One problem is that their will likely be no data on how the tube responds and it's limits. Most tubes have a range where they are fine sound wise and some freq. ranges where they distort badly. Since almost no one has used RF tubes in this way outside of Russian Surplus and such their are a lot of unknowns.
Then you have voltage and current differences. I have built a lot of audio tube amps and you almost never run with the type of voltage and current you do when using the same tube in an RF amplifier.
Philipps 3001,3003 tubes are huge RF/Audio tubes and a lot of guys in Europe are building single tube amps with these and the Russian version of the old RCA 833. These are huge tubes by audio standards and you will need a lot more transformer then you have ever played with when using other audio tubes like the 2A3 for instance......Some guys are playing with the Russian GM70 or GK71 I think as well not as big as the other's I have listed but still very powerful.
Here is the thing you do not need to run the power or current that an RF tube needs on an RF amp but you will have to figure out what will work on your own. You will likewise need to have a alot of caps with various capacitance and ESR rating to tune the sound.
I use nothing but Teflon Cap's in my first stage and I also beat the snot out of them for 30-90 days before I put them in an audio circuit. Brand new Teflon Caps tend to be too brilliant on highs and so clean that it makes the high bias too pronounced. By conditioning them first they lose that odd high freq. bias but keep that crystal clear sound. I use a variety of caps after the first stage usually PIO caps after the first stage add some color and round out the sound so it is not harsh and too perfect. When I say harsh and too perfect think of the difference you hear when a keyboard is used to replicate a trumpet in a sound track compared to a real trumpet the keyboard will sound too perfect to clean and too bright almost harsh.
Oh and big powerful tubes need a lot more capacitor in the power supply section to maintain head room. A lot of people are starting to experiment with these bigger tubes for subwoofer amplification and sticking to known Russian surplus Audio tubes for their highs and mids. Why? Well a beautiful sounding 5-10 watts of high current amplification sound s fantastic will drive most non-ribbon type speakers. I have Carver, NAD, McIntosh transistor and tube audio amps. 1 watt from my various Carver's is more powerful then most Pioneer,Kenwood,Onkio higher voltage 200-400 Watt per channel units. 1 watt out of my tubed McIntosh is more of the same it can drive most speakers no problem.....In college when having a party 2 watts was more then enough to make peoples ear's bleed.
The more narrow the bandwidth you are trying to tune usually the easier it is to fine tune it. I would check the various DIY Audio sites for info on 833, Phillips 3001 and maybe GM70/GK71 that should get you started. You will need to decide if you want to use a push pull set up or maybe you want no output transformer to deal with coloring the sound? If you build with an 833 or larger you should easily be able to drive Ribbon Speakers and that is about as demanding as you can get from a drive standpoint.
Wanted to add the only place I am aware of that has the Phillips 3001 and such anymore is a Tube store out of France I think it is. I will try to see if I can think of the name it has been a long time.
