This may be a better use for the 100TH

[w5hro]

This is really unique

http://www.youtube.com/watch?v=I0FQQGaxggA&feature=related

[W2PFY]

Some of those guys can build nice looking equipment. No point in complaining about the use of such tubes for audio service in the home. I think if you had a big sneeze any where near the thing, the tubes would break from moisture from ones breath!!

I have also added one I found that is rather unique, it has an atomic power supply for the biasing of the tube. You can see the blue glow from the atomic pile center of the chassis. 

http://www.youtube.com/watch?v=2jtR380GUdw&feature=related

[K6JEK]

I bet the iron cost a fortune.  Does anybody know?

[Superhet66]

It would be nice to configure that for double duty as a modulator as well as an AF amplifier.

[w4bfs]

I bet the iron cost a fortune.  Does anybody know?

looked like Tango or Tamura iron ... big bux

[Superhet66]

European Triode Festival, the Netherlands.



http://www.timebanditaudio.com/etf2007/etf2007.html

[KM1H]

Thats a fairy nice amp

Carl

[Superhet66]

Tube Amp. Rack and what it's driving...The Full Picture.

[WBear2GCR]

that would be a pair of 211s or 845s in Class A.
The 805 is a class B tube... fwiw.

                      _-_-bear

[Opcom]

I like the 838. zero bias, reasonable voltage of 750-1200.. I used to not think too much about the older types like that until I heard the Norton Chimes amp through a good speaker. It has 4 of them in pp-par driven by a pair of 6B4's and all kenyon iron. The sound is very umm.. I don't want to start fruiting it up with big words. It just sounds very clear and has a very live sound to it compared to for example the stock Stromberg-Carlson PP 7027 hi-fi amp (sacrelidge!!). The Norton has no feedback and is extremely simple. the Stromberg has overall FB; but by no means do I think the S-C sounds less than very good itself.

The 838 data in the RCA TT-3 manual claims the amplification factor varies according to the amplitude of the input signal and this makes it possible to have low distortion of less than 5%. (The same curves apply to the 805). So, was this claim a marketing ploy, or is it true that a u which increases with positive going grid voltage does improve fidelity?

As for biased triodes like the 203 and 211, and the 845, they are so rare, I cannot experiment with them. A frind supplies me with 838's for the Norton, as he has a "case of them" so he claims.

On the 805 page (62), the RCA TT-3 manual shows an 805 next to an 838 and states: "The 203-A, 211, and 845 - all of the popular so-called 50-watt class - are similar in appearance to the 838. All now have 100-watt plate dissipation rating." This must have heralded an improvement in the anodes of some of these tubes.

In any case, it leaves no doubt to the aesthetics of all of these tubes and the suggestion that they ought to be used in combination for radio transmitters because they would do a good job and look great doing it. They still do today.

[k4kyv]

The 805 is identical to the 838 except that the 805 has the plate lead coming out to a cap at the top of the glass envelope instead of at the base. This allows higher plate voltage to be safely used, and the plate cap tends to dissipate a little of the heat from the plate, so the 805 is rated for somewhat higher plate voltage and power level than what is recommended for an 838.

Also, the external plate cap reduces the output capacitance of the tube and there is less dielectric loss, allowing the tube to operate at higher frequency than you can run with the "100 watt" tubes.

[KM1H]

On the 805 page (62), the RCA TT-3 manual shows an 805 next to an 838 and states: "The 203-A, 211, and 845 - all of the popular so-called 50-watt class - are similar in appearance to the 838. All now have 100-watt plate dissipation rating." This must have heralded an improvement in the anodes of some of these tubes.

That came about after Sylvania invented the graphite anode in response to RCA's suit that banned them from producing TX tubes in 31-33 (I forget the actual date but Sylvania only produced their TX tubes for about 18 months). Sylvania licensed United, Amperex and others to produce them and once they had good market share RCA was licensed.....good payback! In WW2 RCA was forced to give Sylvania a license.

Carl

[k4kyv]

A lot of the old drive-ins back in the 50's and 60's used a pair of 805's to drive the sound system, which consisted of a hundred or more tiny little speakers with crappy sound for each car. They probably ran them in class B since audio quality wasn't much of a concern.  

A better idea would have been a low power AM transmitter that you could tune in on the car radio, but in those days, many cars weren't equipped with radios.  Maybe they could have used both, for those who wanted better quality sound and had a car radio. But who actually paid attention to the film while spending an evening at the drive-in anyway?    I remember they used to be called the passion pit. Remember those old 1962 Plymouths and Chryslers with the 6' wide bench seats?

For audiophile or audiophool use, the 100TL would make a better single ended class-A power amplifier (audiophools tend to disdain pushpull audio).

[WD5JKO]

The 805/838 are really a poor choice for class A audio power amplifiers.

The reason is the high Mu. For class B PP, they run zero bias up to 1250 volts.

To run these class A with about a steady 75w plate dissipation (100w rating), you need a grid bias of about +5v with a plate voltage of +1000v. This means the audio driver must supply the AC driving swing when grid current is drawn over 1/2 of the AC cycle. Yes it could be done, but something like a 100TL would in my opinion be a superior choice since the bias would stay negative over the complete AC drive cycle. This means no grid current, and a much simpler driver circuit..


http://www.scottbecker.net/tube/sheets/079/8/838.pdf

The link above is for a 838 which shares the same plate curves as the 805.


Oh, I once used two 805's in P-P RF on 80m. Playing with that rig, I eventually upped the plate voltage to 2500 @ 400ma for a good old 1KW input. The RF out was 850 watts. I ran this rig for several years and the 805's hung in there. Keeping the current and wattage specs compliant helped. There was headroom aplenty with the plate voltage.

The 805 is a very versatile tube.

Jim
WD5JKO

[flintstone mop]

I still like this one for real high power audio

http://www.youtube.com/watch?v=G7qMVYf85sM&feature=related

Fred

[Superhet66]

I still like this one for real high power audio

Wow, perfect music for that beast,
I suppose that class of amp. would have been found in movie theaters or stadiums. A bit of "Electron Voodoo" with those rectifiers, thanks  

http://www.youtube.com/watch?v=C3_-2fUm6y0&feature=related

[Opcom]

The 805/838 are really a poor choice for class A audio power amplifiers.

The reason is the high Mu. For class B PP, they run zero bias up to 1250 volts.

To run these class A with about a steady 75w plate dissipation (100w rating), you need a grid bias of about +5v with a plate voltage of +1000v. This means the audio driver must supply the AC driving swing when grid current is drawn over 1/2 of the AC cycle. Yes it could be done, but something like a 100TL would in my opinion be a superior choice since the bias would stay negative over the complete AC drive cycle. This means no grid current, and a much simpler driver circuit..

That's one of the reasons why low mu triode drivers such as the 2A3 or 300B are needed to drive them properly. Hey, remember that 6B4 bias shift scheme

I think with the 805 though you would want a much higher plate voltage. The heavy graphite anode structure of the 805 and top plate cap would be ideal for that. Forget the 838.

Can you direct me to the 6B4 bias shift scheme?

[flintstone mop]

A lot of the old drive-ins back in the 50's and 60's used a pair of 805's to drive the sound system, which consisted of a hundred or more tiny little speakers with crappy sound for each car. They probably ran them in class B since audio quality wasn't much of a concern.  

A better idea would have been a low power AM transmitter that you could tune in on the car radio, but in those days, many cars weren't equipped with radios.  Maybe they could have used both, for those who wanted better quality sound and had a car radio. But who actually paid attention to the film while spending an evening at the drive-in anyway?    I remember they used to be called the passion pit. Remember those old 1962 Plymouths and Chryslers with the 6' wide bench seats?

For audiophile or audiophool use, the 100TL would make a better single ended class-A power amplifier (audiophools tend to disdain pushpull audio).

"Back in those dayz" if the drive-in used a carrier current AM for their movie sound, half of the folks would have dead batteries from leaving the ignition on.

HAAA HAAAA
Fred