Grundig 3060 = ECC81 Problem HELP

[Phantomrose1999]

Hi,
Been at this Grundig 3060 for many weekends. Getting close to the end.

Main mystery is the ECC81 Anode voltage difference.

Schematic says One of the Anodes should be at 77v - 87v BUT i am measuring 128V !!!

Tried everything to find out why its so high, but am lost and hoping someone here can help..

ECC81 Schematic and Actual Measured:

Anode 1, 55v-68v Measured = 79v
K1 17v - 18v Measured = 14v
Anode 2, 77v - 87v Measured = 128v

I have checked every resistor suppling the two anodes, and just before the power is slit and sent to each anode, there is a common test voltage point, Just after R50 (22K) the voltage is 207v

The 207V is then sent via resistors to Anode 1, and via another set of resistors to Anode 2. Anode 1 voltage is correct, Anode voltage to Anode 2 is very high

I just cant see where the problem may be.

Note the valve installed is a 6AL5 instead of the ECC81. The set is very old and lay around for decades. I have re-build the power supply and changes just about every cap, except the ones in the RF section.

The AM section seens to go into oscillatrions easily, and tapping the chassis seems to make it go away. There is also a high seueal off the AM station, but when exactly on the station the sound is loud but there is some distortion which i think is caused by the ECC81 over voltage.. ??

[crackle]

You are probably using a digital meter, the original voltage measurements would have been made using an older meter with a lower resistance.
These are quite high impedance circuits and the current drain caused by the volt meter can have a significant effect.

I have just noticed the valve you have. The 6AL5 is a double diode you need a double triode as the AF driver, the circuit I have shows a ECC81 or a 12AT7.
Check you have identified the correct socket for each valve and check you have the correct valves in the correct sockets.

Mike

[Radio Wrangler]

American designation for ECC81 is 12AT7 and has a 9 pin base

6AL5 is the same as EB91 which is essentially the same as EAA91 and is a dual diode on a 7 pin base.

So they shouldn't even fit in each other's sockets.

David

[Phantomrose1999]

My apologies, i wrote down the wrong valve in this post. It is denitely an ECC81 Dual Triode that I am having the above problem with. In fact it's a real ECC81, not the American version, I just removed it to check.

Given that I am using the same Digital Meter on all measurements in the Circu't, i can see why one Anode's voltge would be so much higher than the other.

Please take a quick look at the schematic, there is about 205V, feeding both Anodes via some resistors, but the Anode voltages are way different.

I can't find a reason for this difference.

[Station X]

That circuit extract is way too small and out of focus for me to check. Members with better eyesight may fare better.

You can post .pdf and .zip files up to 4M in size.

[ms660]

Those voltages could be due to the ECC81 loosing some of its emission, but first I would fix the whistling problem then check the voltages again.

Lawrence.

[Phantomrose1999]

I zoomed in, does that help see it ? I dont have a scanner, just a phone camera.

[Station X]

Try this.

[Joe_Lorenz]

Hi,

if condenser C 71 is leaking, it would pull the questioned anode voltage upward, so I would suggest to check this.

Regards, Joe

[Radio Wrangler]

On that diagram, it looks like the anode supply of the left part of the ECC81 ia derived via a few resistors from the anode of the right half.

The left half anode is marked 125V the right half 78V.

Seems very odd. Could you have confused the two anodes?

Or is there RF/spurious oscillation going on which drives your DVM crazy?

David

[WME_bill]

Grundig 3060 radio _ECC81.
Thanks to Phantomrose1999 for posting the full circuit diagram. This clarifies that the HT feed comes from the bottom of the diagram to the junction of R47,R50,R58 at 207V.
There remains some lack of clarity about which valve section you are referring to. I take it that your V2 readings relate to the left hand section on the diagram, with anode voltage of 128V as marked on your circuit extract.
Then the right hand section, the second AF stage is not too far out, with A1 anode 79v, and grid current biassing through 10M.
Quite what your reading of K1 cathode voltage of 17v means when K1 is grounded on the circuit diagram. Please re-consider.
Now the left hand section, the first AF stage with tone controls, has A2 anode voltage of 128v instead of 80v. The anode load 33k+33k (R46 R47),so means a current of 1.2ma instead of 2ma, dropping from a HT feed of 207v. These currents suggest a grid bias voltage across the cathode resistor (470) is -5v, not -1v.
A. Can you tell us please what the cathode voltage is:
(1) to chassis, ie across 470 + 10k
(2) across grid to cathode, just the 470ohm.
B. I wonder about failing/leaky decoupling capacitors. The 22n C87 on input and C67 0.22u output to the tone controls and the decoupling capacitors around the detectors,and tone controls C89 100pf, C71 680pf, C70 33n, C90 47p across volume control.
C. Taking Radio Wranglers point about RF feedback, switch from FM to AM and see what change in voltages..
There seem a lot of small capacitors around the detectors and AF & tone controls which suggests there might have been instablity problems at one time.
wme_bill

[Phantomrose1999]

Hi, apologies for the delay in responding.

I replaced ALL the resistors that feed both Anodes of the ECC81, from the HT line to the anodes of both. SAME disparity in anode voltages !

PS: IT has a 100ohm in to drop the 240v to 220 AC in, it also have a 68ohm after the new bridge rectifier. The HT is 270v ! perfect.

Earlier EVERY single capacitor has been replaced except the main filtering ones.

I am left with a bad ECC81 ? and possible other valves as ALL valves are their american counterparts, not the original ones.

There is a squeak when turning, and i am quite sure its because the band switch contacts are BLACK and need a good cleaning one day. Pressing on the MW piano key changes the pitch of the squeal.

So one day, i will get a new set of valves and some strong cleaner for the switches. Sometime in 2020 that is.

For now, it will have to do.

https://www.youtube.com/watch?v=B7TU6Hiuh1g

[WME_bill]

Grundig 3060 troubles.
You have clearly been doing some good work.
Have you been able yet to measure the cathode voltages around the LH triode, first AF stage. My question group A.
This would help considerably in deciding whether you need to replace the 12AT7/ECC81.
European or US type numbers will make no difference with the usual equivalents. Grundig are a German firm, so will have used european types, such as from Philips or Valvo, who use both series of type numbers for their similar valves.
wme_bill.

[Sideband]

Originally Posted by crackle

You are probably using a digital meter, the original voltage measurements would have been made using an older meter with a lower resistance.
These are quite high impedance circuits and the current drain caused by the volt meter can have a significant effect.
Mike

In post number 2, Mike wrote this possible explanation for the voltage discrepancy. Using a digital meter IN SOME CIRCUITS, can cause widely differing results from the original which were probably taken with an analogue meter of perhaps 10,000 ohms per volt. The impedance of the circuit makes a big difference to the readings with a digital meter. Normal HT and power supply readings will be much the same but in high impedance circuits such as this, differences of 60 volts or so can be quite normal. You probably don't have a fault and it's unlikely changing valves will have any effect. If it's working OK with no signs of stress then it probably IS ok.

[Phantomrose1999]

Ok. could not rest, so put some time into measuring things.

The voltage across the R35 470 ohm resistor is 0.6V !!

I measured all voltages around the EBF89 and the ECC81

Please see attched for voltages.

The Main HT is 277v. after R67 1.3K, voltage is 256V

The unit sequeals very badly when turning and only stops when EXACTLY in the middle of a strong station. Weak stations just whistle.

Tapping the chassis changes the whistle, and pushing on the MW piano button also changes the whistle.

On strong stations the audio seems distorted, and the magic eye does not move much, very little during turning. Would love to undestand the AGC part of this circuit.

[cathoderay57]

Tapping the chassis and pressing the piano buttons are 2 actions that are probably shifting the tuned frequency slightly hence the whistle note will change. The squealing sounds like IF instability; can you confirm that you have changed the screen decoupling capacitors on the ECH81 and EBF89 (C32 22nF & C49 6.8nF)? If you have replaced a lot of capacitors then recheck all of the capacitor earth connections in case you have installed a dry solder joint somewhere. The other possibility is the squealing is being caused by bad AGC decoupling. I agree the AGC circuit is a bit tricky to interpret. It looks as though the EAA91 is the FM discriminator diode pair, while for AM one diode of the EBF89 (the right side) is AM detector and also providing AGC. I'm not entirely clear what the left hand diode on the EBF89 is doing; it is linked to one of the ECC81 anodes via a 22M resistor. The only purpose I can think of is some sort of AGC delay. AGC decouplers to check are C53 33nF on magic eye grid and C86 47nF. Cheers, Jerry

[Phantomrose1999]

PROGRESS AT LAST !!!

I poked aroud with a CRO and the first poke point, stopped the whistling !! yay.

I connect the CRO between the output of the IF transformer 309 and G1 of the EBF89 and the squealings stopped and i can tune the who dial without a single squeak !!! Wow.

Notes:
1) The CRO must be connected at the Transformer point, see photo.

2) If the CRO is connected at the EBF89 G1 point, it still whistles..

There is nothing connected to the EBF89 G1.

I will start checking the resistors connected to the 309 transformer, R14, R15

Do capacitors INSIDE the IF can fail ? Reluctant to open it up unless really needed.

Appreciate any advice

[Phantomrose1999]

ok, So i have checked everything in the path of G1 of the EBF89

C33 33nF replaced long time ago.
R20 2.7M good
R25 330K good
R14 470K
R15 47K
C43 220pf replaced long time ago

Connecting the HP CRO probe between G1 and the nearest ground, stops the oscilation WITHOUT the probe being connected to the CRO !

The signal measured at G1, seems to vary. Sometimes there is no signal, other times low signal, other times, loud and clear signal at this point.

So looks like i must open the IF can...As its still unstable when poking around there.

[Phantomrose1999]

When i lose the AM signal at the Transformer end G! of the EBF89, if i switch to FM, it works fine. Switch back to AM and no sound, but after a while it just comes back.

When there is no AM signal as above, i checked the oscilator of the ECH81 and i get a perfect sine wave, that is about 468Khz higher than the station tunned and accurate on the dial

IT 309 seems very suspicious.

[Phantomrose1999]

Well, last post for 2019.

I had to investigte the IF 309

I removed the cover and check both caps inside the can

C47 100pf. Was measured at 130pf (melted it while re-soldering, re-measured it and it was 110pf, so soldered it back in place.. lol

C42 270pf Was measued at 303pf, solderit back, minimal melting of it.

PS: had no idea these caps melt so easily, never had to change any..

So, put it back together without the Metal can and its back to where it was, with the off-frequency whistle. Quite sure if i re-connect the CRO to G1 of the EBF89 all the whistling will stop

Went to the local Jaycar to buy several resistors, 1M, 2,5,10M.. to test just adding one to the circuit but the shops closed early..ahh

So, wishing all of you a merry christmas and fantastic new year. heading to China on the 27th, will pick up an RF signal generator and boxes of caps and resistors while there..

Stay Safe from Melbourne.