crosley: RFTA (Amp., R.F.T.A Unit); Radio Frequen

RFTA a mystery?

The RFTA is mainly intended to improve the humble sensitivity of HARKO Senior. But:

1) The HARKO Senior input is not ground connected, it is a series circuit of C and L. That means it is an open circuit for DC, which excludes its use as a plate load for a preamp. All the V/5 family is alike as far as I know.

2) ±A is routed through (marked P = positive? while N = negative) on RFTA but not on HARKO Senior. HARKO Senior's missing terminals at the left side mean that Harko is clearly a front end unit.

3) Another strangeness: why is the output of an RF amplifier marked "PHONES"?? and why did they add the audion capacitor of ca 300 pF?

In technical terms the name RFTA appears misleading.

Used as a preamp in combination with a simple receiver: how would the latter be hooked up? possibly to "Phones", but that sounds strange although it might work, provided the receiver input shows continuity for DC (which in those days was seldom the case, series tuning was preferred) to accept antennas with high capacity).

and why the P and N terminals at left hand?

As a phone booster the RFTA would hardly work, since its tuning circuit might not accept audio signals at the input, and 300 pF are not enough for audio signals.

Now marketing comes in: The name RFTA describes its overall function: to improve Harko Senior .Using the "real" technical name, it would not be understood why one should combine two TRF-Audions! The easy adaptation procedure was clearly explained.

How the combination RFTA + HARKO Senior works see here.

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Alan Larsen wrote to us and I think it is better put into here - for all interested readers in R.F.T.A.:


"Konrad is correct about the RFTA and it's placement after the Harko Senior. (See the schematic enclosed) The design of the RFTA apparently wasn't well thought out on Crosley or Israel's part and probably accounts for the scarcity of existing RFTA's. Here is a copy of the rather complicated Crosley directions for using the RFTA with the Harko Senior.

When this unit is used in connection with the non-regenerative Harko Senior, an amplifier tube is used in the Harko Senior Unit with the grid leak and condenser bridged or short circuited. The detector tube is then placed in the radio frequency unit, thus this new unit contains the radio frequency tuner and the detector tube and its control.

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When we consider the complication, hooking together radio modules or doing some change on a radio, we have to know how people lived at that time and what they did in their spare time. We also have to consider how simple radios were and easy to fix or change. An other fact is the cost versus having to work how many weeks or months. The fact that one could only either play music, go to music, have an expensive player piano ro mechanical music or a record player. Radio was the new thing and could also bring in news and other information.

Actual facts are that in 1922 ten times more radios and crystal detectors were homemade against sold instruments. In his book "Radio Manufacturers for the 1920's", Vol. 1, Alan Douglas has quoted "Radio Retailing", March 1928 with the following statistic:

Homemade sets:

1922 1,000,000
1923 1,500,000
1924 1,750,000
1925 1,000,000
1926   750,000
1927   300,000

Factory sets:

1922    100,000
1923    250,000
1924 1,500,000
1925 2,000,000
1926 1,750,000
1927 1,350,000

You can see that this changed as late as 1925.

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