Tandberg Huldra Radioes

Huldra 9 in DX News, no. 5, 1969, DX-listeners club.
Tandberg is probably the most well known of all Norwegian radio producers. Although the original Tandberg company was dissolved in 1978, the Tandberg name lives on in several companies.

Tandberg's Huldra series was the top of the line radio and came in twelve or thirteen different versions over about fifty years:
  1. Huldra 1A and 1B 1934-1936. The first superheterodyne Tandberg receiver, dual conversion with intermediate frequencies 2 MHz and 137 kHz. Push-pull output amplifier.
  2. Huldra 2, 1938-1940. First Huldra with a magic eye, variable selectivity, negative feedback in audio power amplifier, and standard 455 kHz IF. The first Huldra with coverage of 1.6-3.3 MHz (‘The trawler band'). Push-pull output amplifier.
  3. Huldra 3, 1941-1947. First Huldra with 3 shortwave bands. Class A output amplifier.
  4. Huldra 4, 1950-1954. The only Huldra with 8 bandspread shortwave bands, catacomb band switching, thick film silver ceramic coils in the oscillator circuits, traps for improved mirror image rejection and a noise blanker. The first Huldra with intercom function. Push-pull output amplifier.
  5. Huldra 5, 1956-1958. The first Huldra with FM band. Push-pull output amplifier.
  6. Huldra 6, 1961-1962. The first Huldra with a stereo amplifier. Class A output amplifiers. The first to be built with printed circuit boards.
  7. Huldra 7, 1963-1965. The only Huldra with ... nothing new - identical to Huldra 6, except for a minor change in the audio output amplifiers (ECL86 replaced with ECC83 + EL84). Class A output amplifiers.
  8. Huldra 8, 1965-1968. The first Huldra with transistors (in audio amplifiers), the first with continuously variable tone controls and even a tone control defeat button. Also the first with coverage of full international FM band (up to 108 MHz), and Automatic Frequency Control (AFC) in the FM-tuner. The last Huldra with a magic eye, and the last one with intercom. Huldra 8 is the last one with banana jacks for audio input and also the first one with 5-pin DIN plugs for audio input, and with DIN loudspeaker plugs.
  9. Huldra 9, 1968-1971. The first Huldra with FM presets (varicap tuning ), first one with a built-in ferrite antenna for long and medium wave bands, first Huldra with FM tuning knob as bandspread tuning on shortwave, and also the first with an (optional) stereo decoder. This is the first Huldra of the age of Hi-Fi as it is the first one with an output power specification. The last Huldra with tubes (in AM receiver and FM/AM IF amplifier), with variable IF selectivity (DX/local button), and with coverage of ‘the trawler band'.
  10. Huldra 10, 1974. The first Huldra with only silicon transistors, separate IF amplifiers for AM and FM and the first one with stereo decoder as standard. The second generation of Huldra 10 is the first Huldra with ceramic filters in the FM IF amplifier.
  11. Huldra 11, 1976-1978. The first Huldra which has eliminated the loudspeaker coupling capacitors, like modern amplifiers today are designed also. The first Huldra with relay switching for delayed loudspeaker outputs. Huldra 11 has ceramic filters in the FM IF amplifier. The first one with a LED that replaces the incandescent light in the stereo indicator.
  12. Huldra 12, 1978-1983. The only Huldra with ceramic filters in AM IF amplifier, with a silent switch (muting when changing inputs), and the only Huldra where all band-switching in AM-tuner is done with diodes. Huldra 12 has an audio amplifier which is almost identical to the one in Huldra 11, except for some small changes to minimize transient intermodulations distortion (today often called slew-induced distortion) and finally the tiny DIN loudspeaker terminals have been replaced with more solid loudspeaker terminals
To be determined:
  • English lettering: Huldra 9 comes in both a Norwegian and an English version (Thanks for info from K. Marshall, England). My Huldra 10 is in English only.
  • Huldra 6 has printed circuit boards, Huldra 4 does not, when did Tandberg start using PCBs?
The Tandberg radios follow the general history of radio with some time delay. What are features that did not make it to the Huldras? They never had a digital readout or phase-locked loop frequency control in the receiver, neither did they have a synchronous AM detector. They were also too early for things like support for RDS (Radio Data System).

Problems with Tandberg equipment

The main problems with transistorized Tandberg equipment from the 60’s and 70’s, are, in my experience:
  • Dial lights do not work.
  • AM variable capacitor is stuck due to stiffened grease in the main shaft of the variable capacitor. Can be undone by heating or dismantling. Often the dial cord is also broken, as someone may have tried to move the stuck capacitor with the tuning knob and used a little bit too much force.
  • Power supply filter capacitor or output capacitors stop working.
  • One or more output transistors burned out (can be due to leaky output capacitors). Be sure to measure and replace driver transistors and diodes also, otherwise a new pair of output transistors will not last long
  • Field strength indicator and/or center tuning indicator instruments are broken. The glue dissolves with time and the connection to the moving coil is broken. Can sometimes be repaired with some luck and if you are accurate and patient.
  • Selenium rectifier does not work. Can be replaced with silicon rectifiers.
  • Stabistor (stabilyt) in portable radio TP41 no longer works (see image to the right). It stabilizes the voltage to 1.5 Volts and can be replaced by to silicon diodes and one germanium diode in series (2 x 1N4148 + AA119) in parallel with 220 uF as in the successor TP43.
  • Mechanical contacts, in switches or between boards, have become unreliable.
  • Transistors in plastic housing that stop working, or which become noisy

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