Just saying, I'm not intentionally advertising this, but:-

http://www.ebay.com.au/itm/332171054983

I bought one...

The soldering is challenging (I nearly soldered tracks together) I run mine of 8AA Batteries and they seem to last ages and ages, when there's nothing but boring footy on all day, I plug the headphone output of my PC into it and tune any one of my old radios into any one of a bunch of cool vintage internet radio stations! To my surpprise even radios I thought a bit deaf of poor performers, are suddenly belting it out! Must be the close proximity of the signal, but yes I'm glad to have this! Really worth it.

Amazing how the tonal characteristics of different radios in a room come together to give an almost multi-channel, surround sound effect!!! Quite marvelous!!!

I built the Little Jim AM transmitter project that was published in Silicon Chip:- http://archive.siliconchip.com.au/cms/A_105705/article.html

I ordered the printed circuit board from silicon chip and I brought the components from Jaycar. The only component that Jaycar did not stock was the modulator IC chip which I purchased from ebay. The little Jim transmitter works very well. It has a variable tuning capacitor to adjust the transmitting frequency and a pot to adjust the modulation.

I own and restored a 1967 Ford Cortina which still has the original AWA car radio installed. The transmitter is very useful when I take the Cortina for a drive on the weekends. I plug a portable MP3 player into the transmitter and enjoy listening to music through the AM car radio.

Interesting nowadays to see a kit sourced from Japan and not China.

Yeah, that struck me too, that it is Japanese.

It has no volume or tuning control, just 1308kHz steady, making it easy tuning into, a very strong signal which basically over-rides everything on or near that frequency and the volume of the input signal is what matters, at about two thirds volume it is perfect, above three quarters the radio's noticeably start clipping distortion, below two thirds the volume of the radio's noticeably reduces, so a happy medium is easily found between the two, however my AC/ DC console is over-loud and distorting at zero volume, so I'd need to reduce the input volume considerably, but that's easy enough in it'self so no problem at all. There's just a little LED to yet you know it's on!

Not exactly brilliant.
1308 is not divisible by 9, so to use it as a modulator it would not be received by a modern digital tuning AM radios.
JJ

I think USA still uses 10 but the analogue radios won't care. Problem solved.

Marc

It's 9 in Australia.
Which means modern step tuned AM radios will not work with this 1308 rf/modulator.
Still useful for the old receivers, But problem solved? , I do not understand?.
JJ

A few of us on here have built the earlier version of this two-valve AM transmitter:

http://www.6v6.co.uk/transmitters/itx-tube-am-transmitter-with-plug-in-coils-kit.html#

Not exactly portable, but works well enough around the house.

This newer version can also cover short wave.

Re the kit...

Hmmmm....

What do you do if you're stuck with a load of expensive one-time-programmable oscillators that have been programmed to the wrong frequency?

Answer? Make an AM transmitter kit and sell it on Ebay!

Simple!

I have the early version of that kit and it works well. It is not the most powerful out there but it is still fit for purpose and does what is asked of it. Good design, easy to build and reliable.

It is not the most powerful out there

... nor should it be, of course, if it's to stay beneath the regulatory radar.

I use a mains power supply on mine and the signal is strong enough for around the home, as per design.

Yeah that's what's brilliant! It works, who cares about modern AM receivers, I don't nor do I want to own any. It works great for the older ones, which I have, as intended! This one is a bit more powerful, I can pick it up everywhere in the house and backyard, which is fine by me, that's the intended purpose, for which I am using it with satisfaction!
The valve one looks like a good one to try though!

I only brought this up to broaden your and readers knowledge.
On the AM broadcast band as is now, and the operation of modern step tuned radios.
I can understand why you don't want to own a modern AM receiver( soon to become vintage).
But if that's the case you should be looking at building a valve modulator and not a solid state one.

JJ

One of the things to consider, if you do go valve; valves like 6BL8 are prolific & are a frequency changer, but used everywhere else.

You may not be able to directly ground, but if you want it really stable, do consider regulated heater voltage and something like an LR8 to control the high voltage on the RF oscillator. Many of the older Pentagrids are voltage sensitive. There will be no hum modulation from the heaters if they are run on DC.

There are some interesting modules etc. about. There are some very cheap frequency counter ones that can be adapted to the el cheapo Signal Generator, making it capable of being set more precisely on a frequency.

Marc

Photo uploaded to Post 10. I knew I had this somewhere, as we have discussed AM transmitters a few times before. Since taking that photo I have shimmied the PCB 90 degrees so the RCA sockets could be used as intended.