showing off my TV

[jshorva65]

Originally posted by Chad Hauris
You don't want to use an 807 for a part 15 unlicensed transmitter...that is a 25 watt tube at least. The FCC will be calling.
Check out Robert Casey wa2ise's web site for info about tube AM micro-transmitters. You can use parts from an old AM tube type radio.

As Chad pointed out, if you want to build a tube-type transmitter, the 807 is way too much for a Part-15 unlicensed unit. There was a design for a Part-15 compliant AM transmitter published in a Ham Radio book some time ago which I seem to remember used a 6A8, 6J7 and powered by two 6.3V 2A transformers connected secondary-to-secondary with a 6X5 or some similar rectifier tube. The first transformer stepped-down the 120V line to povide a 6.3V heater supply for the tubes and to also be stepped back up to provide an isolated and energy-limited 120V source to be half-wave rectified and filtered to meet the unit's B+ requirements. You could redesign the unit using 6.3V single-ended octal equivalents (6SA7, 6SJ7 and keep the 6X5) or use 12.6V tubes with two 12.6V transformers (12SA7, 12SJ7. 12Z3). Miniature types 12BE6, 12BA6 and 12X4 would also work well with a 12.6V heater supply.

AES sells a transformer with 115V primary, 125V 15mA and 12.6V 300 mA secondaries (AES #P-T442 for $16.95) which would power a transmitter using either a 12SA7 and 12SJ7 or 12BE6 and 12BA6 tube complement. Since the 12SA7 and 12SJ7 or the 12BE6 and 12BA6 would draw a total heater current of 300mA, there would be nothing left for the heater of a 12.6V tube rectifier (12Z3, 12X4 etc.) so a silicon diode or 117Z3 (miniature) or 117Z4 (octal) rectifier would be needed. The 117V 40mA heater of either rectifier tube would connect directly across the transformer primary and is insulated from the plate and cathode UNLESS the tube developed a short. The elimination of the 117V rectifier tube and use of a silicon diode and series resistor instead would reduce the risk of loss of transformer isolation due to a rectifier tube short. There are also reasonably-effective means of protecting the rectifier tube against transients (line-to-chassis bypass capacitors of about 0.01uF 600V shunted by 2.2M 1/2W resistors) which are the most frequent cause of breakdown of the insulation between heater and cathode. The particulars will be the builder's choice. The bottom line is that quite a nice Part-15 compliant transmitter could be built around an octal or miniature tube complement using readily-available parts.

[mbates14]

file not found error on his page.

I gots an old h-out compactron TV tube that might work.

[jshorva65]

Originally posted by mbates14
file not found error on his page.

I gots an old h-out compactron TV tube that might work.

Again, mike, the tube is too big. The TV sweep tubes are all power tubes designed to produce several watts. In the circuit I discussed, the 6J7 is an RF/IF amp used in old radios. In this design, IIRC, it was fed the audio signal at its grid and used as a resistance-capacitance coupled pentode audio preamp to drive the grid of the 6A8 pentagrid converter tube which was operated as a modulated RF oscillator. Again with these old radio receiver RF/IF amp and converter tubes we're in the range of milliwatts with a signal that can be picked up by an AM radio at a distance of 30-50 feet. Use a sweep tube and I bet you could pick the signal up several blocks away. Again, the FCC would be calling and would probably confiscate a device you spent many hours and some cash to build. Plkate currents in these tubes run 1-2 mA or so at a B+ voltage of 120VDC (tube rectifier) or 160VDC (silicon diode rectifier).

Those sweep tubes could be put to much better use in pairs with output transformers and a preamp stage or two in a nice audio amp. A pair of those sweep tubes in pus-pull would probably push 30 watts RMS or more audio into a speaker for mono. Two pairs with two transformers for stereo.

Some old tube manuals like RCA RC15 or RC17 had a circuit for a Part-15 compliant "wireless" transmitter, IIRC.

[Charlie]

I bought one of those AM transmitter kits several years ago from AES that uses a 12SA7. Works pretty good. Using a generous length of wire, it would transmit at least 100 feet. I could be at my neighbor's house, and pick it up from my house.

Ah yes! Fahnstock (sp?) connectors!! Haven't seen those in quite a while. Used to use those on all sorts of home brew projects in the 60's

Anthony

[mbates14]

can anybody post any schematics to any of those transmitters?

my divide by 4 solidstate oscillator (1610mhz) died.

I got like a 6au6, and a 12ba6

would those work?

[mbates14]

the problem I had with my solid state transmitter, is it would not only sound very very crappy, BUT usually, well normally
the farther you walk away from the antenna/xmitter the statickier the signal gets right? well WRONG with my transmitter

it worked rather wierd. the farther i got from it, the audio would drop. it would never get staticky, the audio would just fade and begin to die.

[mbates14]

Ah, i was finally able to get to his site.

But, i have an issue. If you look in the schematic below, What am i supposed to use for a tuning cap/coil? i dont have an AA5

[mbates14]

Any ideas on what kind of coil in the schematic I could use? i dont have an AA5. never had one, never will.

i dont have a 12av6, or a 12be6.

I have the 6al5, the 6v filiment version. I also have the 50c5, but im not going to use a 50c5. im going to use maybe a 12ba6 for the output.

any ideas?? please.

i wonder if i can make due with all the tubes i currently have.

I have a: 6CB6A, 12BH7A, 12AT7, 12AU7, 5LJ8, 6CB6a, 3GK5, (emerson triple triode, no number), 11BQ11, 23Z9, GY7A, 6BQ6GA, 12BH7, 6AL5, 6BH7A, 8LT8, 17BF11, 50C5, 14GT8, 12AU6, 12BA6, 12BA6.

these are all the tubes I have on hand.

Can I use any of these to substitude for the ones in the schematic??

[mbates14]

hmmm. rather quiet.

[Kamakiri]

PM me your address and I'll gladly send you the 12AV6 and 12BE6, on the house

Any other tubes ya need?

[mbates14]

i forgot to ask you this in your PM, but about the 35W4, can you use diode substitude? I got some huge rectifier dioes lying around. I used 2 of them to replace those seleniums in my TV.

if i could use a diode in place of that 35W4, How?

[Kamakiri]

How many of them do you need? I have a bunch.

[mbates14]

a bunch of what.

[mbates14]

oh, BTW Charlie reminded me that I went to far off topic, well, if you would kindly move where it starts into AM transmitter to the DIY forums.

thanks.