pin connection. But your syntax may be a bit complex for an international forum. Better to say it simply: "for audio applications, the pin connection is better as it gets etc...."
Sheldon
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