User's Manual

ALPHA 9500 Interim OPERATING MANUAL

www.alpharadioproducts.com

5 Theory of Operation

5.1 Theory of Operation - Overview

The Alpha 9500 uses a single 3CX1500 (8877) high-mu external anode triode ceramic tube for

ampliﬁcation. The main power supply is an unregulated transformer/rectiﬁer/capacitor power

supply for the high voltage (HV) and heater circuits. All other power supplies are regulated.

The biasing and tank circuits are similar in most respects to its predecessor, the Alpha 77. The

unit has thoroughly modern computer-controlled power supply and control circuitry. Extensive

safety measures protect the ampliﬁer against most off-nominal conditions. It has USB and RS232

interfaces to aid in remote operation. All front-panel features are accessible via these interfaces.

There are 6 main circuit boards in the ampliﬁer and communications between these is via an I2C

bus.

5.1.1 Firmware architecture

The data architecture of the Alpha 9500 revolves around the Inter-IC (I2C) bus, developed by

Philips for the control of medium-to-high-scale consumer electronics. This bus allows a Master to

communicate with a number of Slaves. Each Slave is independently addressable, and data can be

communicated rapidly and bi-directionally between Master and Slaves. The ampliﬁer has been

designed so that a single master communicates with a number of Slaves, each of which performs

a subset of the task required to make an operational ampliﬁer. The time taken for the MC to

cycle through one round of communications with all the Slaves, and perform all it’s own task

establishes a sort of natural “heartbeat” for the ampliﬁer. A sufﬁciently rapid response is possible

with such an architecture that a “heartbeat” rate faster than the response time of the human eye

is possible. The Master controller is located at the back of the ampliﬁer and its ﬁrmware may be

upgraded via a serial or USB connection to a Windows computer.

5.2 Tube