[RapidRonnie]

: The needed blower is a Dayton centrifugal one but some people use
: converted vacuum cleaner motors.

Keyword is blower... a fan just doesn't move enough air with the right
amount of pressure to cool the tube(s). Doesn't have to be a Dayton brand
blower. I don't know if a vacuum cleaner blower would be practical to
adapt and you'd always want to check it for enough air.

Most of them were Daytons. Not all. Royal the vacuum company supplied
a few. AiResearch which became Garrett did a few too.


: If you like to listen to the stereo with the vacuum running then....

Anyone with experience knows you can find low noise blowers and learn
how they are mounted to minimize heat. Don't be silly now... a casual
stereo music listener is probably not going to use these type of tubes.

: you still need a 10-20K:4/8/16 output transformer that is rated for
: 4 kV working on the primary for, oh, 300 watts.

The transformer is not going to be some off the shelf item you can find
without doing a lot of homework... but they are around and can be spec'd
for a project. Regardless it would be large in size and quite costly.
Surplus audio transformers of the 4x/4cx tube family parameters are not
easily found anymore.

They were never ever surplus. None had low impedance voice coil
windings AFAIK.


: This is the reason why power tubes bigger than 811s or 211s find
: little commercial audio application. Sure you can build a delightful
: amp around a pair of 4-400s or 5-125s or any of ten other cool looking
: Eimac or WE/Machlett types...but the transformer is infeasible. Varian
: EIMAC absolutely hated audio for whatever reason and refused to
: consider making the low mu triodes audio people wanted.

One person from early tube amplifier history once told me the tube
selection process for amplifiers his company produced were based on
size and anode voltage first. They did not want to deal with 2kv
plate potentials in a consumer device.

Consumer Audio was not the market Eimac was selling to... Most people
often listen to less than 10 watts of real audio better than probably
80% of the time.

Many people contacted Eimac about getting a purpose built audio
triode over the years. Including myself. They avoided that like the
plague. The bottom line was if there wasn't a government tit somewhere
they were not interested. The 3-500Z they made for years strictly for
hams but the rest of their tubes had government customers. They even
made a special small signal diode that went into HP VTVM probes.