A Homebrew 100W (DC Input) Class 'C' Amplifier

This 7/14 MHz amplifier was built as a companion to my Homebrew HF Transmitter.

It is based on an article 'A 150-Watt Amplifier', published by ARRL in their book 'Understanding Amateur Radio'.

100W Class 'C' Amplifier

It has two 807 tubes in parallel. The 'clamp tube' was done away with by using negative-bias-grid-block keying. Hence the unused tube-socket cutout.

100W Class 'C' Amplifier - inside top 

I attempted using a 'receiver-type' variable capacitor for Pi tank tuning, but heavy arcing between the plates put an end to that.

The project was on hold for about six months, till I succeeded in laying my hands on the wide-spaced variable seen.

The 'receiver-type' variable for Pi tank loading, mounted under the plate/grid current meter, is not visible.

100W Class 'C' Amplifier - inside bottom

The chassis is an aluminium baking tray picked up from the neighbourhood 'pots & pans' trader!

The cutouts were made by drilling/filing with hand tools and the cover homebrewed by cutting/bending aluminium sheet.

A few coats of enamel paint, baked on the kitchen stove, gave a fairly acceptable finish to the enclosure.

Here are the design manuscripts:

Class 'C' Amplifier Schematic

Power Supply Schematic

Class 'C' Amplifier 

Class 'C' Amplifier - Instructions

This amplifier fetched me a lot of DX contacts on 7 and 14 MHz using only simple dipole antennas.

Related post: My first Homebrew HF Transmitter
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My first Homebrew HF Transmitter

It's a 15W CW/10W AM transmitter for the 40m / 20m bands, based on G3OGR -  OM F.G. Rayer's  

article 'QRP Transmitter for the LF Bands' published in the August 1971 issue of 'Practical Wireless' 

magazine.

15W CW/10W AM Transmitter for 7/14 MHz

The transmitter stages are as follows:

ECC81 - VFO on 3.5 MHz
EF89 - Buffer
EF89 - Multiplier to 7 MHz
EF89 - Multiplier to 14 Mhz
EL86 - Final with Pi tank

15W CW / 10W AM Transmitter for 7/14 MHz - top inside

It has a companion power supply cum modulator.

The modulator stages are as follows:

ECC83 - Speeech Amplifier
EL84 - Modulator

Here are the design manuscripts:

Transmitter 

Transmitter Schematic

Power Supply cum Modulator

Power Supply Schematic

Modulator Schematic

Transmitter - Instructions

Using this transmitter, a number of CW DX stations (including a 'W' on 40m) were worked in the late 1970s. AM DX contacts were also made with 4S7 and YB0 stations.

Only simple dipole antennas were used.

Related post: A Homebrew 100W (DC Input) Class 'C' Amplifier
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