Dual-direction rhombic antenna switching network.

Thoughts on the Fort Tuthill QRP Transceiver

On converting the Fort Tuthill 80 to 40 meters

Someone on the FtTuthill80 mailing list first said:

I've just completed my Tut80 and it works really nicely! I'm getting 5+ watts out of it after applying the simple PA mods described elsewhere on this group, and that was easy. Now I am considering to buy a second 80m unit, which I would like to move to the 40m band. I have been told off-list that I need to change only a bunch of components, most notably the VFO and TX low-pass coils of course, probably also a few caps, while I'm not sure about transformer T1 (but I believe it won't change). Anyway, can anyone provide hints/pointers to what actually needs to be changed and with what new values? I have searched this group for previous posts on this subject but I didn't find any, maybe I didn't look carefully enough. If so, I apologize.

I asked about this and was first told:

Far as I know, no one has published a 40m modification. The VFO triples to 80m so you would have to move the VFO to something like 2.3 MHz and redo the tripler to 40m. The transmitter output filters would also need to change to 40m. Don't think (from memory) there are any other frequency determining sections.

And then:

Everyone seems to keep hush on this subject, and I suspect that this is done not to interfere with Doug Hendricks' plans to eventually release a 40m kit. In fact I think there would be no interference because the commercial kit will probably offer more features, as already does the 15m version. I personally have not been spending more time trying to figure out the needed changes myself, but should I get back to that I'll let you know. Sure a 40m version of this excellent radio would be a top seller. In many ways I prefer this one over a (simple) superhet.

There was some back and forth on the mailing list a few months later, it looked like inaccurate speculation about who was made over what.

Then this appeared:

I also like the idea of a Tut40. Here's some thoughts on making the conversion.

It doesnt sound difficult. Nearly all the frequency sensitive components need to be changed of course, but simple frequency scaling should be adequate for that. Here's link to a spreadsheet which will make that easy: http://www.wa0itp.com/tipstricksinfo.html

Yes, Dan runs the oscillator at about 1.167 mc and tripling into the 80M band. You could triple also by running it in the 2.3 Mc range. Or run it on 80M and double it.

Dan Tayloe on troubleshooting

From the FtTuthill80 mailing list, responding to someone whose FtTuthill80 seems to transmit fine but doesn't receiver:

When you transmit, are you getting the typical 2.5w+ out of the transmitter? If so, that eliminates a lot of things.

The VFO should be on pin 10 of IC6, the 74HC4053 chip which is the detector. If you have a scope, check the signal at that point.

The first check is to make sure you get audio though the amplifier chain. If you touch C19, R18, R17, IC4B pin 5, any of these with your finger, you ought to get a loud hum. If you do, your audio chain is working fine.

If that is fine, the next step is to check out the receiver detector, IC6 and the front end filter components.

You should not use another transmitter to transmit into the front end of your receiver! However, you can take another rig (like the K3) and transmit into a dummy load, thin take a 2' section of wire and using it like an antenna touch either side of C51 to try to inject a strong signal into the detector, picking up the signal from the nearby dummy load, which should be within a foot or so of the 2' wire "antenna".

If you an hear the signal in the receiver, move closer to the antenna to see where you lose the signal. Touch the wire to C52/L2, then C49/L3, then R38, then C55, then C59, then C60. Look at the schematic to see where these parts are in the signal chain.

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