NC is $10/ yr....

Never had an issue, and I always drive like my brother.

Stephanie,

Here's a link that explains the process. It's too much to explain here. Plan to spend some time learning how to use it.
https://www.rtl-sdr.com/kiwisdr-tdoa-direction-finding-now-freely-available-for-public-use/

Don

I think I'll go ahead and use the power XFMR I have and then play with the filter a bit. There is more than enough room under the chassis to add a dropping resistor.  I have plenty of adjustable types. Even with 250 volts on both plate and screen, the tube will do 4.5 watts output. I'll just mess with it a bit and see how close I can get to the 315 pv / 225 sv.

Don

Can you share how you accomplished a TDOA calculation ?

I see the wideband noise on my 756ProIII scope. Its pretty much wiping out 3880. I take it this just started today.

This signal popped up on 75M in the Northeast recently.

My attempts at TDoA direction finding places the source in the general vicinity of:
-State College, PA
-Harrisburg, PA
-Altoona, PA
-Hagerstown, MD

Any ideas or comments regarding this?

Don

The choke resistance must have been a major factor here.

Rerunning the numbers and averaging out choke resistances from both EDCORUSA and Hammond, it appears the choke resistances averaged about 350 ohms.

So at 350 ohms, a 55 mA current would drop about 20 volts across it.

So 315V+20V has to = 335V at the choke input.

The rectifiers would have produced a pulsating voltage with a peak ~ = 495Vdc, so (495V-335V)/.055 = a resistor value of 2.9k.

Now 2.9k - 200 ohms = 2.7k, so two resistors of different values in series could produce 335V at the choke input.

Did the authors/editors leave out the 2.7k by mistake? As Cousin Eddy said in Christmas Vacation - "I dunno."  


Phil

Choke is a Hammond, 407 ohms, 14 Hy and 75 ma. I did a search and found that using a choke input filter with a 700 VCT tranny and a single 20 ufs cap, voltage under-load would be nearer 240 volts. Of course, the bleeder on that unit was 30K and not 50. Seems to me changing the PS to choke input makes the most sense.

If you have the exact same PS choke called for, I would measure its DC resistance.

The only way a 200 ohm surge resistor will work with a 700VAC CT transformer and give about 315V is if the PS choke has a high resistance.

Most of these chokes had resistance from about 60 ohms to 150 ohms depending on how much copper and what gauge was used.

It is interesting that no voltages or voltage charts were indicated in those Handbooks or on the schematics, which I why I said you have to take those schematics with a grain of salt and run your numbers before finalizing your circuit.


Phil

Before going further and to save your finals:

1. I know this can be tedious but - check the wiring in this rig against the schematic and note any differences with a red ink pen. I don't recall if you said you had just bought this rig or had brought it out of storage.

2. Make sure the 6146 finals and the 6AQ5 clamp tubes are good and test within specs.

3. Solder a 0.001 uF 1kV ceramic cap to pin 7 and ground at the Clamp tube.

4. Mic gain at full CCW. Adjust the Clamp tube in CW and "0" drive with the 500k pot so the 6146 screen grid voltages are at about 140V. You never said you have adjusted this as yet.

5. This rig has grid-block keying. Check the bias voltages at point "C" (at the junction of the .005 uF and the 2.2k resistor) with a scope and DMM on Keyup and Keydown and compare to the manual.

What happened to the modulator current when this happens?

This transmitter has a Pi input circuit to the final's grid and is not known for parasitic oscillations. Check the condition of the "Driver Section" Bandswitch.

Phil