starting work on the amp

[W7TFO]

I read that and had to go take a leak...

73DG

[Opcom]

"Leakage current" 
That's a good one.

Just 32uA to deflect it to read 6400V on the 1.0 scale.

I read that and had to go take a leak...

73DG

That meter is a good find and might be nice for a hi-pot tester later.

What is a normal current range for a tester that hams would find useful? Do they have to go to 1uA or less to be non-destructive?

[Opcom]

This weekend most of the remaining mechanical work was done on the power supply. Brackets were made for the HV cap and the choke. An air switch is available but has no vane so one is being made. The blower - it was decided to mount it on a shock absorbing mount to reduce noise, so one was made. The blower is quiet but there is always some conducted humming sound and whine.


The blue plastic at the bottom keeps the metal bolt from abrading on the capacitor. The top section is made so the screws are held away from the cap.

[Opcom]

The choke is held in place by a steel strap. It may look like it could be loose but it can not move at all. The air switch happens to fit on the blower perfectly.

[Opcom]

The mount is made of some thick foam rubber sandwiched between two thick aluminum plates with a generous helping of weatherstrip adhesive. The bottom plate bolts to the floor of the cabinet. The big holes in the top plate let a socket through to tighten the bolt.

[Opcom]

and

[Opcom]

Today the vane was put on the sir switch. The modified paper clip soldered easily to the brass vane cut from a sheet. A cable was run from the switch along the power cable of the blower and a connector soldered on. The  blower with air switch was installed and wired in. The connectors allow the blower to be easily removed if it needs service. The blower also has a ground strap that screws to the frame of the rack. There are spare pins in the air switch connector for possible future use.

Blowers have definite ranges of pressure and air flow. This blower for example, if left free, will overload because it moves too much air. The air flow is properly restricted by the load such as the tube to be cooled. The pressure remains relatively constant with varying air flow and the current drawn by the blower increases with increasing air flow. The name plate gives the proper current for the motor. The air flow can be adjusted to give this value by means of a damper in the path of the air. It is quieter if dampers or restrictions are in the output air flow rather than at the blower inlet.

[Opcom]

View from back. There is just enough room for the blower, capacitor, and choke. That means the space was used well!

[Opcom]

The grounding arrangement of the blower. Note the lug end of the ground strap is soldered. All crimped connections are soldered.

This is about it for the power supply except keying, removable power cable, HV fuse, a few low current breakers, and a set of monitor lamps to indicate the progression of control and power supply start-up and soft start. The electromagnetic brain was finally tested with the blower and air switch and all is working correctly. 240V lamps or 120V lamps with resistors in series should be very reliable. LED panel lamps could be used but the ones available locally seem very cheaply made and they look like cheap plastic too. I would like to match up some jewel-lens panel lamps and use them.

Keying could be electronic for the tube but may make trouble because of power supply dynamic voltages when the HV supply is left on. It may as be impossible to have fast enough TR switches. An electronic TR switch may be useful.

The normal keying for this on voice can be by the plate supply with a soft start each time. The soft start should take less than one second to fill the capacitor. Keying the HV supply and retaining soft start is as simple as breaking one 120V wire. So that's about it on the power side of things.

[Opcom]

This is a dual project - the amplifier and jacob's modulated Tesla coil. They are intertwined because we  are building them in the same place and helping each other. We need some help with the MOSFET driver and hope those with experience with FETs can assist with advice. Fortunately MOSFET are cheap as we have blown 2 or 3. So, to give an outline (schematic to follow) the driver design has changed from modulated tube power supplies to a push pull FET amplifier and separate grid driver and DC supplies. The frequency is only 75Khz so on the surface it would seem simple but it is different in practice.

[Opcom]

Here's what we are experimenting with. The simplest way to drive the FETs in push pull was just to tap off the vertical amp of a scope. lots of gain that way. It works well.

The trouble we are having is that there is some 120MHz bursts of parasitic oscillation lasting 1uS or so, around the gates of the MOSFETs and we are afraid of this blowing them.
This parasitic waveform is quite large, well over the gate max volts in both directions.
We do not know how to stop this.
Does putting MOSFETs in parallel invite this?
The 75KHz drive to them from the scope amp is approximately a sine wave, but it is clipped by the zener diodes to a +/- 12V trapezoid or square. The burst of oscllation seems to be where the FET turns on as Vth is reached. It's very strange.

[KD6VXI]

Ferrite beads to quench the oscillation? Maybe a couple.   On the gates of the fets.

I've had to use them on the base leads of high gain amp transistors before to damp vhf energy to keep them stable.

I got the idea from the ARRL solid state design handbook I believe.

You want a mix that is very active at the freq of interest.

--Shane
KD6VXI

[flintstone mop]

My Gawd
Is this an Area 51 project? Some serious engineering for the boring 1500 watt PEP Ham radio crap.

Are you sure that this is for Earthly communications??? Talking to aliens from another solar system?
You might see pop-up ads appear in this post, because it has surpassed 10,000 views

[Opcom]

Good advice on the ferrite beads! There are many strange things going on with that coil experiment and the picture may help explain, the lash up is very something. The coil and 4-400 chassis/power is not shown in the picture. A 2x 811 chassis in the first picture is being used as a test pig.



On engineering, I'm just trying to avoid building weak links into it. If it's made like a battleship it should last a long time. I hope that people won't get bored when seemingly slow progress is made because we are having great fun doing every 'home made' part of it. Many times there are delays because something has to be made or modified and that work can't be shown, only the result, but be assured it was fun to do it. Up til now, the power supply - it's the simple part. The RF part is the hard part and yet to be started.

The second picture is just some panels starting to cover the HV areas for safety reasons while other work is done. It would not do to accidentally stumble into, lean on, or touch something hot.

Does anyone know of a kind of push-on rubberized, cylindrical shaped insulating cap to be put on and cover up stuff like choke terminals, cap terminals, bolts, etc? It's very dangerous to work on this.

[Opcom]

A bag of small blue indicator lamps was found. These have also push buttons in them. Incandescents can burn out but if operated at slightly lower than rated voltage should last many times longer than the spec. These things have all-metal housings, high quality types, with push-in lamps of the bi-pin style. They might be used inside the back of the amp next to the 'brain' panel with the relays, to indicate progress of start-up. When something is turned on, the lamp should light. The push-button feature might be usable as a lamp test or something. It's a lot of extra wiring though.

I have not thought about overload relays but those lamps and buttons should be on the front, and be larger. The regular sized panel lamps were dug out. There may be some more but this should give enough variety and numbers. The question is whether there are enough 'jewel' type lenses that fit the enclosed panel-mount sockets.

I did not find the stash of 1" panel lamps which would be even more better. Also, no two industrial push buttons around here seem to be alike, so I may have to find some. The price of new Allen Bradley is outta sight!! So forget that! Maybe some used ones will turn up and be all the same style.

[W7TFO]

Automotive starter/alternator 90 degree rubber boots work great for insulating large HV bolts.

73DG

[Opcom]

That's a great idea.

[KD6VXI]

I enjoy pieces of vacuum hose,  cut judiciously long.   Makes for great insulation 'posts'  on your hv posts.

I've also used  if you can find them now,  vacuum port close offs.   Basically,  they where larger versions of the bat handle toggle markers that slid on.   

I'm sure those are for off road use only here in California,  but you may find them at your local auto parts store in Tejas.

--Shane
KD6VXI

[Opcom]

Have you had any issues with some of them having perhaps high-Carbon or otherwise being slightly conductive? I would prefer them to go 90 degrees, as the terminals are almost always a '90' when the post and lug are considered.

I found this site which is possibly interesting. Maybe part of this is the desire to insulate, and partly to make certain high voltage terminals very obvious. Red is good.
https://www.electricalhub.com/battery-terminals-and-lugs/insulator-battery-terminal-boots

[Opcom]

Something that has to be done is to shorten the 5-second delay of the Potter & Brumfield fixed delay relay to <1 second for soft start. About 1/2 second looks good. This turned out to be as simple as changing the timing capacitor. A good quality capacitor has to be used.

The current schematic is attached. Its point is the power supply and control circuits are completed aside from adding indicator lamps, that will wait til almost last. Just a 1U panel for that. The RF section is somewhat hypothetical at this point but is generally what is wanted. The ATU is not shown.

[W7TFO]

I have both colors in lots of sizes, never had a leakage problem.

73DG

[KD6VXI]

I haven't with vac hose either,  but that does bring up a good point.   I've never tested for leakage!   They could be hot,  and I'd never know.

--Shane
KD6VXI

[Opcom]

My Gawd
Is this an Area 51 project? Some serious engineering for the boring 1500 watt PEP Ham radio crap.

Are you sure that this is for Earthly communications??? Talking to aliens from another solar system?
You might see pop-up ads appear in this post, because it has surpassed 10,000 views

The two projects are opposite ends of the same hopefully bidirectional thing. beyond that, the attached document and the fact that there are no semiconductors in it at all above a rectifier, is the only information of the project approved for public release. Had to disclose to get funding. 

(but ads I have never seen any here in ages pop up or be summoned from the depths) 

[KL7OF]

Have you had any issues with some of them having perhaps high-Carbon or otherwise being slightly conductive? I would prefer them to go 90 degrees, as the terminals are almost always a '90' when the post and lug are considered.

I found this site which is possibly interesting. Maybe part of this is the desire to insulate, and partly to make certain high voltage terminals very obvious. Red is good.
https://www.electricalhub.com/battery-terminals-and-lugs/insulator-battery-terminal-boots

spark plug angle boots

[KJ4OLL]

Hi,
WOW, you are really making great progress on the amp! The local power Utility grid should be afraid….

A couple of years ago, my Elmer found some switches for our home-brew 3CX3000A7 @ Mouser.
Multiple color lenses, illuminated, different logic options, etc.
We went with two lens colors, (I have not yet connected the lamp power, too excited when the thing actually worked)
but here is how we implemented them:
https://www.youtube.com/watch?v=vywkoK5LKQc