HP 200 Series - User Manual

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Overview

Function Description
Important Technical Specifications
Usage Features
Maintenance Features

This document provides instructions for the Hewlett-Packard 200 Series Resistance-Tuned Audio Oscillators, which are laboratory instruments designed for speed and accuracy.

Function Description

The 200 Series oscillators consist of an oscillator section and a power amplifier section, complete with necessary voltage supplies. The oscillator section employs a two-stage resistance-coupled amplifier with both positive and negative feedback. A frequency-selective, resistance-condenser network provides positive feedback to control the oscillation frequency, while negative feedback stabilizes the circuit. The amount of negative feedback is regulated by a non-linear resistance network, which adjusts according to the amplitude of oscillation to maintain the proper operating point.

Important Technical Specifications

Models 200A and 200B:

Frequency Range:
- Model 200A: 35 cps to 35,000 cps
- Model 200B: 20 cps to 20,000 cps
Output Power: 1 watt
Load Resistance: Designed to deliver 1 watt into a 500 ohm resistance load over most of the frequency range. Special output impedances are available on order.
Internal Impedance: Approximately 50 ohms.
Load Resistance Tolerance: A 600 ohm load may be used with minimal power loss. Loads less than 500 ohms may cause an abnormal drop in output voltage above 10,000 cps.

Models 200C and 200D:

Frequency Range:
- Model 200C: 20 cps to 200 KC
- Model 200D: 7 cps to 70 KC
Output Power: 100 milliwatts
Load Resistance: Designed to deliver 100 milliwatts into a 1000 ohm resistance load over most of the frequency range.
Internal Impedance: Approximately 50 ohms at 400 cps.
Load Resistance Tolerance: Loads less than 1000 ohms may increase distortion at full output but will not otherwise affect operation.

General Power Supply:

Operates on 115 volts, 50-60 cps.

Usage Features

Initial Adjustments:

The oscillator is factory-tested and adjusted; no further adjustments should be necessary before use.
Before powering on, ensure tubes are secure and the Mazda lamp is tightly screwed in.
A warm-up period of 10-15 minutes is recommended when the unit is first used or after a long period of idleness.

Frequency Control:

The main dial in the center of the panel is calibrated directly in cycles per second for the lowest frequency range.
The dial reading is multiplied by the factor indicated on the range switch located on the left side of the panel.

Output Control:

Output voltage is controlled by the amplitude control on the right side of the panel, located ahead of the output amplifier.
For very small audio voltages, it is good practice to use an attenuator between the oscillator and the driven equipment to maintain a low hum level relative to the audio signal.
The oscillator is adjusted to deliver more than its rated power. Operating the amplitude control fully open may result in some distortion, which is normal. For low distortion, operate the oscillator at or slightly below rated output.

Maintenance Features

General Maintenance:

Periodically check frequency calibration and output distortion level.
Thoroughly clean the unit.
Apply a drop of light oil to the bearing on the main dial shaft.

Calibration:

To adjust the tracking of the main frequency selecting dial, a standard frequency source is required.
Procedure:
1. Set the dial to 200 and the range switch to X10.
2. Note the oscillator output at 20 on the dial (200 cps).
3. Set the dial to 200.
4. Adjust the oscillator frequency to 2000 cps using C1 (see chassis diagram).
5. Simultaneously adjust the voltage output to match that obtained at 20 on the dial using the compensating condenser (C6 for Model 200A/B; C8 for Model 200C/D).
6. These settings are interdependent and may require some maneuvering.
7. Recheck output at 20 to ensure it has not changed; if so, readjust output and frequency at 200 to match.
Model-Specific Settings for Output and Frequency Adjustment:
- 200A: 35 (350 cps) and 350 (3500 cps).
- 200D: 7 (70 cps) and 70 (700 cps).
All adjustments are made from the bottom of the chassis with the dust cover in place for accurate final calibration.
If the instrument does not track properly after these adjustments, it may indicate changed resistor values. In such cases, the oscillator should be returned to the factory for range switch replacement and recalibration.

Distortion:

Total harmonic distortion should be less than 0.5% under normal operation.
If tubes are changed, distortion should be measured, as a poor tube can increase distortion without affecting other operations.
Instability of output voltage can be caused by a defective tube in the oscillator section (T1 or T2) or a defective coupling condenser placing a positive voltage on the grid of T2.

Warranty:

Instruments are guaranteed against defects in material and workmanship for one year from the date of purchase.
The warranty covers repairs and adjustments or replacement of defective parts (excluding tubes, fuses, and batteries) if the fault is a direct result of manufacturing defects.
Service during the first year is free, excluding transportation costs to the factory.

Service Procedure:

If a fault develops, notify Hewlett-Packard with full particulars of the difficulty and the instrument's serial number.
Upon receiving shipping instructions, forward the apparatus prepaid to the factory for immediate repairs and adjustments.
Repairs for faults caused by misuse or abnormal operating conditions will be billed at cost, with an estimate provided before work begins.

Damage in Shipment:

Test the instrument immediately upon receipt.
If damaged or not operating properly, file a claim with the carrier.
Obtain a full report from the claim agent and forward it to Hewlett-Packard. They will advise on the disposition of the equipment for repair or replacement.
Include the model number, type number, and serial number when referring to the instrument.