PreAMP PA for Radioberry — Setting and Output Guide
The Radioberry PreAMP Power Amplifier (PA) module requires careful setup for reliable operation. This guide covers the key parameters: supply voltage, constant current limits, BIAS potentiometer adjustment, and the latest component changes.
Power Supply
Use a constant-current (CC) power supply for testing. Do not use a plain voltage-only supply without current limiting — you will risk damaging the PA stage.
| Parameter | Recommended Value |
|---|---|
| Voltage | 8V DC |
| Current (constant current limit) | 1 – 1.5A |
| Optimal setting | 8V @ 1A |
Why 8V @ 1A Is Best
At 8V and 1A constant current, the PA runs cool with very little heat buildup. This makes it much harder to accidentally burn the transistor or surrounding components. Higher current increases heat without meaningful performance gain.
BIAS Voltage Adjustment
The BIAS potentiometer is a critical adjustment. Set it correctly or the PA will not operate efficiently — or worse, it may draw excessive current and overheat.
Procedure
- Start low. Set the BIAS voltage potentiometer to 0.5V before powering on.
- Key the transmitter. Current will only flow when the radio is actually transmitting. There is no standing current draw through the PA when idle.
- Measure BIAS voltage under TX. The correct BIAS voltage is approximately 2V. Do not aim for 2.8V — that is too high for the current revision.
Important: Do not set BIAS to 2.8V. The replacement MOSFET used in the latest revision requires approximately 2V BIAS voltage. The older reference value of 2.8V no longer applies and may cause damage.
MOS Transistor Change
The latest revision of the PreAMP PA no longer uses the AFT05MS004NT1 MOSFET. A substitute part has been used instead.
This substitution is the reason for the changed BIAS voltage — the new part saturates at a different gate voltage, hence the ~2V target instead of the older 2.8V.
Quick Reference
| Parameter | Value |
|---|---|
| Supply voltage | 8V DC (constant current) |
| Current limit | 1 – 1.5A |
| Optimal current | 1A |
| BIAS start point | 0.5V |
| BIAS target (under TX) | ~2V |
| BIAS target (old, obsolete) | 2.8V ❌ |
| MOS transistor (latest rev) | Substitute (not AFT05MS004NT1) |
| Current draw | Only when transmitting |
Summary
- Use an 8V constant-current power supply set to 1 – 1.5A
- 8V @ 1A gives the best thermal performance — low heat, safe operation
- BIAS voltage starts at 0.5V and should be adjusted to ~2V under TX
- Current is only present during transmission
- The AFT05MS004NT1 has been replaced — the new part needs ~2V BIAS, not 2.8V
Authored on 2026-05-15 · Document Version: b2e14a1 · Last Revision: 2026-05-15