Hallicrafters S-40B
The S-40B is a single conversion general coverage receiver covering 4 bands from AM broadcast to 44 MHz. It is a minor upgrade of the S-40 and S-40A with one less tube but all the same functions. All of these sets feature electrical bandspread, BFO, an RF amp and two stages of IF amplification. The S-40 and S-40A use a type 80 tube rectifier and a 6F6 audio output tube. The S-40B uses a 5Y3GT and a 6K6GT for those functions. Other tubes in this set are 6SG7 as RF amp, 6SA7 converter, two 6SK7 for IF amps, 6SC7 for BFO and first audio, and 6H6 for detector, AGC, and noise limiter. The S-77A is an AC-DC version of the S-40B.Advertised price was $89.95 in 1950.
Hallicrafters S-40B
Repairs
The Hallicrafters manual is available in PDF format from BAMA. See my homewpage for a link.
I removed the chassis and front panel, and then cleaned with white waterless hand cleaner. Controls, switches and tube sockets were cleaned with contact cleaner. Several capacitors needed to be replaced. One Micamold cap from the power line to chassis had split in two parts. I replaced it with a cap rated for use as power line filter. I routinely replace the cap to the input grid of the final audio amp, the 6K6 in this set. A slow power-up with an isolated variac followed. The electrolytic reformed properly. Although the set worked decently after power up, the B+ section feeding the converter was lower in voltage than indicated in the voltage chart. The lower voltage caused the converter to drop out at times on the highest band setting. I substituted the 6SA7 with no improvement. What the schematic shows as a 12K ohm resistor was in reality two 24K resistors in parallel. Those had drifted high. I replaced the pair with a 12 K ohm, 10 watt power resistor.
I followed up with an alignment. Tweaking of the RF and the converter stages made for a great improvement in sensitivity. Final sensitivity was excellent on broadcast and very good on the lower shortwave bands. I listened to a couple of SSB transmissions on 20 meters with just a 10 feet hank of wire for an antenna.
Comparing the S-40B and S-77A
I had repaired an S-77A prior to working on the S-40B. Here is a picture of the two side-by-side with a view "under the hood". Both are decent performers, but the S-40B seems to have a slight edge in sensitivity on the highest band.
S-40B (left) and S-77A (right). Note the lack of power transformer in the S-77A.
Hallicrafters ad covered both the S-40B and S-77.
As noted above, the Hallicrafters S-77A was the previous item on the bench.