ferrite rod material for GG filament choke

[KM1H]

This is the new filament choke for a customers Clipperton L that I wound a few days ago, the rod is a 7.5" x 1/2" Type 33 rod that I shortened a bit to fit, I like to use 5-10X the reactance of the input impedance of the tube(s) used. In this case the original choke is 24uH and the new one is 55uH. After tank circuit changes, 100W drive, the Pout on 160 went from 900 to 1200W and holds there to 10M where its 1100W using 4 new Shunguan tubes I bought directly from China. Stable as a rock and no tube color even with a few tests I did with 150W drive from the TS-950SD.

This is a very late model Clipperton L with a PC board holding the tube sockets, input networks and filament choke, Ive only seen a few others. It also has a filament winding CT with a transistor and 1W Zener, no hum reports even on AM. They also used what looks like an AL-80/SB-1000 plate choke and a 5000pf bypass. The circuit is similar to the next edition 4 X 572B Dentron amp, the Clipperton QRO which came out just as Dentron went away. Parts have 1982 dates.

Carl

[K5UJ]

what awg wire did you use on the fil. choke?

[K5UJ]

I suggested 31 beads because that material type is fairly easy to get.  It is actually not the best for 160 m. but will work okay.  To really do it right you'd get a material type (F? J? can't remember now) in some smaller beads, undo the leads to the tube pins, slip on the beads (as many as you can fit) and solder the leads back to the sockets.   The choke Carl made is probably a better way to go.  that 7.5 inch 1/2 inch diam. material 31 rod is available from Amidon; maybe other sources too.

[KM1H]

what awg wire did you use on the fil. choke?

#14, there is 16A of current.

The choke Carl made is probably a better way to go.  that 7.5 inch 1/2 inch diam. material 31 rod is available from Amidon; maybe other sources too.

There are no 31 rods, they are 61 and 33 only. I have both here in 4" and 7 1/2" way cheaper than Amidon.

[K5UJ]

Sorry, I must have been thinking of the material 33 rod.  The 7.5 inch 1/2 inch diameter 33 rod is $20 now from Amidon!  I have one or two of them, one has no. 10 enamel wound on it to make a fil. choke for a pair of 4-1000As but no. 10 may not handle the current for a pair.   That's an experiment waiting to happen.

The material I was thinking of for beads on 160 was 75/J.  Gyro, if you want to try adding beads to your choke leads try to get 75s in a size that will fit on the wire.  A bigger choke like Carl's is probably a better multi-band solution.

[WD5JKO]

Relating back to the post by GYRO that started this recent exchange, a rig for only 160m/80m might not even need a filament choke! Instead use a filament transformer with a split bobbin such that the filament winding is separate from the primary. This is not a good 160-10m option, but for top band and 80m operation this should work. The split bobbin type transformer will also be coupled less tightly; a good thing to limit the initial turn on current surge. I wonder if any suitable transformer such as discussed is readily available?

Edit: There would still be a need for a filament CT. RFC to ground, but it would only need to pass cathode current. One of those old single Pi chokes from an old WW2 tuning unit (~1mH) would do. A few ohms DC resistance would be fine.

Jim
WD5JKO

[KM1H]

Finding the proper old iron will likely be harder than spending the same or less on a rod and wire. My only attempt at using one of those transformers and no choke for a pair of GG 813's in the early 60's didnt turn out well. The articles of the day specified only a few useable part # that had sufficiently low C.

Where a generic split bobbin one may work somewhat is in combination with a rod choke of less than needed reactance/inductance and then modify the input network to compensate. Expect higher drive power for comparable output using a proper choke.

Carl