Kenrich Eagle 500-Next Patient

[Dmans]

All,
Below is the next project for me. It belongs to the same friend as the Palomar Skipper300 and the Kris 600 SSB. Same repair deal as the other 2-He pays for parts and I have some busy work and a learning opportunity.
Story with this one is it is keyed up as soon as the power switch is turned on. Kind of hard to use as intended this way. It has fairly clean sheet metal on it and 7 original Kenrich branded 20LF6 tubes.

Stay tuned.

73's
David

 

[jon666]

i had one kick ass amp

 

[nomadradio]

Wow. A Kenrich Eagle 500 that hasn't burned up the driver tubes or the driver plate choke?

Every one of those we saw had around 27 or 28 Volts on the driver tubes' heaters. The 20LF6 driver tubes would kick ass like they had a nitrous bottle on them.

But not for long. Found that a pair of 30KD6 would last a lot longer in the two driver sockets, once we replaced the incinerated driver-plate choke and driver tubes.

Never have put together the "Chernobyl-proofing" procedure for this amplifier. It also has issues with too much heater voltage on the five 20LF6 finals. It was built for type 27LF6 tubes. Five of them in series adds up to 135 Volts. Made them safe to run from a 120-Volt circuit.

The heaters for the five final tubes are in series, and powered directly from the power cord. Five 20LF6 heaters only add up to 100 Volts. a 125-Volt outlet puts 25 Volts across each 20-Volt heater. I should pull out the notes on the size resistor we use to knock that down to the 100 Volts that's safe for the five final tubes' heaters.

Also changed the fixed grid bias on these, and added a bypass cap on the input coil that would prevent it from oscillating and holding itself keyed when you released the mike.

Could be that the filter cap that powers the keying relay has failed.

But it really sounds as if a bad keying circuit is what has saved this amplifier from itself. Can't cherry the tubes and blow them up if it won't key to begin with.

I'll have to look up the poof-proofing details for that one.

73

 

[jon666]

never had a problem with mine. maybe the guy i bought it from did the upgrades

 

[BlowinSmoke]

Wow, 50-75 bucks a tube.

 

[Dmans]

Update to the Kenrich Eagle 500
I have not been as diligent about taking pictures on this one as the others but nevertheless progress has been made. The Owner had previously purchased a "Refurb" kit from an online auction site and delivered the amplifier to a local CB shop for repair (same shop that had the Kris 600 SSB for 6 months). Anyway, the CB shop replaced 3 transistors in the amplifier and pronounced it done returning the amp and the unused parts of the kit to the owner. I can't recall if he said it ever worked when he got it back or not.

Below are a few pictures of how I received the amp.

First the relay board with the 3 new transistors. (New but not adequate for the job in my opinion)

Parts of the Power supply board and the relay board. (Looks like original electrolytics to me)

Below is a shot of the underside of the power supply board. Lots of crusty 40 year old flux present. I started cleaning off some of the flux on the left side of the board at this point.

Due to all the crustiness of the flux, I found it much easier to remove the entire board to finish this task.
In this shot, I have removed the old electrolytics since there are new ones in the "Refurb" kit.

The original rectifiers are still on the board. They are ICC170's. I don't believe they are made anymore. The "Refurb" kit came with 8 new diodes. I'm wondering how the "Assembler" of the "Refurb" kit would decide which of the 16 diodes to replace and which to leave in the board? I know what I will do to solve this!

More to come.
Stay tuned!

73's
David

 

[loosecannon]

more internal pics please!
(of the amp LOL)

i have an Eagle VIII and as far as i know im the only one who has one.
it has some burned up traces on it, and was always supposed to be my russian tube project but i have never gotten around to it.
the eagle VIII is also 2 driving 5 20LF6's.
LC

 

[Dmans]

LC,
The amp is done but I will open it back up and take more pictures (so I can post them on the forum). I have many more pictures on my phone but can't get them on the computer to post. (No e-mail on the phone, no e-mail on this computer and the I-phone doesn't talk to the IBM computer well)

The amp may be leaving tomorrow as it is finished and I have been using err, testing, it for a week or so but I will get the pictures tonight.

73's
David

 

[Dmans]

Below is a lifted trace on the 12vdc circuit. I believe this to a major factor in this unit not keying.

Top side of the rectifier/filter board before. The tape measure was me deciding weather or not to pull the board or struggle working in a cramped space.

Stay tuned!

73’s
David

 

[Dmans]

Here are a few more pictures of tear down and repair of the Eagle 500.

Below is similar to 1 of the pictures already posted but shows more of the complete HV circuit board. May be a help to those that may have one of these amps with lifted or burned traces.

Filter/Rectifier board removed ready for re-work.

Old parts removed ready for new parts.

Back side of Filter/Rectifier board cleared of old caps, diodes and resistors.

16 new 1N5408 diodes installed as well as new bleeder/equalizer resistors. The circuit board lead holes for the rectifiers had to be “reamed” with a pin vise drill as the 1N5408 leads are pretty chunky compared to the original ICC170’s. The diodes were too big to lay down flat on the board as well. My thoughts are that if there is some air between components and the circuit board they may run a little cooler.

New radial leaded caps installed. (From the “Refurb” kit) A drop of hot glue holds them down to the board. Also replaced were the diodes for the 12v circuit. I believe I used 1N4007’s here.(not included in the “Refurb” kit)

More to come.

73’s
David

 

[Dmans]

More pictures.
Below is the rebuilt rectifier/filter board installed back in the chassis.
A little badly needed cleaning of the chassis took place while the board was out.

Next up the relay board was looked at for bad connections and sketchy work. I replaced the keying transistor with a 2N2905A metal type. Should hold up much better than the small plastic 2N2907 that was previously installed. The electrolytic capacitors on the relay board were replaced as well.

For good measure I replaced the 10pF RF “sniffer” cap and the suppression diodes across the relay coil with 1N914’s.

More to come.

73’s
David

 

[Dmans]

The next 3 or 4 pictures are for LC.
First a complete shot of the underside of the circuit boards.

Next the bottom of the tube sockets.

Below is the bottom of the relay board.

This next picture shows the inline fuse holder that was the main 120Vac line fuse as the chassis mounted fuse holder was broken. I added a 15 amp circuit breaker to the rear panel (owners request) and tied this in line fuse holder between the high voltage of the transformer secondary and the bridge rectifier to protect the heavy iron should a rectifier diode short in the future.

Stay tuned.

73’s
David

 

[Dmans]

So with the rectifier/filter board rebuilt, the keying transistor and support components for the keying circuit replaced, it was time for a test.
I put the amp behind my 139XLR into a dummy load (yes I have one now) and saw 1100 watts pep out on SSB with about 18 watts pep drive. Not too shabby! I measured line current at 11.7 amps and the transformer current on the fused leg at 1.7 amps. The added fan in front of the driver tubes was rattling and very noisy. I removed that fan and rubber mounted it to the chassis. It was still noisy. I found too much axial play in the motor shaft so I disassembled it and added shims (had some for my RC helicopter main shaft!) in front of the rear bushing. Problem solved!

The keying circuit was working fine but when turning on the Preamp, the receive signal disappeared completely. Since the Preamp transistors were previously replaced, that is where I focused my inspection.
Below is how I received the amp.

The picture below shows the correct orientation of the Preamp transistors.

So after removing, testing and reinstalling the transistors, the Preamp worked as advertised. There is certainly controversy over the use of a Preamp but since it is part of the original circuit, I felt obliged to make it work.

Stay tuned.

73’s
David

 

[Dmans]

So after testing this power house for a week or so, it is time to send it back to its owner. I had one more thing I wanted to do to it and the owner consented. The meter in this amp is large, clear and works well for relative output but in dim light it is hard for me to see. I wanted to put an LED behind it and tie it to the operate/stand by switch as an indicator the amp is ready to go.

The LED needed an enclosure to focus the light behind the meter so I made one.

The LED is wired to the operate/Stand by switch and a dropping resistor added to supply the LED with 2.5vdc.

The picture below is somewhat brighter than the light in person and I had to try a few different angles with the camera to capture the light where the meter is still legible. It is really not as bright as it appears in the photo.

And finally a few pictures of the finished product.
Below picture during testing.

A picture of the final section.

And a picture of the driver section.

Another fun project and learning experience for me!!

73’s
David

 

[RLVAlleman]

I worked for Kenrich Electronics for many years, my job was final testing and repair of the entire line of Eagle transmitters.
I have all the original schematics and modification data as well as a case of original Kenrich (logo) 20LF6 tubes, our tubes were made with a taller & stouter envelope.