[ARC5] Regulator noise. (was BC-454 - screen voltage)

Sat Mar 9 16:12:40 EST 2013

Considering that the bypassing is a given my a credible manufacturer it is 
far from enough as shown many times when improving Japans prolific 
offerings. While SMD devices are better the various other styles are not.

Some of the worst examples are magazine articles for ultra low noise preamps 
for VHF to microwave that use a generic 3 terminal to drop the typically 12V 
supply down to what is required. Might as well put a series resistor at the 
input.

Carl

> Hi Leslie - Of course, the 3 terminal regulators must first be bypassed at
> the input and output terminals per the application notes.  Especially if
> there is any "lead length" involved....I've found many cheap devices where
> this cost was ignored and the device radiated like a spark gap
> transmitter.  Cheap insurance.
>
> Once that is done, any associated zener noise that is underlaying is
> another matter.  I wonder what percentage of the output voltage the P-P
> zener noise is.....I've not found that to be detectable (by me) in HF/VHF
> receiver circuits that I have played with...
>
> 73, Tim
> N6CC
>
> On Sat, Mar 9, 2013 at 9:00 AM, Leslie Smith <vk2bcu at operamail.com> wrote:
>
>> Hello Dennis
>> Quote: " Zeners are often even noisier than an ionized gas tube.  But
>> the standard
>> > fix is easy; an RC feeding a load."
>>
>> I have a well informed associate who says the common 3 terminal
>> regulator family  eg LM7812 are noisier than zener diodes.
>> This idea has always intrigued me.
>>
>> I'd be interested to hear your observation on the relative noise output
>> from each device.  Is the noise from a VR tube radiated noise, or passed
>> along the supply line?
>> If the noise is "line-coupled" will an lowpass "LC" kill the noise, eg
>> 1mH choke plus 10nF to common?
>>
>> 73
>>
>>   Leslie Smith
>>   vk2bcu at operamail.com
>>
>>
>> On Sat, Mar 9, 2013, at 13:53, Dennis Monticelli wrote:
>> > Zeners are often even noisier than an ionized gas tube.  But the 
>> > standard
>> > fix is easy; an RC feeding a load.
>> >
>> > Dennis AE6C
>> >
>> > On Fri, Mar 8, 2013 at 3:56 PM, Brian Clarke
>> > <brianclarke01 at optusnet.com.au>wrote:
>> >
>> > > Hello Ken,
>> > >
>> > > The tube characteristics written in tube manuals (whose?) are for
>> > > establishing other characteristics, like life, gain and emission. 
>> > > They
>> are
>> > > not set in stone.
>> > >
>> > > If you want a quiet receiver, I would leave the Voltage regulator 
>> > > tubes
>> > > out - they rely on ionisation of the enclosed gas = very noisy. I 
>> > > know
>> 'coz
>> > > I tried it once - with a BC-454.
>> > >
>> > > If you want to experiment with tube element Voltages, set up an octal
>> > > socket on a breadboard, and measure noise and distortion vs Voltage.
>> Trying
>> > > to do that inside a built receiver makes it very difficult to 
>> > > discover
>> > > what's causing what.
>> > >
>> > > 73 de Brian, VK2GCE.
>> > >
>> > >
>> > > On Friday, March 08, 2013 8:14 AM, you said:
>> > >
>> > >
>> > >  Looking at the tube tables, I see that the screen voltage to the
>> 12SK7s
>> > >> is 150 VDC when the
>> > >> plate voltage is 250 VDC. When the plate voltage is 100 VDC, the
>> screen
>> > >> voltage should also
>> > >> be 100 VDC, according to those tables.
>> > >>
>> > >> Both ratings are for when the tube is operated in Class A.
>> > >>
>> > >> This receiver is still using the original screen-voltage
>> voltage-divider
>> > >> (the two black wire-
>> > >> wound resistors standing up in the back). Screen voltage is 75 VDC 
>> > >> to
>> all
>> > >> the tubes in the
>> > >> receiver, except the 12A6. Plate voltage, with the power supply I am
>> > >> presently using, is 275
>> > >> VDC.
>> > >>
>> > >> I wish to reduce the plate voltage to no more than 180 VDC. I plan 
>> > >> to
>> use
>> > >> a VR-75 and a VR-
>> > >> 105 in series for this.
>> > >>
>> > >> What is the consensus concerning screen voltage to the RF and IF 
>> > >> amps?
>> > >>
>> > >> My plan is to raise it to at least 100 VDC via a resistive voltage
>> > >> divider across the 180 VDC
>> > >> regulated input.
>> > >>
>> > >> In your opinion, what might be the result, both pro and con?
>> > >>
>> > >> In my opinion, this will result in greater gain (due to the higher
>> > >> relative SG voltage) and lower
>> > >> noise (due to the reduced plate voltage) at the RF and IF amps.
>> > >>
>> > >> Ken W7EKB
>> > >>
>> > >
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>>   Leslie Smith
>>   vk2bcu at operamail.com
>>
>> --
>> http://www.fastmail.fm - IMAP accessible web-mail
>>
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