Hiya M.C. You're right. Can't keep my hands off a post about the Pride.
Uh, KSW, discharging the high voltage is a good idea. The bleeder resistors should do their thing in 5 minutes or less, but NEVER trust them. The half-circle piece of spring-brass sheet on the left side is held away from a 'safety bleeder' resistor by the cabinet top. It's meant to put this resistor across the high voltage as the cover is removed. More often, someone powers it up with the cover off (BAD IDEA) and this brass spring still touching one end of the resistor, and the "safety" bleeder gets smoked. In a second or two. It's only big enough to drain the filters, NOT big enough to take the full 2400 Volts.
If you're changing the tube following any kind of "POP!", or "SNAP!" kind of episode, it's a really, really good idea to inspect the underside for scorched parts. A blown resistor or grid choke or bias control or zener could hammer your nice, new, shiny expensive replacement tube in literally seconds. Don't want to smash it flat before you have a chance to talk to anyone with it.
The 4CX350 tube sounds larger, but it is NOT at all suitable for the Pride, ESPECIALLY if you plan to use it for AM. The 4X150A tube will work, but you should probably run only on Low side. It's rated to run only at a lower temperature, because that one is made with metal and glass. The letter "C" in 4CX" means "ceramic". The 4X150 and 4CX250 types have the same parts inside them, but the '250 just takes more heat before the ceramic is damaged. Makes the '150 easy to smash on High side if you don't use a lot of caution and restraint. The 4CX350A tube is rated for far, far, less drive power than the '150 and '250 tubes. In an amplifier NOT equipped to limit drive power, a 4CX350 won't last long. Especially on AM. The original bias voltage must be changed to use a 4CX350A. You'll only end up changing it back when you pop the last '350A in your inventory.
The letter "R" on the end of the type 4CX250R indicates the meanest version, and will work in the Pride if you modify the bias circuit. Stock setup may not turn down the tube's idle current far enough with an "R" installed. Type 8930 is a 4CX250R with a larger-diameter (350-Watt) rated radiator ring. This tube is NOT a "4CX350" type, at all, never mind its power rating. And it will show more peak power than the "B" type tubes, as with the '250R. Only drawback to the 8930 is that the original chimney won't fit. RF Parts sells a teflon chimney that will fit.
And ignore low prices on tubes like this ending in the letters "D", or "F", or "F/J" or "F/G". They're cheap because they were built to use in aircraft. The heaters in them require 26.5 Volts, NOT the 6.0 Volts found in the Pride. Just won't work.
Hmmm. I suppose I should include a link to the replacement High Voltage board we make for the Pride. Takes the place of the original "fraternal twin" boards. Even if you aren't interested, check out the suicide-prevention suggestions in the installaton guide. Could save you a popped tube, and more.
Nomad Radio Heavy-Duty HV board kit
The calibrated eyeball is your best tool when changing the tube in a Pride. A good, hard look underneath for parts that look overheated or damaged, or exploded can save you a bucket of grief, if a critical part has been damaged, like the ones that keep the tube from melting down while keyed.
73
