WG2E AL-82 Modifications
Step Start

I purchased a new Ameritron AL-82 amplifier in 2018. It is primarily used on 160m with an Icom IC-7610 at 45% drive, resulting in an output of 800W PEP. During four years of operation, in discussions with other AL-82 owners, I learned of several problems with this amplifier, the most common being arcing or welding of the relay contacts of RLY3. This relay energizes the primary winding of the plate transformer. Across the NO contact of this relay is a 20 Ohm, 25W resistor to limit the inrush current to the plate transformer. When the relay closes, the relay shorts the resistor allowing full voltage to the primary. The resistor is in circuit only as long as the time for relay closure. An oscilloscope across the resistor showed it to be in circuit for 120 msec. This is not long enough to avoid arcing at the relay contacts. I believe that the duration should be at least 2 seconds.

 

After four years, one of the original Taylor 3-500ZG tubes developed a cathode to grid short. While the amplifier was on the bench for tube replacement, I decided to address the relay problem. RLY3 is driven with 120VAC. I decided to install a 120V time delay relay in series with the RLY3 coil.

 

Unmodified AL-82 Schematic

 

Modified AL-82 Schematic With Step Start Timer

 

The original relays had the wiring soldered to the terminals. To facilitate future replacement I used insulated push-on terminals. I also replaced RLY2. The additional wiring was 16ga stranded of various colors. The time delay relay was purchased from Amazon. (AC 110v Delay Timer H3Y-2 0-60s DPDT with base socket). After removing RLY3, arcing was apparent on the inside of the relay cover.

 

 

The 20 Ohm resistor was originally mounted directly on the relay. Instead, a barrier strip was mounted at an existing hole on the back panel and the resistor was installed there.

 

 

RLY3 is DPDT. I considered paralleling the poles for improved current capacity. However, putting multiple conductors into the push-on terminals was problematic. Enough slack was left at the relay connections to move the terminals to the other pole if it was ever necessary. The time delay relay socket was mounted behind the plate transformer after drilling two holes in the chassis bottom. New wiring was dressed into the existing harness.

 

 

AL-82 Timer Relay Mounting

 

One wiring error in the amplifier was found. One of the loads was improperly wired to the line side of a fuse holder. During the first test it was a bit difficult to set the relay timing to 2 seconds with the 0 to 60 second relay. I changed the time delay relay to a 0-10 second for easier adjustment. The amplifier now starts quietly without the loud hum that existed before the modifications. Recent inspection of the new RLY3 show no evidence of arcing.