Eagle 525 Base Linear?("Not Golden or Browning")

[Bigfoot 256]

I have a question for the builders. I recently traded for a Eagle 500. They guy telling me 1000 watts all day. On the front panel meter it would show high. I've had for a couple weeks getting great reports.
On my externals it would show 450 and swing to at times 600. Phenomenal audio.
This week max i can get it to tune 250 and might swing to 400.
Still has phenomenal audio, but obvious loss of something.
Im not up on my tube jargon. I do know the middle knob is all the way one way and if i move the opposite it cuts back output quickly.
Is this a sign of a tube failing? I dont have a tester to know which one.
I love this big Heavy beautiful box. Want her at peak performance.
Think someone posted link to schematics, ill go see if i can download.
Just curious what would cause it to just start losing umphh. I realize its probably my age... and i dont get around like i use to either lol.
Appreciate any input

 

[Shadetree Mechanic]

What is the middle knob for? Plate or tune? All the way one way is not good. Ideally all the knobs would be near the center of the adjustment. This could cause the plate current to be too high. How hard you drive the amp will determine tube life. As a tube nears the end of it's life, it's output will gradually be reduced. Sounds like the tubes are getting soft.

 

[Bigfoot 256]

Its the Load knob if memory serves me. And yeah that was my thinking, it shouldnt be all the way to one side. I only put 2 watts into it with a swing to 8.
So if a tube is dying... i have 7.. is it one of the drives or both.
If its a final.. just 1 or several (no way to test the tubes)
So to not spend a fortune... could i move tubes till i have 5 good finals and remove the drivers and use my palomar 90a to drive the 5..
Dont want to drop alot into it and it not fix the problem yah know lol

 

[Shadetree Mechanic]

You might be able to swap tubes around but the problem with mixing tubes is that the stronger newer tubes will tend to be overdriven and then quickly fail. Before putting more tubes in we need to figure out why the load knob is maxed out. Maybe someone more familiar with this amp will chime in.

 

[Bigfoot 256]

Yeah im learning but dont want to make worse. Its blown a fuse 2 times now. One while in stand bye, sat for roughly 20 mins "pop".
And again i had it on low, switched to high and could hear some crackling for a second then pop.
I let it cool down, replaced fuse.. fired right back up.... then slowly losing output over the next few weeks.
Im used to transistors lol.
Still works and is still super loud.. just not performing up to par.

 

[nomadradio]

If it has 20LF6 tubes in the two driver sockets they won't last long.

The amplifier feeds about 28 Volts to the heaters on those two sockets.

Type 30KD6 always lasts longer in those two sockets than the 20LF6 type.

That amplifier is a hot rod, but without a red line on the tach. It was built to impress folks who obsess over the wattmeter reading,

But at the expense of service life. It tends to wear out tubes quickly and fail frequently until measures are taken to calm it down a bit.

73

 

[Bigfoot 256]

Appreciate the info, guys. I'll start shopping around for stronger driver tubes. Here's another question.. If i remove the driver tubes.... can i drive the box with a smaller box? I have on my shelf a Palomar 90a. She maxes out at 125 pep. Will I hurt anything else in the Eagle if i drive with that, or do i need to modify the Eagle to allow this. I'm not finding much information online at all about Eagle Amps.

 

[Shadetree Mechanic]

Just pulling the driver tubes, the finals would not be driven. A tuning network would have to be built to drive the finals directly because the tuning network for the drivers is designed for the drivers. I don't think that simply using jumper wires to bypass the driver sockets would work. How to design a tuning network I don't know exactly. If you had to pay someone to do it, it would be cheaper to buy driver tubes. And we still need to figure out why the load knob is maxed out. Might need to modify one of the tuning coils, either short one or two coils or make a new coil with more turns.

 

[Dmans]

Secret CB Vol 4 page 66-67 may help solve the maxed out tune control issue.
(hand written note on page 67)
http://cbradiomagazine.com/CB Secrets Web/SECRET CB VOLUME 4.htm

Can't be of help bypassing the driver tubes. First thought that comes to mind is "Rebuild" the amp as a straight 5.
STM is correct. Probably cheaper and easier to buy new driver tubes.

If you exercise that option I would heed Nomadradio's advice.

Type 30KD6 always lasts longer in those two sockets than the 20LF6 type

Good Luck
73's
David

 

[Danzik]

anyone here ever heard of the kenrich EAGLE VIII?

it is a 2 driving 5 20LF6's just like the 500 and 515, but its built a bit differently.
the driver tubes are on the right, with an empty tube socket space on the PC board.

the final tubes are on the left, and the fan is to the left of them.

power supply and preamp in the back like the others.

i have one of these and have never seen, nor heard of another.

also, do the 26LX6's work as a drop in replacement for the 20LF6's if you cut the right pin off?

different tube sites say its a sub, but the filiment voltage is different so i wonder.

input?
loosecannon

Yes, you can use the 26lx6 in the driver section without even cutting pin 7 as it is a dead end and goes nowhere