Low noise, low microphony, low hum valves

[MarcelvdG]

I thought it was rather detailed already...

Anyway, attached is the schematic of my test common-cathode stage. The output goes to a 100 times amplifier with an NE5534A. The output of the NE5534A goes to a line input of an Asus Z9200U laptop computer and to an A-weighting filter, the output of which goes to the other channel of the laptop line input. The processing done with GoldWave and Excel is already explained in this thread. See also Linear Audio September 2012.

[finisvox]

MarcelvdG,

thanks for your answer. I'm thinking about to make (one more time) a noise measuring set-up, but this time, in a more "permanent" basis.
I have done a well power supply for one of my phono stages, and a pair of Linear Technology LT1115 op amps, that have a very good noise figure.
For measuring purposes, my National VP-7720A could be very suitable.

Cheers !

[finisvox]

In the meanwhile, I have attached a picture of a module that I have built some years ago, and I will use it again, for my "noise-measurements-set-up".
This module have 3 selectors for the gain: the central one have 5 position: 40, 45, 50, 55 60 dB and acts simultaneously for the two channels. The other two selectors, acts one for the left channel and the other for the right one. In this case, they have 4 positions with increments of 1 dB. (0, 1, 2 and 3 dB). This technique is very useful for to use it as "balance" control, for to compensate differences between channels in some cartridges.
Anyway, I will use this module as "noise amplifier". (using only the op amp stage)

cheers!

[Wavebourn]

Originally Posted by Wavebourn

For low microphonic I have some other missile-rocket-science tubes. I won't name them, because I am going to buy supply for myself, then reveal all details.

Here you go:

planar triode 6S17K-V with 8 micron grid.

gm = 14 mA/V, mu = ~150, designed for 10 g vibration, or up to 500 g acceleration.

[mogliaa]

Yep, tested it. A great tube indeed:
http://www.diyaudio.com/forums/3029622-post.html

[Wavebourn]

Originally Posted by mogliaa

Yep, tested it. A great tube indeed:
diyAudio - View Single Post - GS-4V High-mu russian triode for RIAA preamp

Yess, a killer front-ed tube for microphone and phono preamps!
The trick is, the grid is so close to cathode so it better works with input transformer, and biased by grid leak resistor and own input current, while cathode firmly sits on the ground.

[finisvox]

Now, I just have finished to put the power supply into a decent box. Now, I will build some sort of shielded container for the circuits and the "Device Under Test" (DUT). I have not idea how to do it until now, but I will found some cheap solution.
By the way, I'm thinking to use LabView for to make all the signal (noise, actually) analysis and presentation, but I'm new in LabView. Some idea ?
I would like to purchase some good russian valves, but I have seen that all of them (at reasonable prices) are from the outside of the EU. Somebody knows an EU provider ?

Cheers !

[mogliaa]

Originally Posted by Wavebourn

Yess, a killer front-ed tube for microphone and phono preamps!
The trick is, the grid is so close to cathode so it better works with input transformer, and biased by grid leak resistor and own input current, while cathode firmly sits on the ground.

Hi Anatoliy,
Do you have grid current information from the datasheet to estimate the value of the grid leak resistor?
Thanks
Ale

[Wavebourn]

No, it is not specified, and varies from tube to tube. They did not need high resistances in grids, for intended application in rockets at UHF.