1954/55 Motorola 54HF1 Unique Design

[Hi-Fi-Mogul]

After completing the Magnavox W620 and Maestro customers'
changers, I got back to this amplifier.

I had calculated that 140 Ohms for the dropping resistor,
would get me in the Voltages ballpark.

I undid the pre-rectifier side of the 22 Ohm resistor, and clipped
on a 120 Ohm 5 W resistor in series.

The rectified DC current is now 120 V, and the plates of the
50C5s are at 115 V.

I will remove the 22 ohm resistor and put in the 120 Ohm
power resistor only.
The 120 Ohm felt OK temperature-wise to the touch.

The amplifier sound is fine, testing it with a record,
on the V-M changer.

[Hi-Fi-Mogul]

Done with 2 more record changer customers, so today
I decided to use a 100 Ohm 5 watt resistor
in the Motorola amp.

B+ voltage is now 130 VDC, and the tubes' plate voltages
are a few volts below the schematic voltages.

There was too much AC hum left, so I also tacked on
a 10mF 160V e-lytic cap at the B- to chassis
cap position.

The amp is now nice & quiet.

I'll do the soldering manana, and then get the
cabinet parts, speakers and wiring organized,
to re-assemble the Motorola.

[William]

Photos to follow, I hope.

Bill

[Hi-Fi-Mogul]

Photos to follow, I hope. Bill

Bill, photos as requested:

All done and she sounds very fine. Looks fine, too.

I added a strain relief for the AC cord, and installed a
Pfanstiehl P-226 cartridge.

The speaker cone repairs with glue did the job.

The lid has a felt gasket around it like the Columbia 360s did.

I think I'll keep her, as she is definitely not common:
for me, a Motorola Masterpiece.

[William]

It looks great, Mr. Mogul, and definitely a keeper. Thank you for sharing the photos.

Bill