[Boatanchors] Parasitic Chokes

[Rob Atkinson]

I don't know what the PA tube is in that rig but plate parasitic
chokes seem to have varied with time regardless of the tube.  My early
1960s 3-400 rig has the old Ohmite suppressors, non-inductive w.w.
resistors inside many turns of wire but I left them and they seem to
work, at least the rig doesn't take off, however I only run it on 75
m.  My HT-20 with 4D32 originally had a low resistance choke of around
12 ohms inside a coil of maybe 15 to 20 turns and other owners have
reported a problem with the stock choke so I put in 100 ohm 4 watt
carbon inside a coil of 3 turns about 1/2 inch diameter, more like the
usual modern choke.  No problems on 75 and 40 m. with that.   My
3-500Z leenyar has something similar, 100 ohm but metal oxide and a
coil of only 2 turns.

73

Rob
K5UJ

On Fri, Jun 9, 2017 at 6:07 PM, Lee <L at w0vt.us> wrote:
> I just purchased a HT-46 transmitter and a SX-146 receiver I plan to totally
> restore.  Today I checked all the tubes and made a preliminary assessment of
> what all has to be done.  In the process I looked at the 39 ohm 2 watt
> carbon resistor located within the final plate cap's parasitic choke.  It
> could stand being replaced as it has gotten pretty hot in the past based on
> it's color.
>
> I have replaced these resistors in the past with Ohmite OY resistors as
> folklore has suggested.  That got me thinking.  Maybe this is all BS and new
> style carbon film, metal oxide and metal film resistors could be used which
> is contrary to folklore.  I've read the spiral cuts in these new resistors
> is non existent or of very few turns when the resistor is of low resistance.
> 39 ohms is certainly low. So maybe this OY suggestion is like the myth you
> can't use 6146B tubes in 6146 circuits.  (I have used 6146 tubes extensively
> in replacing 6146 tubes with no problem.  Don't go into S-line
> neutralization caps.  The up grade was done because the initial caps were
> under rated in the first place.)
>
> So I have decided to do an experiment when I rebuild the HT-46.  I am going
> to make new parasitic chokes using all 4 type resistors and see if any make
> any difference in the transmitters performance.  I am suspecting there will
> be no difference in transmitter performance from one type to the next.  I'll
> also measure the inductance on all these resistors.  I suspect the
> inductance will be so low my meter will barely detect any inductance or not
> detect any at all.  Proof will be in the pudding.  I'm going to see what
> happens in the real world.
> Lee, w0vt