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Making a console stereo to a speaker amp?
Making a console stereo to a speaker amp?
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Old 25th August 2016, 03:02 AM   #1
spwath is offline spwath  United States
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Default Making a console stereo to a speaker amp?

Hi,
I recently purchased a Loewe Opta console stereo thing, with a nice tube amp inside. Im thinking about removing the tube amp, and converting it into an amp for external speakers.

What kind of work is exactly involved in this? I haven't worked with tube equipment, but have done plenty of electronics work.

Pictures:
Click the image to open in full size.'
Click the image to open in full size.
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Old 25th August 2016, 03:07 AM   #2
planet10 is offline planet10  Canada
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Making a console stereo to a speaker amp?
It is certainly doable. Does the amp have 2 or 4 6BQ5/EL84? Or are those ECL86?

You basically take the iron, tubes, maybe the sockets and build up a new amplifier.

dave
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Old 25th August 2016, 03:12 AM   #3
spwath is offline spwath  United States
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Quote:
Originally Posted by planet10 View Post
It is certainly doable. Does the amp have 2 or 4 6BQ5/EL84? Or are those ECL86?

You basically take the iron, tubes, maybe the sockets and build up a new amplifier.

dave
Here is a diagram of the tubes it uses.
Click the image to open in full size.

Build up a new amplifier?
Wouldent it be simpler to take whats there, and just connect some speaker outs and such, and replace any old/dangerous components?
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Old 25th August 2016, 10:32 AM   #4
aardvarkash10 is offline aardvarkash10  New Zealand
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the mp is a single ended EL84 design - pretty simple and capable of reasonable performance at low output - and this is likely the rub.

Your speakers will need to be very sensitive OR your preferred listening level relatively low.

Planet10 is likely to suggest you "RH84-ise" this amp and that is a good option. The radio and other sections included in the console are probably redundant - restoring the receiver or the phono section is likely to be a very low return idea. Likewise the tone controls - they are largely made redundant as your source (probably digital) will have that built in anyway. This means that it is often easier and more aesthetically pleasing to rehouse the required bits for the amplifier only.

The cost of passive components is such that its really not practical to try and retain them - all capacitors and resistors are scrap-bin bound, and will be replaced by modern better components.
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Old 25th August 2016, 10:44 AM   #5
ColinA is offline ColinA  United Kingdom
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One thing to be very careful of!
That may be a live chassis with no earth safety.

Take care when trying anything with it connected to mains.
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Old 25th August 2016, 12:19 PM   #6
pcan is offline pcan  Italy
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Making a console stereo to a speaker amp?
Of course you may just repair the console and use it as tube amplifier, but don't expect a modern day Hi-Fi experience because by using modern speakers you will not remediate the shortcomings of the original design. The vintage sound may be pleasent still. I see you already turned it on, so I presume that no major issues are present, and therefore no need to take it apart immediately.
I have several early '60 radios of this type on my collection, and also a Loewe Opta similar to yours. The chassis of your radio seems to be the 1959 Clivia-Stereo 4806T/W or something like that for the USA market; it is basically a small 4+4w tabletop chassis inside a bigger lowboy enclosoure to make it look prettier. This is common on German radios of the period; they were built mostly to look good, not to sound good. They often had clever and complex mechanical controls that are the joy of modern collectors but further reduced the budget for the actual electronic parts. Some exception exists, of course. Any console with dual ECLL800 tubes has usually good audio performance, but it is not the case with your console that uses a very standard chassis for the time.

The console has an auxiliary 5-pin DIN line input on the back and the Loewe-Opta round speaker connector, so is very simple to connect modern source and speakers, but even after the restoration you will have to live with the following shortcomings:
- there will be some hum. It will be lower than the current unrestored state, but it will be almost impossible to remove completely because the manufacturer does not paid attention to the wiring placement.
- the low frequency response is poor because the output transformers are tiny. No noticeable issue if you use small bookshelf speakers without a subwoofer.
- stereo channel separation is poor. Again, not a big issue but it is a limitation.
- the tone control is linked to the volume control. Since this radio is a 1959 model, the global feedback is connected to the lower side of the volume control, this way by increasing the volume the tone will noticeably change removing high and low frequencies and increasing the distortion. You may circumvent this behaviour by using a strong signal on the line input (2V pp or more), or you may change the feedback circuit. The preamp tube grids have grid-leak polaritazion, so expect relatively high distortion, poor left and right channel volume tracking and some white noise.
- dynamic will be poor due to the low power available, unless you use high efficiency loudspeakers. The cheapest I know that you may easily find on most big online retailers such as Amazon is the Klipsch R-15M. If someone here knows a better and/or cheaper readily available speaker that works well with a low power tube amplifier I will appreciate any tips, because I am often asked by friends about the cheapest small speaker that works well with tube amps and also has a decent sound quality.

Since you don't have experience on collecting tube radios, I will list some basic facts you need to know should you want to go ahead with the restoration. You will find a lot more information on relevant web sites.
- Unlike most USA-built '50 and '60 radio consoles, on German tube consoles there is no separate power amplifier chassis; the chassis does both the radio and the power amplification. The amplifier is rather weak, 3-5w per channel with 5 ohm speakers; the power is further decreased with modern 8 ohm speakers. The tweeter may be electrostatic but is should not be the case with your console, I see it uses the usual Loewe-Opta speaker connector that looks like a tube socket.
- First thing to do: check and maybe replace the power fuse (put contact cleaner spray on the fuse holder while you are at it). The previous owner may have substitute it with the wrong type, and the original fuse does not had the sand inside to prevent explosion. Also replace/remove the capacitor connected between the mains line and the chassis, near the fuse holder. On my Loewe-Opta it was a ceramic capacitor that may eventually fail by shorting the live mains wire to the chassis. You need to replace it with a UL listed X2 plastic film capacitor or just remove it - it is not essential to the amplifier workings.
- Your console does not have a live chassis, unless something is faulty, but the power transformer wiring on the primary and on the secondary side may be clumped toghether. It would be useful to redress the wiring and put some distance between the primary and the secundary side. I always do this while restoring. Also check the wire to the power switch and add/replace insulation if needed. Check with the ohmeter the resistence between mains plug contacts and chassis just to be sure that there are no shorts.
- the Achille's heel of piano keys radios is the switch matrix behind the keys. Your radio has more than 100 contacts there, and audio signals travels trough at least 4 of them. Use the contact tuner spray to remove the oxide. If the contacts are corroded, the restoration will be far trickier than usual and it may not be worth it.

I encourage you to try restoring this console, it will be a low-budget fun experience. If you want a real Hi-Fi experience, the only parts you may find useful are the power transformer and the EL84 tubes. It may then be financially sound to resell the console (it looks nice and has some collector value) and buy new parts.

Last edited by pcan; 25th August 2016 at 12:26 PM.
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Old 25th August 2016, 01:08 PM   #7
DF96 is offline DF96  England
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Quote:
Originally Posted by ColinA
One thing to be very careful of!
That may be a live chassis with no earth safety.
Very unlikely if it has E series valves.

If it was mine I would want to get it working as it was, not mess about with it.

However, no conversion is needed for external speakers. Just connect them in place of the internal ones. It would probably be fairly easy to arrange for an external line level input. You need to find the circuit diagram and work from that. It won't be hi-fi.
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Old 25th August 2016, 01:35 PM   #8
spwath is offline spwath  United States
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Quote:
Originally Posted by pcan View Post
Of course you may just repair the console and use it as tube amplifier, but don't expect a modern day Hi-Fi experience because by using modern speakers you will not remediate the shortcomings of the original design. The vintage sound may be pleasent still. I see you already turned it on, so I presume that no major issues are present, and therefore no need to take it apart immediately.
I have several early '60 radios of this type on my collection, and also a Loewe Opta similar to yours. The chassis of your radio seems to be the 1959 Clivia-Stereo 4806T/W or something like that for the USA market; it is basically a small 4+4w tabletop chassis inside a bigger lowboy enclosoure to make it look prettier. This is common on German radios of the period; they were built mostly to look good, not to sound good. They often had clever and complex mechanical controls that are the joy of modern collectors but further reduced the budget for the actual electronic parts. Some exception exists, of course. Any console with dual ECLL800 tubes has usually good audio performance, but it is not the case with your console that uses a very standard chassis for the time.

The console has an auxiliary 5-pin DIN line input on the back and the Loewe-Opta round speaker connector, so is very simple to connect modern source and speakers, but even after the restoration you will have to live with the following shortcomings:
- there will be some hum. It will be lower than the current unrestored state, but it will be almost impossible to remove completely because the manufacturer does not paid attention to the wiring placement.
- the low frequency response is poor because the output transformers are tiny. No noticeable issue if you use small bookshelf speakers without a subwoofer.
- stereo channel separation is poor. Again, not a big issue but it is a limitation.
- the tone control is linked to the volume control. Since this radio is a 1959 model, the global feedback is connected to the lower side of the volume control, this way by increasing the volume the tone will noticeably change removing high and low frequencies and increasing the distortion. You may circumvent this behaviour by using a strong signal on the line input (2V pp or more), or you may change the feedback circuit. The preamp tube grids have grid-leak polaritazion, so expect relatively high distortion, poor left and right channel volume tracking and some white noise.
- dynamic will be poor due to the low power available, unless you use high efficiency loudspeakers. The cheapest I know that you may easily find on most big online retailers such as Amazon is the Klipsch R-15M. If someone here knows a better and/or cheaper readily available speaker that works well with a low power tube amplifier I will appreciate any tips, because I am often asked by friends about the cheapest small speaker that works well with tube amps and also has a decent sound quality.

Since you don't have experience on collecting tube radios, I will list some basic facts you need to know should you want to go ahead with the restoration. You will find a lot more information on relevant web sites.
- Unlike most USA-built '50 and '60 radio consoles, on German tube consoles there is no separate power amplifier chassis; the chassis does both the radio and the power amplification. The amplifier is rather weak, 3-5w per channel with 5 ohm speakers; the power is further decreased with modern 8 ohm speakers. The tweeter may be electrostatic but is should not be the case with your console, I see it uses the usual Loewe-Opta speaker connector that looks like a tube socket.
- First thing to do: check and maybe replace the power fuse (put contact cleaner spray on the fuse holder while you are at it). The previous owner may have substitute it with the wrong type, and the original fuse does not had the sand inside to prevent explosion. Also replace/remove the capacitor connected between the mains line and the chassis, near the fuse holder. On my Loewe-Opta it was a ceramic capacitor that may eventually fail by shorting the live mains wire to the chassis. You need to replace it with a UL listed X2 plastic film capacitor or just remove it - it is not essential to the amplifier workings.
- Your console does not have a live chassis, unless something is faulty, but the power transformer wiring on the primary and on the secondary side may be clumped toghether. It would be useful to redress the wiring and put some distance between the primary and the secundary side. I always do this while restoring. Also check the wire to the power switch and add/replace insulation if needed. Check with the ohmeter the resistence between mains plug contacts and chassis just to be sure that there are no shorts.
- the Achille's heel of piano keys radios is the switch matrix behind the keys. Your radio has more than 100 contacts there, and audio signals travels trough at least 4 of them. Use the contact tuner spray to remove the oxide. If the contacts are corroded, the restoration will be far trickier than usual and it may not be worth it.

I encourage you to try restoring this console, it will be a low-budget fun experience. If you want a real Hi-Fi experience, the only parts you may find useful are the power transformer and the EL84 tubes. It may then be financially sound to resell the console (it looks nice and has some collector value) and buy new parts.
OK, great thanks.
I payed $45 for it, was that a good price?

Yeah, I turned it on, seems to work well, no issues, other than tthe tuning is off by 1/2 a number.

Ill try it. My speakers are 4ohm, so it should be better.
Now the speaker outs on tthem, how do they work, its just a hole...
And the aux in, its a din connector, but there is only phono in and tape (out?). Unless its tape in, otherwise I would only be able to use it with a turntable.
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Old 25th August 2016, 02:10 PM   #9
spwath is offline spwath  United States
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Also, its the 05805w, labeled on the back

Where is the edit button for posts?
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Old 25th August 2016, 02:12 PM   #10
Mooly is offline Mooly  United Kingdom
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Making a console stereo to a speaker amp?
Quote:
Originally Posted by spwath View Post
Where is the edit button for posts?
Lower right of your post. Its only active for 30 minutes or so after posting.
 

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