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Old 2nd Apr 2020, 6:45 pm   #1
chokesrule
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Default EM84 Saba villingen 125

Hi. I have been sorting my villingen checking voltages and current with the service manual. Plus after watching mr Carlson on YouTube, found several resistors had drifted in value beyond tolerance. I have found several things which I do not understand. The first is the EM 84 signal indicator. It does not fully close even when receiving strong signal. I checked the voltages and the manual says pin 7 is tied to pin 9 and should be at about 30 volts. I find that if you go out of tune the voltage on 9 goes up to about 80v in FM and 140v in MW. On achieving tune it drops to about 50v. The grid voltage in MW is only-5v and in FM -10v. Reception on FM is great but poor on MW, SW and LW. Are these grid voltages too low? Thanks, Alan
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Old 2nd Apr 2020, 10:10 pm   #2
chokesrule
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Default Re: EM84 Saba villingen 125

As a footnote ,the em84 has never fully closed and the reception on all wavelengths has been poor even before i changed the resistors.
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Old 3rd Apr 2020, 4:05 am   #3
Mitch-W
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Default Re: EM84 Saba villingen 125

Hi,
The pin 9 is the anode of the "amplifier triode" inside the magic eye valve, a part of the EM84.
There should be 28V on FM and 38V on AM on that triode. Sometimes the 470K resistor goes high or open and causes trouble, so check that.

I have a similar radio on the bench with the EM84, and I will check if the shadow angle affects the voltage on the pin 9 as much as you are seeing.

I think that there might be some other problem (and not with the EM84) as the voltages on the pin 1 (g1) are too low for the FM and AM. For the FM if I am not mistaken, if the radio is working correctly, there should be -20 to -35V on a g1 when tuned to a strong FM station with the eye fully closed (with the two halves overlapping a bit).

Also check the resistors that feed the g1. I had it happen before on few sets that those 1M and 2M2 resistors have gone way up. Do not forget to check the capacitors, there might be some paper capacitors that might need to be changed, but I know that SABA started using film capacitors early so there might be very few to replace.
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Old 3rd Apr 2020, 2:10 pm   #4
Chris55000
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Default Re: EM84 Saba villingen 125

Hi!

The EM84 requires –22V to close the bars with 250V h.t. on it's target anode, pin 6, about –18V with the anode voltage supply in your Saba!

Yes I agree there is very little a.g.c. voltage being provided, particularly now many former local MW BBC and IBA (as it then was!) now closed or off the air, and this low a.g.c. isn't always obvious in modern post–war valved sets!

Loss of sensitivity in these types of set is commonly due to low–emission mixer/oscillator or i.f. valves, screen–grid feeds going high resistance, leaky trimming capacitors across i.f. transformer windings, yakky press–button switches, etc., etc!

If you can get a full Service Sheet for the set, even if it's only in German, it should have a sensitivity specification for the M.W. and V.H.F. bands, usually quoted for 50mW output, which is roughly just audible in the usual type of radio speaker!

Chris Williams
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It's an enigma, that's what it is! This thing's not fixed because it doesn't want to be fixed!
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Old 3rd Apr 2020, 7:13 pm   #5
chokesrule
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Default Re: EM84 Saba villingen 125

Hi i have been working on the st all day. There were some wirewound resistors that have been added at some point and not of the right value. I replaced with the values specified in the service manual. I thought this improved the sound . I then resoldered all the components i had changed looking for a stupid mistake, everything was fine. However i then discovered 3 small pf capacitors are missing from the board that holds the ecl 82.. these have something to do with the grids. I put them back in with values as close to what i have in my parts bin. The sound is more distorted. Its almost like they have been removed for a reason. The voltages to the em84 are still the same. I think i will try and get the covers off the transformers and see whats going on in there tomorrow
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Old 3rd Apr 2020, 7:23 pm   #6
chokesrule
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Default Re: EM84 Saba villingen 125

C39 150pf

C41 220pf

C43 22pf replaced with 100pf (all i got right now)

These caps were missing around pin 3 of the ecl82, i do not know what their function is?

R18 the 470K that you have highlighted to check is fine

Maybe i should buy a ebf89 and ech81?
But will have a go trying to get into the filters tomorrow. Thanks
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Old 3rd Apr 2020, 8:03 pm   #7
chokesrule
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Default Re: EM84 Saba villingen 125

I have a signal generator and an oscilloscope can i make use of them to find whats going on?
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Old 4th Apr 2020, 6:39 am   #8
Mitch-W
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Default Re: EM84 Saba villingen 125

These caps are in tone compensation network, and I think 22pF is RF bypass.

What about other capacitors? There must be few other ones. Can you post some photos of the chassis?

Also, I see there are some voltages marked on the schematics, can you check them?
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Old 4th Apr 2020, 2:17 pm   #9
chokesrule
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Default Re: EM84 Saba villingen 125

I think there are shards of mica loose in the ech81. Would this be an issue. I am checking the voltages just now.
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Old 4th Apr 2020, 4:15 pm   #10
chokesrule
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Default Re: EM84 Saba villingen 125

All voltages at testing points are fine until at pin 1 of the ebf89. As follows

Quoted. Measured

AM. 115v. 88v
FM. 105v. 69v


Pin 1 leads into filter 3 if transformer and further before it goes thru there it passes through 2 resistors. I found that these had been replaced by half there value not the original make of the resistors used in the saba! Is there something wrong with the transformers or the components in the chain? Here is a pic of a 4.7nf capacitor which is different to all the 4.7nf caps in the saba, infact its sat next to a cap of the same value which is the usual. Is this a replacement?

With ebf89, a signal comes into it from the if transformer 2 by pin2 which i take it is the grid. If the voltage from the if transformer on pin2 is nor within tolerance, can this cause the voltage on pin 1 to be too low, as i observe? Or has it something to do with if transformer 3? Bit reluctant to open those screening cans of the if transformers, got to admit.
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Old 4th Apr 2020, 4:41 pm   #11
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Default Re: EM84 Saba villingen 125

What does the HT feed voltage to the screen grid resistor measure on no signal AM (switched output side of S2") And what is the actual measured value of the screen grid resistor (R9)

Lawrence.
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Old 4th Apr 2020, 5:21 pm   #12
chokesrule
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Default Re: EM84 Saba villingen 125

As an experiment i changed r9 that goes to ebf89 pin1 from 47k to 23.5k and that brings the voltages within 10volts of desired voltage and i observe on the em84
FM. MW

pin 1. -13V. -1.6
pin 9. 120v. 50v

Fm seems to work better. The work bench is not a good place of reception
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Old 4th Apr 2020, 5:27 pm   #13
chokesrule
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Default Re: EM84 Saba villingen 125

Lawrence is there anyway you could simplify those instructions. Are you saying turn off am, measure the voltage either side of r9 (pic above)?thanks alan
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Old 4th Apr 2020, 5:57 pm   #14
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Default Re: EM84 Saba villingen 125

Quote:
Originally Posted by chokesrule View Post
Lawrence is there anyway you could simplify those instructions. Are you saying turn off am, measure the voltage either side of r9 (pic above)?thanks alan
Select AM, tune to a spot where this no signal or disconnect the antenna and measure the voltage either side of the original screen grid resistor and measure the actual resistance of the original resistor, measuring the voltages under no signal conditions is, in almost all cases, the standard procedure for voltage measurements in RF/IF stages, that's to minimise any effect that the AGC line will have on the voltages of the valves concerned.

Lawrence.
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Old 4th Apr 2020, 6:09 pm   #15
chokesrule
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Default Re: EM84 Saba villingen 125

Thanks Lawrence. I measured 77.4v after the resistor, 196v before the resistor and the resistor measure 47.1k ohms .
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Old 4th Apr 2020, 6:26 pm   #16
ms660
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Default Re: EM84 Saba villingen 125

Quote:
Originally Posted by chokesrule View Post
Thanks Lawrence. I measured 77.4v after the resistor, 196v before the resistor and the resistor measure 47.1k ohms .
That would tally up with the screen grid current quoted in the schematic I'm looking at, however to me the screen grid current quoted in the schematic doesn't tally up with the screen grid resistors supply voltage and the screen grid voltage, let's see what the others think:

https://nvhrbiblio.nl/schema/Saba_Villingen125.pdf

Lawrence.
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Old 4th Apr 2020, 6:38 pm   #17
chokesrule
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Default Re: EM84 Saba villingen 125

Since i put the resistors back to the values on the sheet, and put back the capacitors that were missing the radio sounds a lot better on fm. But, there is poor reception on other wavelengths but that might be the aerial?, i would say as well, the volume pot can can only be used for the first few degrees any more than say 20 degrees and it is too loud which doesn't seem right
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Old 5th Apr 2020, 11:15 am   #18
chokesrule
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Default Re: EM84 Saba villingen 125

These capacitors have a green rust on them. Will this affect their performance or is it just old flux? Here also is the underneath of the chassis. The silver micas on the left hand side are what i used to make up the small pf capacitors i found were missing on the board. A 1.5k resistor had been put in at r10, so somebody else tried the same trick as me ,but i experimented with screen resistor to bring up the negative voltage on pin 1 of the em84. And r106 had been dropped down to 1.5k which should of been 2.2k...i have put everything back to what is on the sheet. I believe the radio works better or at least sounds better . When i start up you can see the bars on the em84 overlap and then split apart . When i first came by the radio, i took the old paper caps out. Had a hum issue, but it was remarked that the set is designed to run on 220v. The voltage selector was in poor condition, ie broken. I thought it unsafe. So i hard wired it to the 220v setting , then added a bridge rectifier and adjusted the HT and heater voltages to run accordingly off the uk mains. It has not once blown a fuse and has had a lot of use for a good few years. Time on my hands with the covid19,i noticed on you tube, a villingen 125 with the em84 completely closed , i decided to get the radio running better. So all i have previously done is change, like for like, the paper caps and put a bridge rectifier in.This is the most detailed examination i have ever tried.
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Old 5th Apr 2020, 12:20 pm   #19
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Default Re: EM84 Saba villingen 125

Looking at the EBF89 g2 voltage in the service sheet and the Ig2Vg2 curves in the valve data I would say that it's wrong for a no signal condition.

Lawrence.
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Old 5th Apr 2020, 1:23 pm   #20
chokesrule
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Default Re: EM84 Saba villingen 125

There is a switch problem on MW. If i push the piano key down it makes the wafer switch bar it slides press closer to the corresponding switch plate. These are the voltages i measure on pin 1 of the em84 pressed down and left to do its own thing.
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