The 3A5 DHT is another interesting valve to bear in mind. Many have used them successfully even in a phono stage. Great examples are Dmitry Nizh’s DHT phono stage and Sheldon’s. I will probably use them as well at some point.
Well, many DHT have been dismissed over the years due to their microphonic sensitivity. True, they are more microphonic, but this is manageable. Look at the 4P1L for example. I built a great preamp a couple of years ago and played around with the mechanics of the preamp to quiet it down. And I managed to, succesfully (as many have as well). The 4P1L sounds fantastic, despite so many turning it down because of its natural singing skills 🙂 Now, 4P1L is looked after, many are building DHT preamps and even full DHT amplifiers.
Looking at the specifications of the 3A5, we can see that the heater is attractive to be used with rechargeable batteries. Well, at least 220mA @ 1.4V is manageable. Key specs are:
- Mu of 15
- Anode resistance (ra) is 8,300Ω.
- Anode dissipation (Pa) is 500mW per valve.
- Vf=1.4V / If =220mA (paralleled filaments)
- Transconductance (gm): 1.8mA/V
- Maximum anode voltage: 135V
How linear is this DHT? Let’s look at the curves first:
