Do any of your neighbors have a grid-tie solar power system?  Those use a switching topology to achieve the 60Hz, perhaps that is where you are getting the distortion, even across multiple distribution transformers.

73DG

120V 60 Cycle  looks lumpy...

Edit:  My neighbor has a grid tie solar system........

I have a bunch of 6V6´s that might do the trick, although I feel I know too little to implement it.
How do I calculate the needed circuitry?

Should I consider the voltage drop across the cathode resistor as the key value?

If, for example, I drive a triode to draw 20ma, I should see 300v between cathode and a 15k resistor to ground?
Biased to draw 10ma during zero signal condition should yield around 150v, and put the modulator halves in balance, cancelling any rf output.
A more negative voltage on the grid would reduce the voltage between the cathode and resistor even more, giving me the possibility to get a 300v PK-PK signal at the output?

//Tommy the tractor technichian

Hi Pat -

Those are good suggestions..

These are actually two identical transformers, 3500 @500 mA each. The primaries are in series and the secondaries in series.
Each has a tag showing a 115VAC primary.  I am running 119V under load on each primary and the balance between the two is nearly perfect.

The pole pigs were 240V pri each. I had only 120V on each one and it still buzzed under heavy current loads.

The pri CT is presently connected to neutral. I have tried the 240 across both without the CT and the buzz  noise was the same.  I also tried a large Variac rated at 50A, 120 VAC across one leg and the Variac started to buzz too, just like the xfmr and choke when I used them.  Any magnetic core buzzes in this supply.  I figured the pri CT would help the balance, but it buzzes whether the CT is connected to the neutral or not.

I will try the 50 ohm resistor between the diodes and the cap. I tried it with 10 ohms before but will increase it to 50 ohms to see what happens.


You said: "Can you use a big 240V variac to bring up the mains voltage from zero to full into the primary of the unloaded transformer and see when it starts buzzing? (secondary not connected and also the pri CT not connected)"

Reread my last post about this.  The xfmr stays quiet with a full pri and sec voltage and a full load across the diode stack. It only acoustically buzzes excessively when the last component, a filter cap, is added and the current draw is above 300 mA.  Otherwise the xfmr is near silent.  When everything is connected and working as shown in the schematic, it remains near quiet when pulling a small 100 mA draw.  The 240K bleeder pulls only 17 mA at 66 watts.

T

I like any tube whether it's RF-purposed or not. Takes more than an RF tube to make a radio set.

I find the 8417 interesting personally, Its low grid bias for one thing. just costly but never mind me,

Steve- Announce and let the volunteer loose!!

One of these might help peek into the dark corners of the mystery:

Do you connect the primary CT to neutral? What happens if you disconnect it and just go line to line across the 240V primary?

Are you sure all these transformers are 240V rated and not 208V rated?

Have you tried inserting a 50 Ohm resistor between the cap bank and the rectifier output to somewhat limit peak currents and does that change anything?

Can you use a big 240V variac to bring up the mains voltage from zero to full into the primary of the unloaded transformer and see when it starts buzzing? (secondary not connected and also the pri CT not connected)

I'm still looking at other possibilities as to why the xfmr is loudly humming.

Here's some test results. Maybe someone will figure out what is happening.  Bear in mind that I substituted or replaced all of the PS components and cannot find anything wrong with its performance except for the loud buzzing that emanates from anything with an iron core, be it transformer or choke.

Tests:

1) I operated the xfmr alone with 240V with a 5K resistor across the output (4KV @ 800 mA)  - quiet.   Also tried 2.5K load (1.6A @ 4KV)  This is over the xfmr rating.  QUIET.

2) Attached the fullwave diode stack with 5K load from diode output to ground (800 mA load)   -  quiet

3) Attached four different filter caps to the diode stack, trying some alone at 30 uF -   quiet UNTIL more than 300 mA is drawn. At 800 mA, LOUD!  The HV PS does NOT like a filter cap with more than 300 mA drawn.  The xfmr is rated at 1A.

It is not laminations cuz I tried two different pole pigs and now using a 3.5KV @ 1A transformer.   The diode stack has been changed as well as the filter caps.   The ripple is normal under full load as well as good regulation from 4900V to 4400.  (full load)  BUT, the xfmr (or pole pigs) make a very loud 60-120HZ harmonic acoustical sound that sounds like a dead short when heavy current is pulled.

The strange thing is if I could run this PS without a filter capacitor (rectified pulsing DC) it would run quiet. But add the filter cap and all hell breaks loose once a load over 300 mA is pulled. It is a linear increase in noise. At 800 mA it can be heard in the other room.

I tried another power supply today powering my 3-500Z amp. I could not detect much acoustical hum at all with a 500mA load, near its rated limit.  So my idea about AC line harmonic distortion seems suspect since this other supply seems to handle it well.

Schematic below. As simple as it gets.  Ripple clean and regulation good.  Primary 120-0-120V sags only one volt for each leg under full load. Perfectly balanced. Nice AC regulation, but LOUD as heck.

BTW, I tried a jumper between the primary CT and the secondary CT. No difference in hum or performance.

This is crazy. Any ideas?

T

** Heck, the way I'm going I might be sticking my head into one of these ...  

https://www.ebay.com/itm/New-PSIB27-Sound-Recording-Booth-Box-Studio-Soundproofing-Foam-Shield-Isolation/362969674891?_trkparms=ispr%3D1&hash=item5482adb48b:g:PtkAAOSwwJ5d5sde&amdata=enc%3AAQAFAAACgBaobrjLl8XobRIiIML1V4Imu%252Fn%252BzU5L90Z278x5ickkBSh1VzQSTzkTiSV5EE%252FHQQwCYEnYBC%252BX%252F5zLsufAcGX9OCceE1xua36PJKnIJEXZ1An%252FtwceJlSjZFQ9etiPUsVELaCyoEYQpSI4thHVhdst8R9Gma2Zytxh0gpi0rAy1XHwXGNMcuPgb3Xg3Xxm3Bv9rrJM%252BsCU%252Bu3IXMAGZiw5wld3ifLVzLnqQjxsGItNYtgOo7gZuNAghnIxNrczg12P29u1Si6OpWtdU8g2LY6STYXKvs%252Bt34ppcnJI8RhCiuspvGCOa2lgoLp8RcWQVdCs%252Fy0%252B6G6rAW6WkZ%252BqIKi%252F0DTn4ukn7KnVtsFz7HudIahhB80WpnNQ5ESJnymgheWKGf6qS5e6twErfv6SNb%252Fr6DUvaoJlIMBBTi0sTHukQTo1SthmQWW67gircvhS5N2uttaXgw4piBJgK0Z8URA1w8Cn12b6DeBGy43L44aLIIZvC58DnTwZRv%252BpvKaB0bAAXo%252FfHYNvAnr4ZGVtptLxHOGrzALC1Lu4yWpWB9ICfxX0V1x%252Bk0Bb2qE32hdTbE1faS0w0p3sr8%252BSt7tKfB4o0rLGPa9pTgHgA4Xbf%252Bde7828QEUCebWgAroFSZLCIXVTRoNlzPOoDQwvXpTLgIZ28r0gj8smgkz9%252BPrUvOI92OO%252Fwy7LbeBpLr60HcRxbr6Ht8cv4RWEC1I5GJA0sv%252FHM26SNLkMJXDc3iVIiOYj4t0GjJ8leHjhLfFaxvu3HN44FpOc72wl54ZkHMD5407XdTY8QglntR6k4CUP2AKPl11DOtckFy3ESXO1AgEjvAtG1j4xVsuQX9SIHVUkbDA%253D%7Ccksum%3A362969674891f7aee62e158440568653625de3e98d91%7Campid%3APL_CLK%7Cclp%3A2334524

I just brought home a large lot of very nice parts.

I haven't had time to sort it out yet.  The facility was a 10kW AM directional station, with recent RF equipment.

A later listing with more info & pix will follow ASAP.

Thanks!

73DG

Found what I had worked out... Oh yes, this was for a Globe Champion 350 circuit - quite similar.

The stock filter and the elliptical filter. FYI

The filter can in fact be made to work at a higher frequency... I dorked with it in LTSPICE some
years back. Trying to recall my results. It was tricky. The Q with the large inductor and small
caps is difficult to work with, iirc. The value of the caps need to chosen carefully, and the
shape of the resulting filter considered as well.

I seem to recall attempting to change the filter to an elliptical type, in essence to brickwall
above something like 5.5kHz. That would be putting the optimum value of cap in parallel
with the inductor.

My interest was not to filter the clipper, but to do a slick job of bandwidth limiting for the rig.
I would not run the stock circuit, and would not run the clipper. They were put in there to
compete with the oncoming SSB popularity, and because at that time the bands were
hot. One could not get another QSO in edgewise, if you wanted
to! The entire band was a mass of heterodynes from one end of the phone band to the
other, on ALL bands pretty much. ESPECIALLY on 75m and 40m... So, being "narrow" was a
thing at that time.

The busiest contest day today is nothing close to an average day back in the 50s and 60s
when these rigs were "modern".

                        _-_-