VK7DX
09-22-2010, 03:31 AM
Hi,has anyone converted a varmint xl-250 to six?
Any tricks involved or any info appreciated.
What is the correct valves for this amp
Any tricks involved or any info appreciated.
What is the correct valves for this amp
View Full Version : Varmint xl-250 to six meters?
KB4QAA
09-22-2010, 03:40 AM
Find a 6m design you like. Disassemble the Varmint for parts. Start from scratch on the 6!
Good luck.
Good luck.
W9GB
09-22-2010, 04:19 AM
Anyone convert a Varmint XL-250 (11-meter/CB) amplifier to Six meters?
Any tricks involved or any info appreciated.
What is the correct valves for this amp
Frank -
This amplifier design, like many from the 1960s and early 1970s, used Television Sweep Tubes.
The ARRL, RSGB and Radio Handbooks of 1950s and 1960s -- ALL had these designs -- the tubes were CHEAP and readily available at every local radio/TV or drug store with a vacuum tube tester in USA.
These tubes were designed to work in your vacuum tube TV ~ 15 kHz (that is at upper range of human hearing/audio). Solid-state TVs were introduced in the late 1960s and 1970s -- totally replacing vacuum tube TVs in the major developed countries.
Production of TV sweep tubes STOPPED in early 1980s in Japan, United States and Western Europe.
Only Russia and Eastern Europe continued to manufacture some TV sweep tubes for televisions in these countries.
Today (2010), ONLY the EL509/EL519 sweep tube is produced by a couple of eastern Europe and Russian mfg.
SO, you have a finite supply of old sweep tubes -- following classical Supply and Demand --
the prices on Sweep Tubes have been rising ever since!
Smart guys have made their $$ by stripping the tubes and pitching remaining chassis and parts.
In fact, the current demand for sweep tube amplifiers -- seen on Craiglist, eBay and hamfests are
the $$ guys stripping the sweep tubes for $$ -- like current metal commodity prices (gold, copper, silver, etc.)!
The Varmint XL-250 used these tubes: 6LF6 and 6KV6a.
The reason your unit has NONE -- is that a former owner cut his losses and sold them for $$ -- or --
the tubes were bad, he tossed them and could not find cheap replacements.
So, you have a box of parts -- that's it.
Your NEXT task is to find an RF amplifier tube rated for operations at 6 meter (50 MHz) -- and that is available in quantity to be affordable in near future. Why don't you look at some of the Russian surplus tubes? -- some are rated up to microwaves (1 GHz)
You last challenge would be to build a 6-meter amplifier around such a tube -- previous metal fabrication and electrical assembly skill required.
Russian GS-35b by W7IUV
http://w7iuv.com/GS-35B.html
King Conversions for Amateur Radio HF amplifiers
(sorry -- no CB or sweep tubes)
http://www.qroking.com/
K8CU Technical Tips - Russian GS-35b
http://www.realhamradio.com/GS35B_Amp_Page.htm
How About Solid-State ? -- forget the tubes
Chris, G3WOS - 450 watt 6 meter amplifier (July 1993)
http://www.tech-systems-labs.com/pdf-files/6-meter.pdf
w9gb
Any tricks involved or any info appreciated.
What is the correct valves for this amp
Frank -
This amplifier design, like many from the 1960s and early 1970s, used Television Sweep Tubes.
The ARRL, RSGB and Radio Handbooks of 1950s and 1960s -- ALL had these designs -- the tubes were CHEAP and readily available at every local radio/TV or drug store with a vacuum tube tester in USA.
These tubes were designed to work in your vacuum tube TV ~ 15 kHz (that is at upper range of human hearing/audio). Solid-state TVs were introduced in the late 1960s and 1970s -- totally replacing vacuum tube TVs in the major developed countries.
Production of TV sweep tubes STOPPED in early 1980s in Japan, United States and Western Europe.
Only Russia and Eastern Europe continued to manufacture some TV sweep tubes for televisions in these countries.
Today (2010), ONLY the EL509/EL519 sweep tube is produced by a couple of eastern Europe and Russian mfg.
SO, you have a finite supply of old sweep tubes -- following classical Supply and Demand --
the prices on Sweep Tubes have been rising ever since!
Smart guys have made their $$ by stripping the tubes and pitching remaining chassis and parts.
In fact, the current demand for sweep tube amplifiers -- seen on Craiglist, eBay and hamfests are
the $$ guys stripping the sweep tubes for $$ -- like current metal commodity prices (gold, copper, silver, etc.)!
The Varmint XL-250 used these tubes: 6LF6 and 6KV6a.
The reason your unit has NONE -- is that a former owner cut his losses and sold them for $$ -- or --
the tubes were bad, he tossed them and could not find cheap replacements.
So, you have a box of parts -- that's it.
Your NEXT task is to find an RF amplifier tube rated for operations at 6 meter (50 MHz) -- and that is available in quantity to be affordable in near future. Why don't you look at some of the Russian surplus tubes? -- some are rated up to microwaves (1 GHz)
You last challenge would be to build a 6-meter amplifier around such a tube -- previous metal fabrication and electrical assembly skill required.
Russian GS-35b by W7IUV
http://w7iuv.com/GS-35B.html
King Conversions for Amateur Radio HF amplifiers
(sorry -- no CB or sweep tubes)
http://www.qroking.com/
K8CU Technical Tips - Russian GS-35b
http://www.realhamradio.com/GS35B_Amp_Page.htm
How About Solid-State ? -- forget the tubes
Chris, G3WOS - 450 watt 6 meter amplifier (July 1993)
http://www.tech-systems-labs.com/pdf-files/6-meter.pdf
w9gb
VK7DX
09-24-2010, 07:58 AM
Thanks for the valueable info.I was thinking of buying a varmint amp but going
on the info rxed its really only a few usable parts.
cheers,Frank vk7dx
on the info rxed its really only a few usable parts.
cheers,Frank vk7dx
W9GB
09-24-2010, 01:33 PM
I was thinking of buying a Varmint amplifier, but going on the information posted -- it is really only good for a few usable parts.
Frank -
Correct. Sadly, this information has been widely available for past 20 years.
Newcomers to radio (or those returning after a long absense) often forget to perform the necessary product/performance research.
There are hundreds of thousands of 1960's/1970's sweep tube amplifiers on the market -- the ones made for illegal CB usage (Varmint, Palomar, etc.)
are the bottom of usefulness to a radio amateur (no bargain) - due to lack of bandswitching and components for multi-band usage.
When I see an advertisement on any public swapmeet, eBay, craigslist for a 10-meter amplifier (mono-band wonders) --
it has usually been the code word for the pirate, freebander crowd that this is a product for CB usage.
The HF radio amateur would desire a good HF amplfiier that is spectrally clean and
has the ability to operate on at least the 80 meter through 10 meter band allocations.
w9gb
Frank -
Correct. Sadly, this information has been widely available for past 20 years.
Newcomers to radio (or those returning after a long absense) often forget to perform the necessary product/performance research.
There are hundreds of thousands of 1960's/1970's sweep tube amplifiers on the market -- the ones made for illegal CB usage (Varmint, Palomar, etc.)
are the bottom of usefulness to a radio amateur (no bargain) - due to lack of bandswitching and components for multi-band usage.
When I see an advertisement on any public swapmeet, eBay, craigslist for a 10-meter amplifier (mono-band wonders) --
it has usually been the code word for the pirate, freebander crowd that this is a product for CB usage.
The HF radio amateur would desire a good HF amplfiier that is spectrally clean and
has the ability to operate on at least the 80 meter through 10 meter band allocations.
w9gb
