New here, looking for ideas...

[VE3GZB]

Hi

After a long time I finally applied and received my license, so I'm looking to build a 1920s/30s style Phone transmitter. I have a limited number of receiving and a few transmitting tubes, coils, caps, etc...I can work with. Nothing high power though.

To work 80 and maybe 40 meters, what would be a good power to start with? Any suggested designs which are popular?

Thanks & 73s,
geo
VE3GZB

[WU2D]

Hello Geo,

Ham transmitters in the 20's were pretty simple and very low power. Heck even the commercial gear was simple. W1VZR Pete runs a Hartley Oscillator, Heising modulated. Then came MOPA's with a bit more stability and output power. These can be effective on 80M if you use some larger tubes like 211's, 811's 812's. 40M is stretching it for a free running power oscillator.

People do run 1929 style type 10 oscillators and I run a 45 TPTG oscillator but these are flea power at 3-5 Watts out. The larger tubes are actually more stable because the big fillament dissipation tends to stabilize the drift and you get more power out! 

In the mid 30's you start to see crystal controlled transmitter designs with push pull stages both in the RF and modulator. Think triodes like 810's modulated by 810's. By the late 30's most of the common architectures are complete and pentodes show up. 

WU2D Mike

[VE3GZB]

The tubes I have include a 71A, a 183 (5 volt version of a 45), a single 47, a few UV99s and a couple of 01As. All triodes (except the 47) and all fairly low power. I also have some British tubes on the way, the most powerful being the PM2 (all receiver tubes you'll notice).

Modulation is something I have limited means so I would have to resort to using a surplus solid state 25 watt audio amplifier and an old audio transformer for step-up. Also I'm not sure if I should grid modulate or plate modulate or consider trying Heising modulation (I have no many old tubes for power). I'm exploring different ideas to see which would be the best approach given what I have on hand. I also have a number of crystals from Digikey (I don't have any old crystals).

I also have to figure out what type of Antenna I should erect. I have loop antennas constructed already but I'm pondering whether to set up a dipole or a Zepp in the backyard (small backyard).

Tubes from a later era which I also have include several 6AG7s, a pair of 807s, a 6L6G, a few different Horizontal output tubes and some 2E26s. To remain true to idea of building a 20s/30s voice QRP rig (simply because I don't know any code), I'd like to refrain from using the tubes which are of a later date (which would probably offer me a better, easier result) and stick with the old technology, just for the sake of reviving it.

I'd like to use a MOPA scheme of course so my frequency doesn't drift during modulation. How far could I expect my signal to go on such low power? Could I see details on W1VZR's Heising-modulated Hartely?

Thanks

[KI4YAN]

go with the most powerful tube as your RF final, and use a lower power tube as the master oscillator, minimize drift. How far you can talk is a function of how many watts of carrier, how good your location is, and how good your antenna is. To say nothing of what the other guy is using...

I'd go 01A-PM2, plate modulated by the audio amp (serious overkill) and xtal controlled until you know it works. once you have this station up and working, make a few contacts, then run the pair of 807's for finals, unless you pick up some bigger plates.

I ran a 6V6 plate modulated for about a month, before getting fed up with how hard it was to actually make a contact with it. Now I'm working on an 807s-modding-812's design.

[KM1H]

Id start off with a 41 or 42 crystal oscillator followed by another as buffer/multiplier. Those are very early 30's tubes that are easy to find at low cost. A 6V6/6L6 in that order will do the same. Depending upon the oscillator circuit, you can later drive it with a VFO.

The PA can be any number of tubes but from an ease of getting it going and stable a couple of 6L6's are hard to beat. Those came out in 35.

Another nice later 30's tube, and a real sleeper, is the 814/VT-154, an easy 100W out on AM with very low drive.

Carl
KM1H

[WU2D]

I like Carls ideas for ease of getting the thing up and running. If you must use a pre-1930 tube, the 71A is a pretty low output tube ( about 2W out on 80m) and so are the 01A's, at 1 Watt out as oscillators.

A type 10 or 45 is a step up but I think the 47 (or 6AG7) or two into an 807 (or 6L6) would be a simple approach and you could try to modulate it with your amplifier using a backward transformer in a modified Hiesing arrangement.

Mike WU2D

[flintstone mop]

Hi Geo,
Welcome to the Club and the mode that people sound like people.
I don't want to post any negative thoughts, but flea or QRP would be something for day time when 40M has a good day or when the sunspots increase. Even 80M is good early in the evenings, but nighttime is a struggle for folks using legal limit and big antennas. The radio highways are a little busy lately, now that we are officially in the radio season 2008-2009.
Good luck, Geo, with your project

Fred

[VE3GZB]

Simplicity is my goal, also because I just like tubes and grew up learning tubes first.....Hmmmm.....lots of food for thought here......the one thing I want to try to do it keep filament voltages the same and in an ideal world if possible, keep the design using directly heated tubes, hopefully all running 5 volt filaments because of simplicity.....if there's an emergency and there's no AC power, I can still use a 6 volt lantern battery for filament power (I have a box with a bunch of 9 volt cells wired in series, totaling about 200 V) but also 5V is convenient because those silly little computer power supplies give 5 volts so readily.

Other tubes such as a 45 (which are darned expensive & rare) have a different filament voltage and that would complicate how I could provide power to it. I have a C183 which is a 5 volt filament version of a 45, so this could be a blessing for me, though I have only one. It works very well!

(Although I've been in electronics most of my life and work as an engineer, I've never built anything stronger than a few hundred mW and put it on the air so naturally I'm concerned about trying my best and keeping the design clean and avoiding needless complication, especially with odd filament voltages and power supply requirements.)

I stumbled across something recently that really caught my eye:

http://greyhairnet.org/uaxhartley/uax_hartley2.htm

This looks very nice to me!! Very beautiful in fact! It's the sort of thing I'd like to build but before I commit to any design and use what parts/tubes I have I'd like to know how well this design operates, what the drift/deviation is like when modulating and how it performs for distance?

How many watts might it deliver (and how many are really needed)?. Has anyone made something like it and can testify how well it works? Is a schematic available? It doesn't look like it's Xtal controlled, could it be a VFO? Would I run a risk harmonics or out of band drift with it? Are any parts critical?

I have old 1920s/30s QST and 1940s ARRL material but some of these tubes and parts listed in them are just not available to me, not even on a good day! So I'm trying to do this on the ultra-cheap budget with what I have on hand (LOTS of it was generously given to me for free by a friend of mine, VE3AWA over in St. Marys Ontario who runs a pair of 10s push-pull, transmitting code....his furthest contact has been down to Florida, I think he only runs about 10 watts at most).

Has anyone tried using loop antennas for transmitting shortwave, like with 10 watts or less on 'phone? I don't have an external antenna set up and the snow is already on the ground so it's lousy weather to build one (even if I had the parts for an antenna).

But I already have a couple of rectangular loops built from last year, I was experimenting with other stuff....I made them out of just 100ft. of 16ga speaker wire wound on a 2X4ft "X" frame with multiple taps for different inductances.

For receiving, I'll be building a 3 or 4 battery-tube type regenerative receiver on the base of this mini-loop antenna (see attached photo). I've already tried it with my HQ-100 which works on only a couple of bands and I get good reception even to Radio China and Romania....I've wound it on an old picture frame and it resonates from about 3 to 8Mhz or so, which covers the bands I want to work when I build my transmitter onto the 2X4ft loop).

Would an indoor loop antenna be any good for transmitting?

[KM1H]

Directly heated tubes eat batteries real fast. Indirect heated tubes and a 6V car battery will last a lot longer.

For a real emergency a 12V car battery and inverter to 120V are very efficient. I ran my house one winter for 4 days ( It was around 17-20 F at night here in NH) using a 1500W inverter off my car (Ford Taurus). A bit of creative wiring (with the mains breaker removed), many extension cords, and switching loads as needed kept the oil burner and circulators doing their thing, kept the refrigerator happy, enough lights using CFL's in selected spots, a hotplate, etc. It was disruptive but not a bad experience. With a 20 gallon gas tank I didnt need many trips to the pumps, my main worry was overloading the alternator which got a bit warm at times so I left the hood up which did the trick

For radio use you can use one of the old DC supplies sold for tube era xcvrs from many manufacturers to get enough power to actually be useful. QRP is a drag at times and in an emergency its a poor choice if it can be avoided. BUT I certainly wouldnt rely on tubes, and the efficiency issue, for any extended emergency.

Carl
KM1H

[Opcom]

If you are willing to go with something a bit more modern, you can get into 808's and 250TH's, and the like.

If the '40's strikes your fancy and a carrier of 20-40W is OK, I have some NOS 8025's, plenty to share.

They have a 4-pin base like the older tubes, so you could sneak one or two of them in and most people would not notice ex ept for the bright directly heated filament of 6.3v. will take 1KVDC (800V in plate modulated service), handle 80mA, and also will do zero bias at 300V for low voltage apps.

datasheets:
http://www.mif.pg.gda.pl/homepages/frank/sheets/049/8/8025A.pdf
and
http://www.bunkerofdoom.com/tubes/tt4/rcatt40265.html

I will be happy to share, I have more than I will ever use.

[VE3GZB]

Opcom, I sent you a PM.