The BM368 RF generator was produced by Czechoslovak Tesla national enterprise in Brno in the 1960s and 1970s. It is a portable source of HF voltage from 100kHz to 30MHz with the option of internal or external modulation.
It is designed for repairs, alignment and testing of radio receivers. It can be used for laboratory measurements in radio technology, equipment repairs at the customer's premises and workshop measurements.
The output HF voltage can be adjusted from 0.5uV to 50mV in five ranges. This voltage can be unmodulated, modulated by an external signal
(for 30% modulation depth, supply a low frequency signal of approx. 1.5V with a frequency of 200Hz - 10kHz), or modulated by an internal signal of 400Hz (+/- 10%),
sinusoidal waveform with a distortion at most 5%, with a modulation depth of 25-35%.
In addition to the HF signal output with adjustable amplitude, there is also an output with non-adjustable amplitude between 0.3V - 1V.
The device is equipped with an analog meter displaying the magnitude of the RF voltage and an indicator lamp indicating power-on.
Frequency range: 100 kHz - 30 MHz in five ranges:
I. 100 kHz - 300 kHz
II. 300 kHz - 900 kHz
III. 900 kHz - 2.7 MHz
IV. 2.7 MHz - 8.5 MHz
V. 8.5 MHz - 30 MHz
The device is equipped with these tubes:
1x 6F32 HF pentode (later pieces fitted with a Soviet 6J1P tube)
1x 14TA31 glow voltage regulator (later pieces fitted with East German StR 75-60)
1x EZ80 two-way rectifier (later pieces fitted with a solid-state rectifier with two KY705 silicon diodes)
2x ECC84 double HF triode
The device is powered from 120V or 220V 50Hz mains voltage. The selector also has an unmarked 230V position, see images below, to help limit the excessive secondary voltage
and overvolting the heaters when operating from a modern 230V nominal mains. The claimed power consumption is approx. 30VA, weight approx. 7.5 kg and dimensions 210 x 265 x 155 mm.
HF generator Tesla BM368 - schematic (older version still with EZ80 rectifier tube)
Tesla BM368 HF generator - front panel (version with labels in Russian, versions in Czech and English also existed).
Tesla BM368 HF generator
Tesla BM368 HF generator back
Tesla BM368 HF generator from the left side
Tesla BM368 mains inlet, fuse and mains voltage selector
Tesla BM368 mains voltage selector in the unmarked position for 230V (two steps clockwise from the 220V position).
Tesla BM368 fuse ratings (these are lower than in the tube rectifier version)
Tesla BM368 nameplate
Tesla BM368 - closed and opened door of the high amplitude output (over 0.3V) and the external modulation input
Tesla BM368 bottom
Open Tesla BM368 HF generator from below - the power supply and low frequency oscillator / modulator with ECC84.
The original EZ80 rectifier tube was already replaced by two KY705 diodes in production, so this is one of the later produced pieces,
almost mid 1970s.
Tesla BM368 HF generator from below with visible knobs on the front panel.
Detail of small parts at the bottom of the Tesla BM368. The small 20uF 6V electrolytic capacitor also isn't in the schematic.
The back of an opened BM368. Below is the mains input, fuse and 120/220V ac mains selector.
BM368 circuits in a shielded space - the HF oscillator with a Soviet 6J1P (6Ж1П) tube (earlier pieces used 6F32) on left and ECC84 tube in the voltmeter circuit on right.
In the middle is a large 500pF tuning capacitor.
Tesla BM368 - a detail of the HF oscillator with 6J1P, 5-range switch, coils and adjustment capacitors.
Tesla BM368 - a detail of the voltmeter circuitry with ECC84 (in this picture it has its cover on).
Shielded space of BM368 viewed at an angle.
Shielded space of BM368 viewed at an angle.
BM368 - filters at the top of the device after the cover was removed.
BM368 - filters at the top of the device after the cover was removed. Coils and polyester and mica capacitors are visible.
BM368 - lifted front panel.
BM368 - behind the front panel.
Tesla BM368 internally modulated signal envelope (on a Tesla BM556 oscilloscope, 1ms/div).
