Linear Amp Behaviour

[KD6VXI]

Not as built but with the 3CPX tubes and a 3500V PS its possible to get close.

Carl

Thanks Carl.

At that power level, 6800 can be interpreted as 75.....  10 percent.


--Shane

[KM1H]

I dont expect long life at those levels, at 3000-3200 they stand a chance as long as they stay cool.

I had one on 75 a few months ago on AM....for testing purposes ya know Anode temp stayed well under redline

[KD6VXI]

I dont expect long life at those levels, at 3000-3200 they stand a chance as long as they stay cool.

I had one on 75 a few months ago on AM....for testing purposes ya know Anode temp stayed well under redline

I can't remember where, but I did read an email put forth by an ex Engineer for Harris Comms, where he had stated the 3CX800 was a Harris tube (built by Eimac spec'ed by Harris".  The ratings, as most commonly know, where dropped.  There are two common data sheets floating around, and a third that I've seen, but do not have a copy of.  The third was Harris marketing...  We all know inflations on marketing materials, BUT, usually Mil-Spec isn't inflated NEARLY like consumer equipment.

I think most hams also realize that if they want something that will last forever at a given power level, that same amp better be able to do near or better than twice Pout desired.  As you stated, 3500 isn't that bad of expected Pout.  I know people that run them regularly at 5Kw.  Much more than 5, and you start having issues with parts being run at the ragged edge. 

Doesn't change the fact that you can pull 6500 to 7Kw out of a trifecta of them, if you have the correct power supply.  Stan's uses an outboard Dahl, 3700 volts (give or take) unloaded, 3500 key down.  Xformer is capable of 5 amps CCS.

Anywho.  Internet's back   Antenna is now a screwdriver on the eves...  BIG difference from a full size ladder line fed dipole!

--Shane
KD6VXI

[Ed/KB1HYS]

What is "Good" voltage regulation for a linear amp?  10% more? less?  I CAN get 3300 volts on here, but it will drop to about 2800 under load. I thought that was poorly regulated so I went with a lower voltage option to get something that didn't show as much swing.  Looks like I should have just kept the original lash up. 

[KM1H]

Commercial ham amps run in the 7-12% range, and a bit more with older ones with less output C.

I wouldnt worry about key down regulation as the filter C will provide energy on SSB and even a bit on CW.
Regulation on old iron with a high DC wiring resistance is poor with a C only filter unless it is bled into submission. For those a choke input is better and regulation can be close to 5% with a key down DC output approaching 90% of the AC.

Shane, I have the original 3CX800A7 spec sheet which uses 2500V, and sneaks in a 800ma SSB single tone rating under "typical" but uses 600ma under absolute maximum. Charley didnt appreciate that Ive been told. 
Ive yet to see any 800 that wont load to beyond 800ma, even at 2200V,  while keeping all other parameters in the black. All show 3500V max for pulse. When the first LK-800A's were built they ran at 2200V or so and then Eimac blessed 2800V for SSB for the first custom models and then Denny went to 3100V with some of the 3CPX versions which was pushing the limit of the 7  450V caps in the PS. Ive gone to 8 caps in most and 9 with 3500V key down and 3CPX's. All I know is it buries a 5KW slug.
The 3CPX has a 4500V maximum in pulse service with a 8A peak BUT at a .005% duty cycle as does the 3CX at 3500V. The only difference is an extended ceramic barrier internally to allow the higher voltage.

Carl

[Ed/KB1HYS]

I'm running a 866 Full wave Bridge config into a Choke input filter. 

[WA1GFZ]

Yea, but why beat the livin crap out of a tube when it can last a lifetime if treated well.
If you want big power build a big rig that can handle it.

[KD6VXI]

Yea, but why beat the livin crap out of a tube when it can last a lifetime if treated well.
If you want big power build a big rig that can handle it.

That's kinda what I was getting at, with saying if you want an amplifier that can comfortably put out 3500 watts, it should be able to PEP at 6.5 to 7 grand output.

I didn't advocate that the amp should be run at 7 thousand.  I said his can do it.  The 800 is a 1200 watt tube, run sanely.

--Shane
KD6VXI

[KD6VXI]

Commercial ham amps run in the 7-12% range, and a bit more with older ones with less output C.

I wouldnt worry about key down regulation as the filter C will provide energy on SSB and even a bit on CW.
Regulation on old iron with a high DC wiring resistance is poor with a C only filter unless it is bled into submission. For those a choke input is better and regulation can be close to 5% with a key down DC output approaching 90% of the AC.

Shane, I have the original 3CX800A7 spec sheet which uses 2500V, and sneaks in a 800ma SSB single tone rating under "typical" but uses 600ma under absolute maximum. Charley didnt appreciate that Ive been told. 
Ive yet to see any 800 that wont load to beyond 800ma, even at 2200V,  while keeping all other parameters in the black. All show 3500V max for pulse. When the first LK-800A's were built they ran at 2200V or so and then Eimac blessed 2800V for SSB for the first custom models and then Denny went to 3100V with some of the 3CPX versions which was pushing the limit of the 7  450V caps in the PS. Ive gone to 8 caps in most and 9 with 3500V key down and 3CPX's. All I know is it buries a 5KW slug.
The 3CPX has a 4500V maximum in pulse service with a 8A peak BUT at a .005% duty cycle as does the 3CX at 3500V. The only difference is an extended ceramic barrier internally to allow the higher voltage.

Carl

IMHO, the CPX version pulse rated V(anode) can be used on all the 'pulse rated" tubes.

At 3300 volts, at .8 amps....    That's 2600 input.  Times three....  Well, all of a sudden 6500 -7 grand PEP out doesn't seem ALL that out of reason.

RIP Peter Dahl.


--Shane
KD6VXI

[KM1H]

IMHO, the CPX version pulse rated V(anode) can be used on all the 'pulse rated" tubes.

At 3300 volts, at .8 amps....    That's 2600 input.  Times three....  Well, all of a sudden 6500 -7 grand PEP out doesn't seem ALL that out of reason.

Thats only 7800 INPUT, figure 5100 or so out on a GOOD day, more likely 4800. That should be fine for SSB without stressing the Pd as long as some good airflow is maintained for a few minutes after the last yakking and before powering off. That anode really holds the heat.

[KD6VXI]

I'm talking 6.5 to 7 grand PEP.  The meters don't read peak A, Carl.


IE, the SB220 doesn't read 2800 volts at .75 amps during normal SSB, does it?  BUT, it will do 12-1400 watts PEP out, depending on band.

We can argue semantics all day long.  It's like Rich and his 68 lb xformer in a 14 kilowatt amp.  I'm agreeing with you, the amp IS a 3.5 to 5 kw pep output amp.  It WILL do 6500-7000 PEP.  Seen it.  Don't recommend it.


--Shane
KD6VXI

[K1JJ]

Yea, but why beat the livin crap out of a tube when it can last a lifetime if treated well.
If you want big power build a big rig that can handle it.

Yes!  And the biggest reason (at least to me) for running the amp way below its ratings is to achieve a super clean output. It's amazing how dirty the side products come up as we close in on maximum power output.  As Jay says, for every 3db in power reduction, the linear amplifier cleans up 9db in 3rd IMD. Now that's a lot and well worth the reason to build around a BIG tube and run it way cool.

T

[Opcom]

darn tootin'. Rather than sell hams an amp with decent overhead, the powers that be prefer to restrict the models for sale leaving hams to push the amp and make rotten signals with it. So to build.

[W3SLK]

That's because the manufacturers can get away with 'truth in advertising'.

[WA1GFZ]

A crap generator is not a linear amplifier

[KM1H]

I'm talking 6.5 to 7 grand PEP.  The meters don't read peak A, Carl.

PEP is a laugh to sell product Shane. Real power is the dead carrier and never mind the minimal intelligence in a few voice peaks, its still the average that counts.

Now if you build a PS like Jim, VE7DX,  with strings of 6800 or 10K uF caps then you can bring the average way up but the 3CX800's will be seriously hurting so now you need a 3x6.