0V2 receiver from Teva
After successfully building my 0V1 receiver with an ECC81 tube, I searched for a suitable template for an even better device. Technik-Versand company from Bremen, had published a number of amateur radio kits under the label Teva, including the Audion receiver presented here. It seemed very suitable for reproduction. In addition, the device was expressly praised by an older OM: He had once possessed such a device. So I set out to build a device in accordance with this circuit template, but without using the kit. I soon found the parts I needed by disassembling old broadcast receivers.
The two-stage audio section with the right-hand ECC81 offered sufficient gain reserves, also for the loudspeaker reception of weaker stations. The left ECC81 was used in a cascode audion formation. The regeneration feedback or respectively the oscillation generation came about in the manner of an ECO oscillator. The feedback adjustment with DC via a bias shift of the system operated in grounded grid circuit resulted in only minor frequency alterations. This receiver proved to be superior to a regenerative circuit using a pentode with adjustable screen grid voltage in my experiments. The regeneration onset was pleasantly soft and the sensitivity was very good. Due to the three antenna connections, the coupling could always be well adapted to the reception situation and to the existing antenna. The upper antenna socket was better for longer antennas, the lowers for shorter ones. The smaller detector level with slacker coupling resulted in less distortion by synchronization in the SSB reception and could be compensated well by higher audio gain, reachable with the two AF stages.
To simplify the replica, here are the winding data for the plug-in coils for receiving the classic SW amateur bands (coil diameter each about 30mm).
- 80m band: abt. 29 turns enamelled copper wire 0,3mm, tapping at 5 turns, parallel C = 33pF
- 40m band: abt. 11 turns enamelled copper wire 0,7mm, tapping at 3 turns, parallel C = 82pF
- 20m band: abt. 5 turns enamelled copper wire 0,7mm, tapping at 2 turns, parallel C = 27pF
- 15m band: abt. 3,5 turns enamelled copper wire 0,7mm, tapping at 1 turn, parallel C = 68pF
- 10m band: abt. 2,5 turns enamelled copper wire 0,7mm, tapping at 1 turn, parallel C = 82pF