Building linear amplifier prototypes

We know way too little about this subject but hopefully [Bob4analog] helped us learn a little bit more this time around. He’s building his own linear amplifiers on what looks like sheets of MDF. This is an evolving design and the two videos after the break show two different iterations. He’s salvaged several components, like transformers from microwaves, as well as built his own components like the plate choke to the right of the tubes in the image above. In standby, the amp sits at 2800 volts, warming the filament before the unit is switched on.

So what’s he got planned for this? Good question, but it appears that there’s more than enough power to drive a long-range transmitter.

First iteration: two tubes

Second iteration: single tube

[via Make]

Comments

  1. datacop says:

    I’m sorry, but 80m (3.5-3.8Mhz) is not even anywhere near microwave (>=1GHz)

  2. js says:

    @datacop

    No one said it was. It said he used transformers from microwaves.

  3. lwatcdr says:

    I can not wait to see him hook this up to a half wave dipole. Or better a Yagi!

  4. HackerK says:

    I bet he doesn’t have a cat in his shed… ;)

  5. fdawg4l says:

    Wow. Respect. “Dangerous as hell” doesn’t even begin to describe it with that much idle potential.

    Never understand shortwave ppl, but good grief their toys look cool.

  6. Bill says:

    Did I also see a Kenwood TS-820? Great hybrid radio.
    The microwave transformer provides plenty of voltage and can stand on it’s own as far as current pull goes with 572’s.

  7. seanfalloy says:

    this makes me wish i took telecomm instead of computer control at school. Very impressive work even though i only understood half of what was going on

  8. twan says:

    Tube amps are really pretty simple devices, note that the 2800 Volts is not used to warm the filaments, that is done by the six volts from the rewired microwave transformer.
    The current throught the tube is modulated by the input voltage, and is in the range of about 100..200 milliamps (at 2800 Volts). The tube is in series with a output transformer which transforms the high voltage/low current signal to a more suitable voltage/current combination.

  9. Fred Cousins says:

    I think a lot electronic enthusiasts outside of the radio world fail to understand that the vacuum tube still has an important role in amplification of RF (radio frequency) at very high power levels for radio transmitters. In this case the creator of this video decided to “roll his own” instead of pay $ 1000.00 or more for a commercial unit. What is commendable is that he rewound inexpensive MOT (Microwave Oven Transformers)for the power supply – most transformers designed for RF amplifier use are very expensive to purchase. And this HAM radio operator used ingenuity. Please be aware that MOTS are half wave transformers with very little current limitation, the shock they provide is not nasty, but VERY LETHAL.

  10. gyro_john says:

    Now THAT is in the finest tradition of electronic hackery. Very inspiring! FB,KD5MHQ es 73 de John, VE5BEW.

  11. Salamander says:

    @ Fred Cousins, I semi agree with you on your statement about the vacuum tube, however high power solid state amplifiers are more common these days than vacuum tubes.

    Don’t get me wrong, there are still vacuum tubes around, however not many/any companies will buy vacuum tube radio transmitters as they are too difficult to replace parts on, and too difficult to maintain.

    Still very much enjoy the hack, always love to see amateur radio hacks!!

  12. Frist let me say “yes linears are simple rf amplifiers” and that’s has simple as simple can go as far as what’s really happening. First the guy that said the filments is only running 6 volts usually is 5 to 5.5 but current wise it’s 20 amp and above. Now the plate can be anywhere between 1200vdc at 1 amp+ to 4500vdc at 1 tp 2.5 amps and alot of that depends on the match with the antenna system, by the way a bad mismatch at this point can cost alot in tubes like $550.00 ea with a bad mismatch and rf current making a u turn at at he antenna taking out the rf deck also blowing the final matching tuner and we havn’t even staarted talking about the possibility of fire to you and your little brother and family and yoir radio itself as well as a house fire. So please don’t take them for granted and this guys seem professional enough and it has a good lay out also. so 73 from Gregory Ellis goodmorning an goodnight from KJ4AYH PS Please becarful with these toys!!!!

    • ThatGuy says:

      The 572B’s are like under 50eur if you know where to look and russians sell those on ebay for 80bucks too. And tubes are quite rugged, one can actually manage to avoid disaster by reacting quickly enough. None of the surprise cratering like with transistors.

  13. hope I didn’t make anybody mad just telling it like I read it and the amps I;ve built myself…his just seemed a little, better organized that mine was, which was a good changed. Please give me some feed back on the use of the MOT for transformer replacement for the more expensive one that is called for…and I mean alot more expensive like $525.00+ When I can usually take a 1100-1300 watt industrial or resturant microwave buy it used for $30.00 to$50.OO dollars if the problem wasn;t the transformer in the first place and I;ve got my transformer and high current dioide also..by for now from gregory KJK4AYH

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

Follow

Get every new post delivered to your Inbox.

Join 93,826 other followers