80 watts amplifier

[lorenzo44]

link for this

http://sbpcb.blogspot.com/2012/10/pa-vhf-80-watt.html

[XXL]

shit design. looks like 80s or 90s. im sure albert will claim it as his. Get one of the new mrf101 amps from enigma. 100w+ and dont blow if antenna is unplugged or high swr.

[teckniqs]

That thing looks more like it's for 12 to 15v.

[Albert H]

XXL obviously can test the specification of an amplifier just by looking at a picture. Smart guy.

This PA is from Solo in Jakarta, and dates from about 1986. For their day, they were damn good. I visited the "Pemancar" shop on a number of occasions when I was working down there. As I recall, they used to drive them with their 5 Watt '1971 driver board for around 80 Watts out at 13V supply.

In those days, radio in Indonesia was a bit of a free-for-all, with many towns just putting up their own local station, usually staffed by volunteers. Most of these stations ran ~100 Watts and were usually stereo.

[XXL]

XXL obviously can test the specification of an amplifier just by looking at a picture. Smart guy.

This PA is from Solo in Jakarta, and dates from about 1986. For their day, they were damn good. I visited the "Pemancar" shop on a number of occasions when I was working down there. As I recall, they used to drive them with their 5 Watt '1971 driver board for around 80 Watts out at 13V supply.

In those days, radio in Indonesia was a bit of a free-for-all, with many towns just putting up their own local station, usually staffed by volunteers. Most of these stations ran ~100 Watts and were usually stereo.

I don’t need to test the specifications. Why would you want to use this outdated, obsolete board with obsolete parts to make only 80w of power when there is simpler, more cost effective methods of achieving this and more. Yes I’m sure in it’s day it was very useful, but totally pointless to build now.

[Albert H]

There are a lot of these boards around. The Indonesians made them by the boatload - they were really cheap, and gave a lot of bang for the buck.

Today, I wouldn't consider using anything other than a modern FET - more robust, higher gain, cheaper - but if I found that I had a boxful of C2694 transistors (which isn't impossible!), I might press them into use for the occasional naughty PA stage. Funnily enough, I recently found a strip of MRF317s (another old device), and did a nice PCB for around 120 Watts broadband. Most professional designers like to use the most modern, most efficient components, but often pirates are constrained by the parts that are easily and cheaply available. You have to remember that putting a rig up a block is (effectively) throwing it away!

The pragmatist in me will design using the cheapest available parts. I used to use lots of 28V aircraft VHF transistors in my rigs (the '3866, '3375, 587BLY PA was mine). The PAs cost next to nothing to build (trimmers were cheap in those days), and gave (typically) 90 Watts out for 100mW drive. They weren't the most efficient - three stages for 28ish dB of gain - but they were really cheap. The three transistors together cost <£2.50, and the trimmers added £1.20. The heatsink used to cost the most! Using a cheap (bulk bought) toroidal transformer, and a folded (homebrew) aluminium box, the rigs cost <£25 to build in the early '80s. At that cost price, you could afford to "lose" three or four rigs each weekend! That's how some stations always seemed to be on, whilst others - who relied on bought-in gear - were often off the air for weeks at a time!

[nrgkits.nz]

Losing three or four rigs each weekend, probably to Eric Gotts. You could also do away with the heat sink and bolt the rig to the underside of a cold water tank, then the cost would come down even more, along with bucket loads of water once Gotts and his pals discovered it.

[Albert H]

Losing three or four rigs each weekend, probably to Eric Gotts. You could also do away with the heat sink and bolt the rig to the underside of a cold water tank, then the cost would come down even more, along with bucket loads of water once Gotts and his pals discovered it.

That happened up a block in Shepherds Bush - as well you know!

One station I built some gear for used sub-audio tones to activate their rigs - various very low frequency tones (too low to get through the rig modulator), detected with NE567 tone decoder ICs. They would have as many as eight rigs set up around South London, and they had a Band IV Yagi on their studio roof. To start with, as Gotts took a rig off, they'd turn the aerial, switch the sub-audio control tone, and the next rig would come on - usually within about 20 seconds!

The "Men from the Ministry" - Gotts and his cohort - got really annoyed, because they were playing "Whack-A-Mole" all over South London. When the station got handheld radios (Icom IC2Es!), they'd put lookouts at their output sites, and would switch sites when Gotts was spotted nearby. This saved them quite a few rigs!

The listeners seemed to get used to the short "Technical Breaks" as they switched sites. They used all sorts of subterfuge to conceal their installations, often with bricked-in gear, or gear in Dry Risers or even Fire Hydrant boxes! They used J-poles and Groundplane Aerials on top of communal aerial masts, with ordinary Band IV TV Yagis for link reception. Most of their rigs were 90 - 200 Watts, and they often broadcast in stereo.

The same methods were used a few years later in Belgrade, with B92, but the penalties in that instance were many times more severe.....

[Bton-FM]

Losing three or four rigs each weekend, probably to Eric Gotts. You could also do away with the heat sink and bolt the rig to the underside of a cold water tank, then the cost would come down even more, along with bucket loads of water once Gotts and his pals discovered it.

That happened up a block in Shepherds Bush - as well you know!

One station I built some gear for used sub-audio tones to activate their rigs - various very low frequency tones (too low to get through the rig modulator), detected with NE567 tone decoder ICs. They would have as many as eight rigs set up around South London, and they had a Band IV Yagi on their studio roof. To start with, as Gotts took a rig off, they'd turn the aerial, switch the sub-audio control tone, and the next rig would come on - usually within about 20 seconds!

The "Men from the Ministry" - Gotts and his cohort - got really annoyed, because they were playing "Whack-A-Mole" all over South London. When the station got handheld radios (Icom IC2Es!), they'd put lookouts at their output sites, and would switch sites when Gotts was spotted nearby. This saved them quite a few rigs!

The listeners seemed to get used to the short "Technical Breaks" as they switched sites. They used all sorts of subterfuge to conceal their installations, often with bricked-in gear, or gear in Dry Risers or even Fire Hydrant boxes! They used J-poles and Groundplane Aerials on top of communal aerial masts, with ordinary Band IV TV Yagis for link reception. Most of their rigs were 90 - 200 Watts, and they often broadcast in stereo.

The same methods were used a few years later in Belgrade, with B92, but the penalties in that instance were many times more severe.....

After reading ‘they had eight rigs setup around London’ I immediately thought DTI whack-O-Mole but you beat me to it!