E.H. Scott All-Wave 15
By Doug Criner
A 1934 model, this receiver, with “only” 15 tubes, is almost a piker among Scott radios. But as shown in Photo 1, it sports the usual Scott refinements, including a chrome-plated chassis and tube shields.
Photo 1
This set did not have a cabinet when I purchased it. Cabinets were sold separately from the chassis, so it’s possible this radio never had a cabinet. I rather think that it is much more attractive the way it is, without a cabinet.
Photo 2 shows the underside of the chassis. Notice the coil turret that rotates with gearing turned by the band selector knob. The idea is that for the various bands, different coils are connected directly into the circuit – avoiding the necessity of a band switch with length variations in coil leads and associated alignment issues.
Photo 2
This set has a push-button on the front of the chassis to cut in a beat-frequency oscillator. The purpose was not to listen to CW or single sideband, but to provide a whistle to hear a weak station's carrier, allowing for precise tuning. There is also a signal-strength meter to help with tuning.
When I acquired this radio, there was no speaker with it. I built an adapter box to allow use of a conventional 8-ohm, permanent-magnet speaker; the black audio output transformer mounted on this small box may be seen at the upper right of Photo 1. The adapter box includes power resistors to substitute for the electrodynamic speaker coils that served as chokes in the B+ supply. I am using an 8-inch, full-range hi-fi speaker in a reflex enclosure. The speaker impedance is matched by a 15-W Hammond #1625 audio output transformer that presents a 5,000-ohm plate load to the push-pull 2A3 output tubes .
The power supply and the two 2A3 push-pull audio output tubes are on a separate chassis – visible in the lower right of Photo 1.
The set has excellent tone. Connecting a CD player to the radio’s phono connection results in very enjoyable music, rivaling modern hi-fi amplifiers. I have tested the frequency response of the audio section: it measures 64-18,000 Hz, plus/minus 2 dB. The test was done with a dummy resistive load.
This particular set is a relatively early All-Wave 15 version – using a 6-pin Wunderlich tube for the 2nd detector. Later versions used a 55 tube for this stage. Wunderlichs were proprietary detector tubes manufactured by Arcturus.
The circuit includes one tuned RF stage, separate mixer and oscillator tubes, three IF stages, the Wunderlich audio detector, and three audio stages. The audio stages consist of: a 56 triode for the 1st AF, two 56s in push-pull for the 2nd stage, and two 2A3 triodes in push-pull for the final audio. Even today, audiophiles admire 2A3s for audio tubes.
The complete tube complement also includes a rectifier, a BFO, and a driver for the tuning meter – for a total of 15 tubes. All tubes are pre-octals with ST-shaped glass envelopes (except for the Wunderlich tube, which is globe shaped). All the tubes have 2.5-V filaments, except the 5-V 5Z3 rectifier.
The radio played when I first obtained it and all tubes tested good. Restoration included recapping and general cleaning. The contacts for the coil turret were touchy, so I removed the turret and polished the contacts with emery cloth, followed by tuner cleaner. The BFO didn’t operate – due to an open in the BFO coil; the problem was where the winding connected to the coil’s terminal, an easy fix.
Unlike many Scotts, the original chrome plating is in good condition.
Interesting information on Scott and his radios is published in E.H. Scott - Dean of DX, 2nd edition, by Marvin Hobbs.
©2006, Doug Criner