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Kenrich Eagle 500-Next Patient

Just don't use 20LF6 tubes in the two driver sockets.

The amplifier feeds around 27 Volts to the heaters. It was designed for an obsolete type 27LF6 that was rare when it was new. Only used in european TVs, never an american model.

Type 30KD6 will work. 20LF6 will flame out and toast the plate choke.

And themselves.

For that matter, the five final tube's heaters are wired in series, powered directly from the 120 Volt line cord. Five of the 27LF6 add up to 135 Volts in series. Running them from 120 or 125 won't cause them any harm. But five 20LF6 heaters in series only add up to 100 Volts. If your line voltage is 125 Volts, each heater will have 25 Volts on it, not 20 Volts.

Same hazard. Seems to me we used a 25 or 30 ohm 50-Watt resistor in series with the five final filaments to make the 20LF6 tubes behave in this model.

Excess heater voltage is only one reason this model tends to flame out, but a common one.

73
 
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Nomad,

There is something in the schematic for these amps that seems weird to me and i was wondering if you might take a look at it for me?

link: https://web.archive.org/web/2015032.../kenrich/eagle_500/graphics/eagle_500_sch.pdf

specifically i am wondering about the bias circuit right in the middle of the page.
you were the one who taught me about this, and to me, it seems weird that there is a
+15 volts going to one grid, and a -15 volts going to another grid.

is there a mistake in this schematic, or is it just something i haven't seen before?

might be doing something with mine finally, as i just scored a great deal on some tubes and a 6 volt transformer (20 amps).
LC
 
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looks like this thread might become the official Kenrich picture depository!

here are my contributions.
sadly, i think i'm going to have to draw up my own schematic, as unless RVAlleman comes back to the forum, there aren't any for the weird version (eagle VIII) that i have.

030.jpg
031.jpg
032.jpg
033.jpg
034.jpg
035.jpg


LC
 
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seems like my amp has an IC where the other versions used a tube.
is this the CW portion of the amp?

here is a datasheet for the Motorola IC that is used in my amp:
https://www.jameco.com/Jameco/Products/ProdDS/24942.pdf

It's an IF amplifier.

this amp had a hard life before it got to me so there are some burnt traces and it looks like some jumpers where traces were peeled up.

in the last pic, you can see that the 1/4" jack for the CW key, and the crystal socket never had anything soldered to them.
I think the guy who used to work for Kenrich said this was more of a prototype, so hopefully i can make a working amp out of it.
LC
 
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LC,
If nothing else, it will make a good case for an LC custom build!

73
David

For sure David!
you know i won't be able to help but change or add something.

im hopeful that there are things on the boards i can just eliminate.
LC
 
+15 volts going to one grid, and a -15 volts going to another grid.

The negative 15 Volts goes to the driver tubes' control grids, the grid closest to the cathode in the schemo symbol. This serves to limit the tube's anode current with low or no drive carrier.

The positive 15 Volts goes to the tubes' screen grids, the middle of the three grids in the tube. Serves to goose the tube's power gain.

73
 
thanks for that Nomad.

it will be nice not to have to add bias in like you showed me how to do with the kris power pump.

obviously my amp is a bit different from everyone else on the planet so i've got some things to figure out.

first is that all the other versions have four relays in them, and mine only has two.
mine also has an IC chip in it and i believe none of the others do.

for those that have the 'regular' kenrich design, you can just eliminate three of those four relays if you don't care about having a receive pre-amp. you can also get rid of the whole preamp section for that matter.

i will have to take a closer look and a better pic, but i believe that my voltage regulator board has a trimmer resistor on it, which might be for setting bias.
so many questions to answer...
LC
 

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