Zenith Transo-ceanic H500

Zenith Trans-oceanic H500

Manufacturer: Zenith, USA
Model: H500
Approximate Date Of Manufacture: 1951
Type: 5-tube Superheterodyne AM BC/SW band radio
Tube lineup: 3V4, 1S5, 1U4, 1V4, 1L6
Status: working, restored
Where purchased: eBay, October 2004

Description

The H500 is one in the line of legendary Trans-oceanic shortwave portable receivers. A web search will return many sites with information on this world famous radio which was owned by explorers, writers such as Ernest Hemmingway, and the military.

I purchased this one eBay and restored it in the fall of 2004. When received it was working, but needed a full restoration including cleaning, recapping, and alignment. It was missing the cap from the whip antenna and one of the brass nuts for the wavemagnet antenna. Other than that it was in good shape and appears to be entirely original. It came with a copy of the full manual for the military version of the H500 (mine is the commercial version). It has the 5H40 chassis.

I found an antenna for sale on eBay which I purchased to get the end cap. I replaced the selenium rectifier with a solid state diode. I added a 9.1V Zener diode to protect the filaments from overvoltage. I replaced the elctrolytic caps. The can with 4 caps was restuffed with modern caps inside. I replaced all "black beauty" paper caps. During testing I replaced the very expensive 1L6 tube with an inexpensive 1R5. The cabinet was cleaned with Murphy's oil soap and black Kiwi show polish. Tubes were tested with my tube tester. All resistors were checked for values being within tolerance. I purchased kno brights, which were missing, from AES, and found a replacement for the missing wavemagnet brass nut at Home Depot. The brass pieces were stripped of varnish, cleaned, and revarnished. The radio was realigned using my signal generator, Sangean shortwave receiver, and DMM.

4 Sep 2005

Some time ago the H500 started showing the symptoms of "Silver Mica Disease" -- thunder-like crackling and intermittent sound. This is caused by intermittent shorts in the silver mica capacitors inside the IF transformers. This is quite common in old radios, especially Zeniths. I decided to wait until I received my oscilloscope so that I could more easily diagnose which IF transformer was the culprit.

Using the 'scope it appeared to be T1, the first IF transformer, where the problem was occurring. I removed the transformer and carefully disassembled it. The mica was in pretty good shape, so I simply cleaned it with silver polish and windex and reassembled it. As a simple check of the transformer I connected the primary to a signal generator at 455 KHz and the secondary to the scope and I confirmed I got output which peaked around that frequency. I reinstalled the IF transformer and the radio now works fine. The IF transformer did not even seem to need adjustment again.