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 11 
 on: Today at 04:45:46 PM 
Started by ka1tdq - Last post by k5mo
NC is $10/ yr....

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

 12 
 on: Today at 04:37:58 PM 
Started by KK4YY - Last post by KK4YY
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

 13 
 on: Today at 04:31:41 PM 
Started by W4RFM - Last post by W9ZSL
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.

 14 
 on: Today at 04:17:59 PM 
Started by KK4YY - Last post by wx3k
Don

Can you share how you accomplished a TDOA calculation ?


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

 15 
 on: Today at 04:14:40 PM 
Started by KK4YY - Last post by wx3k
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

 16 
 on: Today at 03:28:32 PM 
Started by KK4YY - Last post by KK4YY
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

 17 
 on: Today at 03:00:36 PM 
Started by W4RFM - Last post by DMOD
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."  Grin


Phil





 18 
 on: Today at 02:23:17 PM 
Started by W4RFM - Last post by W9ZSL
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.

 19 
 on: Today at 02:00:27 PM 
Started by W4RFM - Last post by DMOD
WELL! I've been following this thread because just this morning I started drilling holes where a power transformer will live for this EXACT SAME MODULATOR...

...As for the power transformer, I have the exact part called for...a Stancor P-6012 NOS rated at 700 VCT and 90ma. A few years ago (before my heart started acting up) I ran this same diagram past the group and the main advice I got was to reduce the feedback capacitor from .001 to 500 pf. I'm making a couple more changes because of parts-on-hand, namely using 25 uf on all the cathodes rather than 20 uf. I'm not going to run the 811A's at 1250 volts yet...

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

 20 
 on: Today at 01:21:52 PM 
Started by K8CA - Last post by DMOD
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

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