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A Brief History of Linear Amp

Linear Amp was started by Peter Rodmell G3ZRS under the name of Heatherlite just over 30 years ago. 

The First Amplifier made was the Explorer under the name Heatherlite. The first units covered 10 to 80m and gave around 800 watts from 2 x 4-400. They would also take the 3-500 as an option to give 1 KW output.

Lauched in 1986 the 2m Explorer using a single 4CX250B or a 4CX350B gave 300 watts on 2m with a drive of only 10 watts. It was ideally suited to the popular rigs of the time, the FT221 and the TS700G.                             

The early Explorers were soon improved by a using a control board PCB and were renamed the Explorer 1000 and later the Explorer 1200 . It also had a sister called the Hunter that used using a single 3-500 which was ideal for the UK limit with it’s 600 watts output.

In about 1993 the business was renamed Linear Amp Ltd.  Models at the time were: 

Explorer 1200          10 to 160m  1200 watts output.

Hunter 750               10 to 160m   750 watts output.

In response to the rising price of the 3-500 the Ranger 811 was launched in January 1998 using the cheaper and more available 811’s.  Two of the first Rangers were bought by OFCOM for the Poldhu Marconi radio station in Cornwall for their demonstration station.

The Pioneer version came out in November 2000.

The VHF/UHF Discovery units were launched in 1993/4 and were initially fitted with a 3CX800A7 with versions available for 2m, 6m and limited numbers of the 70cm version.

The 3CX800A7 was around £200 in those days and represented very good value.

After a visit to Friedrichshafen the business started to look at the Russian triodes GS31 and the GS35 which had many similar characteristics to the 3CX800A7 and 3CX1500A7  but without the requirment for a dedicated valve base.

The 70cms Discovery GS31 was very popular as the top end frequency output of the valve was far better than the 3CX800A7 and it comfortably gave 700 watts output – a lot at the time. GS35 versions were made for 2 and 6.


The first Challenger was made in August 1994 using 2 x 3CX800A7 to give 1500 watts ouput. Dxers quickly realised that each tube was actually capable of 1 kW and it ran them to over 2000 watts output. Almost every keen 80m Dxer with a 4 square on 80m had a Challenger.

A small number of amplifiers with with 3 and 4 x 3CX800A7 were build with a separate power supply to give 3 and 4 kW output. Built to order and called the Invader, a few are still in operation today.


The first Challenger with a GS35B was made in May 2001. Due to the rocketing price of the 3CX800A7 the business also started to look at the 3CX1500A7 as an alternative.  The Chinese started to make them so prices were competitive. The first valves were not very good but later the quality got much better and now they are a very viable alternative in  the Challenger with their higher gain compared to the GS35.

The Challenger was offered in two versions, either fitted with a 3CX1500A7 or a GS35 with a price option difference.

Some orders went for export to the USA. These included a GS31 Discovery for 220 mhz.

The Commercial side of the business was also taking  off at this time with many products including amplifiers for :-

and many others ........

Amplifiers were exported all over the EU and middle east and North America. VHF amps found there way as far as VK and ZL.

Up until Peter’s sale of the business about 2500 amplifiers were manufactured.

Early in 2008 Peter made it known that he wanted to retire and that Linear Amp Ltd was on the market. The business was acquired by Paul Cullen G4KTZ his intention being that it would take him nicely up to his retirement  a few years later.

The same product range was continued this being the Ranger 811 and 572,  Challenger 3 and 4, Discovery 2, 70 and 6. The 6m version was quickly turned into the 64 covering both 6m and 4m in the same box.

A little later the Pioneer was re-introduced. This gave 1KW on HF and was based on an improved version of the Ranger 572.

The whole range now needed to be fully CE marked and a big project was undertaken to test and re-design the entire range where necessary in order to meet all applicable standards. This took several months to complete.

Many design improvements were introduced. Some enabled the product to meet standards and some improved the design and production.

The first major change was to the tune and load variable capacitors on the HF Amplifiers. The original manufacturer stop producing them. Luckily Jackson Brothers in the UK were still around and alternative units were obtained from Jackson and these were engineered into the product range. Thermal trips were also added to all mains transformers. This was required in order to meet standards but was also a highly desirable safety feature.

One highlight of Paul’s time was providing a 70cms Discovery which was used by Jodrel Bank during commemoration of the 25th anniversary of man landing on the moon by allowing the public to send messages which were bounced off the moon and back to earth. The amplifier was placed in the chamber at the focal point of the dish used for the uplink. We calculated that it was firing several Megawatts in the direction of the moon due to the gain of the massive dish!

Paul has run Linear Amp for the last 5 years and now is transitioning to retirement.

Roger at The DX Shop approached Paul in the Autumn of 2012 has now taken over the business, continuing the development of Linear Amp based around hand built products made in UK.

Right from the start the business has always been there at the end of the phone line to help out with customer service and this has become a characteristic of the business. The DX Shop is well equipped to carry on this tradition. We keep a range of demonstration amplifiers that are always available for loan to those embarking on expeditions and field days.