Vacuum tube phono cartridge

ID: 204323
This article refers to the component: To the tube/semiconductor

? Vacuum tube phono cartridge 
05.Nov.09 15:43

Emilio Ciardiello (I)
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Emilio Ciardiello

According to Sibley in ‘Tube Lore’, around the early fifties RCA promoted its 5734 electro-mechanic transducer triode as building block for non-conventional phonographic pick-up cartridges.


As transducer the 5734 offered some interesting features. It was tiny and lightweight, about 19mm body length by 7mm diameter, more or less as any other passive pick-up transducer. Its resonating frequency was around 12 KHz, compatible with the bandwidth of the standard-groove records, popular at that time. More, the vacuum tube transducer was capable of intrinsic gain, giving a fairly high output signal. The claimed sensitivity was 40 volts per degree of shaft displacement.

Recently I found a couple of odd objects that look like phono pick-up assemblies. The 5734 is mounted in a frame of non-magnetic material (bronze?). A L-shaped rod, some 5cm long, is soldered to the shaft protruding from the tube. The stylus is glued on the short side of the rod. The rod itself is supported near the corner by a flexible fork. Here are some pictures of the pick-up.


No name or label can be read on the units, but their manufacture looks very accurate, as they could came from a series production lot.

Does anybody have notice of even small productions of this or similar phonographic cartridges from U.S. manufacturers?

Regards, Emilio

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? Other uses for 5734 
06.Nov.09 00:32

Joe Sousa (USA)
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Joe Sousa

Hello Emilio,

This is great! I had heard about the existence of this cartridge, but had never seen one, and some people said it was never made.

I imagine that this single triode could have been wired as a push-pull driver/phase splitter in a double pentode arrangement. The tube complement for a phonograph sold for the US market might have been might have been 5734, 35C5, 35C5, 35W4. One possible issue with the active cathode as phase splitter, would be hum pickup from the heater.

I had tried to find applications for this tube in the past, and came across two applications in the field of biology.

Muscle tension was measured In both applications:


From the Department of Physiology, Faculty of Medicine,
University of Tokyo, Tokyo, Japan
(Paper Received 30 March 1972)

The following excerpt came from page 239 at

"Tension transducer. Tensions were recorded with an RCA 5734 tube having an
extended plate shaft (12 mm in length) made of a stainless-steel tubing. Its compliance
was 3 ,4g, while its natural frequency of oscillation was about 1000/sec. The
transducer was connected to a conventional bridge circuit, and the output was displayed
on the lower beam of the oscilloscope."


School of Biological Sciences, University of California,
Irvine, California 92664
{paper Received 4 June 1973)

The following excerpt came from page 784 at

"The tergocoxal muscle was exposed, the mesothoracic leg was cut distal
to the coxa, and the coxa was freed from the thorax except for the insertion of the
tergocoxal muscle. A short thread connected to the coxa by a small hook was attached
to the pin of an RCA 5734 transducer tube to record tension. The transducer was
mounted on a manipulator so that the length and tension of the muscle could be
altered. Tension recording was essentially isometric and the resonant frequency of
the transducer without the coxal hook and connecting thread was greater than 2 kHz."


These papers seem to be in the public domain.

I left the question open for you, in case someone finds another cartridge example.



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? Mechano-electronic sensors update 
11.Nov.09 21:58

Emilio Ciardiello (I)
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Emilio Ciardiello

First of all, my thanks to Joe Sousa for the unvalued role he played in looking for old technical materials and to his many friends which gave their contribution. Here the synthetic overview of what has been found.

The 5734 mechano-electronic sensor, also named ‘Vibrotron’, was developed in the late 1946 by G. M. Rose of the Tube Department of RCA. The tube was very small, designed to operate over the audio-frequency spectrum.


A conical rod was used to keep the vibrating mass as low as possible and the transducer sensitivity substantially flat with increasing frequency. No doubt, then, that the tube was primarily intended for audio applications, as phono pickup devices. The pickup cut-off frequency for a standard record reproduction was in the order of 5KHz. 12KHz were required for reproducing a transcription record. Since the first introduction of its new transducer, RCA had built demo prototypes of record players with active pickup heads.


RCA also foresaw the use of its transducer in other audio applications, as electronic microphones. Here the vibrotron, coupled with a diaphragm, offered a high-sensitivity, comparable with the one of a carbon mike, with the negligible distortion typical of dynamic or magnetic types. Here are two electronic microphones built by RCA for demo purpose.


For a while RCA did not sell its vibrotron, but made samples available to those manufacturers of audio equipment interested in experimentation of this device for their future productions. Probably, but this is only a guess, any possible application in the audio field was abandoned due to the increased frequency response of microgroove records. As general-purpose transducer the tube was still in production in the sixties. It was listed at $ 20.30 in single unit quantity in the 1961 Newark catalog.

Joe Sousa and his friend John Memishian also found articles on a similar device, an accelerometer vacuum tube first devised in 1946 by Walter Ramberg at the National Bureau of Standards, known as ‘Ramberg Tube’. Although different in its structure, this sensor operates upon the same principle of the vibrotron, a vibrating anode structure.

The tube is a twin diode, with a fixed common cathode and two plates, one on each side of the cathode. The plates are elastically mounted so that they can move when the base of the tube is subjected to accelerations. The tube has been coded here as Ramberg_tube.

After having cooperated to the development of the prototypes, Sylvania in 1951 introduced an improved version. Both Electronics and Radio-Electronic Engineering in February 1951 reported the introduction of this improved device. The mechanic structure included stops to prevent deformations by excessive accelerations and a second getter was added, to reduce the zero-drift. The tube had a loktal base with a threaded fixing stud. This tube was produced with the Sylvania developmental code SD-759A.

Any further information about little-known applications of these sensors will be appreciated.

Regards, Emilio

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Ramberg tube article 
13.Nov.09 01:02

Joe Sousa (USA)
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Joe Sousa

Thank you Emilio for the kind words, and for the excellent overview you just presented.

The Ramberg article can be read by clicking these thumbnails:

These scans were about 50% larger in pdf format; I think because of the mixed gif/jpg content, so I kept the scans in their original image formats.

Note that the cover has a special note at the top right in a black box, indicating that this is the "Radio-electronic Engineering Edition". This version of the magazine includes the xxA pages, which were edited for professional engineers. The remaining content is for a general audience. The "regular" issue does not include these special pages in yellow paper stock. The special section increased the page count about 10-20%. I have both issues. Initially, this led to some confusion.



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