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[sndtubes]

I have this really cool 4X1000 homebrew xmtr.  It has everything except the plate supply.  I have a 3000 volt 600 mA power supply on hand.  Do you all think this will be adequate or will I need more like 5000 volts?  It covers 75 thru 6 meters but I plan on adding 160.  The modulator is 2 x 3-500z.  They have their own plate supply

[w4bfs]

start with the mod xfmr and the two hv ps .... do a little rev engrng and figure how he meant to run it .... of course, if there is documentation so much the better ...its a start

[kb3ouk]

3000 volts will definitely work with the 4-1000, the only problem is that it's gonna take the whole 600ma that the power supply can put out, 1400 watts out with 1800 watts input. So the bigger question is, will the iron in the 3kv supply stand up to putting out max current?

[VE3AJM]

3000 volts will definitely work with the 4-1000, the only problem is that it's gonna take the whole 600ma that the power supply can put out, 1400 watts out with 1800 watts input. So the bigger question is, will the iron in the 3kv supply stand up to putting out max current?

In class C plate modulated service, that power input level would be almost double what the old AM power criteria was back in the day down there when it was 1000 watts DC input. It is 1500 watts PEP output now, however one wants to interpret/measure that? So.. 1400 watts carrier output...cool...and you'll be running at least 100% modulation. So it begs another question for one to consider, don't you think? I'm just saying.

I'm sure you can throttle back the amount of plate current that the final will draw running the rig into an antenna.
It very good to have a lot of extra headroom for the final though.

Al VE3AJM

[kb3ouk]

Well, I wasn't suggesting to run it like that, it's just capable of putting out that much power.   

[KK4YY]

Well, I wasn't suggesting to run it like that, it's just capable of putting out that much power.   

Clarke's Second Law not withstanding 'eh?

[W3RSW]

Or was thar Asimov's? 

..From Clark orbit?

[sndtubes]

I wasn't really planning to use that 3000 volt supply for anything other than testing.  I have a 5kv transformer and some big caps.  This is a really well built transmitter but I have very little documentation.  It kind of scares me to tell the truth.  If I get it going I may need some assistance adding 160.  I also plan to use it as a cw and ssb amplifier

[kb3ouk]

How is your bias and screen voltages supplied? Separate supplies or grid-leak/dropping resistor? If it uses a single supply, then for SSB/CW use you're gonna want separate screen and bias supplies (bias will have to be adjustable too), unless you have some plan to switch it to grounded grid when you want to run it as a CW/SSB amp.

[Opcom]

I also have one with the same tubes so I could share some info and opinions.

I prefer to operate about 3KV/200mA @ carrier plus the mod plate current meter shows about 500mA on peaks for the modulators - it's very comfortable and the modulator does not have to work as hard.

4-1000 Bias is -200V, screen is run at 400-500V. Both are heavily bled separate supplies on panel mounted variacs as is the 0-25v 1.5A heavily bled bias supply for the 3-500Zs (they take a lot of grid current so that bleeder is 500mA). Does the TX have well built supplies for these things? If you run 3KV to the 3-500Z's, some bias is needed or they will run orange@ 100mA each with no signal.

I usually tweek the carrier output power with the screen voltage and run 35mA grid drive and 60-100mA screen current, depending a lot on output loading etc. Output easily reaches legal limit with this setup without stressing anything.

The screen self-modulates pretty well dropping the voltage of maybe 600-700V through a 2k resistor (500V G2 volts measured here) then an 8H choke. It could be better and there are lots of different ways to do it but it's OK. I tried a 40H choke with and without the resistor and it didn't improve things enough to worry about but actually overmodulated the screen. The TX is running DC through the modulation transformer secondary. It was not intended for that and it reduces performance and fidelity. So, does your TX have a modulation choke already?

I get great signal and clarity reports with it from people that are critical and won't lie to make me feel good. Therefore I'm happy with it despite the faults.

So, my opinion is that you should try the 3KV/600mA supply and see if it is enough, if it stays reasonably well regulated.

A 5KV-based supply (do you mean on each side of CT, or to a bridge, or  DC value?) might overstress things like the modulator iron. If it's 60 years old, like mine from the 1940's, then for sure I know it is from a transmitter that ran 3300VDC on 833's. Putting 5KV on that is asking to buy a new one. It's important to respect the voltage ratings on the modulation transformer.

3-500Z's can run on 3KV all day with a little bias. 5KV is pushing them.

The power supply conflict built-in to that transmitter (and mine) is that the 4-1000 likes a bare minimum of 2500V, prefers 3000-4000V. The 3-500Z's like 2000-3000V. Split the difference. 3KV may be perfect.

On the other hand if you want to push it to 1200W or more carrier, you can do it with 3KV but need 1A to peak of 1.5A.