General FX400 conversion

[uki]

...
50V/.045= 1111R

.045 * 50V = 2.25 W
...

Do you mean 250v instead of 50v ?
Where is the 50 from ? 

Thanks

[AlNewman]

Don't you want to drop 50ish volts?  From 300-250?

[shooter]

A+ 311v at node, 300v at Pin5 PAB+ 242v at node; after the screen R, 240v at Pin6 PA

my idea was to USE TAB B as the PA AND the screen, the 470 to "limit" current at G2


TAP A isn't used.

[uki]

my idea was to USE TAB B as the PA AND the screen, the 470 to "limit" current at G2

I did it but voltage was dropping to 160v ish. and AB R was going really hot.

[shooter]

I did it but voltage was dropping to 160v ish.

 
change the dropping resistor from 8.5K to something like 500 ohms then try
(use gator clips! you'll be tweaking a couple times to "get it right")

[uki]

I did put a 2.2k/5w resistor between rectifier and A, now the A does read 260v and plate voltage right at 250v !!!
now just have to adjust B,  it went down to 235v ish,

Don't you want to drop 50ish volts?  From 300-250?

Oh yeah thanks !!   



now a side thing, filter caps are draining rather fast after turn off , no bleed resistor, new ones 22uF/400v  any thoughts ?

Thanks

[sluckey]

now a side thing, filter caps are draining rather fast after turn off , no bleed resistor, new ones 22uF/400v  any thoughts ?

WAG... Maybe the cathode of the 6AQ5 stays hot enough to keep the tube conducting for a short time after the power is turned off. That would drain the filter caps quickly.

[uki]

WAG...

What WAG mean ?   

[Maybe the cathode of the 6AQ5 stays hot enough to keep the tube conducting for a short time after the power is turned off. That would drain the filter caps quickly.

Well the PA tube does go really hot in temperature!

I think i got the amp tuned with conservative voltages!
 It does sounds good, smooth tone,
volume wise it is warm at 5-6 driving at about between 7-8

check it out the voltages:

after rectifier 318v

A+ 247v
B+ 230v
C+ 205v

V1 p1 0v
     p2 0.866v
     p7 84.5v

V2 p1 0v
     p2 1.3v
     p3 158v

V3 p1 0v
     p2 2.5v
     p7 189v

PA-V4
    p1 0v
    p2 14.6v     cathode resistor 474ohms
    p5 237v
    p6 229v

Does this sounds right? Any suggestion or advise ?

Thanks !!

[sluckey]

WAG means Wild Ass Guess. It really wasn't such a wild guess but it's the first time I've used that logic on this forum.

I worked on an ARSR radar transmitter for forty years. The transmitter tube ran the filament current at 50A while in standby. As soon as the transmitter was energized a big motor driven variac would slowly bring the high voltage up. As soon as the transmitter tube was drawing 50mA, the filament circuit was shut down. No need to keep baking the cathode because the cathode current was enough to keep boiling electrons. My WAG was partially based on this transmitter tube that didn't even need a hot filament to keep operating.

[uki]

filament current at 50A while in standby

WOW   

Now that you mention it the heaters are running at 6.7 i think, something close to that, i did a reading there after a re-solder cos of a bad contact. There was one more tube in the original circuit, with no load the heater read 7v. So probably with that 6th tube the heater would be closer to the 6.3v, maybe that is the reason PA tube is running so hot ?

[shooter]

WOW

Steve worked on the big-boy Radars, the one I worked on, my PA probably wouldn't be big enough to drive his PA

reason PA tube is running so hot ?

those tubes run finger-blister hot, ask me how I know


the math says you're around 7w dissipation so it's cool, just don't touch the tube to prove it

[sluckey]

Yeah, that ARSR-2 had a 5MW amplitron for the output tube. The driver was a 500KW magnatron.

[uki]

Here!!

[shooter]

driver was a 500KW magnatron.

 
that's hair-on-fire kinda power!


were they CW?


most of the TX stuff I worked on was pulsed-power, 25Kw was as far as I ever got, or ever wanted to.  I'd walk into the 5MW shack and I could feel my electrons aligning   

[sluckey]

were they CW?

No. Pulsed. 2µS pulse width and 360 PRF. The 5MW output power was only about 3.6KW average power.

[shooter]

 
only 4KW


the "beam" was a 5KW CW klystron PA, everything else i've worked on Radars, MRI's, have been pulsed. 


whenever I went up to the 5MW search radar, i did "sense" something, was weird, almost like walking up to a 3Tesla magnet.
sorta like the rock song "Can you smell that smell..."  it was like "can you feel that force"  only met one other tech, military or civilian that "thought something is different now"


good times!
thanks

[sluckey]

Oh they definitely have a feel in the air and 360 pulses per second has a definite sound! Our radar was also used by the USAF so we would get a yearly inspection. The eval team had id badges that had a neon bulb built in. It would light up whenever they got in a danger zone.

Sorry for the derail uki.

[uki]

Sorry for the derail uki.

It is all good im enjoying it !!     The amp is almost done anyway, I may tweak the PS a lil bit more, working on the case/box now.

What is:   2µS  ?

[shooter]

micro second, 1/1000th of a second 
in order to "exceed" manufacturer's suggested operating conditions you only turn "on" the PA for a real short time

[sluckey]

What is:   2µS  ?

It's a very, very short time... 2 microseconds

When the transmitter fires that 2µS pulse out the antenna, it only takes 12.36µS for that pulse to travel 1 mile, strike an airplane, and return to the antenna and receiver. IOW, 12.36µS equals one radar mile. 12.36 is a number that is ingrained into every radar technician's soul. It's all about time.

[sluckey]

micro second, 1/1000th of a second 

One microsecond is 1/1,000,000 of a second.

[shooter]

 
been wood cutting, splitting, stacking, math isn't getting though today

[sluckey]

working on the case/box now.

That's a lotta stuff in that small box. I like unusual projects like this. What was originally in that box?

[uki]

working on the case/box now.

That's a lotta stuff in that small box. I like unusual projects like this. What was originally in that box?

It was a reel-to-reel recorder.  Pics on 1st post.

It had a lot more stuff stuck inside, i got rid of the reel machine, it was really heavy, now its like 1/3 of the weight.
About 90% done , still need some nice panel, actually two, ill add one for the controls and another bellow above the PT and speaker for the power switch, fuse hold, and pilot light. Also a finishing for the baffle, looks sloppy.
Its operational and going for a gig tomorrow !!! 

Got pics !