[NJARC] Selenium rectifier replacement

Fri Apr 24 02:21:43 EDT 2015

Yep Dave, that is what I am saying.
The selenium rectifier is a pretty poor rectifier but it is more efficient then a vacuum tube rectifier since it has no need for heater power.  
The reason for the series resistor in a selenium rectifier circuit is to limit the charging current demanded by the filter capacitor.  The selenium rectifier is current limited anywhere from about 35 mA to 450 mA depending on voltage rating and the size of the selenium stack.  The Sarkes Tarzian Selenium Rectifier Handbook is on line as a pdf file and explains the need for the series resistor and the current ratings of the various models.
With the external series resistance and the high voltage drop in the selenium rectifier, the voltage regulation is pretty poor.  15% to 20% voltage regulation is to be expected.  In other words, the higher the load current pulled out of the power supply, the lower the output voltage will drop.  Vacuum tube rectifiers have much the same voltage regulation problems as selenium but the the peak non repetitive current is a bit higher.
Silicon rectifiers do not have this problem, this is why they have replaced both tube and selenium rectifiers.  Maximum forward silicon diode current is usually one amp and three amp silicon rectifiers are as inexpensive.  Peak non repetitive currents are in the tens of amps range.  There is little internal resistance in the silicon diode and the voltage drop is usually less then one volt so the voltage regulation is much much better.
If one is concerned that the average output voltage will be too high when the selenium rectifier is replaced by silicon, then use a filter choke with an appropriate current rating to reduce the voltage and improve the voltage regulation of the power supply even further.  Ultimate regulation using an LC filter requires a bleeder resistor to load the power supply enough so that the inductor always has the minimum required current flowing through it.Jim

     From: Dave sica <davesica at gmail.com>
 To: "antqradio at sbcglobal.net" <antqradio at sbcglobal.net> 
Cc: "njarc at mailman.qth.net" <njarc at mailman.qth.net> 
 Sent: Thursday, April 23, 2015 11:54 PM
 Subject: Re: [NJARC] (no subject)

Jim,
With selenium that's always promoted as good practice for reasons that sound valid to me. Are you saying you think adding a resistor then makes no sense too?
-- Dave "not an engineer" Sica

Sent from my iPad

On Apr 24, 2015, at 12:27 AM, <antqradio at sbcglobal.net> wrote:

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No experience with this vendor but I did find the schematic of this power supply.
http://tubecad.com/2008/11/blog0151.htm

In reading the technical description, I fail to see the need to add resistors in series with the solid state rectifiers to "better mimic a tube rectifier".  All I see in this is that one is taking a better silicon diode rectifier (as compared to a vacuum tube rectifier) and then adding series resistance to make the voltage regulation worse.  That is to say that the rectified and filtered voltage will change more with load current (increase the filtered ripple voltage) and then apply this to an IC regulator to restore regulation.  This makes no sense to me.  
The same idea is used when replacing a selenium rectifier with a silicon diode.  Jim  
      From: Joe Devonshire via NJARC <njarc at mailman.qth.net>
 To: njarc at mailman.qth.net; dvhrc at mailman.qth.net; NEARC_Radio at yahoogroups.com 
 Sent: Thursday, April 23, 2015 7:56 PM
 Subject: [NJARC] (no subject)

 Has anyone had any experience with this product or other products from this company?  Good / Bad. etc... Joe Devonshire http://glass-ware.stores.yahoo.net/ps2solo.html  

GlassWare Audio Design
Thanks for supporting the Tube CAD JournalSEARCHHome > PS-2 Solo
The same regulator the PS-1 uses, but without the heater PS
 PS-2 SoloItem# PS-2 Reg Kit$39.00Heat Sink Height: 1.5 inches2.5 inches Availability: Usually ships the next business dayThis item is currently out of stock!
Product Description
No doubt that this little circuit board (4.5 by 4.25 inches) will make life quite a bit easier for many tube fanciers.

On this extra thick (0.094 inch), US-made PCB with 2oz-copper traces resides a single high-voltage regulator, with its own raw power supply, including the rectifiers and power-supply reservoir capacitors. In other words, except for the power transformers, the PS-2 Solo PCB holds all that is needed to make a superb tube B+ power supply. The PS-2 Solo regulator can power a line-stage amplifier, headphone amplifier, or phono stage. (It might also work in a tube power amplifier, if the current draw isn’t excessive.) This high-voltage regulator uses a high-voltage series regulator to achieve a quiet and stable regulated B+ voltage, which can span from 50V to 300V, while delivering up to 80mA of current.

Furthermore, both a full-wave-center-tapped configuration and a full-wave-bridge rectifier arrangement can be used with this PCB. The PS-2 Solo PCB, like the Janus Solo PCB, holds only a single high voltage regulator, unlike the original PS-1 regulator PCB which held both high voltage and low-voltage regulators. Thus, the tube heaters must find their power source elsewhere, such as an AC winding or a simple DC power supply or regulator power supply.

The PS-2 Solo kit comes with all the parts needed to populate the PCB, including the heat sink, standoffs, and 14 voltage-setting resistors, which allows the following output voltages to be set:

50V 60V 65V 75V 110V 120V 125V 130V 135V 140V 150V 160V 165V 170V 175V 180V 185V 195V 200V 210V 215V 220V 225V 240V 250V 270V 300V

All the resistors needed

All the capacitors needed (Nichicon, Panasonic, RTI or Wima)

LD1085 low-dropout voltage regulator

Heatsinks for TO220 device

Four sets of PCB standoffs with O-rings

Four HER108 ultrafast 1A 1000V rectifiers

IXCP 10M45S HV constant-current source

24-Page User Guide

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