new project for winter...

[N2DTS]

Well, I got the quad of 4x150's built and it works well, I built two screen modulators and they both work great, everything else is working great, so its time for a new project, something I never got to last winter.
A low power home brew single band (40 meters) AM rig.

Something like a 6146 modulated by a pair of 6l6 tubes, or a super DX60, a pair of 6146's with screen modulation.

D104 input, not hifi, I want clean but punchy audio like a low power rig should have.
A super dx60 or a single band ranger, xtal control, 7280 to 7295 needing no grid tuning (preset).
Mic gain, maybe a tone control, tune and load, plate current meter, modulator plate current if its plate modulated.

Or maybe a 4x150 run at 6146 voltages with little or no cooling (I am hooked on those tubes).

I need some sort of nice looking box/cabinet to build it in, or I guess I could make it a rack mount thing.

What is the power output of a DX60?
I have heard many great sounding DX60's with the usual mods.

Also, I suppose no one makes crystals anymore, but that is the easy way to do a 40 meter AM rig.

[Pete, WA2CWA]

Also, I suppose no one makes crystals anymore, but that is the easy way to do a 40 meter AM rig.

ICM still supplies them:
http://www.icmfg.com/hamradio-manufacturers.html

[N2DTS]

Thanks for the info.
Guess I could have 2 each for the usual frequencies made up, 7280, 85, 90 and 95 should do it.

Also, I suppose no one makes crystals anymore, but that is the easy way to do a 40 meter AM rig.

ICM still supplies them:
http://www.icmfg.com/hamradio-manufacturers.html

[N2DTS]

I am thinking about a single 4cx250b at 800 volts or so, screen modulated by the solid state modulator run off the same power supply.
I have a boatload of old 4cx250b tubes.
They are smaller then a 6146, take very low drive, and not much screen voltage, the screen modulator takes care of screen protection.

800 or 900 volts on the plate, I need to see what kind of power output I would get, it would make for a very small rig size wise.
I can test it by pulling one tube out of my 4x150 rf deck, hooking up the screen modulator and the rf deck to the same power supply and turning the plate voltage down to 800 volts.

Or, I could plate modulate it with a pair of 6l6's and the 25 watt mod transformer, not sure it would even need any air at the 50 watt output level.

 

[w4bfs]

Eimac had a note about the 4x150 / 4cx250 family about a min air flow past the base to keep the seals cool .... it said the flow was needed for just fil power ... of course they also had an expensive socket to sell !!!

[KB2WIG]

I think you should build a 813 rig, modded by 811s or even 2e26s, using a power transformer as a mod transformer. Thats watt I think you should do.

Think of the children.

klc

[N2DTS]

Maybe.
But I ran a pair for a year in loctal sockets at 300 watts out.
That is NO air flow past the base as it was stuck in a socket like an octal tube.
The RF deck is still that way, still works.

I would use the right socket and be safe, but I do not think they need much air unless you push the tubes.
I checked the loctal sockets and they show no signs of getting hot.

Eimac had a note about the 4x150 / 4cx250 family about a min air flow past the base to keep the seals cool .... it said the flow was needed for just fil power ... of course they also had an expensive socket to sell !!!

[w1vtp]

Also, I suppose no one makes crystals anymore, but that is the easy way to do a 40 meter AM rig.

ICM still supplies them:
http://www.icmfg.com/hamradio-manufacturers.html

Pete

I've used this guy with good results

http://www.af4k.com/crystals.htm

[N2DTS]

Thanks Al.

I have some of my old ones but they were for the CW section I think.

Also, I suppose no one makes crystals anymore, but that is the easy way to do a 40 meter AM rig.

ICM still supplies them:
http://www.icmfg.com/hamradio-manufacturers.html

Pete

I've used this guy with good results

http://www.af4k.com/crystals.htm

[w5gw]

As far as VFO suggestion, this is not vintage, but works great.

There are DDS boards on eBay using the AD9850 chip for about $10.  see http://www.ebay.com/itm/AD9850-DDS-Signal-Generator-Module-0-40MHz-IC-Test-Equipment-Sine-Square-Wave-/390769215986?pt=LH_DefaultDomain_2&hash=item5afba909f2

Couple this with an Arduino microprocessor and make a rock solid Digital VFO - see http://www.ad7c.com/projects/ad9850-dds-vfo/

I built one and added a small buffer amplifier using a couple of 2N2222 transistors to get about 5 V P-P which is more than enough to drive my Viking II

It is enclosed in a case with the digital readout and voltage regulator to go from 12 VDC to 9 VDC to power Arduino. You tap off the Arduino's 3.3 regulator to power the DDS board.

Note: Output of these DDS boards rolls off pretty fast above 10 MHz, but for a replacement VFO for any transmitter that uses doubling or tripling in circuit like the Viking II does, it is perfect. Total cost for case, Arduino, DDS board, 1602 LCD display and misc parts was perhaps $65.00

[N2DTS]

Well, I want simple, and I have built VFO/exciters and they are easy, without the digital hash and garbage and phase noise. Its very easy to make a small vfo in a small box, 2 tubes and a handful of parts, but it does not beat plugging in a crystal.
Three crystals and a switch would take care of the job, 7285, 7290 and 7295.
Its not like this would be the only rig I have.

[W4RFM]

The 12BY7 is your friend. 

[N2DTS]

Yes, seen it done with a 5763 also.
The 4cx250 takes very little drive, so I think a 12BY7 into the grid would do.
I found a circuit in a handbook with a 6b?? something tube that drives a grid of a 6146 in a screen modulated setup, I could try that setup.

The 12BY7 is your friend. 

[N2DTS]

Did a test, took one tube out of my 2x4x150 rf deck, hooked up the screen modulator and ran both off the same supply at 600 to 800 volts.
I had to change the pie net coil (plug in) to match the new setup, but I could not get the thing to work well at a reasonable power output. The 4x150 wants more plate voltage to work well under screen modulation.

So its back to the design phase, 4D32 modulated by a pair of 6l6's?
Or a 4D32 screen modulated like a turbo dx60, 20 to 25 watts out?

[N2DTS]

As a test, I think I will pull two of the 4D32's out of the 3x4D32 rf deck and hook the screen modulator up to that and see how it works off one supply.
I think the dx60 does about 12 watts out after mods, a 4D32 should do about 25 watts carrier.
Now how to go from a D104 to a 600 ohm line level without transformers....

[N2DTS]

Would the circuit in the dx60 drive a 4D32 as well as a 6146?
I think that would be easy to make in a small space, and it supports a d104 input.
I hear great sounding dx60's often.

Crappy power supply, full wave bridge to a 15 uf oil filled cap, center tap for lower voltage, a tube for grid drive, a mic preamp and the dx60 screen mod with the modifications listed on this site into a 4D32 at 700 to 800 volts.

[WD8BIL]

Brett........ I have a single 4CX250B in the Viking Bud (VK1). At stock voltages I get, on average, 75-90 watt carrier.

I have a variac on the plate transformer primary that'll lift the voltage to just over 1KV. That makes the tube really stand up at 150 watt carrier on cw. The 807s can't mod that to 100% so I run the variac at 120% for a 135w carrier and get 100% mod.

But most of the time the variac is turned WAY down to give 20w carrier to drive the amp to legal limit.

[N2DTS]

Yes, a 4x150/4cx250b would plate modulate very well up to about 250 watts carrier.
They work at 500 volts on up to 1600 or 1800 with plate modulation.
They are rated at 1600 volts and 200 ma for plate modulation and 2000 volts and 250 ma for CW.
That is 320 watts input (275 out) for ONE tube.
They screen modulate VERY well at 1500 volts on up to 2000 volts, but at 600 to 800 volts they do not put out much power at all with low distortion levels.

For a very small rig, a plate modulator is a pain, a mod transformer, two modulator tubes, phase inverter AB1 or class B driver transformer, various voltage levels needed, bias circuits sometimes, screen protection.
A ranger or a G76 is quite amazing for the amount of stuff they got into a small package.
My home brew single band ranger would be DX100 size and weight....
Anything I build just tends to get huge...

[N2DTS]

I did a test, took two of the 4D32's out of the 3x4D32 deck, hooked up the screen modulator to it, powered the rf deck and the screen modulator off the same supply at 600 to 800 volts and it worked very well, 35 or 40 watts out and 150 or more watts pep, and it sounded very good.

So a 4D32 with a screen modulator puts out enough power to be useful, sounds good, and will be simple and easy.

There are a number of circuits for the dx60, I am not sure if they will do the 4D32 as well.
Some circuits use a separate -120 volt supply, some do not, and I was surprised to find they use a 6DE7 dual triode, a miniature 9 pin tube!
I also know the Knight kit T150 transmitter used the same tube for a pair of 6146's, same as a 4D32 really.
There are a number of circuits, I do not know which one to try.
And why not use a 6080/6as7 or some big low mew dual triode that is good for some power?

The solid state modulator is great but it needs some high voltage parts and some big heat sinks.

[N2DTS]

I ordered four 6de7 tubes (they are cheap) to experiment with.
I like the circuit from Ed (KS3K), d104 in, only 2 tubes.

[Opcom]

Those 6080 and related tubes are favorites around here because of their high current. Never tried one as a screen modulator but they should accommodate a heavy bleeder where needed to absorb negative screen current. It would be nice to find a schematic for a DC coupled totem pole arrangement instead.

[N2DTS]

I have a lot of those 6080's and even the JAN shields for them.
I use one in the screen voltage regulator in the 4x150 mod deck and that is it.
I always wanted to use them in audio service but never came up with anything.

[Steve - K4HX]

This rig uses a 6080 as a screen modulator.

http://amwindow.org/tech/htm/ne1stx.htm

[N2DTS]

Wow, thanks for that!
Very interesting!

This rig uses a 6080 as a screen modulator.

http://amwindow.org/tech/htm/ne1stx.htm

[Opcom]

ask and you shall receive! 

Audiophools have been using those for a long time to drive speakers directly. Fine if you have 20 of them.. and the results are not so great without a lot of fussing and a lot of idling current whereas you probably won't ever wear them out as screen regulators or modulators.