The AM Forum

A useless post but I can't help myself.  I have gathered a few more parts for the 813 rig modulator, a couple of chokes (for a total of 40H) and a 4KV 2uF cap.  All are for the Heising reactor.

Rich

I spray painted my '610 modXfermer black......


klc


a useless reply, but I can't help myself.... ..

putting chokes in series to come up with adequate inductance (assuming 30 to 50 H) is ok as long as you consider the breakdown voltage rating per choke as described in a parallel thread .... under transient conditions it is probably safe to assume that the higher inductance chokes will develop higher voltage drops (V = L di/dt) ... keep them insulated from each other as well as the chassis .... make the plastique lexan box

The voltage issue may be even worse than in the case of power supply chokes as previously discussed.

With 100% modulation, the peak plate voltage on the tube (and hence on the modulation reactor) would be double the B+.

And many people go above 100%.

So the peak voltage spec on chokes used for mod reactors should be something like 3 times the B+ -- or preferable more.

I suppose if you are putting power supply chokes in series, it makes sense to put the one with the highest voltage spec closest to the tube plate as it will get the highest peaks,  and the one with the lowest connect to the B+ of the PS

The UTC S-33 are rated for 4KV.  I bought them from someone who told me they are 20Hy each for a total of 40Hy.  All the UTC docs I can find show them as 8Hy chokes.  >:(

 I don't think 16Hy will do it.

So bummed.

Rich

Hmmm... In the case of a string of reactors in a Heising chain, would not the audio ripple voltage simply divide across each choke based on its individual inductance, regardless of it position in the chain?  (Just like a string of resistors)

In contrast, when using an L- C - L  filter in a power supply, the second choke sees less ripple voltage across it because of the filtering caused by the  first C.

?????

T

"Hmmm... In the case of a string of reactors in a Heising chain, would not the audio ripple voltage simply divide across each choke based on its individual inductance, regardless of it position in the chain?"

That's true. But I'm thinking of the voltage on the choke.

Consider a mod reactor made from two power supply chokes.

The choke closest to (and attached to) the power supply output would have the B+ voltage on one side (the side attached to the power supply output) and other the other side would have a peak voltage of B+  +  1/2 the peak audio voltage.

The other choke, the one attached to the tube plate, would have the same B+  +  1/2 the peak audio voltage on one terminal, and on the other terminal (the one attached to the tube plate -- actually to the RF plate choke) would have B+  +  the full peak audio voltage on it.

So the second choke in my example would need to handle higher peak voltages.

OK, I see what you're saying. You're referencing the measurements to ground on all chokes and I'm measuring across each reactor individually.    


Placing all reactors on Plexiglass would at least help reduce the frame-to-ground breakdown problem on the upper choke?  

T

I agree.

I'm perhaps somewhat anal on this issue because I've bought a couple of the UTC S series chokes in the last few years and found both had shorted turns but no shorts to the case.

Probably I just had bad luck.

But the S series was UTCs low end, amateur line, so perhaps the CG, PA,  or LS series chokes would be better.

Still, you make a good point about the upper choke(s) seeing more voltage to GROUND/Chassis than the lower ones. I never thought about that.  I use a pair of 150H chokes in parallel in the 4X1 rig, so no problem, but I have used series chokes in the past and didn't take precautions due to not realizing this... ;D

T

You guys are all missing the import concern here.

Who has a 40H HV choke for Rich?

In the older 1930's catalogs those chokes were listed at 20Hy. Then, somewhere along the line, UTC changed the inductance down to 8 HY but didn't change the model number. UTC had a tendency to do things like that -- change the product but not the part number. Must have messed up designers back then.

Better measure them with a DVM that has a inductance scale to see which ones you have.

I have one of the 8HY models, but it tests at 0.47 HY probably due to shorted turns.

Makes a good door stop.

But if yours are good 8HY models they make good power supply chokes.

Dave

That is crazy!  I will measure one and if it is 8H then I will use them in my plate supply as you suggest.

Rich