Transistor Mobile HF Linear Amplifiers


The linearity is certainly in question.. Most of them just were not made to be as perfect as possible or to comply with spectral purity rules, as most ham radio 'equivalents' are. These were mostly made to deliver the most power for te lowest manufacturing cost consistent with a hopefully long service life if not abused. These were made on the 1980's and were popular with truck drivers. Although they could be used in amateur radio if a suitable set of low pass filters was installed after the amplifier to reduce harmonics, the vast majority of these clandestinely manufactured amplifiers found themselves connected between a CB radio and an antenna.

not for sale. not for use on CB band. for educational display only.
mcsl100_2090.jpg
This contraption is actually an old Cobra remote-mountable CB strapped underneath a Silver Streak 150 linear amplifier. It was found under the seat of a wrecked car in a junkyard. Someone had them a nice little package!
mcsl100_2091.jpg
The 2-transistor amplifier takes less than 4 watts of drive and would make a good booster for some of the recent low-power backpack HF sets. The safe operating rating of the amplifier is 100W PEP (or single tone output with appropriate cooling).
sl100_2068.jpg
"TX Eight Hundred" linear amplifier uses four 2SC2879 output amplifiers and one MRF454 driver. The driver is operated class A. The output stage is arranged as a pair of push-pull amplifiers operating through a combiner. Class AB biasing is provided for the output stage. The safe operating rating of the amplifier is 400W PEP (or single tone output with appropriate cooling). The name "Eight Hundred", as with most "CB" and "ham" type linear amplifiers, tends to indicate the maximum power input, not the output. Like most such amplifiers, the driver is capable of severely overdriving the output stage, and care must be exercised to avoid damaging the amplifier in this way. An attenuator can be used to reduce the RF input to the driver stage.
sl100_2069.jpg
The driver is at the upper left. It can barely be seen.

updated 20160620

A note from a gentleman about the TX800 performance and other matters. I believe it is important and interesting to post this information from the person who originally built the amplifiers. He would know more about them than I would. Rebuttals and corrections are always welcome on bunkerofdoom. (text below added with permission).


Today I came across the Bunker of Doom website,,, read with some amusement the posts on C.B Linear Amps... I built the original Silver Streak 150's and 250's at Sundance Electronics in Garden Grove CA back in the late 70's and early 80's. The one you have pictured is one of the newer models made/sold in the last 2 decades by one of the original owners of Sundance. I built the TX line of amps through the 80's and early 90's.

The TX800 with 2SC2290 driver and 4 2SC2879 finals will absolutely do every bit of 800 watts @ 13.8vdc/200A measured on a Bird Model 43 wattmeter into a 50 ohm dummy load. The amp had attenuation on the input to reduce the drive to the first stage with added attenuation for the "low" and "med" settings.

Yes I know the IMD is high when driven this hard, but the intention of the amp was to be powerful in a small package, we were not too concerned at that time with perfect spectral purity. Keydown time was short due to the extremely small heatsink, even with 2 fans. I repaired a few that came back with damage from excessive heat, transformers melted off the board etc. I recommended no more than 400 watts carrier but a lot of users drove them to 600+ watts carrier with no problems other than the AM sounding "tight" or compressed. I ran mine personally at 250 watts carrier on A.M and never had a problem or complaint, amp still did 800+ P.E.P. Used the amp at 600 watts output on 10M F.M. many times, also without any problems or complaints.

Many amps produced from the 60's to present DID claim a lot more output than they would actually produce and that was (is) always a pet peeve of mine. The TX 600/800 was never intended (by me) to be used as an S.S.B amp but the keying delay feature was included for those who chose to try it. The single transistor driver with unregulated bias circuit was the main problem, along with excess drive. The excess drive could be remedied on S.S.B. by adjusting the ALC on the transmitter to stop overdrive of the amp input. Many users worldwide proved that method.

I made a TX300 (same heatsink & chassis as the 600/800) that was excellent for S.S.B that featured 2 - 2SC2879 transistors and a regulated bias circuit. Worked great on A.M and F.M as well although they got fairly warm. I recommended 125 to 150 watt carrier output max but many pushed them harder only to find out that excessive drive ruined the great sounding amp.

I built and repaired many amps from the 70's to 2002 then gave it up to work in Telecom/Cellular. I am pretty sure that I have worked on every type/model amp ever made thru 2002. Most of the C.B. "Linears" made now are cheap crap and the names on them are pirated from the amps made decades ago with no affiliation with the original manufacturer.

I still have a huge collection of radios & amps, tube and transistor, from the C.B heyday but they sit collecting dust and mouse poop for over a decade.

Nice to see that my amps are are still around. I know a lot of people who bought them from me decades ago and they tell me that they command a premium price used because of their performance.

Just wanted to give my side of your depiction of my amps.

Thanks

Steve