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5088
This is a wonderful sounding radio. The Grundig 5088 USA has all
English wording on the radio. It has four bands, FM, BC, SW1 and
SW2. The 5088 has five push button tone controls and four tone
knobs.
Performance of this radio is surprising. I used a short antenna lead
connected between the radio and the forced air supply duct work. The
radio picks up
many short wave international stations. There is an internal FM dipole and
a "PU" input for a phonograph cartridge. A novel rotating
ferrite stick antenna is mounted inside and rotated by the left outer knob for
best BC station reception. Following are some restoration highlights.
Restoration was straight forward. All wax/paper capacitors were replaced with
modern 630volt Premium quality PPT Metalized Polypropylene film dielectric,
aluminum foil electrode, components. Several resistors were measured bad
and replaced. All other resistors were extremely true to their tolerance.
The selenium rectifier was under performing, not supplying sufficient B+.
The rectifier was replaced with a diode bridge of 1N4007 and a series resistor
to compensate the Vfwd (voltage drop) of the selenium array.
Alignment revealed the IF stages to be significantly off peak. The dial
scale frequency alignments were very accurate and precise except for the lower SW
band. Once the IF was properly aligned and the oscillators realigned all
the bands and dial scales line up well. All alignments adjusted easily
(once the German alignment methods/techniques were understood) and all sensitivities met or exceeded
factory specifications.
This unit was in service in my 12 year old son's room at a "Torture
Test". He fell
in love with its detail and the functional EM34 tuning eye. (A "Dimmer" switch
has been added to the
EM34 to extend the phosphor life.) Listening to
WWV (at 10 and 15 Mc) is soothing. I anticipate the rhythmic passing of
the seconds and the slowly wavering signal strength will gently lull him
my boy
off to sleep (Here's hoping).
My son gave this radio a good work out. That way I am sure it will survive
standard daily service. This is a beautiful unit that I restored not
only to look and sound good but also to be a reliable "Daily Driver".
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 Click on image to enlarge. |
The exterior was cleaned and
treated with rejuvenating oil. All dials were cleaned in the
dishwasher. A final few coats of paste wax gives the radio a nice
sheen. |
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Some internal pictures during restoration.
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The Selenium disks have been replaced with
1N4007 Diodes and 0.01 ceramic caps across each diode. A voltage
dropping resistor (three green wire wound in parallel) was chosen for
proper B+. |
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| The yellow items are the replacement
capacitors. The DVM shows low B+. The black horizontal can
above the meter holds the selenium disks with in. |
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The blue "Jelly Beans" on the left
are paper capacitors. The Resistor on the right has a Blue band
indicating the general resistance range to aid in component location
during troubleshooting. It appears that Grundig considered the
repair technician in their parts selection. Click
here for resistor details. |
SWII band oscillations:
After running the radio for some time (two weeks) it developed an oscillation
problem on the SWII band from about 17.5 to 18.3 Mhz. Consulting with the
experts at RadionMuseum.org found that
component placement near the ECH81 tube. Particularly the capacitor C33 to
chassis ground. One can put the radio near oscillation then with a plastic
stick move the C33 closer to the tube socket to start oscillation. Moving
it away prevented oscillation. The tube was weak on the triode
section. That tube was replaced after the capacitor tweaking. The
radio has not oscillated under "torture testing" (my 12 year old son)
since then.
Tuning Eye saver:
I have added an STSP miniature switch "with quick disconnects" to
the Tuning Eye B+ circuit. It is a simple bat handled switch that bolts
through an existing vent hole. It has been soldered in between the B+
switch on the phono pickup switch contacts 4k and 4i and the tube socket. An original
terminal strip can be found under the chassis for easy hook up. That is
where the tuning eye socket lead wire feeds from above the chassis. All parts
are available at Radio Shack. This modification is easily
reversed.
Thanks to the participants at http://www.radiomuseum.org/
for all their help. An informative discussion about this radio can be viewed
at http://www.radiomuseum.org/dsp_forum_post.cfm?thread_id=41660. Stop in and say Hi.
There are extremely knowledgeable and helpful
people at the   .
Volume control repair
The volume control became intermittent.
The radio would blast loud then go back to normal. Poking around the
volume control found one of the wires to a solder lug when moved caused the
failure. So repair or replace. I have no replacements so a delicate
repair had to be undertaken.
Disassembled |
 The
rivets were tightened. |
Rotor is chipped. |
 Chipped
rotor glued with plumber's Epoxy. |
 Cleaned,
reassembled and lubricated. |
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Tweeter Repair.
 Take
it apart. |
 The
deteriorated black foam is the problem. |
 This
pad is wool like and is in good shape. |
 Separate
the diaphragm from the grill, clean and inspect. |
 Check
the copper foil strip for tarnish and clean. |
 Replace
the copper foil strip. |
 Replace
foam pressure pad. |
 Reassemble
and test before melting the plastic rivets closed. |
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Click on image to enlarge.
Disassembled
The
rivets were tightened. 
Rotor is chipped.
Chipped
rotor glued with plumber's Epoxy.
Cleaned,
reassembled and lubricated.
Take
it apart.
The
deteriorated black foam is the problem.
This
pad is wool like and is in good shape.
Separate
the diaphragm from the grill, clean and inspect.
Check
the copper foil strip for tarnish and clean.
Replace
the copper foil strip.
Replace
foam pressure pad.
Reassemble
and test before melting the plastic rivets closed.
