Selenium Rectifier

ID: 47493
Selenium Rectifier 
30.Mar.05 07:29
0

Omer Suleimanagich (USA)
Articles: 429
Count of Thanks: 36
Omer Suleimanagich

Does anybody out there have suggestions for the ideal replacement for a
selenium rectifier?

Bridge rectifiers, what type?

0.01 caps, are four needed on a pre-made bridge?

Dropping resistors, should B+ be taken down to original specs?

What kind of dropping resistor and what wattage if it gets very hot?

Could a capacitor replace the dropping resistor on the B+ and is this safe?

These are all questions that I keep pondering.

Omer

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 2
Replacement of a selenium rectifier 
30.Mar.05 19:59

Ernst Erb (CH)
Officer
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Ernst Erb

In prinziple (for others): If you don't know the consumption (Amps.) you have to know either by the schematic or often you can read the ratings of the old rectifier. In any case you need to know the current you want to rectify.

Second you need to know what voltage you should get after rectification. Why?
A rectifier has always  some dropping resistor and there is a great difference between slenium and silicon diodes.

Then you can choose either a suitable bridge or four diodes - for instance 1N4007 - to create a bridge.

The following resistor should be "big" enough to easily take the current (heat). The ohms you might measure with a pontentiometer if you have one which can take the current (solid wire, rather big). It is not very critical but you have to run the set and to begin with a too high value and lower it until you get your voltage (aproximately).

I think you are safe if you start with 300 ohms but the value may be much less, perhaps down to 100 or 50 ohms.

Since diodes or bridges are small you can try to build them (without the resistor) into the old selenium because the selenium did have to absorb much more temperature. Watch the temperature of the dropping resistor for an hour and don't put it near cables or inflammable materials.

It is mostly a rather easy job. Good luck.

PS:
In principle you can use a capacitor to get the needed current (not the voltage!). You would have to start with too low values if you don't calculate it. But you would have really to get only the currant needed, not the rated current of the rectifier or so. This would be safe and you would not use a dropping resistor.

Your first question can't be answered without data, the second I did not quite understand but probably is now solved?

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 3
Selenium Rectifier data in RMorg 
31.Mar.05 00:06

Robert Sarbell † 22.3.22 (USA)
Articles: 363
Count of Thanks: 27
Robert Sarbell † 22.3.22

Good evening Omer,

By using the SEARCH block at the top of most forum pages, members can find many references to specific items of interest.

We are both aware that the most technically correct German word would be advisable to search for. . . .in this instance I chose "selengleichrichter" (selenium rectifier).

The following items are an extracted copy of the resultant page. . . . . . . . .
Please accept my apology for still not completing a "major uninstall" of an incorrect default version of the Java script!!



Full-text search: There are more than [maxHits] hits in public pages. Please try making the search criteria more specific.
in: Forum Texts Public pages Models Makers Collectors
exact search

No hits in Attachments.

39 hits in Forum / Texts Pages: 1 2
Shown: From 1 to 20 of 39.

Date Author Subject Board
28.Jun.2004 Holger Pflug saba: SABA Freiburg 7 Automatic RADIOS IM RADIO-MUSEUM
11.Mar.2004 Dirk Becker gemeinsch: VE301W; Restauration- Nachkriegsumbau-hier Frage RADIOS IM RADIO-MUSEUM
19.May.2004 Dietmar Rich grundig: 1088; Musikgerät RADIOS IM RADIO-MUSEUM
20.May.2004 Eilert Menke fwf: Heroton 662GW, Hinweis RADIOS IM RADIO-MUSEUM
03.Jul.2004 Klaus Pahr Übertragerspule defekt? RADIOS IM RADIO-MUSEUM
18.Oct.2004 Jürgen Stichling emud: II GW Luxus; Favorit RADIOS IM RADIO-MUSEUM
26.Dec.2004 Frank Blöhbaum pgh-elektr: RPG 64 - viel zu hohe anodenspannung - was tun? RADIOS IM RADIO-MUSEUM
06.Jan.2005 J. H. philips: 214A (214 A); RADIOS IM RADIO-MUSEUM
02.Jan.2005 Wolfgang Eckardt stern-sonn: 65/52W (neu); Sonneberg RADIOS IM RADIO-MUSEUM
27.Jan.2005 Klaus Pahr grundig: TK23 Automatic; Verzerrte Wiedergabe RADIOS IM RADIO-MUSEUM
28.Feb.2005 Paul Schmidt zenith: (Ch=5G40); Transoceanic G500 RADIOS IM RADIO-MUSEUM
11.Mar.2005 Andreas Steinmetz grundig: Grundig 495W Netztrafodaten RADIOS IM RADIO-MUSEUM
23.Mar.2005 Marc Gianella sondyna: Sondyna Resonar RE5520 - Reparaturbericht RADIOS IM RADIO-MUSEUM
12.May.2004 Henning Oelkers Unbekannter Hersteller Radio Frankfurt III Apparate rar oder unbekannt oder selbst gebaut
21.Jan.2005 Michael Schott Wer kennt dieses Tonbandgerät? Apparate rar oder unbekannt oder selbst gebaut
30.Jun.2004 Klaus Pahr Selengleichrichter defekt? Tipps und Tricks zu Radio Reparatur, Restauration
13.Nov.2004 Matthias Hasenmayer Ab wann ist ein Gerät "verbastelt"? Tipps und Tricks zu Radio Reparatur, Restauration
22.Nov.2004 Walter Haring Rar, unbekannt, selbstgebaut? Jedenfalls schön+rätselhaft TALK, talk, talk - nur für Mitglieder sichtbar
19.Feb.2005 Henning Oelkers Brandursache: Röhrenradio TALK, - nur für Mitglieder sichtbar
19.Mar.2005 Martin Renz Linksverkehr für Strom in Innsbruck? TALK, - nur für Mitglieder sichtbar


19 hits in Models

Shown: From 1 to 19 of 19.
Manufacturer Model Year
Telefunken Radios Deutschland Visiomat 43 FE14 (FE-14) 1957 - 1958
Stern-Radio Berlin, VEB, RFT, - vorm. Ph... Contura 2500 1976
Heliogen, Hermann Pawlick; Bad Blankenburg Akkula 51110 1930
Radio und Fernsehen, VEB; vorm. PGH; (Os... Zweikanal-Service-Oszilloskop EO 213 1988
Stern-Radio Rochlitz, VEB, RFT, (Ostd.) ... 5E61-DU (5E61DU) 1950 - 1952
Eben, Dipl.-Ing., Dachau MK 3331 (MK3331) 1961
Eben, Dipl.-Ing., Dachau MK3332 (MK 3332) Studio 1961
Heli Gerätebau, Hempel KG; Limbach-Oberf... Sensit IC RK88 (RK 88) abNr.70001 1984
Robotron-Elektronik Zella-Mehlis, VEB; Z... Meiningen 2003 Automatik 1978
Blaupunkt (Ideal) Malta 7220 1955 - 1956
Blaupunkt (Ideal) Colombo 7230 1955 - 1956
Stern-Radio Staßfurt, VEB, RFT (Ostd.) -... Donja 101 1965
Stern-Radio Staßfurt, VEB, RFT (Ostd.) -... Sibylle 108 1967
Stern-Radio Staßfurt, VEB, RFT (Ostd.) -... Sibylle 104 1967
Stern-Radio Staßfurt, VEB, RFT (Ostd.) -... Sibylle 4 53GTG106 1967
Stern-Radio Berlin, VEB, RFT, - vorm. Ph... Garant 2130 1977
Graetz, Berlin-Treptow; Nachkrieg = Alte... 158W 1951 - 1952
Gerufon Radio Walter Velten KG; Quedlinb... Musikus 54GW 1953 - 1954
Stern-Radio Rochlitz, VEB, RFT, (Ostd.) ... 5E61-D (5E61D) 1951 - 1952


No hits in Manufacturers.


No hits in Collectors.


I apologize for taking up so much space to adequately reply; however, I shall make an effort to provide for all new USA members (and some not-so-new members) in a separate thread, a list of some (of the many) threads which may prove very beneficial.

Most of the threads are written by our German colleagues, however, they have expended much effort to make our participation most rewarding, and most of the threads are written in grammatically correct English.

Respectfully,
Robert



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 4
 
31.Mar.05 00:18

Hans M. Knoll (D)
Editor
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Count of Thanks: 60
Hans M. Knoll

Hello Gentlemen,
 a little bit you can find here ( in special english) ;-)

http://www.radiomuseum.org/dsp_forum_post.cfm?thread_id=41660

Hans M. Knoll

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 5
 
31.Mar.05 01:56

Robert Sarbell † 22.3.22 (USA)
Articles: 363
Count of Thanks: 23
Robert Sarbell † 22.3.22

Good Morning (very early morning) Hans,

Your discussions with Mr Pinyot (and his advice to you....... ;-) ;-) I shall remember the numbers 41660 as I remember Mr Kirst!!

I have sent the thread 41660 to Dr Omer Suleimanagich by direct email this morning, just after he posted his question.

Hans, your English is far superior to our use of the German language. I am hoping for some one to refresh my memory to the thread which provides a long list of the technical terms in German language (for us to search).

Mit Freundlichen Grussen,
Robert


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 6
Selenium Rectifier 
31.Mar.05 07:50

Omer Suleimanagich (USA)
Articles: 429
Count of Thanks: 26
Omer Suleimanagich

Thank you gentlemen for your prompt reply!

The reason I posted this question, is simply the curiousity of how many of you approach this problem when you are not able to get the correct B+ needed for the radio to run properly.

Recently, on a Telefunken Opus 55, I replaced the the selenium rectifier, with a bridge rectifier rated at 1000 PIV/ 4amps, with a 150 ohm dropping resistor rated at 50 watts. To many here, over kill(!), but I don't want to fix the same problem twice! The B+ is coming from a replica transformer of the original (check my bio page for the place that made it), and gives just a little more juice than the circuit needs for the B+ (280 volts DC @100mA)

I attempted to use 0,01 uF capacitors (four) between the bridge rectifier, but upon doing so, it greatly affected the treble on the radio. The capacitors used , were of the polypropylene kind rated @630 volts( does a bridge reactifier have something in it that plays the same function as the 0,01 capacitors do on a home brew?).

I would love to see the ideal circuit here for selenium rectifier replacement, with thermistors included. Somehow, I like using bridge rectifiers because they're clean, as opposed to a diode "christmas tree" rectifier.

Omer

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 7
Alternatives for consideration 
31.Mar.05 17:12

Robert Sarbell † 22.3.22 (USA)
Articles: 363
Count of Thanks: 23
Robert Sarbell † 22.3.22

Omer,

I offer my solution from years ago. . . . . . .please keep in mind the posting above from Mr Erb, and the offerings by Herrr Knoll.

Background: My father-in-law bought a Grundig model 5295 NEW in Germany in winter 1962. . . . . .and gave it to my son in 1985

The selenium rectifier, pn AEG B250C150K4, had to be replaced. According to prevailing acceptible substitutions, recommended in SAMS Photofact for the model 5299 (which was essentially the model 5295 without speakers), were the 1N540; 1N1763; or the 1N3194.
In 1985, there was an abundance of 1N4004 diodes rated as 400PIV at 1 Amp. . . . .which was a preferred substitute to the first 3 diodes above.

A 6-terminal strip with 4 of the 1N4004 diodes was substituted in the same location as the original AEG rectifier pack, and has caused absolutely no difficulties since replacement. I did not add any supplemental resistance or capacitance.

The schematic for your Telefunken Opus 55 depicts an AEG selenium rectifier with a B250C140L rating. . . .for all intents and purposes approximately 10 milliamps variance. The K4 and L designations I do not address in order to allow "detail-oriented" members to expend some research.

Within the last 10 years or so, most service technicians recommend the 1N4007 diodes which offer 1000PIV at 1 Amp with some resistance or capacitance added. I believe that with proper selection, one does not need such "excess capacity".

I cannot address the "ideal" circuit, because ideals are like opinions. . . . .we all have one.

I am prepared to offer a total and complete voltage comparison of the original 5295 schematic with the voltages I recorded after my SAMS Preferred substitute replacement suggestion (taking into account the 1N4004 as equal to the 1N594/1N1763/1N3194).

NOTE: I have also seen the TCG-125 diodes used in the same arrangement as the 1N4004 described above.
Respectfully,
Robert

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 8
Additional alternative - rebuild the original AEG rectifier 
11.May.06 19:55

Robert Sarbell † 22.3.22 (USA)
Articles: 363
Count of Thanks: 28
Robert Sarbell † 22.3.22

Dear Radiofriends,

I have been fortunate enough to find on ebaY USA, a very nice Opus 55TS which was advertised "for parts".

The radio is playing very nicely at the present time, with nearly all components being Original. However, there is a very slight hum, and after playing for approximately 40 minutes or more, the original rectifier begins to experience the effects of "old age", and break down.

However, a gentleman from RMorg gave me an AEG selenium rectifier (more than a year ago) which is in like new condition - part identification of the cylindrical AEG is as follows:
AEG
M 2x385 C125 R
611/56
qlu 23467
Note: I am aware of the difference in the respective circuit wiring for this s-r.

I believe the 56 inner parts (cells) are essentially identical to the 36 cells in the present rectifier in my Opus 55TS:
AEG
B350 C140 L
511/36
19066 TFK

I realize that I must "reconfigure" the cells within the cylinder to agree with the schematic for use in the Telefunken.

Have any members performed a similar "rebuild" of a selenium rectifier?? I realize the typical procedure is to use the silicon diodes. But with essentially unused internal parts, what major items am I failing to account for?

Respectfully,
Robert
NOTE: I am presently photo-documenting the procedures as I proceed with the "transplant operation".

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 9
 
12.May.06 06:23

Omer Suleimanagich (USA)
Articles: 429
Count of Thanks: 32
Omer Suleimanagich

Hi Major!

Here are two solutions for replacement of the selenium rectifier. Whatever you do, place a high wattage dropping resistor of about 100-150 ohms on the B+.

The first photo is actually from my Opus 55.  The second was taken off of rec.antique radio phono. Attachments:

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 10
 
12.May.06 14:30

Robert Sarbell † 22.3.22 (USA)
Articles: 363
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Robert Sarbell † 22.3.22

Good Morning Omer,

Thank you for the suggestion. I believe I have seen the second photo just recently posted within our forum by one of our respected RMorg members - Herr Georg Richter on 10 May. . . . . . .see the thread "Ersatz eines Selen-Brückengleichrichters".

I have been in the habit, for most of my 3 years in RMorg, of reading many of the threads posted in German and the other foreign languages.

The replies earlier in this thread have discussed the "typical silicon diodes" bridge rectifiers. I was hoping that one of the European members may have considered a similar repair using the AEG circular plates.

Respectfully,
Robert
NOTE: I am aware of the solid state bridge rectifiers and have one which is configured to replace the present AEG original.

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 11
Diode Type, Diode Bypass Capacitors 
14.May.06 07:25

Paul Moyer (USA)
Articles: 17
Count of Thanks: 25

Omer,

The choice between a bridge rectifier and individual diodes is purely an appearance or convenience and not a performance issue.  The diode performs only as a check valve for current flow and the only performance characteristics of significance for these rectifier diodes are forward currrent, peak forward current, and reverse breakdown voltage.  Whether the diodes are individual or in a molded bridge configuration the required ratings are identical.  The molded rectifier bridges that I am familiar with do not have internal diode bypass capacitors.

Peak forward current occurs when the radio is turned on and a large inrush current flows as the filter capacitors charge.  (Actually, the highest peak currrent occurs when a radio is turned off very briefly so the tubes are still hot and then turned back on, because now since the tube cathodes are already hot the tubes will draw additional current from the power supply which will add to the charging current for the filter capacitors.)

The reverse voltage that is "seen" by the rectifier diodes is the highest voltage that is reached on the first filter capacitor plus the peak reverse voltage of the transformer winding that feeds the diodes.  (The peak voltage is the RMS value multiplied by 1.414.)  The highest peak voltage will occur shortly after the radio is turned on when the filter capacitors are fully charged but before the tubes warm up and begin pulling current.  What this math leads to is that the diodes will "see" twice the peak DC voltage that occurs on the input filter capacitor during the radio warm-up.  For instance if the normal operating DC voltage on the first filter capacitor is 280 volts, this voltage might well rise to 320 volts as the radio warms up.  In this case the diodes would "see" 640 volts, so the required reverse breakdown voltage must be significantly greater than 640 volts.

Generally if a diode is operated in a circuit where the peak current or reverse voltage rating is exceeded, the diode will be instantly distroyed (usually the diode will short).  A shorted rectifier diode will hopefully cause the line fuse to blow, but if the fuse does not blow the power transformer will be quickly destroyed.  So it is very important that rectifier diodes are chosen that operate well within their maximum ratings.

When diodes were a new technology it was costly to build high-current high reverse-breakdown diodes so many different combinations of forward current and reverse-voltage ratings were built.  In the present time, now that diode manufacturing techniques have been greatly improved, it's cheaper to manufacture and stock less variety and standardize on universal diode types that will fit a wide variety of applications.  The 1N4007 diode with ratings of 30 amps peak and 1 amp continuous forward currents and 1,000 volts reverse breakdown voltage will work perfectly in any tube radio that I am familiar with where a selenium rectifier is being replaced.

Individual diodes are an excellent choice for those who are stuffing them into the original selenium rectifier can.  Some molded bridge rectifier models may also fit into the selenium can.

The diode bypass capacitors are used to supress AM radio interference.  Silicon diodes are a fast switch when the current flow reverses, and this fast switching creates a broad spectrum of harmonics.  This switching noise can easily be verified on rectifier diodes without bypass capacitors using a transistor radio tuned between stations and moved to the vicinity of the recitifier diodes when the tube radio is operating.  The transistor radio will pick us the switching "hash" noise as it is moved close to the diodes.  (You may find that more of the switching noise is received when the transistor radio tuning is set near the high-frequency end of the dial.)  The switching noise will disappear when the diodes are bypassed with a capacitor.

While I have not seen design guidelines for sizing these bypass capacitors, I do know that the larger the current flow through the diodes and the lower the source impedance (power transformer winding impedance), the larger the capacitor value must be.  If the value of the bypass capacitors is too large then a reverse current will flow through the bypass capacitor that will tend to discharge the filter capacitor when the diode is reverse-biased.  If the capacitor value is too small then the switching noise will not be completely suppressed.  Typically a value between .001 and .01uf will work properly.  Remember the diode bypass capacitor will "see" the same reverse voltage as the rectifier diode, so the capacitor voltage rating must be chosen appropriately.  A 1KV voltage rating is a good choice.

It is not possible that rectifier diode bypass capacitors could affect the high-frequency response of your radio.  Something else must have happened at the same time that led you to this conclusion.  Perhaps a lose wire, a poor solder connection, or a tone control that is dirty or has a slider with a poor contact.  You can verify this by measuring the high-frequency response or gain using an AC generator and voltmeter.  The filter capacitors are the effective power-supply source impedance for the amplifier stages of the radio.  The impedance of these filter capacitors is very low, particularly at the high-frequency end of the audio spectrum.   This low impedance totally "swamps" any possible contribution of the diode bypass capacitors.

Paul

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 12
 
14.May.06 09:31

Omer Suleimanagich (USA)
Articles: 429
Count of Thanks: 20
Omer Suleimanagich

Thanks for the reply,

I eventually took care of the Opus 55 last fall, with the aid of four 0.0047 mfd ceramic caps rated at 1000 volts, in accordance to Herr Knolls suggestion.  In addition, I replaced the sockets for the power tubes with two new Cinch'es, completely mimicking the old wiring.

The radio, now sounds fabulous, with a deep woody bass!

What was going on with the myler caps, I couldn't figure out, but now, I keep a bag of 0.0047's to snub the rectifier in future projects. 

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 13
Comments on a 1N2484 diode bridge  
15.May.06 16:23

Robert Sarbell † 22.3.22 (USA)
Articles: 363
Count of Thanks: 25
Robert Sarbell † 22.3.22

Paul,

Thank you so much for the excellent explanation of the use of the silicaon diodes for the bridge rectifiers for our vintage radios.

In your third paragraph which discusses the "initial" high peak voltage seen at the first PS capacitor, after replacing the selenium plates in the original AEG in my Opus 55TS, the "power on" DC voltage immediattely rises to almost 365volts and peaks there for no more than a second or so and then drops precipitously and at a steady rate until approximately 12 - 15 seconds later it stabilizes at 280 -281 volts. . . . as specified on the Telefunken schematic.

This occurs after replacing the dual 50/50uF PS electrolytic capacitor with new 47UF 450VDC caps. Unfortunately, the selenium plates still have too much voltage loss - after nearly 3 hours the voltage coming from the first filter cap has dropped to approx 264 volts. . .

I have seen 2 radios (some time ago) which used a silicon bridged unit that had the 4 1N2484 diodes. . . Can you comment on the use of these diodes in the vintage European radios?

However, I would much prefer to stay with the selenium rectifier if I could obtain one.

Respectfully,
Robert

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 14
1N2484 Diodes, Voltage Sags 
16.May.06 05:39

Paul Moyer (USA)
Articles: 17
Count of Thanks: 19

Robert,

The 1N2484 diode has a reverse breakdown voltage of 600 volts, a continuous forward voltage rating of 750 ma, and a peak current rating of 30 amps.  As I explained in my previous submission a 600 volt reverse breakdown is too low for these radios because of the high DC voltage (greater than 300 volts) that occurs before the tubes warm up.  The continuous and peak forward current ratings would be fine, but because of the insufficient reverse breakdown voltage these diodes should not be used.  Really good rectifier diodes like the 1N4007 are cheap these days.  It's not worth risking a power transformer.

Are you certain your power supply voltage sag is caused by the rectifier?  A gassy tube or a leaky coupling capacitor could cause excessive current drain on the power supply causing the voltage to sag.  If excessive current draw is your problem it would most likely be caused by the audio output stage.  Monitor the voltage across the cathode resistor on the output tube.  This voltage should stabilize after a few minutes of operation.  If this voltage continues to increase then the output tube is either gassy or the coupling capacitor to the control grid is leaky.  In your case where the power supply voltage is dropping, the cathode voltage on the output tube should decrease as the power supply voltage drops if the output stage is healthy.

When working on one of these radios it is always a good practice to measure the output tube cathode voltage a few minutes after turning on the radio to verify that the operating current for that tube is correct, and then check this voltage again after an hour of operation to verify the tube and coupling capacitor are stable.  The audio output tube is capable of drawing enough current to damage power supply components (or the output transformer) so it's operation needs to be carefully checked.

On the topic of retaining a selenium rectifier, it probably is a really good idea to replace it with silicon diodes.  I am not a chemist but I understand that when a selenium rectifier fails it can release toxic gas, and retaining a selenium rectifier adds unnecessary risk for the power transformer.  I suggest stuffing the silicon diodes and the diode bypass capacitors in the selenium rectifier housing.  Depending on how much heat is given off by the added appropriate power resistor to drop the power supply voltage down to the specified operating voltage when the silicon diodes are installed, this resistor can also be stuffed into the selenium rectifier housing.  Just install the resistor at the top of the rectifier can (above the diodes) to minimize heating of the rectifier diodes.

Paul

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 15
 
16.May.06 07:59

Omer Suleimanagich (USA)
Articles: 429
Count of Thanks: 18
Omer Suleimanagich

Gentlemen,

I concur with Paul regarding silicon over selenium, for rectification.  However, my computations tell me that the selenium rectifier in the Opus 55 is functioning at 95%.  For a fifty year old, that's pretty darn good!

The last three Opus 7's I worked on in the last few months, all had selenium rectifiers that were working at 80% - 85% of spec.  In each case (they all had noisy transformers) after I squelched the noise with red insulating varnish, I bypassed the original 50/50mfd cap with a new JJ brand, 50/50 mfd cap, rated at 500 volts along with a snubbed bridge rectifier and dropping resistor.  All electrolytics and paper caps were replaced as well.

From what I was told, if the selenium rectifier is not running too hot and its working within 5% of spec. the recommendation is to keep it.  If its running very hot and is working at less than 90% of spec, its time to go with silicon.  Many times, I try to maintain all the voltages within ideal spec., meaning that I'll take the B+ up to where the schematics have it labeled. 

Here is one of the EBay junker units I brought back to life.

Attachments:

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 16
 
25.Jul.06 00:19

Robert Anders (USA)
Articles: 15
Count of Thanks: 25
Robert Anders

Goodafternoon,
The link below will give many examples for half and full wave rectifiers.
Within both, you will find a variety of components.... including selenium that vary due to their capacity,


http://search.msn.com/images/results.aspx?q=Selenium+Rectifier&srch_type=2&FORM=QBIR

Regards, Robert

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 17
 
03.Sep.10 20:41
9559 from 55363

Timo Haveri (FIN)
Articles: 15
Count of Thanks: 17

Paul Moyer wrote: "What this math leads to is that the diodes will "see" twice the peak DC voltage that occurs on the input filter capacitor during the radio warm-up.  For instance if the normal operating DC voltage on the first filter capacitor is 280 volts, this voltage might well rise to 320 volts as the radio warms up.  In this case the diodes would "see" 640 volts, so the required reverse breakdown voltage must be significantly greater than 640 volts."

This is true for a half-wave rectifier (one diode) but does this really apply to full-wave bridge rectifiers? There is always two diodes effectively in series in a 4-diode bridge. When two identical diodes are in series, one diode will only see approximately half of the voltage applied across them. I believe putting diodes in series is a common trick to increase the peak inverse voltage rating. So an individual diode in a rectifier bridge with a filter capacitor in the output will see only the peak DC voltage not twice that.

Could someone confirm if the above is correct or am I wrong?

Best regards, Timo

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 18
rectifier 
11.Feb.15 15:34
26878 from 55363

Victor Lourenco (P)
Count of Thanks: 8

Hello Omer

I want to replace a de rectifier from my Telefunken D775 wk.

Do you think, i can use a 600v 4a to replace the original? Using also the big resistor that you use on your Opus 55?

Best regards

 

Victor Lourenço

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 19
Selenium rectifier 
11.Feb.15 18:03
26908 from 55363

Michael Mehnert (D)
Articles: 48
Count of Thanks: 14

Hello Victor,

do you need this type of rectifier for your radio? I have a few of them. The are all checked, voltage drop approx. 30V.

Please contact me via email.

Michael

 

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 20
selenium rectifier 
13.Feb.15 03:10
27011 from 55363

Tony Bartunek (CDN)
Articles: 16
Count of Thanks: 9

Hi Omer,

About selenium rectifiers, it is easy to calculate the value of voltage dropping resistor, simply by Ohms law. I = E/R   (europians are using U symbol instead of E for voltage). So if you need to drop 25 volts and total current is 0.1 A,  reverse Ohms law to R= E/I ,  ( 25 volts / 100 mA )= 250 Ohms.

Wattage is calculated by P = E x I    ( 25 volts drop X 0.1 A)  = 2.5 Watts. For safety reasons, this resistor's wattage should be at least trippled of quadrupled, so use  250 Ohms / 10 watts resistor.

But that is not only what I'm writting. You were talking in this article about Telefunken Opus 7 noisy/buzzing power transformers.

I repaired a few, too, and every one Opus 7 had this problem. I tried to tighten the core, and placed a clamp on it and re-mout this transformer separately from chassis on rubber blocks, that helped, but you sealed it with " red insulating varnish" you said. What kind of varnish is it, what brand and what exactly and how did you do it?

Regards, Tony at www radiodoctor.org  or radiodoctor@xplornet.ca   (in Ontario, Canada)

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 21
Red GLPT Insulating Varnish 
14.Feb.15 18:47
27095 from 55363

Omer Suleimanagich (USA)
Articles: 429
Count of Thanks: 9
Omer Suleimanagich

Perhaps, loosening up the transformer to get to the windings (completely removed from the radio and NOT connected except, to a variac) and injecting the varnish with a syringe (metal tip, just opened enough to spurt) between the transformer windings, and then dialing up a variac to the transformer , up to 110VAC, for a minute.  This should be repeated , until the transformer is , internally saturated with varnish

But remember, excercise extreme caution and safety!

BTW My thoughts on selenium, is that they can cause eventual harm to the radio!

 

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 22
selenium rectifier 
18.Feb.15 22:56
27230 from 55363

Tony Bartunek (CDN)
Articles: 16
Count of Thanks: 16

Hello Mr. Omer,

Thanks for the info on red GLTP, I will try it on my next repair of Opus 7 transformer,

Regards, Tony at www radiodoctor.org

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