A taste for Triodes?

[Paula A]

Came across this while looking for certain info relating to possible replacements for the hated PX4 (to my ears a triode is a triode is a triode).. What a bible. My 1940's Vortexion was stuffed to the gills with transformers and was about as far removed from a Williamson r-c amp as you could get.. Looking at these diagrams they ring many bells with 30's and 40's amps I have owned..

http://www.nutshellhifi.com/library/Rosetta_Stone.html

[pwdrive]

Interesting circuit techniques there Paula.

Lawrence.

[Shaman]

Hi Paula, PX4, common as muck in its day, rare or cost prohibitive now, yes they are on Ebay, but silly prices for a valve that might be duff. Triodes were at the start of radio, after cats whisker etc, a Dr Flemming valve, and perhaps one of the best valves, no matter what you may think, the PX4 was chosen for its " tonal quality", i guess now its fidelity. It can handle a fair output, was replaced by more modern counterparts, its a shame it was not continued, your amps link shows its versitility, and Quality, lovely Amps...regards...Alan.

[Paula A]

As an alternative I see a lot of people who know their stuff saying KT61 or pen45 .. far easier to use a pen65 unless the 4v heater is crucial.. Electrically when triode strapped they are very very similar to the characteristics of a PX4

I'm very surprised none of the "reproduction" companies who are turning out fantastic quality KT88's etc haven't seen a market here yet. I replaced a pair in an ancient amp with pl504's triode strapped and forgot about the designated 4v filament winding. The other valves were 6v heaters and the 504's will run happily hot on that.

When I finally get moved by the end of the year I think I will start up experimenting again with some seriously vintage designs. I like the look of the 1920's parallel feed push pull amps. The more I look the more I see a potential for an OTL push-pull output stage using some of those dawn age ideas. Might be fun finding some cheap directly heated triodes with punch though. Still thinking on that one.. after all we get so stuck on "traditional" thinking.. a valve output stage takes it's output off the anode through a transformer connected to HT+ .. same current is dragged kicking and screaming from the cathode at a way healthier voltage.... so no need for a huge lump of iron, a simple toroid in the cathode lead perhaps?? (I have been looking at the centre tap of the filament transformers in the WE push-pull stages and going "hmmmmmm.. wonder if")

BTW.. My "hated" comment was purely because of the "audiophools" driving the price of them through the roof.. after all they really ain't that special when you think that they are going to be burned out in amplifiers full of leaking waxies and off value carbon rod resistors. Personally I prefer the sound from a class A output stage pushing about 8 watts from a parallel pair of triode strapped 807's than any ab1 or 2 misbiassed (or god forbid cathode bias) and underweight output transformer thing.. at more like £20 for the 4 needed for stereo A valve amp designed by me would be a very very different affair. I think off the charts sometimes.