PREAMPLIFIER " ELECTONE PIANO BUILT BY DAVID BOGEN CO., INC. 9-30-37

POWER AMPLIFIER " ELECTONE " PIANO MADE BY DAVID BOGEN CO., INC. 40 WATT INVERSE FEED BACK FIXED BIAS 9-30-37

NDDEL PR3 - P03 Super Electone Piano
Wiring Assembly. Delay Switches Details
Polarizing Switch and Power Stage Circuits

PREAMPLIFIER " ELECTONE PIANO BUILT BY DAVID BOGEN CO., INC. 9-30-37

POWER AMPLIFIER " ELECTONE " PIANO MADE BY DAVID BOGEN CO., INC. 40 WATT INVERSE FEED BACK FIXED BIAS 9-30-37

AMPLIFIER CIRCUITS:
The output transformer is especially designed and if it is damaged, an exact re placement is nece 8 sary.
The tone control is subject to wide variations according to individual requirements Some forms depend on the cathode by-pass for control; therefore, replace this component with exact value.
Use only glass tube8 in the input, as the leakage isle 88, and only glass tubes in the output, because of the possibility of a short to the shell.

NOISE ELIMINATION: First suspect dirt on the pick-up screws.
are insulated with lacquer, but this is not perfect. Clean with a vacuum- cleaner with blower attachment, which should be run for a few minutes so that the hose will be free from dirt. A thin strip of paper can be worked between the strings and the pick-up screws to remove stubborn particles of dirt.
Moisture may get into the wooden strip supporting the pick-up screws. This can be dried by placing in the bottom of the piano a pint fruit jar which is 1 / s filled with calcium chloride. This should be renewed when it disintegrates. When the strip is dry it should be oiled with Nujol.
Another source of noise may be leakage in the input group (the two in - megohm resistors and the. l-mf condenser). Replace with the best components obtainable. In severe climates place the 8e three components in a small cardboard pill-box and fill it with paraffin wax, bringing out the leads so they can be readily connected to their proper points.

Hum may be due to trouble in the filters, unmatched output tubes, or a poor bias rectifier, if trouble is confined to the amplifier.
Electrostatic pick-up to sorews is shielded by the back-board of the piano. This board must make good contact with the ground clamps. Il proper contact can not be established, cover the back-board with tin-foil she laid in place and grounded.

REGULATING PICK - UP SCREWS:
This must be done with the help or a professional piano tuner who must be a tono regulator. The tuner should tone regulate the piano very soft, paying attention to evene 88 of tone and not even as of volume. Then he can strike the note 8, telling the serviceman at the rear of the piano, if the pick-up screws need adjustment. Turn screws to right to make louder to the left to make softer. Take care that screws are not turned too far to the right, so that the strings will touch screw when a very hard blow is struck on the key.
These screws should ordinarily need no attention during the life of the piano. Only in case of buckling of the mechanism or tampering need the so be touched.

SETTING MASTER LEVEL CONTROL:
The striking of the hannor on the strings sets up tremendous transients in the electrical circuit which last a small fraction of a second. These tend to overload the amplifier and when the average output of the amplifier is 3 or 4 watts, the transients may be of the order of several hundred watts. Accordingly, a 40 - watt amplifier is used for low average power. Do not set the screw-driver type volume control too high. The instrument is not supposed to sound much louder than an ordinary acoustic piano.
Overload causes rattling similar to speaker cone rattle 8. Do not blame the speaker until you are sure.

SWELL PEDAL ADJUSTMENT:
The mechanical connection from the smell pedal to its control should be set so that with the pedal completely depressed, the sound from the speaker is just not noticeable.

Special parts and further service information may be obtained from Krakauer Brothers 191 Cypress Ave., New York City.

AMPLIFIER CIRCUITS:
The output transformer is especially designed and if it is damaged, an exact re placement is nece 8 sary.
The tone control is subject to wide variations according to individual requirements Some forms depend on the cathode by-pass for control; therefore, replace this component with exact value.
Use only glass tube8 in the input, as the leakage isle 88, and only glass tubes in the output, because of the possibility of a short to the shell.

NOISE ELIMINATION: First suspect dirt on the pick-up screws.
are insulated with lacquer, but this is not perfect. Clean with a vacuum- cleaner with blower attachment, which should be run for a few minutes so that the hose will be free from dirt. A thin strip of paper can be worked between the strings and the pick-up screws to remove stubborn particles of dirt.
Moisture may get into the wooden strip supporting the pick-up screws. This can be dried by placing in the bottom of the piano a pint fruit jar which is 1 / s filled with calcium chloride. This should be renewed when it disintegrates. When the strip is dry it should be oiled with Nujol.
Another source of noise may be leakage in the input group (the two in - megohm resistors and the. l-mf condenser). Replace with the best components obtainable. In severe climates place the 8e three components in a small cardboard pill-box and fill it with paraffin wax, bringing out the leads so they can be readily connected to their proper points.

Hum may be due to trouble in the filters, unmatched output tubes, or a poor bias rectifier, if trouble is confined to the amplifier.
Electrostatic pick-up to sorews is shielded by the back-board of the piano. This board must make good contact with the ground clamps. Il proper contact can not be established, cover the back-board with tin-foil she laid in place and grounded.

REGULATING PICK - UP SCREWS:
This must be done with the help or a professional piano tuner who must be a tono regulator. The tuner should tone regulate the piano very soft, paying attention to evene 88 of tone and not even as of volume. Then he can strike the note 8, telling the serviceman at the rear of the piano, if the pick-up screws need adjustment. Turn screws to right to make louder to the left to make softer. Take care that screws are not turned too far to the right, so that the strings will touch screw when a very hard blow is struck on the key.
These screws should ordinarily need no attention during the life of the piano. Only in case of buckling of the mechanism or tampering need the so be touched.

SETTING MASTER LEVEL CONTROL:
The striking of the hannor on the strings sets up tremendous transients in the electrical circuit which last a small fraction of a second. These tend to overload the amplifier and when the average output of the amplifier is 3 or 4 watts, the transients may be of the order of several hundred watts. Accordingly, a 40 - watt amplifier is used for low average power. Do not set the screw-driver type volume control too high. The instrument is not supposed to sound much louder than an ordinary acoustic piano.
Overload causes rattling similar to speaker cone rattle 8. Do not blame the speaker until you are sure.

SWELL PEDAL ADJUSTMENT:
The mechanical connection from the smell pedal to its control should be set so that with the pedal completely depressed, the sound from the speaker is just not noticeable.

Special parts and further service information may be obtained from Krakauer Brothers 191 Cypress Ave., New York City.