HRO Sr. Receiver, 1935-1936 era

HRO Front
HRO Sr. and Power supply

HRO Sr. top view

HRO Bottom
HRO Sr. under-chassis view

Here is a nice HRO Sr., rack mount version. Also shown is the rack mount power supply. The grill work on the power supply is not a speaker, as many people believe, but rather is just an opening for access and cooling of the rectifier tube.

The coil system for the early HRO system is as follows:

Coil A = 14mc to 30mc general coverage or 27mc to 30mc bandspread.
Coil B = 7mc to 14.4mc general coverage or 14.0mc to 14.4mc bandspread.
Coil C = 3.0mc to 7.3mc general coverage or 7.0mc to 7.3mc bandspread.
Coil D = 1.7mc to 4.0mc general coverage or 3.5mc to 4.0mc bandspread. (GC is great for 160 meters)
Coil E = 900kc to 2000kc.
Coil F = 500kc to 1000kc.
Coil G = 175kc to 400kc.
Coil H = 100kc to 200kc.
Coil J = 50kc to 100kc.

Notice that a few of the coils (A,B,C and D) have bandspread capability. Another set of coils (JA, JB, JC and JD) were made for the HRO Jr family that did not have the bandspread capability built in.

The change between general coverage and bandspread is made by swapping the position of four screws in each coil set that adjusts the "tap point" within the coil. This takes less that 1 minute to perform.

This is the 6 volt filament version of the radio and uses the following tubes: four 6D6's, three 6C6's, a 6B7 and a 42. The power supply uses an 80.

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