Hello!
I wanna buy some new capacitors for the older paper and electrolytic capacitors in an old tube radio.
The radio:
Link on radiomuseum:
Stereo-Vollsuper ST6501 Art. Nr. 03604 Radio QUELLE GmbH
It's a big stereo radio, with beefy speakers, just look at the sizes of the loudspeakers:
The amplifier board: (the free tube socket is for a connector that goes to the tone control)
The schematic:
In GREEN , RED and PINK, I highlighted some electrolytic capacitors.
What series of what brand should I use there, for very good audio quality at a resonable price?
For the green one, I think I will use a very long life capacitor (like Nichicon ULD)
For the red ones, I think some nichicon audio grade, like UFG (fine gold) or UKA/UKZ. I think UKZ since its nichicon best electrolytic audio capacitor, at least in the datasheets.
For the pink ones... I don't know... They are electrolytics, maybe I can put some film capacitors. They are important since they are in the signal path and they block the low frequencies for the tweeters.
Now, the paper capacitors are bad, all of them, no comments.
I need to replace them. I'm in Europe, but I can order from American companies too, as long as the shipping is free (the order is over 70$)
Suppliers:
Europe: TME, Farnell
USA: Mouser, Digikey
For paper capacitors, the metallized polypropylene film is what I need.
The store that has axial PP capacitors for all the values that I need is Mouser, I found the Illinois Capacitors MPW series being the only one that has all the values that I need.
Another alternative are the Vishay MKT1813 POLYESTER capacitors, but I don't think that polyester is as good as polypropylene...
Or the MKP1839 capacitors, I like them, but they don't cover all the values that I need. Same for MKP1845.
Another alternative is the WIMA MKP10 series (they have a good reputation in the audio community), but they are radial, So I need to make the leads axial like this:
Then solder them, of course.
A map of all the capacitors that need replacement, with their positions, dimensions, values and types. Very handy.
So:
What capacitors shall I buy to replace the old capacitors in this tube radio?
I aim for a warm sound, with decent highs and good lows.
I'm not much of an audiophile, but this radio is very rare and has a very good audio potential, so I want to give it very good components.
I also want to buy from a single place, that it has a diverse catalogue, like Mouser or Farnell.
Thanks!
I wanna buy some new capacitors for the older paper and electrolytic capacitors in an old tube radio.
The radio:
Link on radiomuseum:
Stereo-Vollsuper ST6501 Art. Nr. 03604 Radio QUELLE GmbH
It's a big stereo radio, with beefy speakers, just look at the sizes of the loudspeakers:
The amplifier board: (the free tube socket is for a connector that goes to the tone control)
The schematic:
In GREEN , RED and PINK, I highlighted some electrolytic capacitors.
What series of what brand should I use there, for very good audio quality at a resonable price?
For the green one, I think I will use a very long life capacitor (like Nichicon ULD)
For the red ones, I think some nichicon audio grade, like UFG (fine gold) or UKA/UKZ. I think UKZ since its nichicon best electrolytic audio capacitor, at least in the datasheets.
For the pink ones... I don't know... They are electrolytics, maybe I can put some film capacitors. They are important since they are in the signal path and they block the low frequencies for the tweeters.
Now, the paper capacitors are bad, all of them, no comments.
I need to replace them. I'm in Europe, but I can order from American companies too, as long as the shipping is free (the order is over 70$)
Suppliers:
Europe: TME, Farnell
USA: Mouser, Digikey
For paper capacitors, the metallized polypropylene film is what I need.
The store that has axial PP capacitors for all the values that I need is Mouser, I found the Illinois Capacitors MPW series being the only one that has all the values that I need.
Another alternative are the Vishay MKT1813 POLYESTER capacitors, but I don't think that polyester is as good as polypropylene...
Or the MKP1839 capacitors, I like them, but they don't cover all the values that I need. Same for MKP1845.
Another alternative is the WIMA MKP10 series (they have a good reputation in the audio community), but they are radial, So I need to make the leads axial like this:
Then solder them, of course.
A map of all the capacitors that need replacement, with their positions, dimensions, values and types. Very handy.
So:
What capacitors shall I buy to replace the old capacitors in this tube radio?
I aim for a warm sound, with decent highs and good lows.
I'm not much of an audiophile, but this radio is very rare and has a very good audio potential, so I want to give it very good components.
I also want to buy from a single place, that it has a diverse catalogue, like Mouser or Farnell.
Thanks!
Don't forget to replace the selenium rectifier with a silicon rectifier, if you want to use the radio on a regular basis. Selenium rectifiers degrade over time and may fail. You may take advantage of the increased current capability and lower voltage drop of the new rectifier: increase the value of the main filter capacitors, and add a 4H 50 ohm choke to reduce the residual hum.
It is a nice radio and is worth the effort to restore it properly. To replace paper capacitors I use polyester axial cilindrical capacitors (usually Vishay, Cornell-Dubilier and Illinois Capacitors), because they have good electrical properties and have similar size and shape of the old ones. The capacitor in series with the tweeter may be a film capacitor or a non polarized electrolytic. Check the value of the EL84 cathode resistor, it may have drifted. There is no need to select expensive audio grade capacitors. Quelle was a budget brand without internal R&D and production facilities. They sold standard parts, mostly cheaply made in east Germany, and your radio does not have a push-pull audio amplifier or other features that were more common on the high-end German radios of the time such as Saba or Telefunken. It will sound nice but it is not a Hi-Fi device.
It is a nice radio and is worth the effort to restore it properly. To replace paper capacitors I use polyester axial cilindrical capacitors (usually Vishay, Cornell-Dubilier and Illinois Capacitors), because they have good electrical properties and have similar size and shape of the old ones. The capacitor in series with the tweeter may be a film capacitor or a non polarized electrolytic. Check the value of the EL84 cathode resistor, it may have drifted. There is no need to select expensive audio grade capacitors. Quelle was a budget brand without internal R&D and production facilities. They sold standard parts, mostly cheaply made in east Germany, and your radio does not have a push-pull audio amplifier or other features that were more common on the high-end German radios of the time such as Saba or Telefunken. It will sound nice but it is not a Hi-Fi device.
I have used Vishay from Mouser many times and they are quite good. You won't be disappointed. Wima's are good, too..just a little extra work. I like them for tight space. Like pcan said, this isn't a HiFi radio, so I wouldn't be so concerned about things. It will sounds great when you are done.
There is no need for "very good components"; ordinary good commercial quality is fine, because that is what the radio was originally built with. It isn't hi-fi.
Leaky paper caps can be replaced with plastic film caps, such as polyester or polypropylene.
Old electrolytics should be replaced with new electrolytics.
Leaky paper caps can be replaced with plastic film caps, such as polyester or polypropylene.
Old electrolytics should be replaced with new electrolytics.
Thanks for the replies!
Aha, so you guys say that this device isn't Hi-Fi so it doesn't need very good components in it. Noted.
I think I will buy Wima MKP10s, they're cheap. I can get 14 Vishay MKT1813 PET capacitors at the same price as 40! Wima MKP10 PP caps...
Also, the Illinois Capacitors MPW series are also cheap, and axial.
In the communist countries, this was the best you can get from authorized shops. It was one of the, if not the best radio made in the GDR. Not to mention the exaggerated 1000 DM price in GDR and muucchh cheaper in Western Germany
The most exotic thing that it has is the magic eye tube, Lorenz EMM803, I even got its original warranty card. It's used but it lights up pretty bright.
I think I will modify the circuit so I can put an EM84 or Soviet equivalent, and for stereo indication a green LED next to the "Stereo" marking on the glass panel.
The selenium rectifier is working well, I reformed it at various voltages, from 50 to 200V for a couple of hours (10 hours all added up) and it works pretty well.
Next, I'll measure the current, voltage drop, temperature of the rectifier with some different resistance loads.
The power supply unit (The rectifier is made of 40 stacked selenium diodes)
The anode voltage (285V) is important because it also goes into the stereo decoder:
Oh, also, why the 5uf electrolytics that are coupled to the tweeters are rated at 150V?? Maybe there are some spikes in the audio signal?
I'm referring to these capacitors:
Aha, so you guys say that this device isn't Hi-Fi so it doesn't need very good components in it. Noted.
I think I will buy Wima MKP10s, they're cheap. I can get 14 Vishay MKT1813 PET capacitors at the same price as 40! Wima MKP10 PP caps...
Also, the Illinois Capacitors MPW series are also cheap, and axial.
In the communist countries, this was the best you can get from authorized shops. It was one of the, if not the best radio made in the GDR. Not to mention the exaggerated 1000 DM price in GDR and muucchh cheaper in Western Germany
The most exotic thing that it has is the magic eye tube, Lorenz EMM803, I even got its original warranty card. It's used but it lights up pretty bright.
I think I will modify the circuit so I can put an EM84 or Soviet equivalent, and for stereo indication a green LED next to the "Stereo" marking on the glass panel.
The selenium rectifier is working well, I reformed it at various voltages, from 50 to 200V for a couple of hours (10 hours all added up) and it works pretty well.
Next, I'll measure the current, voltage drop, temperature of the rectifier with some different resistance loads.
The power supply unit (The rectifier is made of 40 stacked selenium diodes)
The anode voltage (285V) is important because it also goes into the stereo decoder:
Oh, also, why the 5uf electrolytics that are coupled to the tweeters are rated at 150V?? Maybe there are some spikes in the audio signal?
I'm referring to these capacitors:
Actually, if it were hi-fi it still would not need expensive components - but that is a topic for another thread. If it were hi-fi you might decide to use polypropylene instead of polyester, but that can bring problems sometimes because PP caps are generally much larger in physical size.Richard9026 said:
I would get rid of the selenium rectifier. When it fails you will get nasty smelling somewhat toxic smoke.
The tweeter caps were 150V because that is what they had available. No need for the replacements to be such high voltage. You could replace them with 4.7uF film caps - this is one place where a film cap will actually work better than an electrolytic. If the treble seems too loud afterwards then add a small resistor in series - to compensate for the much smaller ESR of a film cap.
I think this is bad advice. I did not see a bad or "degraded" selenium rectifier in the radio workshop for 35 years.
Long time ago I have replaced a few shorted out AEG selenium rectifiers (the ones with tubular shape), and the charred remains of the power transformer, mainly from Telefunken radios of the late '50. That kind of rectifier surely goes bad (and stinks a lot when it does), I've seen it with my eyes. You are right about the more recent flat kind, I also never saw a bad one, but if you check the output voltage now, it is usually a bit lower than the schematic value: they have started to degrade. When I don't foresee a frequent use, I leave them in place and I simply add a fuse on the HT transformer wire. This may be done on this radio, I only saw that kind of selenium rectifier on lab and industrial equipments and it always works.
The flat Siemens etc rectifiers are not affected, and the ones in the black tube have probably
never been intended for decades of use (but millions of them still operational). However the
mains fuse should blow in any case so that preventive exchange does not seem to be necessary.
If you do so the dc voltage and inrush current will be higher as indicated before.
I own Siemens tube amplifiers with 250 watts and would not even think about touching the selenium
diode bridges.
never been intended for decades of use (but millions of them still operational). However the
mains fuse should blow in any case so that preventive exchange does not seem to be necessary.
If you do so the dc voltage and inrush current will be higher as indicated before.
I own Siemens tube amplifiers with 250 watts and would not even think about touching the selenium
diode bridges.
Aha.
I know that Selenium rectifiers (the ones with stacked square elements) usually fail open, not shorted.
I think I'll buy some Wima MKP10s. And I'll sacrifice some cheap resistors for their leads to make the wima caps axial.
Will the radial red wimas with prolonged leads look good? (as in the photo in the initial post)
What makes an amp "Hi-Fi"? The fact that the amp isn't Push-pull and is Single-ended is just one factor, and there are maany types of PP and SE amps.
Specs from the datasheet:
(note that these specs are for a 60's tube amplifier, not a '90s IC)
"For all measurements, the Solo, Jazz, Bass buttons are pressed and the tone controls are fully turned up.
AF-Stage
Output: 4 W per channel with 10% harmonic distortion; f = 1 kHz
Output Impedance: Z = 6 Ohm
Ripple voltage: 10 mV
Sensitivity: 10 mV at 25 mW per channel f = 1 kHz (50 mW Overall Performance!)
Crosstalk: 40 dB at 1 kHz and 4W
Frequency Response: 40 . . . 25 000Hz at 4 dB roll-off and 4W "
The speakers are huge, dual cone:
(the photo isn't mine, is from here )
Also, some versions of these radios had "HF Stereo" written on the glass front panel. Does HF mean High frequency or High fidelity? 🙂
I know that Selenium rectifiers (the ones with stacked square elements) usually fail open, not shorted.
I think I'll buy some Wima MKP10s. And I'll sacrifice some cheap resistors for their leads to make the wima caps axial.
Will the radial red wimas with prolonged leads look good? (as in the photo in the initial post)
What makes an amp "Hi-Fi"? The fact that the amp isn't Push-pull and is Single-ended is just one factor, and there are maany types of PP and SE amps.
Specs from the datasheet:
(note that these specs are for a 60's tube amplifier, not a '90s IC)
"For all measurements, the Solo, Jazz, Bass buttons are pressed and the tone controls are fully turned up.
AF-Stage
Output: 4 W per channel with 10% harmonic distortion; f = 1 kHz
Output Impedance: Z = 6 Ohm
Ripple voltage: 10 mV
Sensitivity: 10 mV at 25 mW per channel f = 1 kHz (50 mW Overall Performance!)
Crosstalk: 40 dB at 1 kHz and 4W
Frequency Response: 40 . . . 25 000Hz at 4 dB roll-off and 4W "
The speakers are huge, dual cone:
(the photo isn't mine, is from here )
Also, some versions of these radios had "HF Stereo" written on the glass front panel. Does HF mean High frequency or High fidelity? 🙂
10% harmonic distortion is not hi-fi (except for some SET fans).
-54dB hum is not hi-fi.
What is written on the front panel is marketing, not technical information. In this market segment "stereo" means two speakers - however close together they are. "HF" may mean dual cone, or separate tweeter, or nothing at all.
-54dB hum is not hi-fi.
What is written on the front panel is marketing, not technical information. In this market segment "stereo" means two speakers - however close together they are. "HF" may mean dual cone, or separate tweeter, or nothing at all.
I think that HF Stereo might indicate an onboard stereo decoder that enables stereophonic listening to FM broadcasts. Many othe so called Stereo radios operate stereophonically solely with stereo phonographs or tape recorders.
Best regards!
Best regards!
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