Hot enough to burn the paint off

[kopcicle]

...needs a second toob

 

[nomadradio]

...needs a second toob

Used to hear that a lot, back when AM operators would ignore my advice to get the AL1200, and bring us a new AL1500 to get the 10 meter band enabled.

The guy would see that cover plate, clearly where a second tube would go. The "mo Watts" guy would want a price for adding a second 8877. I would reply that a second AL1500 would do the job, just for the power supply. Can't run two tubes on a 1-tube power supply. But two power supplies would power two tubes okay.

And if I detected skepticism, I would suggest we could remove the single 1500-Watt tube and install the two 3-500Z that made the second socket necessary. Pointed out that the tube-socket chassis was the same for both models. Just a choice. Keep the power supply and install two smaller tubes, or buy another AL1500, combine the power supplies and move the tube from the second unit into the first one.

Never had a customer take me up on either option.

Not once.

73

 

[543_Dallas]

Looking at the pictures Nomad posted I'd be willing to bet that tube wasn't in there when the paint was blistered. I have saw a few ceramic tubes that have been ran hot and they are usually a tarnished brown color. Maybe there just old and thats normal but they were CB amps and lived a hard life.

I run an AL-1200 in AM service and at 300 to 400 watts carrier I've never managed to burn any paint. I do use CW mode and run the blower on high for AM. Putting a fan speed switch on the back was the best thing I ever did.

My 1200 was built in the late 90s. The tube was lightly tarnished when I got it and the tank coil shows similar discoloration to the amplifier in question, actually a little worse.

It did have some bad filter caps and open bleeder resistors but after replacing those and the rectifiers for good measure it has been trouble free. Plan on replacing those with an amp that old.

I really like the 8877 and use them in another amp but they won't last if you don't treat them right. The day my 3cx1200a7 dies it will probably be replaced with an 8877.

Adding another tube to the al-1500 isn't worth the trouble. Just my opinion but at that point the tank circuit needs to be upgraded or replaced with 1/4" copper tubing optimized for 11m. It would also need a better blower, better fitting chimneys, and a vacuum variable on the plate side of the tank circuit in addition to the obvious hv transformer and filament transformer.

 

[kopcicle]

heh heh

 

[Retro CB Guy]

Hello All: Yeah this ain't right. Got a neighbor a few miles down the road with a pair of 3CX1500A7's and when first fired it, it heated up the room NOT RIGHT!

After costly repairs and proper impedance matching and the proper bias circuit and tuning the amp settled down and did the usual output and with a Temp-O-Matic indicator on top the amp above the tubes it was around 95 to 105 F. Also installed meters to keep an eye on the grid current and other voltages and currents.

Hope your not over driving the amp. The thing to know is that a few more watts doesn't mean anything as it takes at least 6 dB or 4 times the power to show a real increase. So many operators have squeezed too many watts out trying to max it all out at the cost of expen$ive Tubes and transistors. Not worth it, unless you just have to see the watt meter go over farther.

Jay in the Great Mojave Desert

Jay sent you a PM, please check that when you get a chance thanks sir...

73's - Retro