The AM Forum

Wow.  Is this guy pushing these 813's or what?  I assume this is a pirate station somewhere.  4 813s not even showing color

http://www.youtube.com/watch?v=_qmC7s_jBfA

Anybody know anything about this?

I'm not so sure about the construction style...

What were the CX1500s being used for? Meter showed monkey swing but kind of a backwards tube lineup.

I believe the Cx1500 were the modulators; the 4 x 813's were the class C final.  I'm guessing that was fairly low frequency judging from the tank coil. 

Cool to me as it's the ultimate JSing of one of my favorite tubes.  And it seems those 813 are holding up with 4300 volts - what a tube

Al

Gives in the description that it's for 1620 to 1830 khz. Says later in the comments that it will do a minimum of 200 watts and a maximum of 3000 watts, wow.

I'm impressed  :o

I've heard that the 813 can handle 4kV without flinching.  I think K1JJ has pushed them that hard or harder with air flow. This guy has no air flow.

I would be scared to be anywhere near all that open wire and chassis. His neighbors must have fun with 3kw to an end fed antenna
Fred

That 813 setup is from Greece where apparently  the government doesn't care who broadcasts below about 1000 kc. There was a thread on here some time back where an operator was trying to use a large solid state amplifier as a modulator, driving a large transformer driven at 8 ohms to match a high powered final tube amp. I think I read somewhere that 813's are not to show color when operating? 

Yeah, I would think with the graphite plate showing color means they're being piss beat. I would think it would take a heck of a lot to get that type of plate to glow.

A little blushing?  Generally speaking you are right but my first push pull 2X 813's on RTTY would show a slight but of blushing with no apparent ill effects. 

However, on AM service we must be mindful that not only are we running the tubes near or past maximum recommended power level, but we also are applying quite a bit more peak voltage.  With say, 125 % positive peaks (given, say 2500 volts @ 320 ma  = 800 watts input) that works out to be ≈ 5600 volts on modulation peaks.  So, that's what's going on inside the beastie. 

Tough tube. But the amazing part of that video is the those beasties were tolerating the plate voltage plus the modulation peaks. 

Short answer, yeah, avoid the blush - it's not worth the extra tenths of a dB you would get from pushing them.

Al

Hi Al, I'll bet those tubes scream with an IR camera!! Do you have one? Does anyone have one and would post pics with it? 

Hi Terry.  Missed you at the New Yawk visit.  Had lots of fun but missed the little french girl at Mo Joe's   :(

I wish I had one of those IR cameras.  We have 'em at work but unfortunately, I lost that benefit when I retired

Al

I think 4KV is the 813 linear amp high limit.  More than that and they will dissipate too much at idle. (And still be linear)

I've run 3KV, plate modulated, at 150% modulation.  A pair will put out 800 watts carrier at that level.

I used  lantern chimneys with a lot of air.  The limitation is not the voltage, but the amount of power dissipated.  When run at 3KV plate modulated, they seem to be near their "red plate glow" limit when heavily modulated, so adding more plate voltage would put them on the hairy edge. Sure we can PB them, but seal failure is usually the biggest risk.

They are supposedly a 125 watt tube without air. I would rate them close to 250 watts with a chimney and good breeze.   Really an outstanding tube.   It is my second favorite glass power tube next to the 4-1000A.

T

I worked in Engineeering at a company big into LED lighting--I couldn't see the IR LEDs but the camera in my cel phone could!

At the risk of displaying my ignorance, could someone explain the acronym "JS" I see used on this board?

Thanks and 73,
Brian KA9EGW at britewerkz dot com

 ;D ;D

Gladly...  JS stands for "jockstrap."  It's from the mid to late 1960s teenage AM crowd in New England.... possibly originated by Tim/HLR.  

There are rigs that are built in a JS fashion and there are JS artists.   When someone throws a project together (haywire) without much regard for neatness, durability or simply professional techniques or design, it could be called JS. Using under-rated components might also be considered JS. In the beginning we were all JSers.

Some are proud of their ability to JS something together and keep it working. Others gag when they see it. All depends on your tastes, I guess.

T

Bob, W1RKW, I just noticed your signature. The Day The Earth Stood Still (the original 1951 version) is my favorite Si-Fy movie ever! I watch it at least a couple of times a year. I'm surprised I don't know every line Klaatu speaks by heart yet.

My favorite line is:
"It is no concern of ours how you choose to run your own planet, but if you threaten to extend your violence this earth of yours will be reduced to a burned out cinder."

Why I don't know, I guess it just speaks of mankind and how we react to most things with violence.

cya