ARCHIVED FORUM -- March 2012 to February 2022READ ONLY FORUM
This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
The rectifier type in question is neither silicon or germanium but selenium.Menahem is right (wow, did I say that? )The series resistor has two jobs;First job is to compensate for the somewhat higher output.Second job is to protect the rectifier by dampening the rush-in current to the large filter and reservoir cap(s).
Martin
Wow, timing is everything.
Menahem Yachad:http://w3hwj.com/index_files/RBSelenium2.pdf
...and thanks for the article link (which I just linkified )
My Dirigent is certainly in the top 3 of my favourite B&O possessions. I'm actually not sure what the other two are...
--mika
Menahem Yachad: You are correct about a GERMANIUM diode having a voltage drop of ~0.2VDC. But the rectifier plates are NOT Germanium, they are SELENIUM. And the Selenium rectifiers have ~1VDC drop, which increases with age.
You are correct about a GERMANIUM diode having a voltage drop of ~0.2VDC. But the rectifier plates are NOT Germanium, they are SELENIUM. And the Selenium rectifiers have ~1VDC drop, which increases with age.
I must admit that I never realized that there could be another version, the Selenium version.
I know the different kind of rectifiers by sight, but didn't exact realize what they were made of. (I started at school when germanium was already/almost replaced by Silicon.)
Then again, when does that really make a difference? In an amplifier it doesn't make a big difference if there are a few volts extra. I've measured dozen (and more) times that voltages are not always exactty the same as mentioned in the diagrams. Keep in mind the changing mains voltage here in Europe.
But thanks for sharing and correcting.
chartz: Beobuddy: A Silicon diode has a higher forward voltage (0,6-0,7V) than the older germanium version, which has only 0,2-0,3 V Er... What ?
Beobuddy: A Silicon diode has a higher forward voltage (0,6-0,7V) than the older germanium version, which has only 0,2-0,3 V
A Silicon diode has a higher forward voltage (0,6-0,7V) than the older germanium version, which has only 0,2-0,3 V
Er... What ?
Never heard of ?
Beobuddy:Then again, when does that really make a difference? In an amplifier it doesn't make a big difference if there are a few volts extra. I've measured dozen (and more) times that voltages are not always exactty the same as mentioned in the diagrams. Keep in mind the changing mains voltage here in Europe.
The issue is less that of the increased voltage, and more to do with the much lower internal resistance of a silicon diode. An uncharged capacitor presents a load close to a dead short, and the higher internal resistance of the selenium has the effect of limiting the current. If simply swapped for silicon diodes the currents can become very large and it is this that tends to cause problems.
Martin.
No problem - it's no fun if we don't learn something new every day. This issue of limiting currents is very interesting. It's one of the ways which modern manufacturers cut costs and design products whose sound (and performance) is of much lesser quality than it could be.
Resistors solve many interesting problems.
2 examples:
1. The main filter capacitors in modern amplifiers are much smaller than they could be. So, the sound is much smaller.
Martin + Martin described the overcurrent problem at initial switch-on. That overcurrent can destroy the rectifier diodes over time. Larger capacitors = larger overcurrent.
The solution is really quite simple, but it requires 2 extra parts, and a little extra PCB real estate, but in the modern cut-throat way of business, even that's too much to give the customer.
Just insert a 10-50ohm 10W resistor between each large capacitor's power output and the B+ (or -) rail.
This is called a snubber resistor, and it absorbs the capacitor's high current, releasing it (relatively) slowly, so that the diodes are not damaged.
So if you have an amplifier with original 5,000uF capacitors, you can replace them with 10,000uF, with the snubbers, and not worry about damaging the rectifiers. And even so, the new 10,000uF capacitor is STILL smaller (size) than the old 1970's 5,000uF capacitor!
Ametherm has introduced a new type of Inrush-limiting Thermistor which solves this problem very elegantly, but the downside is that the air inside the amplifier is now a few degrees hotter. At switch-on, the thermistor has its full resistance of say 25ohms, and then within 20-30 seconds, it heats up to close to 200 degrees, and the resistance drops to less than 1ohm. So this thermistor must have its own private real estate on the PCB, where the heat will not damage any other components.
2. Upgrading Op-Amps in modern amplifiers. Most amplifiers come with really poor quality op-amps in the preamplifier stages. Again, a matter of cost. The really good-sounding op-amps are not what's called "unity-gain stable". That means that they will oscillate, and self-destruct if you just do a straight exchange.
There are many other issues involved (additional capacitors required), but such an op-amp's output pin is not permitted to be connected (in the normal way) to the downstream coupling capacitor.
So here, just insert a 47ohm 1/2W resistor between the Op-amp output and the coupling capacitor, and the problem is solved. An excellent-sounding op-amp which benefits from this, is the TI THS4032.
Don't have the faintest idea where you guys are talking about but still interesting.
One question though. What does Martin means with the remark as mentioned below?
There are not a lot of caps in these lovely machines, but of the few there are I can't help noticing that youdidn't replace the filter/reservoir cap.
Martin or others, I don't seen any other caps besides the blue ones I already have replaced. Is he talking about the disc shaped red component(s) around the filters cans?
Brengen & Ophalen
I mean to say, that there are not many electrolytic capacitors in the Dirigent.You replaced all those on the circuit boards but not the large filter/reservoir capacitor.That's the large cylindrical capacitor bolted to the chassis near the mains transformer.A high voltage multi-section capacitor.
The red discs are ceramic capacitors. I suggest you don't touch them since some of them formpart of tuned circuits and a full alignment of the tuned circuits could take hours, even for a trained tech guy.
Actually, if you already replaced the discriminator capacitor (the electrolytic capacitor sitting across the output from the detector/discriminator),the symmetry alignment should ideally be checked.
Martin,
I see what you mean. A member send me a link to order a can cap which is 50/50/50/100DC 350V.
This type can be used? Have to check the dimensions first.
The suppresion cap which showed me on Ebay has been ordered as well.
Thanks...
Leslie,
Only just found this thread but you've done some absolutely beautiful work! Howver, I have two questions, if I may -
- What do you use as the replacement grille pegs on your MS150s? A good number on mine have broken and I've not found anything that fits really well.
- How did the making of the replacement cable cover for the SC80 stand go? If it was a success, would there be any possibility of you making another for a fellow member whose SC80 is also missing its cover?!
@AdamS, you mean the one on page 5? It's just an ordinary black wallplug that has to be cut on length. Would you like me to send you some (for free) except for posting costs?
I did not made the SC80 cover because my friend Jaqcues from who I trade this furniture found the original cover so I was quite lucky. However, it's quite tempting to make one myself. Somebody here in Holland offered me an original but not sure if he still has it and how much he wants for it.
Found another Beolink 7000 that needs new caps. All working fine now..
Now my BV type K's are completely finished..
And some paintwork to do on the faceplate of the Dirigent. Martin advised me to use 3 colors of Humbrol paint in order to get the right color.
Humbrol Enamel! Now you take me back 50 years to when I started building airplane models, and Humbrol was the only game in town.
Enamel - Poisonous stuff - give me a break. Now they have all this environmentally-conscious "safe" stuff which doesn't last.
Pfff... Leslie so unbelievable many Beolink 7000's
It looks again all like new :) ...
Corsica out, serves you right! Holland, great game again!
Exciting day yesterday when Holland won the match so a good start to do some restoration today on other things like another Beovox 5000 flatpanel which was in bad condition.
Next will be refoaming and cleaning of white CX50's and CX100 which already are in mint condition except for one tiny repair :-)
This one..
And refoaming offcourse.
And washing cloths..
And get rid of these annoying yellow stripes caused by sunlight (luckily only 2).
And now we have a white-orange van Persie...
Look better now Leslie :)... Are these 5000's those from ''Sanne'' for Marktplaats ?...
Don't forget to mount again with new double sided tape the bass ports and recap it with Low ESR elco's or MKP's :)
Niet echt Salvador, zoals Paul altijd zegt, zolang als het goed werkt moet je er van af blijven.
Is recapping of the old flat panels an issue? From what I've heard they are pretty robust technically.
Cheers!
Leslie: Niet echt Salvador, zoals Paul altijd zegt, zolang als het goed werkt moet je er van af blijven.
Dat snap ik... :) Toch doe ik het sinds kort wel en merk toch altijd wel verschil... bij sommige audio merken is het verschil zelfs belachelijk groot..
B&O gebruikte (en gebruikt..) wel kwaliteitscomponenten, maar ik denk dat met nieuwe caps vooral stemmen etc. toch net ff dát stukje mooier klinken..
Basspoorten opnieuw vastplakken kan ik je wel aanbevelen.. bij mijn panel's die ik tot nu toe heb gehad zaten ze altijd los en het is van datzelfde plakkerige isolatiespul tape.. maar dan dubbelzijdig :)
Je zou eens moeten kijken welke merken er voor deze caps gebruikt werden... en aan de hand daarvan ze zowieso vervangen :) Frako klinkt altijd slecht (vaak goude elco's of bruine elco's (maar dan staand in receivers etc..)
Maar wat Paul zegt klopt wel.. maar preventief onderhoud om het ook weer echt als nieuw te laten klinken kan ook geen kwaad :)
It depends on how they sounds... if the voices sounds thát B&O good and the Bass sounds smooth and... you hear (if the amp is good ofcourse) no grsskkfhkkrr sounds then the caps are in good condition...
But most of the times that I've (passive) speakers here with Gold collored elco's or BP elco's they are not in good condition... Remember if you replace them... don't buy cheap caps without quality... Best choice is Vishay, BC, Wima or Visaton ... Panasonic (FC series) and Nichicon or Nippon Low ESR caps are also very good (and most of the times with better specs than the original caps in good condition..).
Menahem Yachad: .Here is an article which explains the issues very clearly. http://w3hwj.com/index_files/RBSelenium2.pdf
.Here is an article which explains the issues very clearly.
http://w3hwj.com/index_files/RBSelenium2.pdf
Interesting article.
In the next few days I will receive 2 BM900's. The complaint is that they hum. So, I will start some experiment with replacing the rectifier. (Supply cap was replaced some time ago).
Manbearpig:Is recapping of the old flat panels an issue? From what I've heard they are pretty robust technically.
IMHO not unless something is actually malfunctioning. I looked into this with my BL5000s - the crossover has a couple of electrolytics, and they are both in the bass network, unlikely to affect the sound much. The rest of the audio path has all of one electrolytic capacitor, apparently in the compensation loop of the hybrid amp. Didn't bother.
Beobuddy: Menahem Yachad: .Here is an article which explains the issues very clearly. http://w3hwj.com/index_files/RBSelenium2.pdf Interesting article. In the next few days I will receive 2 BM900's. The complaint is that they hum. So, I will start some experiment with replacing the rectifier. (Supply cap was replaced some time ago).
If the hum is audible from the speakers check the voltage from the regulator.The Beomaster will hum (often regardless of the volume control setting) if the voltage supplied tothe amplifiers is too high (!)A good setting is usually just below 24 Volts.(Adjusted using trimmer 902).
If the hum comes from the set physically, replace the transformer. Quite a few different transformers were usedin production and certain type(s) are known to develop a quite impressive humming (while actually still working very well).
Dillen: If the hum comes from the set physically, replace the transformer. Quite a few different transformers were usedin production and certain type(s) are known to develop a quite impressive humming (while actually still working very well). Martin
Thanks for the tip. I can confirm about a BM900 which actually has a physically hum. This one needed a donor transformer as another one can't be easily placed inside the cabinet where the original is located.
Typical detail is that they were brought in with the humming complaint. I connected them and there appears no audible humming from both.
With the menitioned article in mind, I think it could be the so called "selfhealing mechanism" from the Selenium rectifier.
So, I start with that and will see what happens. As you suggest, I will try to to drop the voltage just below the 24V. Maybe rewiring the transformer for 240V use would be the first wisely thing to do.
-
.....
Is prima, dan ga ik wel weg :)
As we are not on the Dutch subforum, could everybody please stick with English.
Will keep that in mind!
Ok, volgende klus, oops, must be in English....
Okay, next job.. finished refoaming CX50's and 100's.
This is how I got a BL4000. Needs some restoration...
New cloths, red, white or blue?
Maybe white so because of that that I need to make the grill white as well..
Finished Beolab 4000 which can be used as a center speaker.
Changed black into white cloth...
Sprayed all 3 panels in white..
Brasso copper polish to give the laquer a shiny look...
Polishing panels...
Et voila...
Beste Leslie,
Waar bestel jij de Mecanorma wrijfletters om het front van de BL5000 mee te herstellen? Mijn versie is in goede staat behalve de cijfers en strepen van de volumeslider.
Alvast bedankt,
Dave
Dave, moderator(s) does not allowe me to reply in Dutch!
Anyway, this where I have my decals made if your talking about the Beolab 5000?
It's not Mecanorma...
4x Frutiger LT Std 55 Roman Zilver metallic Gegoten vinyl, metallics 10.00 mm 115 mm 10 mm € 36,96
Cheers, hope this will help
..
My B&O products: Beosound 9000, Beosound 2300, Beosound Century, Beolab 8000, Beolab 6000, Beolab 4000 x2, Beolab 3500, Beolab 2000, Beolab 10, Beolink Active x2, Beotime, Beo5 x2, Beo4, A9 keyring x2, LC2 dimmer x6 and growing....
Hi Leslie,
how did you remove the top and base plate of the BL4000s without damaging them?
BR
Riven
Temperature controlled heatgun Riven. It wil come loose by itself eventually. The topplate consist 2 parts, metal carrier which is attached on the (plastic) housing with thick foamtape and on top of that the thin aluminium plate. I choose to remove the whole topplate to prevent damaging.
Dear Leslie,
These decals are the black rub-on letters to replace the original black printed numbers behind the volume slider (nr's 1-10). How do you restore the black lines?
Greetz,