Don, > >...the Scott had push pull 25L6 (6L6 with 25 volt filaments), ... > > The tube is a beam power tetrode like the 6L6, but two are > quite different. > The 25L5, 35L6 and 50L6 were designed for ac/dc radios, they > are physically > much smaller and have nowhere near the scrote of a 6L6. They > are more like > a 6V6 than a 6L6. A later miniature version is the 50C5, > which is similar > to a 6AQ5.
Thanks for pointing that out, I never looked up the tube, and assumed it was just like a 6L6! The Scott only runs about 120 volts on things, so power output is low, but its very clean, about 3 watts likely. > > I have a Scott SLRM with pushpull 25L6's, and it sounds very > good on AM. It > is not a real communications receiver, though. It is more > like a high > quality late 1930's broadcast radio. Most of the precision > technology went > into careful shielding to prevent the local oscillator from > radiating. The > rx was used on board the Liberty Ships during WWII as an > entertainment > radio. They didn't want the enemy to home on the signal from > the oscillator > and discover the location of the ship. I knew it was designed to prevent anything radiating out of the receiver. They really went to extreme methods to prevent any LO radiation, completely closed cabinet, not even a single vent hole, total shielding between the rf coils in the RF amp, etc. I knew it was designed just before WW2, and also knew it was designed for use on ships, but I did not know about the liberty ships. Its only real drawback is the frequency resolution, the stability is very good, the noise is very low, good bandwidth choices. I had problems with the magic eye tube, it was too dim till I increased the voltage to it...I think I built a little separate high voltage supply and got the plate voltage up to 200 volts, and the tube is nice and bright. The mixer design they used looks very interesting, and works very well. Its a pentode, and they use one grid for rf, another for the LO injection. I have not seen that circuit design in any of the handbooks or other receivers, they use multigrid converter tubes (4 grids) which are very noisy, or use tubes with 3 grids but inject the LO into the rf grid or the cathode circuit, not another grid like the Scott. The circuit Scott used seems to be very quiet, but isolates the LO very well from the tuned circuits in the mixer RF input. The Scott I have is just like new,, and in 10 years or so has not had a single problem other than the dim magic eye tube. Radio shack made a good foam suspension speaker with wizzer cone that fits in, and sounds very good! Another great thing about the Scott SLRM is that both 80 and 40 meters are on the same band (2). Tuning is a little touchy, but no band changing between 80 and 40 meters! Its quite a good receiver for AM when things are not crowded, and when the band is packed, I don't want to listen anyway, too much of a chore on any receiver. Its nice to use when hanging around the shack building things, a real fine sounding classic! Brett N2DTS > > Don K4KYV > > _________________________________________________________________ > Add MSN 8 Internet Software to your current Internet access and enjoy > patented spam control and more. Get two months FREE! > http://join.msn.com/?page=dept/byoa > > _______________________________________________ > AMRadio mailing list > AMRadio@mailman.qth.net > http://mailman.qth.net/mailman/listinfo/amradio
