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Author Topic: "Inheriting" a RBA5 WWII Radio  (Read 5770 times)

Posts: 83

« on: January 09, 2013, 08:38:30 AM »

Hi All-

My dad always told me he bought a radio when he was much younger that could receive whistlers (VLF style radio).  We never got the radio out as a kid, and in the last year or so he has said that I can have the old radio. 

Over Christmas I looked up the number and found that is a WWII era RBA5 receiver and power supply!  So that is pretty exciting.  I have no idea if it works or how to test anything on it.

So my question is pretty simple: where do I start?  What should I do with it?  I found a manual online for a RBA7, which is close. 

I would just appreciate some helpful advice and places to start.  I am also wondering if there are any safety concerns I should be aware of (charged caps or something).

Thanks all!


Posts: 6764

« Reply #1 on: January 09, 2013, 09:36:12 AM »

Steve:  The typical ham, after ogling the thing for 30 seconds, would next open it up and have a look inside.

Quite often that 'look' determines if the thing should be resurrected or used as a conversation piece.

If it's to be resurrected, then the first order of business would be to check the tubes.  The caps will no doubt have to be replaced.  That in itself require the question to be answered, 'to use or not to use' period type components.  If it's to be resurrected to be used, then go with the modern components.  The resistors will need to be checked because back then the carbon composition resistors changed value drastically through the years.

The wiring itself will have to be evaluated for disintegration, etc.

That's where you start Steve.  Rotsa Ruck!

A Pessimist is Never Disappointed!

Posts: 3160

« Reply #2 on: January 09, 2013, 05:32:26 PM »

Steve -

I see you are in Iowa City (many memories 83-95), met Jim Van Allen in 83 when in grad school.  Last saw him in 1999, when I was on campus.

Look like this RBA-5 example ?

Check page 6, USS New Jersey Oct. 2003 newsletter
(An RBA-5 being brought on-board, loan 2003)

The new design (RBA series) was going to blend the advantages of the TRF designs of the RAK but eliminate the regenerative detector in an effort to keep the radiation on the antenna to a low level that prevented enemy DF of the receiver location.
... the new receiver (RBA series) was not a superheterodyne, the BFO had to track the tuned frequency, providing a 1kc heterodyne which allowed CW to be readily copied.

There were a couple of reasons for not designing the new LF receiver as a superheterodyne.
First was to allow complete coverage of the tuning range of 15kc to 600kc and second was that fact that the conversion process in a superheterodyne creates a lot of internal noise in the receiver - not a real problem on HF or SW, but a serious determent to good LF performance.
At $3000 each, the new RBA receiver was certainly expensive and a look inside the receiver reveals an incredible level of electro-mechanical design and construction. The tuning ranges from 15kc up to 600kc in four bands. The illuminated dial readout is direct in kilocycles along with a two-dial logging scale. The mechanics of the design allow for super-smooth operation of the tuning system. The Gain adjustment controls the sensitivity of the receiver and a gear-driven auxiliary gain control operates from the tuning dial and provides constant gain levels across the tuning range. Two meters are provided, one to monitor Output Level in db and one to monitor the B+ voltage. An Output Limiter is provided for noisy conditions or unexpected strong local signals with the Output Level adjustment setting the output limiter's maximum level. Two levels of selectivity are provided, Broad selectivity is limited to about a 1300kc audio roll-off via an internal LP filter and the Sharp position is provided by a 1kc bandpass filter for CW in noisy conditions or in cases of interference. Audio output is 600 ohms Z and is intended for earphones although the RBA will drive a matched loud speaker if necessary.
The separate power supply, CRV-20130, provides the filament voltage and B+ requirements via an armored cable with heavy-duty connectors. The power supply will easily operate two receivers for emergency conditions and two separate connectors are provided. This is the same power supply used for the RBB and RBC receivers.
The power supply has a cold-cathode regulator tube (OC3) and a HV rectifier (5U4.) The RBA uses eight tubes, three 6SK7 RF amplifiers, one 6J5 Triode Detector, one 6SK7 BFO, two 6SJ7 AF amplifiers and one 6K6 AF Output.
« Last Edit: January 09, 2013, 05:52:23 PM by W9GB » Logged

Posts: 29

« Reply #3 on: January 15, 2013, 09:22:37 PM »

As a US Navy Radioman, I USED the RBA (and RBB + RBC).  It's a very sensitive TRF type (no local oscillator for the Japs or Germans to pick up!), and goes from about 10 kcs to the bottom of the AM bcst band.  I used to regularly copy the Navy xmtg station at Big Jim Creek, WA on 12 kHz... at that time, they sent fleet broadcasts to submarines, and the sigs could be heard 5 by 9 at periscope depth (with no antenna showing), just N. of Austrailia.  I'd find a friend with a Variac, and bring the supply voltage up in 10% increments per hour, keeping in mind that line voltage back then was about 115-117vac MAX... not the 125-129vac we have today.  With a proper antenna, you'll be able to copy the experimental stuff on 135-137 kHz.. those "whistlers" are actually eddy currents AROUND THE EARTH... way cool.

Tom - W0EAJ

Posts: 16

« Reply #4 on: January 23, 2013, 09:13:25 AM »

If you have the receiver and power supply but no connectors try:

William Perry Co in 702 (Rear) Beechwood Rd, Louisville, KY, 40207 (502) 893-8724, FAX (502) 893-9220 Eastern Time
- Connectors:Amphenol, Bendix, Cannon, Burndy, Cinch and Winchester

With the ARRL working on LF/MF band allocations and the 600 meter experimental band in operation there are signals out there. A websearch for 600 meter band will get you to their website. I have the RAK/RAL receivers and RBA/RBB/RBC, all fun sets and your operating table will not blow away even in strong winds . Nick Englands "Navy Radio" website has pictures and info.

Good Luck and Happy BoatAnchoring!!!

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