Zenit U415 DHT Preamplifier

Zenit U415 DHT preamplifier

Zenit U415 Direct Heat Triode Preamplifier in Choke load configuration.

My original idea is to build Telefunken RE134 preamplifier but after I finished it I found that my tube is weak because it is used tube and I didn't have any tube tester to test it before I use. So I change my configuration to support Zenit U415 that it's very close construction and specification. So I need to change some operating point from 250V supply to 150V and the current is down from 10mA to 5mA . So final configuration is below.

* Preamplifier tube is Phillips ( Zenit ) U415 run in LC configuration.
* Anode choke is Lnaudio ( Electraprint ) 100H 20mA
* Rectifier tube is Phillips AZ2
* U415 filarment is using 2 stage LM317T 1st stage is voltage regulator and 2nd stage is current regulator

U415 preamp schematics

Sound is very good , It's natural sound , a lot of detail , good dynamic , good in both high and low. When I using this preamplifier with R120 it's very good match better than #26 and Bas , I never like R120 sound until I use this preamp with R120 that drive by ML-6. Now I love my R120 very much after its found the match preamp. But when I use this preamp with my F2A PP it's to much high.

Telefunken RE134 using Telefunken AZ1 Mesh plate as rectifier

So what about TFK RE134 sound , because my tube is weak its can run over 10mA so I use with 7mA configuration . the sound is more smooth but less detail than U415 but I'm not sure about the accuracy of the tube so I need to find new pair.