Whoopsie, my bad - due apologies The circled earth point stole my attention on the commute...The drawing shows that the South-West is disconnected, as I suggested.
Whoopsie, my bad - due apologies The circled earth point stole my attention on the commute...The drawing shows that the South-West is disconnected, as I suggested.
Why not?Can a battery be used as an alternative to "noiseless heating voltage"?
And the first switched mode power supplies (using vibrators) were invented.Later when automobile used 6 or 12V batteries, vacuum tubes were adapted to this new de facto standard.
I tried another power supply from Nady TCM 1050.A mod I've done on this PSU was to cut the trace between C6 and C7, and solder in a resistor there. If memory serves, you are pulling around 300mA and cannot loose more than 4V, so ~5 ohms is a good first try. 5 ohms into the stock 1000uF is about 20dB down at 120Hz, which improves the 7806 from 60dB to 80dB.
You can also replace the 1000uF with a 4700uF (the layout has space), which is worth another 10dB of filtering at 120Hz.
Still remained? As in, it was unchanged?But unfortunately the hum and background still remained
Well, if the grounding arrangement is as much f...ed up than in the other, it's no wonder.I tried another power supply from Nady TCM 1050.
There filtering is about the same as you suggested.
But unfortunately the hum and background still remained ..
Unfortunately, I did not try your option, because. I've already remade the microphone in a different way.Well, if the grounding arrangement is as much f...ed up than in the other, it's no wonder.
You never reported if arranging the grounding as I suggested brought any improvement.
Thanks for the guidance.vmanj
In this thread and another you ask questions and do not seem to listen to what people post.
IIRC all your questions have been covered in the past in older threads at this forum
The biasing stuff can be seen in schematics or on the web there is nothing new that you posted.
power supply design for low noise can be found in books.
Some of the replies have good information
Anyway there are "better" ways to heat and bias in some circuit fragments that have not been posted in the threads
Very little less..Still remained? As in, it was unchanged?
I'm sure I read somewhere (Morgan Jones?) that using batteries for bias voltage in a valve mic is not as good an idea as you might think with respect to noise. Less hum of course than a rectified and smoothed AC supply, but it is not free of noise. Chemical cells have a grainy current which is noticeable when you apply a lot of gain to it.Why not?
The first "wireless" sets used batteries for all voltages, quite often 2 or 4V for heaters and about 80V for B+ (the name B+ originates from "battery positive").
Later when automobile used 6 or 12V batteries, vacuum tubes were adapted to this new de facto standard.
Not for heating, only for bias (cathode)..I'm sure I read somewhere (Morgan Jones?) that using batteries for bias voltage in a valve mic is not as good an idea as you might think with respect to noise. Less hum of course than a rectified and smoothed AC supply, but it is not free of noise. Chemical cells have a grainy current which is noticeable when you apply a lot of gain to it.
Fine for heating, but heating and biasing, maybe not.
As I understand it, the battery in the cathode should ONLY be rechargeable (1.2..1.5V) - e.g. lithium battery AA or AAA ?Battery definately cant be considered noiseless ,mush and hum can still creep in ,
Ive used a Ni cad or Nimh cell in the cathode of preamps and it works well enough , presenting only a fraction of an ohm at the cathode instead of the 5 ohms of the series dropper scenario , the anode current of the tube itself maintains the battery ,but regular usage is required or else your doing a check with a meter
A coin cell supplying grid bias in a tube mic might be worth a look , if you were really careful about your leakage resistance a coin type cell might last 10 years or more , downside of any kind of battery is if left unattended for a period of time voltage drop and chemical leakage might become an issue .
Maybe a tube mic with an externally accessible slot for the grid battery , ie when not used for prolonged periods the coin cell is removed .A negative wired 1.5v cell lines up just about right with where an EF86 grid wants to be with cathode grounded .
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