The table below gives pertinent information for octal tube rectifiers with 5-volt filaments and the same pin out. The voltage drop will vary nominally from amp to amp and tube to tube.
| Tube Type | DC mA | PIV | FIL AMPS | Max ACV | DCV | DCV DROP | Slow warm up |
| Diode Rectifier | 412 | No | |||||
| 5AR4 / GZ-34 | 250 | 1700 | 1.9 | 450 | 402 | 10 | Yes |
| 5V4-GA | 175 | 1400 | 2 | 375 | 387 | 25 | Yes |
| 5V4-G | 175 | 1400 | 2 | 375 | 386 | 26 | Yes |
| 5U4-GA | 250 | 1550 | 3 | 450 | 379 | 33 | No |
| 5U4-GB | 275 | 1550 | 3 | 450 | 377 | 35 | No |
| 5U4-G | 225 | 1550 | 3 | 450 | 377 | 35 | No |
| CV378 / GZ37 | 250 | 1500 | 2.8 | 450 | 375 | 37 | Yes |
| 5R4G/GY/GYA | 250 | 2800 | 2 | 750 | 367 | 45 | No |
| 5R4GYB | 250 | 3100 | 2 | 900 | 362 | 50 | No |
| 5Y3-G/GT | 125 | 1400 | 2 | 350 | 352 | 60 | No |
Example: your Bassman RI has a GZ34; if you want more compression and you wish it clips a little sooner you can change the GZ34 to a 5AU4 rectifier to lower the DC about 25 volts (voltage drop). Now the amp is running at lower power (about 40 W) and will compress more. An easily reversible mod if you don't like the results.
WARNINGS: Lower voltage = lower current. You may need to reset bias. The 5U4 draws 3 and the GZ37 draws 2.8 amps of filament current. The filament windings in your power transformer might not be up to the job if the stock rectifier draws 2 amps.