[R-390] Two new tutorials posted on the R390A FAQ site

[alex kosman]

Hello, I absolutely  agree,  those old input AC  filter make the
"differential relay" mounted in many modern houses to turn off the electric
supply.
If someone wants to open the old filter and replace the caps it will work,
but its not electronics but archeology !!
And, applying HV to cold tubes is a bad idea too. I used in many cases in
the 60' a delayed relay  (rectified  heater voltage can be used to add a
555 or else) with relay that connect the HV after 10 sec or more. Did that
in many receivers, automation circuits and more (miss those days).
Another  story, for those who insist to use rectifier tubes, the circuit
has an engineering  problem.
I dont have the schematics in front of me but I remember that the circuit
is grounded at one side and at the cathode  is under HV, that means that
there is hv between the cathode and the filament, the  26Z5 in this case is
made to resist but in many cases the isolation between the cathode and the
filament fail. In many countries a separate floating coil was made in the
main transformer just for the rectifier tube to avoid this stress. if you
use solid state rec. you eliminate also this problem.

many best regards to all,
Alex
Kosman Alex
Electronic Engineer
Mobile:  972-52-2812797
alexkosman10 at gmail.com






‫בתאריך יום ד׳, 24 ביולי 2019 ב-20:14 מאת ‪Brown Beezer via R-390‬‏ <‪
r-390 at mailman.qth.net‬‏>:‬

> Thank you Perrier
>
>
> -----Original Message-----
> From: Perry Sandeen via R-390 <r-390 at mailman.qth.net>
> To: r-390 <r-390 at mailman.qth.net>
> Sent: Tue, Jul 23, 2019 10:16 pm
> Subject: [R-390] Two new tutorials posted on the R390A FAQ site
>
> Yo Bubba Dudes!,
> Al has posted two new tutorials I've written.
> The first is how to replace the OEM large and dangerous AC input filter,
> FL101 with a modern computer input style filter.  They are smaller and work
> better than the OEM and best of all won't shock the dickens out of you if
> there is no 3 wire ground ans you are grounded when touching it.
>
> The second is an electronic regulated PS circuit.
> Now why would you really want to use it.
> I'm so glad you asked.
> Besides good B+ regulation there is IMNSHO a much more important feature.
> Almost all have given up 26Z5's because of cost and use SS diodes.  And
> here lies the problem.  When first turned on before the filaments have a
> chance to warm, up full B+ is applied to the tubes and filter capacitors.
> Both aren't happy with this. This causes tubes to be stressed and causes
> premature failure.
> Now they're not making the tubes we use anymore and the prices are slowly
> rising so prolonging their life has direct economic benefits for us.
>
> This wasn't a problem with filament rectifiers as B+ would slowly rise as
> the tube warmed up.
>
> So the circuit I came up with has a RC delay for a slow B+ rise.
> An additional benefit that is new to this is the LR8 three terminal
> programmable HV IC. With just two resistors it can be set from 12 to 450V.
> This can be used on any B/A receiver.  Used alone it can replace a 0A2 or
> any other gas regulator. What is so very helpful is that one doesn't need
> an input dropping resistor.
> All the details are on the tutorial.
> Regards,
> Perrier
>
>
>
>
>
>
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-- 
Kosman Alex
Electronic Engineer
Mobile:  972-52-2812797
alexkosman10 at gmail.com