Henry 1KD-5 Restoration

A while ago I bought a Henry 1KD-5 of an Internet auction.

It was sold "As is for spare parts or repair"

Unfortunately, I did not ask any questions about it so when the amplifier arrived, I was a
little bit shocked over what I saw when I opened it up. 

The first look inside (Top view)

What a mess..... Dead bugs, grass, dust and dirt! Perhaps it has been a boat anchor for real! Maybe there is a dead fish inside somewhere...

The first look inside (Bottom view)

RF input circuits seems to be intact.

Conclusion
The first inspection of the amp was a little bit disappointing.
I realized that it would cost a lot of money to repair this amp, more than I could expect to cash in
if I would sell it later on.
But the winters in Sweden are long and I thought that maybe it could be fun, and maybe I could
learn something from it.
So how should I proceed? I needed a to do list.....

The to do list

• The main transformer is missing, and I need to find a replacement
• Vacuum tube is bad.
• Tube chimney is missing.
• Tube top cap is missing
• Roller inductor is misaligned and has no, or poor contact to the coil.
• Filter capacitors are old and needs to be replaced.
• Power cord is old and dried up and power plug is loose.
• Aluminium side cover that holds the zener diode bridges is missing.
• One bottom cover is missing.
• Perforated aluminium top cover is missing.
• BNC contact for RF input is oxidized and needs to be replaced.
• One foot is missing.
• Tuning knob is not the original one.
• Front panel lamps are missing.

In order not to get discouraged I also wrote a thumbs up list.

The thumbs up list

• The analogue meter on the front panel is working.
• The band selection switches are ok
• All ceramic capacitors are ok.
• Zener diode bridges are ok. (These are expensive)
• Switching relays are not in best condition but ok for operation.
• Blower fan is a little noisy but working
• The external cover and front panel is in almost mint condition. Nice!
• Bottom section looks intact and needs probably no attention.

So lets get started!

The power supply
I thought the best place to start was to fix the power supply and then go on from there.
The transformer had just been cut loose and removed, leaving the wires hanging unmarked.
So I had to check the schematics and measure and follow each wire.
This was a little harder than I thought because the schematics are not 100% accurate.

Picture showing missing transformer and loose rectifier bridges.

After a long search on the Internet I found that Digi-Key was selling the original transformer for
the amp. It is a Peter Dahl transformer made by Hammond Manufacturing.
Dude! This one was expensive, but I could not find a replacement with both plate and filament
voltages small enough to fit inside the chassis.
The transformer was custom made so it would take a month before I received it.

While waiting for the transformer to arrive I ordered new filter capacitors to replace the old ones.

The new filter capacitors.

The unmounted board with filter capacitors and bleeder resistors.

Old filter capacitors removed.

Capacitors replaced and bord reinstalled.

Still waiting for the transformer. Will it ever arrive?
As mentioned earlier the side cover plate holding the rectifier bridges was missing.
But what did it look like? what was its dimensions? I had no idea.
Luckily, I found a video on YouTube posted by "Troy Radio Service" clearly
showing the side cover.
I stopped the video and did some measuring on the screen using a measuring tape.
Then I used my own amplifier as reference to scale the measurements from the
screen.

Side cover cut and drill holes marked.

The completed side cover with ventilation holes.

Finally, the transformer arrived!

Transformer mounted in place.

Power section with new side cover completed.

The power cord looked dry and the plug was in poor condition, therefore
I decided to replace them with new fresh ones.

Time for the first smoke test
First smoke test went well.
The voltmeter on the front panel was showing about 3100V/DC just as expected. However.
The filament voltage was showing about 6V/AC.
That is 0.75V more than the maximum rating of the 3-500Z that is 5.25V

Hmm..... My thoughts about this.

It is a small transformer with high filament current flowing through the tube and there ought to be
a significant voltage drop when the tube is connected. Moving on......

After restoring the power supply, I felt confident enough to order a new tube.
I chose to buy from RF Parts because they could also supply the chimney and top cap that I needed.
Also, they give one-year warranty on their Taylor tubes which are tested before shipment.
I have purchased from RF Parts before and I think it is a good trustworthy supplier.


Fixing the roller inductor
The roller inductor was in a really bad shape.
It was misaligned and when measured with my LCR meter I found that in some positions along the
shaft the roller had poor or no contact with the inductor coil.
Perhaps this was the main reason for the catastrophic failure that followed and totally wrecked
the amplifier.
I also found that somebody had put in 25A fuses instead of the 15A that should be used.
Bad choice!

Tube section with roller inductor.

Roller inductor removed.

Coil L2 removed.

Coil L2 and roller inductor shaft cleaned and dipped in silver rinse.

The roller inductor itself was put in the dish washer (Without my wife knowing).

After reassembly and some greasing of the shaft it turned out very well.

Roller inductor tightened, cleaned and reassembled.

Roller inductor and coil L2 reinstalled.

Old BNC connector replaced with a better one from the junk box.

Wohoo! Tube and chimney has arrived.

When I received the package from RF Parts, company I got a little bit nervous.

Despite all the stickers "Fragile" and "Glass inside" the package was damaged.
The people that handles these packages just don't care.
It is nowadays up to the sender to reassure that their goods will survive a nuclear blast, at least.

Fortunately, everything was well packed inside and it all survived the transport

from the US to Sweden.

Tube, chimney and tube cap.

Tube, chimney and tube cap installed.

Time for the second smoke test

Now it was time for the second smoke test.
I plugged in the amplifier to a variable transformer and turned it down to 0V.

While listening for sounds, watching out for smoke and strange smells I slowly turned the

voltage up while monitoring the multimeter on the front panel.

At about 50V input I hear a strange sound. What's that?!

My pulse is high, tension is high, and adrenaline is pumping. It was just the cooling fan!

I stopped at 100V input and listened and smelled for a minute.
Everything seemed Ok.
I slowly increased the voltage up to 230V. The High Voltage meter showed just above 3000V.

Tube, first test. Nice glow and a warm smell.

I later reinstalled the tube and turned the top cap 180 degrees so that the connection would end up

at the right side instead of left, making the installation easier.
From other pictures I found on the Internet i think that is the way it should have been installed.

So how about the filament voltage now that the tube is installed?

As expected, there was a voltage drop when putting a load to the transformer.
Now the voltage was within the specs, even if it was in the upper range.

Filament voltage during first test.

Lets see, what is left on the to do list?

The main missing and faulty parts have been replaced or fixed.
But there were still things that needed my attention.

The updated to do list

• The main transformer is missing, and I need to find a replacement
• Vacuum tube is bad.
• Tube chimney is missing.
• Tube top cap is missing
• Roller inductor is misaligned and has no, or poor contact to the coil.
• Filter capacitors are old and needs to be replaced.
• Power cord is old and dried up and power plug is loose.
• Aluminium side cover that holds the zener diode bridges is missing.
• One bottom cover is missing.
• Perforated aluminium top cover is missing.
• BNC contact for RF input is oxidized and needs to be replaced.
• One foot is missing.
• Tuning knob is not the original one.
• Front panel lamps are missing.

The making of new top and bottom cover plates
The top perforated aluminium cover was missing and I needed to make a new one.
I purchased it from a metal store, and it was much cheaper than expected.

Perforated aluminium 1000x500mm.

Top cover cut to the right size.

Bottom cover rf input section.

New chassis feet.

Bottom covers and new feet mounted in place.

New top cover and new screws.

Amplifier restored and operational.

Well that was it.

The amplifier is putting out 700W+and I am quite happy with the result.
The blower fan is a little bit noisy, maybe it's normal? I don't know.

Some of you readers might have noticed that this amplifier is the US model without the 10m band

installed. 10m operation was only available on the export models.
The amplifier is however factory prepared with the components installed for 10m operation.
The mod requires just a little soldering and some mechanical work.
I will perform this modification later on and also post some pictures here on my blog.

But first I will enjoy operating QRO with this amp for a while.

Emil, sm7tkr