Changing the Capacitors in a DX-50

This lovely transmitter is 33 years old! I thought we’d celebrate by changing the electrolytic capacitors! It appears that some of the capacitors were changed in 2009, but many are original to the transmitter. Gates Air recommends replacing the electrolytic capacitors during the course of regular maintenance cycles. Dried-out capacitors can lead to a variety of mysterious fault conditions including low drive levels, poor audio quality, difficulty starting the transmitter, and so on. See Harris service bulletin AM-579-JK.

DX-50 transmitter

Some of the Low Voltage Power Supply capacitors were at least partly dried out. They felt a little bit light and one of them rattled when I shook it.

Replacing large PA capacitors

Gates Air has a full replacement kit, part number 973-2100-391. When I looked into it, the price of this kit is very reasonable and is closely aligned with the prices from Mouser Electronics.

Old capacitors for disposal

Here is a full list of capacitors needed, I put the Mouser part numbers in just in case:

NomenclatureAmountGates Air PNMouser PN
Cap, 5,100 uf 350 V17524-0341-000598-DCM512T350DG2A
Cap, 5,500 uf 200 V4524-0219-000
Cap, 15,000 uf 100 v2524-0322-000
Cap, 76,000 uf 40 v4524-0342-000
Cap, 120,000 uf 40 V*2524-0380-00075-36DX124G040DJ2A
Large Capacitors for DX-50 transmitter

*See Harris service bulletin AM-474-TLH for information on the -8 volt power supply.

Board is green, Returned to service

Most of the capacitors in the PA section were original to the transmitter, as well as those in the 30-volt and 60-volt driver supply.

One important detail; pay attention when installing these things. You do not want to reverse the polarity on an electrolytic capacitor, it will likely explode. These units are pretty big and the explosion would be loud and messy.

With that done, I also went through the transmitter and reset all of the voltage levels according to the factory test data sheet. When it was returned to the air, it sounded great!

Another Ask

This one is targeted mostly toward my European readers (however, read on).

I received the following email from Olkesandr in Ukraine, it seems the Russians stole his transmitter:


My name is Oleksandr (last name redacted). I am chief editor of Ukrainian radio station CCR 648 AM. We are looking for an used am transmitter 25 or 50 kwt. Probably Your company has one for sale?

That is interesting. I asked for a few more details and received the following:

I am originally from Crimea. But in 2014 I had to leave my native town. I have been living in Kyiv since 2014. In 2017 our team of journalists launched informational broadcasting to the occupied Crimea from Chongar (it’s 1 km from Crimea in Kherson region). First we started broadcasting on 105.FM 5 kwt. But in 2018 our signal had been jammed by russians occupants. In 2019 we started broadcasting on 648 AM (10 kwt). In 2021 we increased the power to 25 kwt. But in February 2022 our transmitter was captured by russians. Now we are looking for an 25-50 kwt AM transmitter. We are going to install it in Kherson region (in controlled by Ukraine territory). I supposed we’ll be able to cover by our signal all Kherson region, Zaporizhzhya and Crimea.

Digging around, I found two news stories about it: Apparently, the Russians removed the Transmitter. By the way, Krym (pronounced cream) is Crimea in Ukrainian and Russian.

Missing Harris DX-50 transmitter, serial number MPS104705-00001

Missing Harris DX-50 transmitter

A little bit more digging around and I found some more pictures of the transmitter site: Radio Crimean Community transmitter site

Google Maps Link: Chongar

That is an interesting setup; the FM antenna is a stack of six, looks like 1/2 wave spaced six-element yagis, vertically polarised. The AM is a slant wire that goes almost to the top of the tower.

That area is still occupied by the Russians. As it is one of the two usable land transportation routes, it is likely that it will be unusable for some time after it is deoccupied.

So, here is the ask; I know that many Medium Wave transmitters have been turned off in Europe over the last several years. Is there any in that power range that is available to be moved to Ukraine? Preferably something that is still in good working order and on or close to 648 KHz. It is a long shot, but worth asking.

AM radio in Electric Vehicles

I have been reading with interest the ongoing discussion about AM radios in Electric Vehicles. Rather than rehash the what, I thought it would be nice to dig into why it is happening.

My first thought is that many of the electronics use PDM or PWM to control various stages of charging, converting, or discharging the storage system. I quick review of a typical EV basic diagram shows that there are several systems involved

Searching through various chip makers’ data sheets on Li-ion battery chargers, DC voltage to voltage converters, regenerative braking systems, traction motor inverters, and so on shows that all of those systems use PWM. Some of those PWM frequencies are right in the AM band, while others are not. That explains why different manufacturers have different takes on AM radios in EVs.

Basic Electric Vehicle

All of those electrical components are controlled by an electronic system that handles battery charging,

This basic diagram shows several sections that rely on PWM to function. The traction inverter is very complicated, with sensors running to each motor and each wheel for traction control, etc.

I imagine the average EV driving down the road in a cloud of PWM-based electrical noise. Whether or not that creates interference with AM reception depends solely on the PWM frequency the chip manufacturer chooses. That is not all, even when sitting in the garage charging, the Li-ion battery chargers use PWM.

It seems a monumental task to attempt to mitigate the noise issue. The real question is; does the general public and more specifically, those who want to own an EV care about AM broadcasting?

There are many alternative entertainment options these days. I would say the average Tesla driver listens to iTunes.

It would be interesting to test MA-3 reception in a Tesla. That would be a real-world test to see how the HD Radio codec stands up to electrical noise. I would say the same about DRM, but you would need to find a receiver first.

One of the perks

Occasionally, I get to go for a nice walk in a snowstorm. No, I am not being sarcastic. It is the middle of March and winter has decided to make an appearance. One of the FM stations we take care of went off the air and the remote control was not able to get the transmitter to come back on, so a stroll through the woods was necessary. This station is located at Sam’s Point Preserve, in Craigsmore NY.

Self-supporting tower has ATT and a Low Power TV station

The site is owned by Vertical Bridge. There are a few tenants on the tower and fortunately, somebody left the gate open before it snowed. I was somewhat dreading trying to wrestle with it when I got to the site.

The problem itself seems to be due to a power hit; the main transmitter was off and the remote control, a wheezing Genter VRC-2000, was not able to control either the main or the backup. Those should be replaced at some point.

Neighboring tower

There are several other towers up here for various cell carriers, 911 dispatch, etc.

My SO decided to come along.

My phone said we walked 2.7 miles round trip, which sounds about right. The station is back on the air. When I can get up there with a vehicle in a few weeks, I will look into the remote control problem.