Lord Garth wrote:

"Michael A. Terrell" wrote in message
...

The water cooled 25 KW finals used in the RCA TTU-25 series used
optically aligned elements, and no one ever managed to get more than 50%
output out of a rebuilt tube which is sad, because RCA designed it to be
rebuilt. The bottom of the tube had a removable cover to get inside the
tube, through the water jacket. Most attempts at rebuilding were so bad
that you couldn't even use the tube in the aural cabinet for 12 KW. The
tube used a pair of 1000 A, 1.5 VAC heaters.


Was there a mechanical alignment issue? The tubes I spoke of were only
pumping 5KW but the four of them were glowing cherry red. The transmitter
was only off after the station cut over to the standby transmitter about
once
a month.


They never figured out what the problem was. RCA had shut down the
small line that made the tubes and scrapped all production equipment,
along with the original drawings, so no one knew exactly how they were
made, or how to rebuild them.

The tubes went from $400 for new production, to $30,000 for used or
surplus tubes that still had full output. When they were in production,
they were too cheap to replace, so no one tried to rebuild them. Once
in a while a transmitter building was cleaned out or torn down and they
would find a stash of spare finals that some engineer had put away for
future use when they were cheap. A good final was worth more than the
transmitter that used it by the early '90s, when I moved and rebuilt a
TTU-25B. The tubes were made for UHF service, and the odd filament made
them useless to ham radio service so they were kind of orphans.

BTW, these tubes are in one of the early RCA Transmitting Tube
manuals. I think it was in the TT-5 printing.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida