The AM Forum

I built a dual 4-400 linear, running 2500v on the plate. Unfortunately, I only had 110v in the shack, and that is just not enough.  I want to rewire it for 220 since I have the opportunity to get that into the shack now. The question is, what's the best way to go inside the amp?

There are two filament trannys, one for the 4 866 rectifiers (I know, but I like them) and one for the two 4-400s. both of these require 110v input for the correct output.  The plate tranny I can work with  to get the voltage I need, 220 will end up giving me about  3100 out.

The 220 will be supplied by a 4-wire run, 2-110v lines, neutral, and ground.

So the plate tranny goes accross the two 'live' wires for 220, and one (different) phase to neutral for each of the filament transformers?   I also want to put in a 110v bus for future work, like a modulator deck, or do I just keep adding to each leg to keep the load equal?

I just want to keep it safe.

Ed,
     I would put the plate iron primary on both 220 legs, like you said, but........
I would keep all of the 110 stuff on the same leg of the 220 and the neutral leg.
this may create a slightly unbalanced load, but you wont have any differences in potential between stuff running on 110. It will help prevent ground loop problems.

Always put the filament primary power in parallel with the fan motor so you can't light the tubes without air

Although this wouldn't apply to Ed's situation, here is a trick that might be useful to other readers.  One popular rig that comes particularly to mind is the BC-610E.  It requires rewiring the power cord, probably replacing the power switch, and using a 220v outlet even though the rig runs entirely off 110v.

When the voltage sags on just one leg of the 220, it is boosted on the other.  This is due to the voltage drop in the neutral being additive to the opposite leg, which runs 180° out of phase with the loaded side.  For years I have used that to my advantage when running rigs whose plate transformers have 110v primaries only. I wire the HV plate transformers to one leg, and everything else to the opposite side.  That way, when the modulators and final amplifier plate supplies pull the line voltage down, the filament voltage and rf drive are actually boosted slightly, just at the moment when a little extra filament emission and grid drive would be desirable.

If all 3 wires are the same gauge, the boost to the opposite leg should be exactly half the sag voltage, since the total sag in one leg is evenly divided between hot and neutral.

I agree with putting all the 110v stuff, except for the HV plate transformers, on the same leg to reduce the likelihood of ground loops.  Better still, use an isolation transformer.

Some possible options:

• Rewire the filaments to put them in series, and run the filament transformers off the 220 input. For example, two 4-400's in series, and two pairs of 866's, each in series.
  
• Connect the filament transformers across both legs of the 220, with their other leads to ground. Since the neutral only carries the difference current, I don't think you'll have an issue with a ground loop.
  

HTH.

73,

Bill W1AC

I wouldn't recommend doing that.

Modern transmitting tubes are designed to run at a rated voltage,  not current. Running the filaments in series could result in unequal voltage distribution between the two tubes, due to irregularities in the filament characteristics.  Running tubes at other than proper filament voltage will shorten their life.

An ideal transformer would work as described, but it is highly unlikely that a real transformer designed for 110v operation would operate at double the primary voltage to get double the secondary voltage.  The volts-per-turn that the transformer was designed for will be exceeded. Expect the primary to heat up, possibly enough to burn out the transformer, as the core becomes magnetically saturated on each cycle and you no longer have the inductive reactance to limit the current through the winding.  The primary current even with no secondary load will still be excessive, enough to heat up the transformer.

I don't think it would make a rat's arse difference whether the primaries of the two transformers are connected in parallel, across one leg of the 220, or in series with each transformer across one leg, as  long as the common connection between the two transformers in series is connected to neutral to make sure the primary voltages divide out equally.  If the wiring to the 220v outlet is so under-rated that the current to filament transformer primaries would cause a serious unbalance, then that run, and maybe the entire house wiring needs to be replaced with something that meets the electrical code before the house goes up in smoke.

Good Information Guys!  I guess I was assuming that i would need to keep a balanced load, but if I can put all the filament stuff on one leg that will simpler. 

next thought, fusing the 220v primary? Both legs yes? with fuses, If one leg goes, then there is still 110v on the wiring.  How about a dual ganged circuit breaker?

Dual ganged breaker. I use the panel mount ones as an on off switch.
Also at least a fuse on each transformer primary in case one fails.

Hi Ed,

I use a triple-gang/3-pole circuit breaker in the 240 VAC input to my homebrew transmitter. The third gang interlocks the 120 VAC primary of the 2x 4-400A screen supply, so if the plate circuit breaker trips, it immediately pulls down the screen supply, thereby protecting the 4-400A screens, even though the screen supply has it's own overload protection circuit to protect the screens. This breaker is a panel-mount package. And I have tripped it a few times.  

Like Frank, I have a fuse in each leg of the 240 VAC input for unconditional line and load protection as well.

73,

Bruce

Ed,

I'm not so sure about some of the advice given that I just read about your problem.

To do things correctly.  I would run a separate 220V line from your breaker panel through a 2 pole 220V breaker.  Connect it to your plate xfmr.  I would then run a separate 110V line from the panel through a single pole breaker.  No need to worry about keeping the loads balanced if you run from the panel.

I would NOT attempt to get 220V from two separate 110V lines that start from two separate 110V single pole breakers.

I just reread your post.

The best way to do what you want is to run a 3-wire cable (plus ground) from a two-pole 220V breaker.  Red and black wires go to the breaker poles, white wire goes to the neutral and the ground goes to the same neutral (ground) in the breaker panel.

Connect the plate xfmr across the red and black lines (220V)  You can connect the filament xfmrs from either the red and white or black and white (110) lines or put one xfmr on each.  Don't worry about ground loops, not going to happen with filament xfmrs.

DO NOT run the two filament xfmr primaries in series across the red and black (220V) lines WITHOUT using the neutral connected to the center connection point.

Running the two primaries in series without the neutral connection will cause the 220V to divide unequally across the two 110V primaries.

You will need to use a 220V 3-wire (red,black,white) (plus ground) line cord coming out of the amplifier cabinet.  You will also have to look at the on-off switching.  Not sure how it's done in your amp , BUT you will need a two pole switch that disconnects both the red and black lines.  NO need to switch the neutral line.

You may also have to look at the line fuse or fuses.  You will need to fuse both the red and black lines (two fuses).  Or, maybe the amp has a two pole breaker that also acts as the on-off switch.  Not sure what your amplifier has.

These are some of the things you must review to complete the changes correctly.

Hope this helps,

Fred

This phase thing with electricity took a while for me to understand. WE lowly home owners have single phase to our house. So when we are dealing with 220 it is really the OTHER hot wire from the pole pig. Is that considered Phase?
We get two hot wires and the center tap of the pole pig is the neutral.
The green wire is SAFETY ground.

Hooking up an electric hot water heater is just the two hot leads. The center tap (or neutral) not needed to operate.

side note: In the Philippines the voltage there is 220. BUT you only get the two hot leads from the pole pig. The neutral and safety ground is up to you. The utility grounds the neutral from the transformer at the pole. You do not get that center tap connection in your house. Maybe they do this so people do not mis-wire and get 110 vac.
SOOOO we have the old problem in the Phils of getting a little tingle when you touch an appliance and you wear no shoes.
Delivering and connecting AC wiring and volts is interesting to me

Fred

The plan was to use an existing dryer feed line (we moved the dryer) that was a four wire system from the box. Two breakers in the box.  I wasn't really worried about that bit.  It was the stuff inside the power supply that got me wondering.

Ed. Your line voltage is 110/220 and not 120/240 ?   Just curious.


Sam

Good question, I just measured it at 125V at the outlet!!

Then you have 250 volts. The pole pig delivers 250 volts with the winding center tap the third conductor attached to ground in your breaker panel.
When you run the neutral in your rig float it above ground. Only connect the fourth ground lead to chassis. This way all the 125 volt return currents flow through the neutral lead not chassis ground. This way when you hook the rig chassis to your RF ground system there will be no AC current flowing into the RF system. Neutral and safety ground should only meet in the single point connection inside the breaker panel. This way there will be no AC ground loops or voltage offsets between safety ground and RF ground.

It may also be worth your while to measure between the two "hot" conductors at your distribution panel.   125V between neutral and one hot conductor is not a guarantee of 250V between the two hot conductors.


Sam

SCHWEET! ! ! ! ! ! ! ! ! ! !

Look up some amps that will run on both voltages and study some schematics of what has worked.  SB200, SB220, Thunderbolt ect... 

I asked this before and it turned into a big discussion. It seems that everyone has an idea of how to wire up 220 when using 110 loads in the amp.  In the end, I just got very confused.  I had one guy telling me that if i listened to guy number 1, I would be dead from shock and the other guy said that if I listened to guy 2, Then I could burn my house down :(   


SB:

I have an RCA power line monitor plugged into my home wiring.  Its 128v sometimes.  Right now its 123.  I have 10 volt swings on a day to day basis here. Seems normal.

We have of the largest sized homes in one cul D sac and just one 50kW transformer.  I saw it down to 110 a couple times and ran outside to confirm my theory..  ALL four heat pumps where running on all Four homes including mine.

C

That's amazing Clark, (would that be 50kva???) how the power company squeezes all they can out of a pole pig. I read somewhere that is preferred operation for a pole pig to be almost to its limits.
GFZed's post is a very accurate description for connecting your amp.

A lot of us 'borrow' the dryer connection for 220/240. The thought is that Ham radio operations and the dryer won't be used at the same time.

Fred

Keep the neutral away from chassis gnd as Frank said. Older ham gear does NOT do this.

Neutral and ground only get connected together in the main panel in the house.

Yes it's only one phase Phredd Phirst.

I'm also on a 50 KVA pig. We usually sit at 125 to 126 volts. Sometimes in the summer it will drop to 118. It is down the street 1 pole but feeds this place just fine.

four, 4bedroom homes on that one 50 or just your house? Right now its 118 on mine. People must be still running the heat pumps.  ITs only 49 outside..  I have 304Tls to keep me warm.

Hello All!

     when it comes to "messin'" with filiment voltages, just remember that 4-1000's don't grow on trees!

Tnx,

I have 7 in the closet and dont even own own a 4-1000 rig.. :)

C

Actually they do. Good used pulls from broadcast rigs and "shaker tables" make them one of the cheapest horsepower per dollar tubes out there. I have never paid more than $25 for any of my spares. No one wants them other than hard core home brewers.

Now the sockets and chimbleys are another story.......................................