Clegg Apollo 6 Six meter Ham Linear Amplifier converted on the bench

Описание: Another project I bought many moons ago. Clegg Apollo 6 linear amplifier. It uses a pair of 8236 tubes. It is a single band, 6 meter only amp. Clegg, which was later bought by Squires Sanders made premium, high-quality equipment. This amp was made to match the Clegg 6 meter Venus transceiver. Clegg was formed by Mr. Edward Clegg in 1951 and was sold to Squires sanders in 1963. This amp came out in 1965. In 1968, Mr. Clegg bought back the Clegg name and in 1971 sold it to ISC (International Signal and Control Corporation) Around 1980 Clegg stopped manufacturing and was not heard from again.
This amp was well made and has some premium circuit and protection features. It has 3 meters, power output, plate current, and grid current. Interesting that it does not have a voltmeter. It has a power on switch marked Filament. This Filament switch will light up the tubes and low voltage, but will keep the amp in standby mode and won't let it key until the HV switch is on. The other 2 switches are the HV on and HV off switch. The HV is actually switched on and off by a relay. The relay is on the input (120ac side) of the HV transformer. It is much easier and safer to switch the 110 ac coming into the HV transformer versus the HV coming out the transformer. This can only be done if the HV transformer is a separate transformer from the low voltage transformer. Also, switching HV is a bit more difficult than switching 110v. This amp does it right. It uses a relay as supposed to running the power thru a switch. A relay does a much better and safer job than a switch does. One of the problems with many amps, like Heathkit and Drake, is they run all the ac input power thru the main power switch. Over time, the switch fails. Also, if the switch arcs, that arc can possibly bite your finger turning on the switch. The HV relay in this amp is under the chassis, near the HV transformer. If the HV relay arcs, you won't get bit. The switch is also self latching. The HV on switch is momentary and spring loaded. The HV switch applies power to the relay coil and once the relay closes, it powers itself up. Hence, no constant power on the switch. Since the HV relay self latches, to turn off the HV only, it has another switch, a momentary switch that opens the power to the HV relay coil. It also has a separate relay for overcurrent. It is in series with the plate current. If the voltage drop on the plate current is too high, that voltage drop powers the overcurrent relay and the overcurrent relay will open the coil to the HV relay. Overengineered or smart? This amp has an OA2 voltage regulator tube for the regulating the screen voltage and adjustable negative bias. The - bias pot in the back can be used as a gain control or dial a watt....to a certain extent. Also has a Grip tuning cap on the front. This is an input tuning cap. The dead key of this amp for AM can go from 3 watts to 75 watts. Even on average, this amp is a swinging machine. It is what I would call a 'Modulator' type amp as it does more swinging on the output then the input in ratio swing is. It is heavy and well made and got good reviews on the Ham sites.
The 8236 was a tube I was not familiar with, so I googled it up. The 8236 uses an Octal base, like the 6L6 family of tubes. and was used both as a Horizontal Deflection tube (Sweep Tube) and a RF output tube for 30mhz and below. Surprisingly, the 8236 has a plate dissipation of 50 watts. This is 10 watts more plate than the previous King of sweep tubes, the big bad M-2057's and the 8908's! Since I thought the M-2057's were the King of Sweep but now the 8236 bests them. Of course, there are bigger glass tubes, but we are talking about sweep tubes and now there is a new King of Sweep, the 8236. It must not be very well known or used much as this tube can be found for cheap on Ebay.
I did 2 hacks, errrrr I mean mods on this amp. First, it was converted from 6 to 10 meters. Mostly input and output coil taps, then some cap and choke changes were also needed. The other mod was this did not have an automatic keying circuit. It needed either a foot switch or a Ham radio that had an amp output keying line to key this amp. I installed a Nomad keying circuit PCB. So now when its in operate mode, the Nomad PCB will sniff the watts coming in and key the amp.
I love this amp. Its a modulating monster with big bad cheap glass tubes. I think I'm going to keep this one.