Lion Cub Scout 2-Tube Radio Set

by Random73

October, 2014

When I was in Cub Scouts in early 1960’s I wanted to make the 1-

tube and 2-tube radio sets described in the Bear and Lion

handbooks. I never did, but I also never forgot about them.

Here is a scan of the Lion handbook schematic diagram, from

http://www.peeblesoriginals.com;

I found only a handful of forum posts on internet that discuss

this project, but none said they had actually built it. One post

noted that there were some errors in the diagram;

James T. Hawes Post subject: One step beyond the Bear radio

Posted: Sat Aug 07, 2010 2:02 am

Maybe some of you remember the Lion radio, too. My 1954 Lion book

included an upgrade to the Bear radio. The Lion radio included a 1U4

grid-leak detector and a 3Q4 power amplifier. Both tubes are pentodes.

The power amp could actually drive an output transformer and a

dynamic speaker.

Still, the wise Cub Scout built the 1S5 Bear radio. The Lion radio

drawings are full of booby traps.

As I examine the Lion schematic and pictorial today, I find several

errors: (1) The filament circuit is incomplete. (2) The schematic shows

the B battery backwards. (The battery on the pictorial connects the

right way. Go figure.) (3) Also on the schematic, the A battery polarity

is right, but the symbol is backwards. (4) The two grid resistors are a

thousand times too small.

…

James AA9DT

I have the following comments regarding Mr. Hawes’ numbered

remarks;

Remark 1; I disagree. The filament circuit is completed to

ground via pin 5 of the 1U4. Not shown in the schematic is the

fact that pin 5 is internally connected to pin 1, as well as the

suppressor grid.

Remark 2; I agree that the B battery schematic symbol, not

including the polarity marks, is backwards. I disagree with his

parenthetical remark, “The battery on the pictorial connects the

right way”. The B battery’s polarity marks are reversed in the

pictorial.

Remark 3; I agree that the A battery schematic symbol, not

including the polarity marks, is drawn backwards.

Remark 4; I agree that the callouts of the two 3.3K (orange-

orange-red) resistors should have instead been two 3.3M (orange-

orange-green) resistors.

The battery symbol errors in the schematic are minor since the

polarity marks are correct relative to the circuit. So, really,

only the resistor callout errors would have affected the

successful performance of the circuit, unless the builder tries

to copy the pictorial layout shown in the handbook.

There were several errors in the layout pictorial, with the most

significant being the reversal of the polarity marks for the B

battery;

Another minor error in the handbook schematic diagram is the

missing notation of pin 1 of the 3Q4.

I redrew the schematic, with corrections;

In my experience 3V4s are more common than 3Q4s. The RCA Tube

Manual states that a 3Q4 is electrically identical to a 3V4.

Only their pinouts differ.

Here is the schematic redrawn, with 3V4 substituted for the 3Q4;

Other suitable substitute tubes include the 1N5GT for the 1U4,

or a 3Q5GT for the 3Q4 (or 3V4). I have both of these octal-base

tubes, and sockets, available for this project. Here is my

1N5/3Q5 variation of the Lion Cub Scout receiver.

I have four miniature volume controls, each having the attached

DPST switch. They are listed as 1 M, but three of them measure

around 640 K, and one measures 720 K. I expect any one of them

should work fine in this application, but with slightly more

current draw from the B battery (125uA instead of 45uA).

I used a New-Old-Stock J.W. Miller #2008 ferrite bar antenna. It

is spec’d as 360 to 440 uH, presumably by sliding the coil

assembly back and forth over the ferrite bar. When set to 360uH

a 250 pF tuning capacitor should cover the 530 to 1650 kHz

broadcast band OK. I put a 500 pf fixed capacitor in series with

a 410 pf tuning capacitor to achieve about 250pf.

Sunday, 28 September 2014- I started fabricating the breadboard

two days ago. For the base I am using two 8”x10” pieces of

corrugated cardboard, glued together. I made a grid cap and

solder terminals from 5 mil brass stock.

Wednesday, 1 October, 2014- Breadboard completed;

I built this set using only parts already on hand. As a

consequence, some of the resistors and capacitors consist of

series or parallel strings to achieve the right values for the

circuit.

I tested it using my replica #477 B battery, rated 67½ volts,

instead of a 90 volt battery. The radio worked fine using a 62

foot longwire antenna and a connection to house wiring ground.

The top of the tuning range was just above 1650 kHz (KFOX).

There was plenty of volume and adequate selectivity for

listening to any of the local stations at KLAC-570 (Dodgers

baseball), KFI-640 (Tim Conway, Jr.), ESPN-710 (Lakers

basketball), KABC-790, “The Answer”-870, KNX-1070, 1480-religous,

and 1650-Japanese. I could tune in classical music KMZT-1250 but

there was significant ACI (adjacent channel interference).

After testing I made an enclosure for the speaker, using

corrugated cardboard. The sound quality is much better with this

enclosure installed.

Lion Cub Scouts Elective 4, Two Tube Radio Set

To address the ACI issue, I retrieved my “Select-A-Tenna”

passive preselector tuner from downstairs and inserted it into

the antenna circuit. I inductively coupled the longwire antenna

and ground circuit to the Select-A-Tenna, and placed the radio

set adjacent to it. There are no physical connections to the

radio. This arrangement greatly improved the selectivity

performance, such that I was able to tune in many additional

stations with very low ACI, including XETRA-690, KFWB-980,

Disney-1110, KEIB-1150, KMZT-1250, one Persian, one Chinese, and

multiple Spanish stations. I adjust selectivity versus volume by

varying the distance or orientation between the radio set and

the Select-A-Tenna.

Final Installation, for both Display and Use

I am happy that I heard the Kansas City Royals win the 2014

American League Championship on this set. I took the photograph

above right after the game.

Update 14 January 2015- The 3Q5 was microphonic, so I made a

plug-in adapter to use a 3Q4. It works great.

Update 5 March 2015- I ordered last week and received yesterday

New-Old Stock two 3Q5GTs and a 1N5GT from Antique Electronic

Supply. I cleaned the pins of one of the 3Q5s and put it in. It

works fine, no more microphonic behavior. I prefer the look of

the radio set with both tubes being the 8-pin octal type. The

two remaining tubes will be the spares for this set.

Partial Station Log, at Beverly Hills, with Select-A-Tenna;

CALL FREQ. TRANSMITTER MILES KW DAY/NIGHT

KLAC 570 LOS ANGELES 11 5

KFI 640 LA MIRADA 25 50

KIRN 670 SIMI VALLEY 5D/3N

XETRA 690 TIJUANA, MEXICO 133 77D/50N

KSPN 710 VAN NUYS 8 50D/10N

KABC 790 LOS ANGELES 5

KLAA 830 NORCO CORONA 44 50D/20N

KRLA 870 GLENDALE 50D/3N

KHJ 930 LOS ANGELES 5

KFWB 980 EAST LOS ANGELES 12 5

KTNQ 1020 LOS ANGELES 50

KNX 1070 TORRANCE 15 50

KDIS 1110 MONROVIA 23 50D/20N

KEIB 1150 LA PUENTE 24 50D/44N

KMZT 1260 PANORAMA CITY 24 20D/7.5N

KFOX 1650 EAST OF CULVER CITY 10D/0.49N

THE END