grid circuit swr...

[N2DTS]

Well, I started redoing the 4D32 deck grid coils, and found I have no good B+W coil stock, nor do I have any good enameled wire to make coils.
I have real thick stuff, and real fine stuff...

I suppose no place local will have any.
 

[N2DTS]

Well, I got my enameled wire and re did the grid coils in the 3X4D32 rig, and added neutralization and the grid goes down to 1.2-1 swr and does not change with modulation.

Waiting for a chassis to re do the 2x4x150 rf deck.
I will add neutralization and better cooling.

[W3RSW]

Great!  Knew you could do it.
FB OM.
Where did you find the wire?  RS's three pack of " magnet wire?"

[N2DTS]

I did not even look at radio shack, I did not know they sold it.
I got it off ebay, $6.00 for 200 feet of #24, should last me a while.

The RF deck worked fine un-neutralized, but the solid state driver did not like it.
Much less change in grid current with plate tuning (almost none) and no change of swr with modulation.

I hooked up the icom 756 pro2 as an exciter and after redoing the other rf deck, will look into turning the VFO-exciter into a CW rig.
A single 6146, about 40 watts out I think.
I need to come up with a plan for converting one of the home brew receivers to CW.
I have a nice product detector circuit prototyped, but need to figure out the bfo/offset/narrow filter things.

Fun with ham radio...

 

[k8pz]

For the record, a good source for enameled wire of whatever size you need is your local motor rewind shop. Just about any city with some industry will have at least one shop. I have great luck with the smaller shops. If they don't just hand you a few feet, a small donation to their coffee fund is all it takes.

Steve   ..

[N2DTS]

But like bearing supply houses, they are getting very rare...

[W3RSW]

Brett,
It's been a couple of years since I bought some but R.S. had a three pack of #22, #26 and #30 spools.

Still do at "sale" prices. urk.

http://www.radioshack.com/product/index.jsp?productId=2036277&znt_campaign=Category_CMS&znt_source=CAT&znt_medium=RSCOM&znt_content=CT2032227

But it's great for winding those toroids for coupling and filters, etc. Will last me a long time.

[KB2WIG]

"I got it off ebay, $6.00 for 200 feet of #24, should last me a while."


I've got several rolls of the rat shack stuff. It is high priced, but thats expected of radio shaft. It's a question of 'Do I need it now?'. I did, so I purchased.

I have a roll of Belden #34 that I bought from Ralph, W2wme, back in the 70's. That roll has and will last a long time. I'm sure my wife will be throwing it out when I become a SK (or actually a dead D10-4).

KLC

New Years Resolution. -  Become a AM gangstra and strap everyone. Then you'll all be sorry.

[N2DTS]

The 3x4D32 rig is done and working very well, new grid coils, but the big improvement was adding neutralization.
I used the setup K1JJ did on the pair of 813's modulated by 813's, a tuning cap in the grid circuit between the tank ckt and ground, and a copper strap close to the tubes for a pickup.
Worked a treat, easy to adjust, no high voltage to get your hands close to.
Very low and steady SWR on the icom driver.

So I tore apart the 2X 4X150a deck, which started out as one tube on a very small chassis, then had another tube added, which pushed things to the limit.
So close, I found the B+ had jumped to the grid coil at some point.
No space for any neutralization parts, so I tore it apart and started rebuilding it on a bigger chassis.
Cooling will be improved, and with plenty of space, voltage will not be an issue.

Two tubes did 300 watts carrier out (1200 volts, 300 ma) without getting warm, and I think the tubes would be loafing along at 1500 volts and 400ma.

After an old buzzard transmission, I could hold my hand on the tubes and they felt just warm, not hot, from a poor flowing muffin fan mounted inside the chassis, not much air flow really.

I might add 80 meters.
I also might try hooking it up in place of the 2x 813 RF deck and running it at 1500 or 1600 volts, and use the 4x150 modulator deck with it.
That would be a 2x4x150x2x4x150 rig...

One 4x150a has 250 watts of plate dissapation in a small tube, more then an 813.

If I built a modulator using four 4D32 tubes and used it on my 3x4D32 rig, it would be a 3x4D32x4x4D32 rig.

[W3RSW]

Wow! Lots OF 3's & 4's.  Keep paralleling those babies and you'll be able to run you 250 watt monitor speakers right off the cathodes. 

Good going.

[N2DTS]

Yes, thinking about it, in the past I had built a 4x813 amp for the flex stuff, which ran very hot at 200 watts carrier, but four 4x150a's would have 1000 watts of plate disipation...
Very low filiment power and lower plate voltages as well.

I suppose you could grid modulate it with low power and/or run AB1 for a clean signal.
Two 4x150a's do 600 watts in AB1.

Not that I have any use for an amplifier.

And I am just jumping on the X bandwagon, notice how everything is advertized as 2x whatever..
X is in.

[N2DTS]

Making progress on the 4x150 rf deck:

http://n2dts.smugmug.com/Ham-radio/i-VCw9F2g/A

And, I scored 3 new 4x150a (Eimac) tubes for $45.00 each.
That is a good price for a tube with 250 watts of plate dissipation.

I have all the holes drilled, and will prime and paint the chassis tomorrow.

I added grid band switching for 80 and 40 meters and neutralization.

The hard part is going to be making a bottom panel with a BIG hole in it for the fan.
Big holes in sheet metal are a pain!

[N2DTS]

More progress:

http://n2dts.smugmug.com/Ham-radio/i-QJBq4hR/A

[Opcom]

About those sockets, they may not provide the kind of "over the base seals" cooling recommended by Eimac.
That whole bottom surface needs to be cooled according to them. It's the heater energy.
I know a lot of folks don't do it, even some military examples, and the 'right' sockets are high cost.
It might be impractical to drill holes and groove the top with a Dremel.
What do you think about the cooling of those tubes?

Anyway, please let me suggest this 12VDC blower instead of a fan. Japan Servo FBDC12H7P-949. It's quieter than most fans. It makes 24CFM at 0.1" static (15CFM@0.6") The tubes need a minimum of 7.2CFM for a pair, and you can use a good intake filter, like a 4" metal mesh filter, and still have enough oomph in the blower (YMMV).

It makes far more airflow that the blower in the SDP-1000L, a 1KW input amp here with two 4X250's. It cost $4-8 depending where. ($4.95 http://www.mpja.com/12VDC-3-3_4in-Japan-Servo-Blower/productinfo/18224%20FN/) It's not Chinese made. It's quiet enough I use it on a 200W power supply that runs 24x7 on my desk. The original Chinese fan communes with its ancestors..

Size / Dimension 97mm x 94mm x 33mm
Rated Voltage 12 VDC
Fan Speed 3500 R.P.M. (Revolutions per minute)
Maximum Air Flow 23 CFM (Cubic feet per minute)
Noise Level 56 dB-A
Power Connector / Function 3pin, Speed Sensor (Tach Out Put)

data sheet attached.

[N2DTS]

Thanks for the blower tip!

The rig has been running those loctal sockets for a year, plenty of old buzzard transmissions and even with low air flow, the tubes only get warm to the touch.

I do have the normal air system sockets in a modulator I run, along with a real blower.
I also have 2 more air system sockets, 2 different types, they made a lot of different sockets to fit these style tubes...

The way I run these tubes, 300 watts out, 360 watts in, 60 watts of plate dissipation out of a total of 500.

If I ran 400 watts output, the plate dissipation would likely be about 80 watts (40 a tube).

I got the new deck done and tested:

http://n2dts.smugmug.com/Ham-radio/i-cbTgZb3/A

Bigger chassis (taller) so the fan moves a lot more air past the tubes.
I have a few tweaks to do, label things, fine tune the neutralization, and maybe adjust the grid coils so the grid tuning stays the same on 80 and 40 meters, or at least very close.

I ran it a while at 400 watts out, shut it off, shorted the high voltage and felt the tubes, slightly warm to the touch, about 90F I think.

The 4D32 rig puts out a lot more heat at the same power input and output.
They take more filament power though, about 3 amps more.

In the future, I want to make an octal to spade lug adapter and run it in place of the 2x 813 rig, and take the voltage up to 1500, and modulate it with the 4x150a modulator deck, it has its own power supply.
A pair of 4x150's modulated by a pair.

[N2DTS]

Along with other projects, I put a filament transformer in the 2x 4x150 rf deck, and hooked it up in place of the 2x 813 rf deck. I made a cable to hook it up to the control deck that runs the 813 rig and fired it up on 40 meters.
I ran it up to 1500 volts and 400 watts of carrier output without any problems.
At that power level, the tube temp was 107F.
Modulating it with the 4x150 modulator deck, I got lots of positive modulation, it would do 2kw peaks easy.

I then switched to 80 meters, and the ricebox had a problem driving it (swr) till I added 20 feet of coax between the two.
I tuned it up at 1500 volts, did a yay lo, and the plate tuning cap arc'd.
I turned the voltage down to 1000 volts and it still arc'd.
I think the cap warped from the arcing, its marginal for 1500 volts.

I guess something is off with the tank coil since the thing worked ok on 40 meters.


 

[N2DTS]

Yep, I found one of the plates on the tuning cap warped, I corrected that and hit the plates with some fine sand paper to smooth things out.
Wish I had a bigger (wider spaced) cap, but this one will do.

If I increase the voltage to the RF deck, that increases the plate impiedance of the thing, so which way do I need to go with the tank coil to lower the voltage on the plate tune cap?

The coil is made from something like number 4 solid wire since an 80 meter coil with tubing would be very large...

[N2DTS]

I hooked the 2x 4x150 deck up in place of the 2x 813 rf deck again after bending the warped plate tuning cap plates back and sanding them to remove the rough edges.

I set the RF deck voltage at 1000 volts, ran it to 300 ma, got about 250 watts carrier out, then hit it with modulation.
Wow, no wonder I cooked the cap, the 4x150 mod deck can do 600 watts and I am running about 300 watts input on the rf deck. That is 2x the audio power then the rf power, what peaks!
Running 250 watts carrier, and running the modulation at about 85% negative, I was off the scale in the positive direction and doing 1500 watts pep!

I had a short qso with John, N2XD without anything crapping out.

Tube temps got up to 107F.

I really need a wider spaced cap so I can up the voltage on the RF deck some, plus with all that audio power, its easy to hit very high peak voltages.

 

[N2DTS]

Anyone got a higher voltage cap to trade/sell?
The cap in the rig now is a Johnson 154-2 which is 350 pf at 2000 volts,and something 150 pf and 3000 volts would be good.

Here is a picture:
http://n2dts.smugmug.com/Ham-radio/i-phqTm8g

It can be longer, but not wider or taller.
I suppose they made a cap that was 150pf or 200 pf and 3000 volts in the same size ?

[KA2DZT]

The 2KV cap is a bit close.  3KV would be better.  I have a 3KV cap in my 50 watt rig, about 650 volts B+, plate modulated., never had any arcs.

Fred

[WU2D]

That is very nice work on these decks. It is amazing what neutralization can do to settle down the drive situation. Even tubes that "do not need it" NEED IT.

[N2DTS]

Yes, at 2kv, I am pushing the cap to the limit.
There is no DC across the cap, but the rf voltage is at the limit at about 1200 volts on the plates.
I never had an arc running it with the 811 mod deck with a common power supply because the most I can get out of that is 1250 volts, and the modulator drags down the plate voltage some, reducing the peak power and voltage.
Things really change when you run seperate supplys.

I never used to bother with neutralization, but the rigs tune up much better with it.
The 813 rig still does not have it, and does not seem to mind much at all, but I might add it.
With it, both the 4x150 and 4D32 rigs have a stable grid drive, it does not change with final tuning, and does not change with modulation.

SWR to the rice box is still higher then it should be, but the tuner in the rig tunes it out just fine.
I wonder what could be done to lower the swr enough to not need the tuner.
A resistor across the grid coil? Less turns on the link coil?


With a higher rated cap, I could turn the plate voltage up to 1500 volts and see if anything blows up.

The 4x150/4cx250 tubes make for an interesting RF deck, I could likely get more power out of them then the 2X813 rf deck, and that deck is huge.
The 4x150 runs lower voltages as well, which makes for smaller parts.

Odd that the RCA tube manual says you need to modulate the screens of these tubes to get good modulation, but I seem to get insane peaks with the screens self modulating.

[W2VW]

Brett, how about putting 300-400 pF in series with the existing cap?

[N2DTS]

I thought of that at about the same time you did I think.
On come caps, you can pull every other plate and get 2x the spacing, but not this one.
A door knob in series might do the trick though, at least as a test.

[N2DTS]

I tried the cap in series, first I used 500pf at 5000 volts, it worked ok, then I tried a 100pf cap, could not load it up right, then I tried a 1200 pf cap and it worked well also, so I left that in.

Turned the voltage up to 1500 volts, got 400 watts out, over 2 kw with modulation, measured the tube temps, 80F, looked the max temps up in the tube manual, 175C for the base, 200C for the plates.

175C is 347F so I have a ways to go.