- Joined
- Apr 10, 2016
- Messages
- 82
I am not a tube guy, and I didn’t want to clutter up the Russian tube thread with these comments, but a few things are striking to me about the U47 mic with the VF14 that could be tested, to understand the magic of this combination. I am not a tube guy, so forgive me if these are frankly stupid.
Looking at the Telefunken U47M (mic) and U47N (power supply) schematic at Dan Alexander dated 9-1-55 (https://danalexanderaudio.com/wp-content/uploads/2018/01/Schematicscans002-1080x716-1080x675.jpg):
(I am sure this is in our archives, but this is the one I saw)
1. We all know the heater and plate come off of the same 105 V supply, which is dropped by resistors to 34 V at the plate and 36 V at the heater. There are no electrolytics in the mic body, only in the power supply, connected by a cable . It seems to me that the performance of the mic would be prone to B+ fluctuations, which would affect both heater and plate simultaneously.
Would strong signals be prone to an interaction between heater and plate, not unlike sag in a guitar amp? If so, could it act as a form of mild pleasant compression on strong signals, accounting for some of the “magic?”.
2. The voltage at the plate seems low to me compared to other tubes. What sonic signature does a “starved plate” impart on a microphone?
I was just thinking if it wasn’t the microphonics of the VF14 tube, could it be something else. The fact that there is only one capacitor (the output cap) in mic body schematic jumped out at me.
I will never own a vintage U47 with a VF14, so I can’t test these ideas, which may be just wrong. I do know if you overengineer a 1950s Fender guitar amp like a 5F1 with more modern transformers or more robust power supply filtering, you lose some of the charm.
Forgive me if these ideas are frankly stupid.
Looking at the Telefunken U47M (mic) and U47N (power supply) schematic at Dan Alexander dated 9-1-55 (https://danalexanderaudio.com/wp-content/uploads/2018/01/Schematicscans002-1080x716-1080x675.jpg):
(I am sure this is in our archives, but this is the one I saw)
1. We all know the heater and plate come off of the same 105 V supply, which is dropped by resistors to 34 V at the plate and 36 V at the heater. There are no electrolytics in the mic body, only in the power supply, connected by a cable . It seems to me that the performance of the mic would be prone to B+ fluctuations, which would affect both heater and plate simultaneously.
Would strong signals be prone to an interaction between heater and plate, not unlike sag in a guitar amp? If so, could it act as a form of mild pleasant compression on strong signals, accounting for some of the “magic?”.
2. The voltage at the plate seems low to me compared to other tubes. What sonic signature does a “starved plate” impart on a microphone?
I was just thinking if it wasn’t the microphonics of the VF14 tube, could it be something else. The fact that there is only one capacitor (the output cap) in mic body schematic jumped out at me.
I will never own a vintage U47 with a VF14, so I can’t test these ideas, which may be just wrong. I do know if you overengineer a 1950s Fender guitar amp like a 5F1 with more modern transformers or more robust power supply filtering, you lose some of the charm.
Forgive me if these ideas are frankly stupid.