grundig: 5088 USA componant and alignment questions.

Gentlemen,

I am restoring a Grundig 5088 USA model and need some help with my first non-US radio restoration.  I am using a schematic found at www.rad-io.de  I have found it to be mostly accurate except for some of the audio frequency circuit architecture.  There are differences.

A friend of the family has translated most of the words.  So my questions are with the missing information below:

The resistors have the resitance printed on the body and a single color band on one end.  What does this band represent and what are the values of the colors?




I have identified three types of fixed capacitors; Paper (Papier), Syrofome (Styrofier?) and Ceramic/mica (Keromic?).  However, there are some paper capacitors that have a plastic like blue coating.  The schematic clearly identifies these as paper.  Is there more to these capacitors? Are they special (i.e., inverse temperature, resonant) capacitors?



Once I have replaced all of the paper and electrolytic capacitors (and the occational off tolerance resistor) RF alignment is next.   The IF frequencies (10.7/460) and the transformers are identified. However, there are plenty of other adjustments with no explanation.  Where might I find the alignment procedures? 

Please forgive me if this information is readily available on the internet.  If so, then please recomend an appropriate web site.

Thank you in advance for your time,
Paul.

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Hello Paul,

i come back next time here with informations for You.

First here Aligment. This the Export Version (not US) of the 5088.
Maybe Waveranges are different. I mean, thats is not a great problem.
AM/FM  If are allways the same!

Text for Components.
 Mr. ERB would have that these informations shall for general purposes.
This is more to do for me, and finish next days. Now finish
Look here:


http://www.radiomuseum.org/dsp_forum_post.cfm?thread_id=42358

Short info for you:  blue Condensers are Papertype , color on Resistors : minor matter.

Greadings Hans Attachments:

• 5088WE_alig.1 (192 KB)
• 5088WE_aligm2 (179 KB)

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Hans,

Thank you so much for the alignment information.  I have played the radio since replacing the paper capacitors, electrolytic and the single "out of 20% tolerance" resistor with a new 5%. 

The radio plays very well on FM.  Clear and clean sound.  The AM bands receive stations.  Even the short wave bands receive with a three foot piece of wire. 

I discovered if my hand comes with in close proximity to the tone switch assembly a hum will be produced. I therefore deduce that is why there is a ground wire going to the missing screen that should be stapled on the cabinet bottom.  Please comment.

I am a bit curious about the low B+ voltage right after the bridge rectifier.  I read 261v dc and 255v dc (MW/UKW) at 119vac line (mains) and the voltage selector is on 110volts. (There are two selections 220 and 110).  The schematic notes 275 and 270.  Is this B+ too low? 
(DVM input impedance 7 Meg ohms). 



Hopefully with additional trouble shooting and an alignment I can discover the problem of the low B+. 

Thanks again for the alignment information,
Paul.

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Hello Paul,

its fine, that I can help you with  GRUNDIG  Service Paper.

To your next question about B+
First:
a transformer produce different output voltage on Power line 60C/s or 50C/s ,  at 60C/s  they are lower, there is physical given.  ( check the Heater voltage  6.3 V,  you can see  that for reference) 
Second:
that's a general Problem in Europe with selenium rectifiers.
They get old. That means, dropout voltage ( ratio of Vin to Vout), goes higher.
The result is a lower output voltage. There is not a solution elsewhere to serve this problem.

The only way is, replace this selenium with four-silicon diodes 1N4007 .in bridge configuration.  Additional, must each diode are shunted with a high voltage condenser  approx. 4,7 nF,   400V AC! 
 See fig1 

After then, the B+ is too high. Dropout loss is much lower. It's necessary     to insert a high power type resistor up to 220 Ohms and 7 Watts, in one of the lines from transformer to the new bridge. Dimension must be make  by your self,  to change the value of this resistor by observing the B+ voltage . The value of  this resistor is given, when B+ voltage  is in +/- 10 % of diagram values, at rated  Line voltage.

Your question about  hum.
This is a little difficult for me.
First,  I am not the Designer of this set, and more then 18 years is a longtime.
There are two versions in use that time.
In the Cabinet under the "Tone control bass, jazz etc."  the inside is sprayed with a metallic  varnish.  (graphite), also the bottom -plate.   

Sometime  maybe 1957 the connection is made by a cooper plate  and a wire to chassis.
Grounded  mostly near of TA or TB input terminal. on your Photo i can see this nearly.

Later,  under one of the circular gum and a copper foil on the right point  inside of cabinet.
I never now where. I mean from backside, into the cabinet,  seen  in front left or right
position.  Sometimes on rear side. 
If you use a Ohmmeter .you can test this . A value of the varnish up to 10 000 Ohms are O.K.
I am sorry, I can say not more. 

Best regards Hans

 

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Hans,

Thanks for the rectifier replacement instructions.  I am a bit embarrassed to admit that it never occurred to me that the rectifier may be bad.  Boy what a surprise when I cut open the rectifier's can and all the disks came spraying out all over the work bench.

I did replace the old rectifier with the new diodes, capacitors and three 470 ohm wire wound resistors in parallel to achieve the specified B+.  The radio is now more sensitive. 




Some of the tube bias voltages are off.  I am not being specific since I have more troubleshooting to do.  I verified several bias resistors to be on spec. I proceeded to test the tubes and discovered several to be weak.

My next task is to replace several weak tubes and recheck all of the tube bias voltages.

I will report back with my findings.

Also - Are EM34 eye tubes available in Europe?  They are difficult to economically locate in the US. 

Thanks again,
Paul.

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Hello Paul,

 EM34 / 35  are in europa also rare and expensiv.
please  contact these Adress

rsc@home.nl

or mego@fdonkers.net

both from nederland

In Germany, collectors use the US Type 6E5 ,  from russia.
Only 3 soldering points must be changed.

I can give you information abaut that.

Regards, Hans

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Hans,

In the alignment procedure

• 5088WE_alig.1 (193 kb)
• 5088WE_aligm2 (180 kb)

The AM-IF Alignment 460kc "Remarks" call to dampen the opposite coil with a series resistor/capacitor string.  To where should this string be connected?  From the coil signal side to ground or across the coil winding?

Could this "Dampening" effect also be accomplished with a very small signal output from the RF generator?

Thanks,
Paul.

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Hello Paul,

damping the Circuits means, each from the hot point ( anode or grid) to ground.

The opposite side from the circuit, is alllways groundet with an condenser.
In a high quality set, that is not easy to see.

The reason of damping, ist not to become a lower signal, but to make a decoupling from the  fast coupled ( more then critical) circuits. 

If jou not like to make that, you must repeat  the procedure 3 to 4 times,  for each filter, exactly.

In production, for an exact alignments of a 3 circuit filter, or moving bandwide 2 circuit filter,  it is necessarry to use an Sweeper and screen.

This procure is much more komplicated  and expensive.

I think, all is clear now.

Best regards, Hans

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Thanks to everyone (and a special thanks to Hans) who contributed and answered my questions regarding the Grundig 5088 USA.  I posted some pictures on
http://www.ppinyot.com/G/grundig.htm (link corrected 5/27/09)

Following the dampening procedure Hans described I re-aligned the unit.  The unit receives exceptionally well.

Should I post the pictures from the web site in this forum under the specific model?

Thanks again,
Paul
 

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Hello Paul, 
thank you for this fine and informative Report.  I am a little bit happy, that RM.org can assist you.  
To your report on the URL, unfortunately, Mr. Max GRUNDIG can see that!
In germany i have never seen an special report like that.

I say: verry good.

Thanks for the report, good luck.

Hans

On what positions you can or must,  post all this,
i am not  " the man  for that questions" . sorry!

 

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There is an adjustment R32 rheostat (a two wire variable resistor in a network with R30, C62 and C63) on one of the plates of the EAA91 tube.   With an oscilloscope on the plate the voltage responds to the signal strength as the tuner passes transmissions.

What is the function of this adjustment and how should it be adjusted properly? 

This should be the last question for this radio.

Thanks again,
Paul

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  Hello Paul,
 The questions: There is an adjustment R32 rheostat (a two wire variable resistor in a network with R30, C62 and C63) on one of the plates of the EAA91 tube.   With an oscilloscope on the plate the voltage responds to the signal strength as the tuner passes transmissions.
What is the function of this adjustment and how should it be adjusted properly? 
my answer: this trimmer R32, adjust and brings, the AM-Rejection to an maximum.  AM- Rejection makes a supression of amplidute modulated (unwanted) signals. 
This function is the primary performance of the Ratio -Detector invented from Stuart Wm. Seely and Jack Avins from RCA Labs. 
To adjust this function the equipment must have an high standard.
In 1958 GRUNDIG brings this simple message:  " Alignment can be done with Scope only" Thats a little bit naivety i think.

Two yeahrs later, " Allign control R...  until a max. AM supression is obtained ( with Sweep Frequency Generator_ oscilloscope possible only)

No further informations.   
My comment: since nobody can nows what Equipment is on Workbench,  no one will give advice with that Paper.  Maybe after align,  its  worse, then bevor.

Now my advice to you:
1. Inject an AM -Modulated Signal of 10,7 Mcs on G1 ECH81, the signal strengt should be for 4 to 6 Volts DC on C56 10uF Ratio Electrolyt. Adjust R 32 for minimum audible Mod. Frequency ( 400 to 1000 C/s) depents from your SG.

2. Or very simple, but good ( i to that offten) receive a weak FM Signal from Air, select one noisy signal (with much noise in background) Adjust R32 for minimum audible noise. Thats all! This procedure can used for all Sets Tube or Solid State. (Transistor  with an Ratio)

For your better understanding, i spend an original picture with text, from an RCA Print  ( Seely, Avins)   There you can see, what is shows on an Sweeper_Scope Equipment. Only as PDF ( to much bits)

So Paul, i hoppe is all clear?

Best regards
Hans

 

Attachments:

• Ratio- Testing (163 KB)

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Hans,

I used both of your methods for adjusting R32 below:

Now my advice to you:
1. Inject an AM -Modulated Signal of 10,7 Mcs on G1 ECH81, the signal strengt should be for 4 to 6 Volts DC on C56 10uF Ratio Electrolyt. Adjust R 32 for minimum audible Mod. Frequency ( 400 to 1000 C/s) depents from your SG.

2. Or very simple, but good ( i to that offten) receive a weak FM Signal from Air, select one noisy signal (with much noise in background) Adjust R32 for minimum audible noise. Thats all! This procedure can used for all Sets Tube or Solid State. (Transistor  with an Ratio)

Now my advice to you:
1. Inject an AM -Modulated Signal of 10,7 Mcs on G1 ECH81, the signal strengt should be for 4 to 6 Volts DC on C56 10uF Ratio Electrolyt. Adjust R 32 for minimum audible Mod. Frequency ( 400 to 1000 C/s) depents from your SG.

2. Or very simple, but good ( i to that offten) receive a weak FM Signal from Air, select one noisy signal (with much noise in background) Adjust R32 for minimum audible noise. Thats all! This procedure can used for all Sets Tube or Solid State. (Transistor  with an Ratio)

With the assistance of a good eye tube and a decent ear, Methode 1 was the best for me and the avaiable FM "Noisy" stations.  The control dipped quite easily and I was able to determin a minimum adjustment point rapidly.

Now that the radio is getting regular exercise a new problem has cropped up.  When it is tuned on the SWII band (8.3 - 18.5 Mhz) at about 17Mhz it begins to change tone.  More treble with a phasing sound and the reception gets louder (along with the static).  Then a little higher it begins to quietly oscilate.  At about 17.5 - 18 Mhz it thumps and goes silent.  Further up twards 18.5 Mhz it starts to "motor-boat" or thump (no reception here). 

I re-alingned the IF and the two SW and the BC bands.  It seems to be a little bit more stable.  If I tune through this zone slowly it will not thump and motor-boat.  But it sounds as though there is an increase in sensitivity.

I will be trouble shooting this tomorrow.  The first thing I will do is inspect the Variable Air capacitor. I hope to make progress and report back. 

Thanks again for all your help,
Paul Pinyot.

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Hello Paul, 
i agree with your decide that Methode 1 is good.  Booth versions have remarks.
Version 1  depends from the quality off the SG. 
Version 2  On other hand what signal  comes i the set from arial. 

Many SG's  have addional  to the AM Mod. more or a little bit of Residual FM Mod.  In this case you can not align the AM Supression while simultaneos an FM deviation is present. 

In case 2: align with Antenna -signal, must additional to the wanted FM Signal an AM - modulated are present.
This AM comes from an Multipath Signal performed by Reflections in the environs.
Like the ghost on TV.

If they not present, ( is normal good)  you can not reduce this when not audible!

To your new trouble with SW.
Last Days my scanner has an failure, i must buy a new next days.  Without i can not speak!;-) My english is not so good. Papers can give more informations.  
I think, the wiring of ECH81 pin 2 ( RF -Section) and Pins 7,8,9 ( osc-section) is not enough separated . The space between these (RF and Osc) must be maximum if posible.
Maybe  you   have moved the wires if you inject the 10,7 Mcs for align of R32.

At last i can tell you, this is a difficult failure for Lab. Ing.  Nor each can solved this problem.  Via the ocean i can also not make that.

More infos then when i have an new scanner.

Greadings, Hans

 

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Hans,

I have remedied the run-a-way oscillation problem by moving components and distancing capacitors away from the base of the ECH81 valve (tube).  It seems that the replacement capacitors were installed too close to the tube base. 

Moving the capacitor closer to the tube base (when the radio is tuned close to 17.5 MHz and just ready to oscillate) forced it into oscillation.  Distancing the cap from the socket improved the operation considerably.

Secondly, the hum problem (previously mentioned) was solved by installing grounded aluminum window screening in place of the missing bottom cabinet shield.  When a shielded cardboard replacement is available I will replace the screen with the more original component. 

Lastly, I added a small toggle switch to the EM34 B+ line in series with the phono pick up switch.  This allows the eye tube to be extinguished, extending its useful life, when the radio is operated for extended periods of time.   The modification included a quick disconnect so the back is easily removed.  Since the connections were modified at an existing terminal strip point it can be easily reversed leaving no trace of the modification. 

Thanks again for all the help and support.

Paul.

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Hello Paul,
 Thanks for your report. I am glad that's all find's a good end!

To the 17,5 Mcs Problem.  I think you now, because the IF Frequency   is only 0,460 Mcs, the space between  RF and Osc, is verry low on 17,5 Mcs. Its only 2,62 %.

Additional to the cause off close wiring of RF and Osc. 

When you align, the RF Trimmer  is difficult to handle on high frequencys. The Osc will bee synchonized, with the RF Circuit. In  such cases, you shoult start  align with Rf Trimmer full clockwise (max Cap) and align Osc first, then RF  and you can observe, the Osc was moved. Now only one time more align the Osc, and only one time more the RF and stopp.

 If you repeat once more, the distance beetwen OSC and RF is to low and you can observe the Problems you hat describe.

Hum screening. That's good what you have done!

EM34 
This is an verry good thing do to. The German Manufactor "GRAETZ" Altena have many years a  separate button, to switch "off" the expensive  Mag Eye in the same way if you to.

O.K. Paul, I wish you all the best with your hobby, good luck.

 Hans from Franconia near Nuremberg, 

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