Nice auction win, $40.00 US and the silly $8.00 actuion fee awarded me a Grundig 4085.
So far I have the back off and found:
1. All tubes are originals.
2. Dust from the past 61 years (radio was made in 1956)
3. All switches and push buttons work mechanically (not powered up yet), although they are stiff.
4. Cabinet will need refinishing, and in some places the veneer replaced / repaired.
5. The radio dial and AM antenna rotation cables are still good and in working condition.
6. The "graphic" equalizer display still works via the pots.
7. Glass and artwork looks great.
8. The original power cord will need replacement, someone did the pull it out of the wall by the cord trick and pulled the plug off the end. (note: this is a two wire cord, will probably update it to 3 wire with chassis ground)
9. One wood brace is in three parts from someone pulling off the back forcibly at the auction house (that buyer was disqualified by the auctioneer and why I won it), easy repair and did not damage the back panel.
10. Speaker grill covering is in need of replacement, wicker type.....should be able to find a suitable replacement for it.
Schematics attached, I know all the electrolytic capacitors will need attention, as well as the radio active rectifier (probably, no well before first power up). Anyone have any other suggestions to "modernize" the electronics?
I will post some pictures of mine later, but some good ones can be found here Grundig 4085 - Italian Art Radios (not my site, just one I found while researching the radio).
So far I have the back off and found:
1. All tubes are originals.
2. Dust from the past 61 years (radio was made in 1956)
3. All switches and push buttons work mechanically (not powered up yet), although they are stiff.
4. Cabinet will need refinishing, and in some places the veneer replaced / repaired.
5. The radio dial and AM antenna rotation cables are still good and in working condition.
6. The "graphic" equalizer display still works via the pots.
7. Glass and artwork looks great.
8. The original power cord will need replacement, someone did the pull it out of the wall by the cord trick and pulled the plug off the end. (note: this is a two wire cord, will probably update it to 3 wire with chassis ground)
9. One wood brace is in three parts from someone pulling off the back forcibly at the auction house (that buyer was disqualified by the auctioneer and why I won it), easy repair and did not damage the back panel.
10. Speaker grill covering is in need of replacement, wicker type.....should be able to find a suitable replacement for it.
Schematics attached, I know all the electrolytic capacitors will need attention, as well as the radio active rectifier (probably, no well before first power up). Anyone have any other suggestions to "modernize" the electronics?
I will post some pictures of mine later, but some good ones can be found here Grundig 4085 - Italian Art Radios (not my site, just one I found while researching the radio).
This is a relatively common radio with a big chassis that allows easy access to all the components; if the radio part is not working properly, you will find plenty of informations on specialized forums. I have several german radios of this age and they usually are easy to restore. Just try to keep it as original as possible, there is no need to rip & replace everything. Compared to later models, this one has a useful feature you may want to take advantage of. It is possible to bypass the tone controls completely and use the radio as a powered speaker with a very simple reversible modification. Just connect a jack with a switch between the volume wiper and C74. You may want to do this instead of using the factory external input because On the original configuration the output stage negative feedback is applied to the lower tap of the volume control. This means that when you turn the volume up over a third of the total rotation, the gain and the distortion of the amplifier will increase noticeably, and the higher and lower frequencies will decrease. This is a clever arrangement on AM radios to increase sensitivity for faint stations, but it carried on german FM radios until mid '60 and utterly destroys any Hi-Fi ambitions.
Another quirks of late '50s Grundig radios is the grid connection to the EL84 socket. Grundig at the time was using Siemens tubes exclusively, The Siemens-manifactured EL84 had pin 1 and pin 2 tied togheter internally. The socket was wired to put the signal on pin 1, nominally a "do not connect" pin. If someone replaced the tube with a non-Grundig one, the radio would not work because on standard EL84 tubes the grid is wired at pin 2. Just check the socket and move the 47K resistor to pin 2 eventually.
My quick check list for restoration of the power and low frequency part of this type of radios:
replace the power cord with a 3wire type. Rearrange the wires at the primary side of the transformer and power switch to keep them separate from other wires and radio parts (add insulation if needed). Replace any mains side capacitors with proper modern safety ones. Replace the fuse with a modern one. Add a slow-blow fuse between the HT secondary and the rectifier. Replace the selenium rectifier with a silicon rectifier followed by an additional RC filter cell (as example: 220uF 450V capacitor and 150 ohm 7w resistor). Replace all the original filter capacitors - I try to keep them in place and add the new ones in a concealed way. Remove the oxidation from the piano-keys contacts (oxidation on this contacts will often lead to motorboating). Replace the cathode and grid capacitors on preamp and output tubes. If the FM is not working, replace the ECC85 tube - it's the first tube to go out of service on german radios.
Another quirks of late '50s Grundig radios is the grid connection to the EL84 socket. Grundig at the time was using Siemens tubes exclusively, The Siemens-manifactured EL84 had pin 1 and pin 2 tied togheter internally. The socket was wired to put the signal on pin 1, nominally a "do not connect" pin. If someone replaced the tube with a non-Grundig one, the radio would not work because on standard EL84 tubes the grid is wired at pin 2. Just check the socket and move the 47K resistor to pin 2 eventually.
My quick check list for restoration of the power and low frequency part of this type of radios:
replace the power cord with a 3wire type. Rearrange the wires at the primary side of the transformer and power switch to keep them separate from other wires and radio parts (add insulation if needed). Replace any mains side capacitors with proper modern safety ones. Replace the fuse with a modern one. Add a slow-blow fuse between the HT secondary and the rectifier. Replace the selenium rectifier with a silicon rectifier followed by an additional RC filter cell (as example: 220uF 450V capacitor and 150 ohm 7w resistor). Replace all the original filter capacitors - I try to keep them in place and add the new ones in a concealed way. Remove the oxidation from the piano-keys contacts (oxidation on this contacts will often lead to motorboating). Replace the cathode and grid capacitors on preamp and output tubes. If the FM is not working, replace the ECC85 tube - it's the first tube to go out of service on german radios.
Thank you pcan, that gives me some information I was missing and will make the restoration go easier (especially the info on the grid connection to the EL84 socket).
This is going to be a fun project for me, it is such a beautiful design looks wise and I cant wait to make it look like it did when first made.
This is going to be a fun project for me, it is such a beautiful design looks wise and I cant wait to make it look like it did when first made.
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