Swinging Choke

[W7SOE]

I have not obtained a proper smoothing choke for my 813 rig yet.

I know the differences, advantages, and disadvantages of the swinging chokes have been discussed to death. 

Simple question, could I replace the 10 Hy choke in the K1JJ maul PS with a 5-25 Hy swinging choke?

Thanks

Rich
 

[KE6DF]

My thinking is that if you are going to have only one choke in a power supply it can either be a swinger or a smoothing choke.

Generally swingers are used in choke input configurations. If cap input, a smoothing choke is a better choice.

Normally a swinging choke is used as the first choke (closest to the rectifier) in a two stage filter with the second choke being a smoothing choke.

[KM1H]

With enough C after the swinger you will have no ripple problem and it will improve regulation. Big caps werent available when chokes ruled the earth.

Carl

[W2VW]

How about low resistance xfmr secondaries? Was the mfg process and/or core material problematic?

Signed,
A few years younger.

With enough C after the swinger you will have no ripple problem and it will improve regulation. Big caps werent available when chokes ruled the earth.

Carl

[KM1H]

Old tech CT transformers had higher resistance secondaries than what is used in modern amps. As long as the choke has the minimum L plus a bit as required from the HB formula or graph it doesnt matter what C is after it. Of course a bleeder is required which is also part of the formula.

[k4kyv]

As long as the choke has the minimum L plus a bit as required from the HB formula or graph it doesnt matter what C is after it. Of course a bleeder is required which is also part of the formula.

That used to be the accepted way of thinking.  But the C does make a difference - in dynamic regulation. The meters may show good regulation with low C, but put a scope or LED meter in the circuit to measure the instantaneous voltage, and you will see that the voltage hops all over the place with a varying load, such as with a class B modulator, slopbucket linear or class C CW final.  The mechanical movement in the meters has too much inertia to respond to the instantaneous peaks and valleys.

I have found that running a voltage in the vicinity of 2000-2500v and current peaking 500 ma or so, 25 mfd is a good compromise.  Low C, from 1 to 8 mfd, results in poor dynamic regulation.  Using much more than 25 requires step-start to avoid blowing fuses charging the capacitors when plate voltage is applied, although the more capacitance the better the dynamic regulation.  25 doesn't  give perfect regulation, but it usually doesn't require step start.

Poor dynamic regulation can  result in audio distortion in an AM modulator or slopbucket leenyar, or a horrendous looking CW waveform.

With a plate modulated AM rig, regulation is improved when using a common power supply for modulator and rf final.  The final acts as a heavy duty bleeder.

[W2VW]

What I'd like to know is what makes it possible to wind power transformers with lower resistance secondaries than the old iron.

Is it advancement in core material?

[k4kyv]

Probably core material, and core and winding dimensions.  It is not only a question of winding resistance, but one of leakage reactance.  The tighter the coupling between primary and secondary, the lower the  leakage reactance.  Leakage reactance has a lot to do with how good the regulation is when using a capacitor input filter.  Old technology plate transformers would most likely have poor voltage regulation when used with modern day solid state diode rectifiers and high-capacitance capacitor input filters

[KM1H]

What I meant about the C not having much of an effect in a choke input was the unloaded soaring voltage which can take out transformers and 866's. I thought that was plain. Its also well explained in the old HB's.

Electrolytics are puting a lot more C in small packages then they did even 5 years ago and the good ones have higher ripple ratings and lower ESR. Ive been replacing 20-30 year old 150-220 uF lytics in customer amps with 330 and 450uF Snap-In style that have the same footprint and often less height. Many amps came with step start or I add them.

I recently came into a bunch of CDE industrial grade 1250uF 500V  105*C can caps for in process and future PS projects for under $2 each and they are 2-3 year old date codes from scrapped never used equipment. Dimensions are 4" tall by 2" wide. That should give me all the dynamic regulation I'll ever want and even eliminate the need for regulated screen supplies in AB amps.

Some are using even bigger caps up to 5600uF in amps using tubes with handles.

Carl
KM1H

[W2PFY]

What I'd like to know is what makes it possible to wind power transformers with lower resistance secondaries than the old iron.

I'll take a crack at this. I think a modern transformer will use a larger gauge wire. The insulating qualities on the wire have improved is another factor allowing less thickness of insulation materials between the windings. The materials between the windings is probably some sort of new plastic as compared to a treated paper of yesteryear. Then the steel used in the core is the final factor that has better magnetic properties.

Just an uneducated guess at this end.

[k4kyv]

What I meant about the C not having much of an effect in a choke input was the unloaded soaring voltage which can take out transformers and 866's.

Even the instantaneous voltage peaks  that the meters don't read, which can be present in choke input filters with low filter capacitance, can break down insulation.

When I modified my Gates BC1-T to allow it to work on CW, using the stock 8 mfd filter cap, and 65 henries of inductance in the choke, the plate meter read 2700 volts key up and 2600 volts key down.  Looked like excellent regulation.  But when I tried monitoring plate voltage with a scope, I was getting peaks of over 4000 volts as I sent random dits and dahs.  Increasing the capacitance to 25 mfd, and  reducing the bleeder resistor from 100K to 50K cut the peaks down to about 3 KV, and the keyed waveform looked much better, even though it was still not perfect.

[KE6DF]

I was getting peaks of over 4000 volts as I sent random dits and dahs.

I played around with the Duncan app PS program a bit. I can't simulate a varying load, so it's not the same case.

But it's interesting looking at what kind of voltage spikes you get during power on.

With a choke input power supply, with a 3KV transformer and a silicon diode bridge, a 10Hy choke and an 8K ohm load, I tried various sized filter caps.

With a 5 uF filter cap, you get a 4400 volt peak output from the supply. After startup, the output is about 2600 volts.

Changing to a 25 Uf output cap gives you a 4250 volt peak.

Changing to a 100 uF output cap you still get a 3850 volt peak.

In all cases, the steady state output voltage was around 2600 VDC

With the large output caps, it was very suprising to me that you get such high voltage peaks with a choke input filter.

Looks like you need plenty of overdesign in filter caps and choke voltage ratings.

It would be nice if this program had some way to simulate dynamic loads.

[Tom WA3KLR]

Dave,

I'm not familiar with the Duncan program, but see if you have a behavioral switch or voltage controlled switch in the simulation library.  Then drive the switch's control pin with a square wave generator set to xx milliseconds delay.  Have the switch tie an additional load resistor to ground.

If the program doesn’t offer such resources, I highly recommend downloading Linear Technology's LTSpiceIV.  It's free and does a lot.

[Opcom]

I was getting peaks of over 4000 volts as I sent random dits and dahs.

I played around with the Duncan app PS program a bit. I can't simulate a varying load, so it's not the same case.

But it's interesting looking at what kind of voltage spikes you get during power on.

With a choke input power supply, with a 3KV transformer and a silicon diode bridge, a 10Hy choke and an 8K ohm load, I tried various sized filter caps.

With a 5 uF filter cap, you get a 4400 volt peak output from the supply. After startup, the output is about 2600 volts.

Changing to a 25 Uf output cap gives you a 4250 volt peak.

Changing to a 100 uF output cap you still get a 3850 volt peak.

In all cases, the steady state output voltage was around 2600 VDC

With the large output caps, it was very suprising to me that you get such high voltage peaks with a choke input filter.

Looks like you need plenty of overdesign in filter caps and choke voltage ratings.

It would be nice if this program had some way to simulate dynamic loads.

In the duncan program, there is an option for a step load what will show this. or try to. change the load to constant current, then select stepped load, and input the on and off key current drains. This is not your circuit, just show s the program.

[KE6DF]

"In the duncan program, there is an option for a step load what will show this"

Thanks, I didn't notice that option.

With it I can come closer to modeling a CW rig with a sudden demand for power occurs when the key is closed.

It's not quite right, because a class C final is more like a resistive load rather than a constant current load, but at least it gets closer to the real situation.

So I set up a model with a load as follows:

2500 VAC output from the transformer
100  ma bleader load for the first 1.5 seconds which is enough to stablize after turn on.
A step change to a 500 ma load intended to model key down.

With a choke input filter with a 15Hy choke and:

5 mf filter - the voltage at 100 ma is 2400vdc, the voltage spikes down to about 1700 when key is closed, and then stabilizes at 2200 VDC with the 500ma load

20 mf filter - the voltage at 100 ma is 2400vdc, the voltage spikes down to about 1900 when key is closed, and then stabilizes at 2200 VDC with the 500ma load

100 mf filter - the voltage at 100 ma is 2400vdc, the voltage spikes down to 2100 when key is closed, and then stabilizes at 2200 VDC with the 500ma load

The waveform when the key is closed looks like a damped sine wave.

With a capacitor only filter of 100mf, the outpt drops from about 2410VDC tp 2370 when the key is closed. No overshoot or damped oscillation occurs. There is a lot more ripple, however.

A choke input filter really takes care of the ripple problem but it's a little like pulling a trailor with a bugie cord.

Another thing that would be fun to model would be thyratron grid keying like the circuit in GE ham news that someone posed about a while back.

Another interesting study would be dynamic behaviour when using a resonant filter.

[WA1GFZ]

I hope swinging chokes wear their protection from STDs