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Thursday, July 9, 2015

1T4 / 3V4 Regenerative Portable

Since getting a 3S4 QRP midget transmitter I've been thinking about building a receiver to match it. I wanted to use tubes along the same lines as the 3S4 and, at the same time, have a late 50s style. The late 50s/early 60s ARRL "How to Become a Radio Amateur" featured a two tube regen with a 3 1/2" National type K dial. That sort of style was what I was looking for.

I finally found the receiver circuit at Bob's Data: Useful Electronic Data and Project Plans and I have a National Type K Dial to set the style.

I've found the parts I need and have played with them to figure out a layout I like. The chassis is marked up and I'm ready to drill.

 Parts List (use 1/2 watt resistors):R1 1 Meg
R2 39K
R3 100 K Potentiometer
R4 47K
R5 2 Meg Potentiometer
R6 47K
C1 11-194 pF Variable (7 full plates)
C2 9-19 pF Variable (one ¾ inch diam. plate)
C3 100 pF
C4 .002 uF
C5 .01 uF
C6, C9 1 uF @ 100V
C7 .05 uF
C8 .22 uF
L1,2,3 Wound on same PVC form
T1 10K to 8 ohm Audio Transformer

Tuesday, July 7, 2015

A Ross Hull Three Tube Regen

A couple of weeks ago I spotted a radio on ebay that looked really interesting. I've been doing some research on it since then.

This radio is a three tuber with a tuned RF stage, regenerative detector and a single stage of audio  ... not unusual for an early 30s shortwave set except for the mechanical layout. All of the tubes are mounted horizontally with the RF tube projecting through the RF/Detector stage shield.  This layout allows for a compact set. The National SW3, for example,  is a three tube regen with a tuned RF stage. It measures 9.5"x7"x9". This set is only 7"x5"x6.5", less than half the size of the SW3.

A search found the original described in the June 1931 issue of QST. Ross Hull designed this set to demonstrate the capabilities of the new type 33 audio pentode.  He bragged about the gain of the AF stage and being able to drive a speaker to good volume. Why, then, didn't he include a volume control? You have to detune the RF stage if a station is too loud. Along the way, though, Hull did, in typical Hull style, came up with the clever mechanical layout. Hull was also an early VHF advocate/experimenter. This layout allows fairly short leads. I have to wonder if he was thinking ahead to 60MHz when he sat at the drawing board designing this radio.