How to remove 50Hz noise reduction

Fantasia 622 bright

Hits: 4010 Replies: 10
graetz: 622; FantasiaMatthias Hasenmayer
Jun 20, 2005  1

Hello,
have now given my "Graetz Fantasia 622" a "fresh cell treatment". Ie. Both El95, the ECC85, and the ECH81 have been replaced as well as a number of capacitors, thanks to "Isotest6". The radio has a good sound again and has a strong reception with AM and FM reception and also plays for several hours at a time without any problems.
Today while dusting, the radio was on VHF, I noticed something that is inexplicable to me. With the radio it is possible to switch off the mag. Eye (EM34) during operation. Now the following phenomenon:
1.
If the mag. Eye is switched off and I run my hand on the dial over the mag. Eye, I have a humming noise as I approach the EM34. The volume of the hum is the same regardless of the volume set on the device. However, if the mag. Eye is switched on, this hum cannot be detected. Just as with medium wave reception, it does not matter whether the EM34 is switched on or not, there is no hum.

2.
At high volume, the EM34's fan flickers to the beat of the music, similar to a level indicator. But strangely again only with FM reception.
With medium wave the fan of the EM34 is stable at the same volume.

My questions to the experts. Are such errors known (typical for the device)? What is the best solution (possibly defective ground connection)? As I said, capacitors that failed during "isotesting" have been replaced with new ones. According to the measuring device, resistances at the socket of the EM34 are also OK. The device's current consumption is OK. Is the gold layer on the glass bulb of the EM34 possibly a shield, and if so, is it possibly faulty?
Unfortunately, I am not a trained radio mechanic, but still find the old devices fascinating, especially when they work.
In perplexity and with kind regards ...
Matthias Hasenmayer

Hans M. Knoll
Jun 21, 2005  2Mr. Hasenmayer,

in this thread: http://www.radiomuseum.org/forum/fachfragen_im_forum.html

On Talk Talk, you may find answers from members who are not editors but want to be available to help you.

If things cannot or will not go on here or there, I will join them.

The background to this action is:
Time and again it is rightly said that at the moment you can only find answers in the forum that come from experienced editors who have worked for many years.
This is also often useful.
 
Committed collectors or hobby technicians, on the other hand, cannot have their say.
Why?
The hobby technicians may not have applied as editors for that reason, but everyone could because you think that you will not be able to compete with the professional experts, or if the answers are incomplete, you fear the www.

That is a reasonable assumption.

So here's a new attempt to improve something.

I am of the firm opinion that professional knowledge can also help, consultants or
Future editors to improve their knowledge.

As the link is, it shows in Talk_talk, there everyone can answer the professional and there can be a professional discussion on the internal stage where committed knowledge from the hobby can be complemented with professional knowledge.
But I also hope that members will now log in there.

The text has been changed by me for better understanding.

With regards, Hans M. KnollErnst Erb
Jun 22, 2005 3 (Only) Talk is not visible to guests and search engines, so it doesn't matter if assumptions and incorrect views appear there every now and then - as long as it does not remain there irrefutably.

At the talk we only have the order that editors there generally do not give technical answers, otherwise we will have all inquiries at the talk. You won't find such answers later and the same requests for the same model will reappear later ... As is usually the case with other forums.

It is therefore important that the editor briefly writes why there is now a request in the talk - usually three days after the unsuccessful request - and that he posts a summary of the good points in the original thread at the end.

If you convey that earlier, the editors have "no bread". That would be the only reservation for this welcome approach, which was also justified.

To the editors:
Via the link "Administrators" at the top right, members can find the link "Group membership", a selection list with which they can display the various administrators, officers and editors. We currently have 97 editors. It strikes me that only a few are also active. I mean we should Delete rights that have not been used for a long timeso that we can take on more (new) editors sooner.
 
A short time ago someone showed displeasure that they cannot post. Anyone who reads immediately finds out that it is not important for the editors that they are radio technicians or electronics engineers, but that completely different criteria apply, according to which the officers judge an application as an editor.
 
Addendum:
The link doesn't seem to be available to all members yet. But we will make up for that.Jens Dehne
Jun 22, 2005  4


Hello radio friends,

without additional information, I can only make assumptions about the cause of the "appearance". Basically I assume that the voltages specified in the circuit diagram for the "problem device" are within tolerance.

I am not aware that such a phenomenon is typical for the device.

Only the anode voltage to the fluorescent screen of the EM34 is switched via the "Magic eye" button, at the same time the effectiveness of the noise suppression is switched. The special feature (only applies to the x622 devices from Graetz) in this circuit is that the triode system of the EM34 is used for noise suppression.

In the course of production, some changes have been made, the C263 is reduced to 1nF and is only switched to the grid of the triode ECF80 when the switch is set to "VHF", the switch G1-G2 is no longer used (permanently closed) and a 2.2nF of C335 to C336 has been installed.

See you later!
Jens Dehne

 

Here is the manufacturer information:

In order to suppress the noise when receiving very weak stations or when tuning between the stations in the VHF range, the "Fantasia" received a field strength-dependent noise suppression. This suppression can be switched off and influences the frequency response of the LF amplifier in such a way that the medium to high low frequencies are reduced when the input voltage is low. The impression of noise is weakened as a result.

The principle of the circuit is that the C / GA of the display tube is increased to 1nF and a capacitor of 2.2nF (also 1nF) from the control grid acts on the grid of the output tube or the anode of the LF pre-tube. If there is no control voltage at the grid of the "magic eye" (weak or no transmitter voltage at all), the tube has its greatest gain. By increasing the C / GA, the 2.2nF (1nF) capacitor is practically in series with the input capacitance of 10nF at chassis potential and cuts the low-frequency noise. With a stronger incidence of the transmitter, control voltage is fed back to the "magic eye". This reduces the input capacitance, so that the series connection of the 2.2nF (1nF) capacitor becomes ineffective from a certain control voltage. The low frequency response then remains unaffected.Matthias Hasenmayer
23 Jun 05 5 Hello Jens,

First of all, thank you for your comments.
In fact, all measured voltages are within tolerance. Maybe I had expressed myself unfavorably. The radio itself plays cleanly on all wavebands and is also very strong.
To the 1st phenomenon:
There is also no "noise" between the stations. The noise cancellation works in my opinion. I was just surprised that the radio is touch-sensitive in the area of ​​the EM34, but only when the EM34 is switched off, and then only when the button is set to "VHF". To provoke this humming tone, which sounds like 50Hz, you have to run your finger on the dial over the EM34. If you move your finger away from the EM34 on the dial, the hum becomes weaker and disappears. It's like making something vibrate. This humming sound, if provoked, is also not volume-dependent. I. E. you can only hear it with the volume control turned down or turned down.
Regarding the 2nd phenomenon:
If the radio is operated at normal room volume and the EM34 has been switched on, it also shows the field strength of the station currently being received, as it should. So far so good. Now the following facts: I am receiving a strong FM transmitter, the compartments of the EM34 are practically closed. Then I turn the volume control to maximum volume. At that moment, the fan begins to vibrate in time with the music, similar to a level indicator on an amplifier, tape recorder, etc., and the playback is audibly overdriven. Compared to my "Stradivari3", which also has a push-pull output stage, you can actually crank it up to the maximum without causing major distortions in the reproduction. Sure, when and who is listening at maximum volume, but my other radios do not have this appearance. There is the display of the mag. Eye not somehow volume dependent. As I said with normal room operations, none of this is noticeable. But I think there is still a bug hidden somewhere.
How does a used ECF80 actually affect? It is guaranteed to still be the originals. Unfortunately, I don't have a replacement tube of this type at hand at the moment.

Best wishes
Matthias HasenmayerJens Dehne
Jun 24, 2005  6


Hello Matthias,

where you write here in the forum and not in the "Talk", I want to answer here too. Here, too, we will proceed systematically, first of all the cause of the "strange hum effect" should be found and eliminated.

If you look at the circuit diagram around the EM34 and consider the "hum" via the magic eye, which is independent of the volume control, you will see that the only connection from the "MA" to the audio amplifier of the C263 (1nF or 2, independent of the volume control) 2nF) is.

Now we are interested in the following voltage values: both sides of the R414 (560Ohm), of pins 4, 3, and 5 of the EM34 and the voltage values ​​of the triode of the ECF80, pins 1, 9, and 8.

Then we'll see!

Best wishes
Jens Dehne

Matthias Hasenmayer
04 Jul 05 7 Hello,

Thank you for the starting points for troubleshooting. Unfortunately, due to lack of time, I have not yet been able to search for the error in the device. However, I will follow Mr Dehne's advice and post it here again.

Many greetings MatthiasMatthias Hasenmayer
Jul 10, 2005  8Jens Dehne
Jul 12, 2005  9

Hello Matthias and all other readers,

after the measured voltages, I can first make the following statement:

  1. The anode voltage for the power supply is OK., The values ​​are within tolerance.
  2. The voltage values ​​at the ECF80 deviate too much from the values ​​in the circuit diagram and initially suggest that the ECF80 systems are "used up". But this is not the case!
  3. According to the manufacturer, the voltages are measured with an instrument.
  4. For a "normal" digital voltmeter, internal resistances are specified as 1MOhm for all DC voltage ranges, higher quality ones are specified as 10MOhm for all DC voltage ranges. You can now calculate the required parallel resistance (about 177 kOhm at 1MOhm) and measure it with a corresponding parallel to the multimeter. Then the voltages will be correct according to the information (and tolerances) in the circuit diagram!

In my Post 4 I already pointed out changes and deviations from the circuit diagram. It also says in the repair service lists

However, every change also has certain causes, which I can only assume here.

To flicker the EM34: The capacitor C263 connects the control grids of the EM34 and the triode ECF80. At high volume, the amplified LF from the anode of the pentode ECF80 reaches the control grid of the EM34 and superimposes the field strength-dependent DC voltage coming from the ratio detector (C261). However, the EM34 is hopelessly overdriven with a corresponding amplitude and the observed effect occurs.

Now, however, I can't explain the "hum" from Post 1 yet. It would also be helpful to know whether this effect also occurs when the noise suppression amplifier is disconnected. To do this, simply unsolder the C263 on one side and observe the effect. Please also test the hum sensitivity of the ECF80 by touching it! Then we'll see.

Have fun and greetings!

Jens Dehne

 

PS: My very personal opinion and observation of the amplifier part in this device is the following:

The use of an ECF80 has not proven itself, the dimensioning is not optimal. With radio reception, the full level is already reached at a little over half of the setting range of the volume potentiometer. Also, the ECF80 does not seem to be particularly suitable for AF purposes, some tubes show a tendency to "clink", others hum permanently more or less due to the effects of the heating. I conclude here that there is a lack of processing.Arpad Roth † March 27, 2017
Jul 12, 2005 10 The ECH80 tube mentioned several times in Post 9 should probably be an ECH81 ;-)
Little devil in the keyboard ....
Kind regards. ArpadJens Dehne
Jul 12, 2005  11

Thanks Arpad,

... already corrected!

My "keyboard devil" feels particularly comfortable in the warmth!

Best wishes

Jens Dehne