This multi-band Coronado receiver we rescued from a neighbor's trash heap seems to be complete, except for speaker(s). The wood cabinet is 33" high, 20" wide, 10" deep. Tubes seem to match the socket lettering and are: 80, 76 shielded, (2) 6K7GT, 6K7 metal, 6B7 shielded, 6F6G, plus 6U6/6G5 (tuning indicator, apparently).

We'd like to identify the model and find a schematic, but the only markings that seem significant are on the back of the chassis: A 67/20 and 7R 951873. The underside of the power supply transformer is marked 7 16 36 (a date?).

We'd appreciate any help, hints or suggestions that you could provide.

Wes Nelson

: This multi-band Coronado receiver we rescued from a neighbor's trash heap seems to be complete, except for speaker(s). The wood cabinet is 33" high, 20" wide, 10" deep. Tubes seem to match the socket lettering and are: 80, 76 shielded, (2) 6K7GT, 6K7 metal, 6B7 shielded, 6F6G, plus 6U6/6G5 (tuning indicator, apparently).

: We'd like to identify the model and find a schematic, but the only markings that seem significant are on the back of the chassis: A 67/20 and 7R 951873. The underside of the power supply transformer is marked 7 16 36 (a date?).

: We'd appreciate any help, hints or suggestions that you could provide.

: Wes Nelson

Coronado (Gambles/Skogmo) marked their chasis as well as the notes in the cabinets, and you are in luck as the model number should be 6720 that you list in your initial query. However Coronado radios seem to have 2 numbering systems for model numbers, and when they switched from one system to the other is not clear as they seem to overlap some. Aparently the discrepencies may be explained by the manufacturing plant/company. From all indications it should be officially a 1937 model. The speaker was an electro-dynamic type, and the impedance you would want to match is 7000ohms on the primary (6F6 side) A "universal impedance matching transformer" "can work", but would not look at all original, but would be simplest apporoach, then it is a matter of simply installing a filter choke across what would be the "field coil" windings of the old electro-dynamic speaker. Again, it is a simple fix, and can be accomplished with Radio shack parts essentially, but it would not look at all original. A speaker from a 6V6 would have a lower impedance primary(6000 ohm vs 7000 ohm), but it could be an option if nothing else is available. If the latter approach is tried, there should be a resistor added in the primary circuit to reduce current flow through the 6F6.