[baldrick]

If you were to build a 304TL amplifier you could coax 700 watts RMS of audio power from a single push-pull pair of 304TL tubes.  However you'd need to run plate voltages of 1000VDC - 1500VDC.
There are transformer and inductor sets available if you wanted to build one, but the transformers alone cost $28,000  see here

[FullRangeMan]

If you were to build a 304TL amplifier you could coax 700 watts RMS of audio power from a single push-pull pair of 304TL tubes.  However you'd need to run plate voltages of 1000VDC - 1500VDC.
There are transformer and inductor sets available if you wanted to build one, but the transformers alone cost $28,000  see here

OH Dear friend Baldrick,
I wish I could read circuit schematics and all the data behavior tube stuff.
As a alternate view of this tube world see this real info: there is a small transformer garage builder in my city, he already made me two toroidal transformers for under 100dollars each.   No Silver wire thoug.
Gustavo

[FullRangeMan]

That would be Win Analog

There is other amp that use this 833A tube, it is the Japanese WAVAC 833A around 70K dollars the cheap model.
http://www.wavac-audio.jp/poweramp_e.shtml
Gustavo

[Niteshade]

There is nothing wrong with RF tubes. In fact, I like them allot. Maybe more so than AF tubes.

What I do not like:
1. Red plates with convection cooling, or red plates period. (Even if it's supposed to run that way!)
2. Expensive RF tube based AF amps that are made to perform at a fraction of the tube's potential when it wouldn't take much more effort to double performance or quadruple it.

What I do like:

There is a much wider variety of RF tubes than there are AF tubes. The possibilities are limitless! I like high power and all the virtues it entails. Don't buy a V8 only to run it like a lawn mower engine!

Note: Tube guidelines are simply guidelines. What they print isn't necessarily the best way to use/design a specific tube. It's there so you get a feel for how to design around the tube. I am saying this because I have seen things done that are bad for tubes and/or expensive and stupid to do. Encasing a large power tube in glass and making little air slits on the top is one such example.   

Hi NiteShade,
You post get my attention as Iam a new fan in tubes.
Please could you explain why RF tunes is not a good thing. IF need send me a PM.
Thanks,   Gustavo

[FullRangeMan]

There is nothing wrong with RF tubes. In fact, I like them allot. Maybe more so than AF tubes.

What I do not like:
1. Red plates with convection cooling, or red plates period. (Even if it's supposed to run that way!)
2. Expensive RF tube based AF amps that are made to perform at a fraction of the tube's potential when it wouldn't take much more effort to double performance or quadruple it. 

Dear NiteShade,
1# Bad cooling is a big problem indeed. Seems in Euro Zone there is a stupid law agaist open tube amps to protect childrens, so some brands made stupid cages to cover the tubes. Do you think 211 and 845 need a cooling fan??

2# I think a low power(20W per tube) 211 or 845 will made the tube last much more! Or Iam wrong??
Thanks for your first hand info, Gustavo

[Niteshade]

A 211 has a plate dissipation of 100 watts, or more than twice a 6550's. A Single ended 6550 can produce 15 watts.  A single ended 211 could produce 50 watts or more. That is why I say these big, expensive amps are not running the tubes to their full potential. If you want 20 watts, go with a SEP EL34 amplifier and save allot of money.

Many people might not know this: Large power tubes do not have a large amplification factor. It's usually 10x to 20x for graphite plate triodes. That means: 1 watt in, 20 watts out for 20x. If you want 50 watts out, the following needs to take place:

1. A B+ of around 1,100v is required.
2. A clean drive of a around 2.5 to 5 watts to the grid (depending on the tube) ****
3. The proper primary impedance: around 10,000-15,000 ohms

**** The best way to achieve this drive power is to use a pentode! 
So there we have it: A triode that is actually amplifying a pentode. You're not gaining anything if you want pure triode sound.

I like the 813 tube. It's a large RF power pentode. I think it's the best power RF pentode available since it can be driven with a simpler circuit than a large RF triode. It has considerably more gain than a 572, 845, 211, etc.

[FullRangeMan]

Dear NiteShade, I see you have large experience in tubes, I appreciate you share your knowledge with me.
I will look some 813 date sheet, to know a bit more. Do you like 813 as Pentode or Triode??

P.S.> Iam surprised the 813 cost only 49.95 dollars at tubedepot, a real low price for such a good tube.
The 807 pentode is even more affordable at 29...

[baldrick]

If you want 50 watts out, the following needs to take place:

1. A B+ of around 1,100v is required.
2. A clean drive of a around 2.5 to 5 watts to the grid (depending on the tube) ****
3. The proper primary impedance: around 10,000-15,000 ohms

Problem is that the transformers required to achieve a B+ of 1100V and the output transformers that can handle that type of voltage with the required impedance are very scarce and extremely expensive!

[Niteshade]

The B+ isn't so bad. A voltage doubler can be used with a 500v transformer. There are outputs rated for up to 35 watts off the shelf, but getting one for 50, single ended is what bothers me the most. Edcor won't make one!    So it's off to find someone who can make it.  The 35 watt transformer can be pushed a little and get really close without any issues. They can easily hit peaks of 50 without damage of sonic degradation. What damages outputs is usually sustained excessive current or when a tube shorts out.

[baldrick]

While we're transformer hunting, Hammond makes the 1642SE that can handle 75 watts single ended but the primary impedance is 5K so it would have to be used with smaller 811 tubes in parallel.  The reality check here is that it sells for $375.

It would make a kickass setup, though - 75 watts in single ended class A and enough heat to melt an igloo.

[JohnR]

Not to sidetrack off the important topic of kV+ SETs... but I rather like EL34 amps...

So there

[JohnR]

The 807 pentode is even more affordable at 29...

807s would make a cool little push-pull amp. But I believe they are basically a 6L6, I'm not sure that is what you're looking for.

[Niteshade]

I forgot about the 1642SE. Good idea! The 811 is a fine tube and inexpensive for what it does. 572B's can be subbed. The price is high, but then again- a 75 watt SEP is worth allot and can push almost any speaker (at least down to 88db well). To me the price is well worth it. I see amps with far less impressive hardware selling for thousands. The trick is not to waste all your money on eye candy. Put it in hardware instead.

BTW: I could use a couple 811 SEP mono blocks right now. It's only -9 outside! 

Yeah, El34's are "da man"! Inexpensive, sturdy, high performers. TungSol 6550's are hard to beat too.

While we're transformer hunting, Hammond makes the 1642SE that can handle 75 watts single ended but the primary impedance is 5K so it would have to be used with smaller 811 tubes in parallel.  The reality check here is that it sells for $375.

It would make a kickass setup, though - 75 watts in single ended class A and enough heat to melt an igloo.

[Niteshade]

Yes, 807's are similar to 6L6GC's. They're made a little better. They make great amps. There is an octal based 807 (related to the 6BG6G) that's a sweep tube.

807s would make a cool little push-pull amp. But I believe they are basically a 6L6, I'm not sure that is what you're looking for.

[JohnR]

Yes, 807's are similar to 6L6GC's. They're made a little better. They make great amps.

I have a pair of 5k UL OPTs that appear to be an early version of the Acro TO-300s, for this very purpose. One day. Thanks

[Niteshade]

Make a SEP 807 with those transformers. You won't believe the quality. 


Here is one of favorite tube places: http://www.rfparts.com/tubetran.html

This business has been around for years. I've purchased many an 807, 572B, etc.. from them.

Another item of interest for DIY'ers could be large RF transistors. Big, easy to work with and many models are very powerful. They're made so that it's easy to attach them on a flat heat sink (i.e.: 2sc2290) and point to point wiring is not out of the question.

[JohnR]

Make a SEP 807 with those transformers. You won't believe the quality. 

No doubt... I wouldn't have thought they would handle the DC...?

[Niteshade]

The trick is to use DC biasing, around 400v on the plates and roughly 300v on the screens. Your idle current will be low. What's the DC resistance of the primary? I would use a tube rectifier as well.

SEP's sound different than SE amps. They have better mids and the low end feels less restricted. Highs are about the same.

BTW: You could use EL84's in a SEP with a 5K transformer.

Note: It's better to run SE's & SEP's in tetrode mode. Triode mode restricts performance. Besides, you can make a muchquieter amp when in tetrode mode vs. triode or ultra-linear.

[rollo]

Hey Nightshade have you investigated Bartolucci transformers ? Very impressive. www.audiomarketing.net/bartolucci.htm


charles

[Niteshade]

I think this is what you meant: http://www.audiokit.it/ITAENG/Trasformatori/Bartolucci/Bartolucci.htm

The other link didn't work. I never tried them before but will look into it.