The amplifier on lamp GU74B.

The choice on this lamp has fallen on reasons of reception of target capacity up to 1 kw at small dimensions. The lamp is included under the circuit with earthed grids, its(her) high steepness therefore is not used. It is connected by that the amplifier was projected under transiver with the transistor target cascade capacity 100. 120 Vt. In typical variant of inclusion with the general(common) cathode mode AV is used, target capacity makes 600 Vt. This mode can be recommended, if target capacity transivera makes 25. 30 Vt. Efficiency of such amplifier is low (a current of rest - up to 300 mA), that is connected to maintenance of a linear mode of amplification(strengthening). Lacks of this variant, besides low efficiency - necessity rigidly to stabilize pressure(voltage) of screen and managing grids. If it is used transiver with target capacity not less than 70. 80 Vt, it is expedient to include a lamp under the circuit with the general(common) grids. In such circuit distortions brought by the cascade depend on a choice of a working point on the characteristic of a lamp a little. It allows to reduce a current of rest at the same level of distortions. The lamp thus works almost in a mode In, having heated the anode in pauses considerably decreases, and it is possible to receive the big capacities and efficiency. Add here absence of necessity of stabilization of pressure(voltage) of managing and screen grids - advantages it is available. Unique lack of such amplifier small factor of amplification(strengthening) (10. 15 dB) and accordingly big, rather than in amplifiers with the general(common) cathode, capacity of excitation, but almost all this capacity is not lost anywhere, and acts in loading. The basic circuit of the amplifier is shown on rice 1.

The basic characteristics of the amplifier:

The current of rest of a lamp is very small, it(he) poorly changes depending on an anodi pressure(voltage) and a copy of a lamp, usually does not exceed 30. 50 mA. In the experimental purposes target capacity 1400 Vt (Uá=2200 In, Iá=1,0 À) was received. Certainly, it is a short-term peak mode. After 5 years of operation practically at daily work on air for 1. 2 hours of appreciable loss of issue of a lamp it was not observed. The main advantage of such amplifier, in my opinion, concludes(consists) in his(its) simplicity. The power supply (rice 2) is simplified up to a minimum. Only anodi pressure(voltage) and a pressure(voltage) of heat is required. For a feed(meal) of automatics it is used straightened nakal'noe a pressure(voltage).

Design

The amplifier is executed in a metal box in the size 450õ380õ230 the mm, divided(shared) by a cross partition on two compartments. In one compartment the power(force) transformer with the high-voltage rectifier settles down. In the same compartment on the forward panel measuring devices and switches of a network, the fan and devices are located. In the second compartment divided(shared) by a dielectric partition, the lamp, an anodi throttle and details of the P-contour are located. Variable condensers and galetnyj the switch fasten to the forward panel. Beskarkasnye coils of the P-contour are kept by trunks on galetnom the switch, condensers and an anodi throttle. The compartment with a lamp from above is closed by a dielectric cover. The fan is located on a back wall in a compartment of a lamp, whence it(he) extorts air. Air acts through apertures in the bottom cover opposite to a lamp, passes through panel'ku and edges of the anode of a lamp. The lamp is established vertically in a pipe, vykleennoj from fiber glass fabric on epoksidnoj to the pitch directing air through edges of a radiator. As all grids of a lamp directly incorporate to the case of the amplifier, there is an opportunity of application self-made panel'ki which can serve, besides the anode, an additional heat-conducting path. The lamp obzhimaetsja around of a conclusion of a screen grid a powerful collar from bronze, or medi, and a collar is densely fastened to the chassis. Through this collar in addition on the chassis is allocated(removed) warmly. On conclusions of a lamp it is put on ceramic panel'ka from old lamps, for example 12Æ1Ë or 2Æ27Ë. A lamp it is possible to have as vertically, and it is horizontal. Certainly, application is not excluded and for ÃÓ74Á. it is very important for "firm" panel to provide effective heat removal from a lamp. Edges in the anode are located rather densely, therefore it is required to provide sufficient pressure of air "to stretch" through the anode not less than 30 ì\÷. Fans such as "turbinka" are most effective for these purposes. But they rather seldom meet, and it is difficult to pick up suitable variant on capacity and the sizes. With success it is possible to apply flat fans from old COMPUTERS. To be guided follows on variants with a pressure(voltage) of a feed(meal) 220 In and, it is desirable, metal blades. In the described amplifier the flat fan of the French manufacture with plastic blades productivity of 60 m '/÷ is applied. In a nominal mode it(he) is used at the lowered pressure(voltage) of a feed(meal) - 160. 170 In. In modes when the amplifier is very long used on transfer, on the fan submits a full pressure(voltage) - 220 In. Flat fans badly work on submission of air, it is more rational to use them on "vykachku". Certainly, it not the best variant since hot air passes through blades and heats up the fan. Therefore it is better to use completely the metal fan which project for such heavy operating conditions. Though it is possible to use anyone with some stock on productivity, in the described amplifier five years the fan, former before in operation, moreover and with plastic blades works.

Details

In quality Ñ8 any variable condenser with a backlash between plates not less than 2 mm and powerful springing tokos'emami cases rotornyh plates will approach. It is necessary to pay attention to initial capacity, she(it) should not be more than 10 pF. To block a range 1,8 MGts, the maximal capacity should be not less than 500 pf. 3,5 MGts it is enough for a range 300 pF. The condenser from radio station RSB5 is applied. For reduction of initial capacity vyfrezerovany lateral metal walls. Mobile contact which is on this condenser, is used for connection of additional condenser S7 for ranges 1,8. 3,5 MGts. If it is supposed to work only on nizkoomnuju loading, in quality Ñ9 it is possible to apply the variable condenser from old lamp receivers with a backlash not less than 0,3 mm. For a range 1,8 MGts total capacity Ñ10 and Ñ9 - not less than 3000 pF. At choice S1 it is necessary to pay attention to capacity and reliability of contacts. Contacts should be removed from earthed elements of a design for minimization of brought capacity. If not it is possible to provide the general(common) initial capacity of the P-contour less than 35 pF, Ñ8 it is possible to include not in beginning L1, and having receded 0,5. 1 coil from the anode. Anodi throttle Äð3 should be reeled up on a skeleton with good dielectric durability (ceramics, ftoroplast). It(he) can be executed partitioned, i.e. through some of coils to do(make) backlashes of 2. 3 mm, that also reduces the general(common) capacity and probability of parasitic resonances.

Automatics and indication.

Contacts Ê1.2 at transition to transfer zakorachivajut stabilitron VD1, removing locking pressure(voltage). For management of the relay transistor keys on VÆ1 and VÆ2 are used. It is made that it was possible to use a pressure(voltage) +12 In TH from transivera for switching the amplifier. At inclusion of relay K1 the time delay (R4, Ñ12) is applied. For what it is made? In quality Ê2 the powerful relay with the big backlash between contacts is applied, time of operation of such relay is much more, rather than time of operation of small relay K1. Therefore at the moment of transition from reception on transfer there can be a unstable condition of the amplifier when Ê1 has already connected transiver to the amplifier, and the aerial for the account inertsionnosti Ê2 yet is not connected. Now it is uneasy to guess, that will occur in the amplifier if in transivere there is no such delay, i.e. at the moment of transition to transfer at once on an output(exit) ÒRCVR is VCH a signal. At the best, will burn slightly constantly contacts Ê2. The worse variants it is much more - down to "prostrelivanija" than a lamp. If you are sure in the transivere and precisely know, that VCH the signal on ÀNÒ a socket appears with a delay (sufficient for operation Ê2 in the amplifier), can simplify automatics of the amplifier, for example includes in parallel both relays and to use one key.

In the amplifier one transformer T1 by dimensional capacity 1600 Vt is applied. Nakal'noe the pressure(voltage) is in addition used for a feed(meal) of the relay of automatics. It would be desirable to tell about this winding especially. It is not necessary to pawn her(it) with a stock i.e. to use with obviously big diameter of a wire, rather than it is required for a lamp (3,6 À). At the moment of inclusion when the incandescent filament of a lamp still cold also has the minimal resistance, in a circuit very big current which can destroy her(it) proceeds. The the winding has the greater stock, the the greater destruction receives an incandescent filament at each inclusion of the amplifier. Therefore at calculation of diameter of a wire nakal'noj windings it is not necessary to expect her(it) for a current more than 4 And.

The anodi rectifier of features has no. It(he) is collected under the circuit of doubling of a pressure(voltage). The secondary winding should provide 800. 900 In at a current up to 2 And. The maximal return pressure(voltage) of a chain of diodes should be not lower 3000 In, the maximal current - not less than 3 And. Each diode zashuntirovan the resistor for uniform distribution of a return pressure(voltage). Shunting condensers are applied for elimination so-called " white noise " which sometimes arises, and for "absorption" and uniform distribution of instant peaks of an overstrain(overvoltage) of a network. These peaks can arise owing to transients which the 100-th shares of second last, but it is enough of it for breakdown of diodes. At use of the transformer on P-shaped iron it is necessary to observe some rules of winding: network and secondary windings divide fifty-fifty and have on both cores. Network S1 the switch of revolutions of fan S2 - on a current > 0,5 should be designed for a current > 12 And, And. In the rectifier of automatics VD1... VD4 it is possible to use any silicon diodes 25 Â/1 And.

Device RA1 in the power supply measures (rice 2) Uá and Iá - depending on position of switch S3. For graduation serve accordingly Rç and R4.

ÐÀ1 (Rice 1) serves in the amplifier for measurement of a high-frequency pressure(voltage) on an output(exit) of the amplifier. Condenser S11 serves for alignment ACHH of a measuring instrument. With help KZ expose indications ÐÀ1, having loaded the amplifier on an equivalent of loading.

Adjustment

The mode of a lamp at submission of required pressure(voltage) is established automatically. Adjustment is minimal and is reduced to selection of taps(removals) from coils L1 and L2 (rice 1), that it is the best way to make by means of a measuring instrument frequency characteristics. At absence of devices the P-contour adjust achieving the maximal target capacity, having loaded the amplifier on equivalent resistance 50. 75 Ohm. At correct adjustment the failure of an anodi current in a resonance does not exceed 15. 20 % from value at the upset P-contour.

Joining with transiverom

In many publications about amplifiers with submission of excitation in the cathode it is spoken about entrance resistance of such device about 50 Ohm. Unfortunately, it not absolutely so. Entrance resistance changes depending on working frequency. It needs to be taken into account at a choice of the circuit of the coordination of the target cascade transivera with an input(entrance) of the amplifier. Otherwise, as it frequently happens, on some ranges the amplifier will not give that capacity with which it(he) provides on others.

Entrance resistance of the amplifier makes: on 1,9 MGts - 98 Ohm; on 3,5ÌÃö - 77 Ohm; on 7 MGts-128 Ohm; on 14 MGts - 102 Ohm; on 21 MGts - 54 Ohm; on 28 MGts - 88 Ohm. This problem does not arise, if in transivere is antennyj a tuner, or the target cascade has manual adjustment of the P-contour on each range. Then optimum it is possible to coordinate an input(entrance) of the amplifier to an output(exit) transivera. In a case when in transivere there are no fine tunings of the target cascade on the resistance of loading which is distinct from 50. 75 Ohm, this procedure should be carried out upside-down, i.e. entrance resistance of the amplifier to result to 50. 75 Ohm with the help of the elementary agreeing device. This device can be established in the amplifier or to execute it(him) in the separate case and to use both with other amplifiers, and with aerials which resistance is distinct from 50. 75 Ohm. In our variant of the requirement to such device minimal - it should pass(miss) capacity up to 100 Vt and result entrance resistance of the amplifier (47. 140 Ohm) to standard - 50. 75 Ohm.
On rice 3 one of variants of such device is given. It is a usual P-contour. As inductance it is possible to use a variometer or the coil with taps(removals), it is possible to replace condensers of variable capacity with constants, preliminary having picked up them on each range. The coil has 17 coils, a wire - diameter 1,0. 1,2 mm, beskarkasnaja, is reeled - up on opravke by diameter 15. 17 mm. She(it) is curtailed(turned) by a ring on diameter galetnogo the switch that taps(removals) had the minimal length. From one end of the coil taps(removals) are made from each coil, the last - is any through 2. 3 coils. Galetnyj the switch - on 11 positions. It is enough this step of adjustment for the optimum coordination.

For long and non-failure operation it is necessary to subject a new lamp to training. Especially it concerns lamps which anywhere did not work, but have lain some years. Than the lamp is more senior - that longer she(it) needs to be trained. In domestic conditions the lamp is maintained energized with heats of 10. 20 hours. If the lamp has more than 10 years - some days Then it is necessary to submit an anodi pressure(voltage) and again to sustain even 6. 10 hours. If there is an opportunity, in the beginning it is better to submit the lowered pressure(voltage). Having blown thus it is required small, let the lamp will get warm. After that some days are better to work on air at the lowered capacity. And only after that it is possible to deduce(remove) the amplifier on a full mode. It is not necessary to overlook to give before switching-off of the amplifier a little to work to the fan that the temperature of an environment of a lamp has gone down.

A.Tarasov (UT2FW) ut2fw@izmail.uptel.net
68800 Odessa regions of. Reni p.o. 65
Ph. ( 04840 ) 2-62-33
Site of the author http: // www.qsl.net/ut2fw/