391
Item nr.
Three tube set for speaker
Production | The Netherlands, 1995. |
---|---|
Bands | MW; connectors for loudspeaker, B+, grid bias, A, Gnd, Ant. |
Tubes | A415, A415, B406. |
Cabinet | None. Size 29x20.5x19.5cm. Weight 3.0kg. |
Power | Batt 4V (filament), 7V (grid bias), and 90V (plate). |
Documents | schema. |
Buying complete installations, including prefab sets, became usual in the late twenties. In the early and mid twenties, broadcasters were active in publishing schema's, and helping their listeners to construct the sets.
Obtained | 2/2015 from Klaas. |
---|---|
Condition | 8. |
Disposed | Sold 10/2016. |
Sound sample | PLAY SOUND The B406 output tube was introduced in 1925. If you built this radio in 1925, you could listen to Church Radio Bloemendaal (wavelength 200m) and NSF (1050m), and enjoy many Dutch public broadcasts for 90 years, until the close of public AM transmitters on September 1, 2015. |
The sounds come out a bit weak but I can clearly hear Groot Nieuws Radio on 1008 and Nostalgia on 747kHz. The T.K. control (regeneration) brings the set in and out of oscillation only in a small range, it is easier to control the feedback with the filament rheostats.
The schema I found inside the radio is the same as the one in the other Three tube set, but with some modifications made in blue ink. To my surprise, the power switch does not cut off both plate and filament batteries (the grid bias need not be interrupted). In the ON position, both batteries are connected, of course. Position 0-Va disconnects the filaments but leaves the plate battery conected. Position 0-Vf disconnects the plate batteries but leaves the filament connected. I did some current measurements. The three filaments consume about 0.2A together. I measured the B+ currect using a 160R resistor in the B- lead. When operating, B+ consumption is about 6mA, but this is influenced by the rheostats, of course. Increasing fliament temperature makes the current larger. The current can vary between 5 and 8mA, so the radio consumes barely over a Watt of power (roughly half a Watt of filament and half a Watt of plate supply)!
If you switch off the radio by turning the power switch to 0-Vf, plate current is cut completely and the set is silenced, but the filaments continue to draw their full current, so the battery will be empty the next morning. If you set the switch to 0-Va, the filaments are cut off completely and the tubes stop drawing plate current, too. Still I measure about 6uF of current; I think the leakage through bypass capacitors. This seems an acceptable way to silence the set, becuse even after a two week holiday, your plate battery has lost only 2mAh. But still it surprises me why the switch doesn't have a position in which both are cut off.