Grundig 3060 Resto in progress 300V ??

[Phantomrose1999]

I am getting working a Grundig 3060 which has been idle for so long that all the knows were frozen solid.

Tasks done so far:
- Free'd Volume, Tuning, both AM / FM.
- Clutch needed adjustment
- Had to re-wire the AM dial cord after removing the metal dial backing plate
- Broke the Anenna direction indicator, was frozen solid. need to find another
- Changed all wax and blue caps.
- Added new Bridge recrifier with 4x 3A-1000V diodes
- Added 10W 100ohm resistor to drop voltage.

PROBLEMs:

1) The measured voltage after the 100ohm resistor is 300v. Schematic says it should be 270v. Is 300v too high ? should i drop it

The audio is a little distorted, not as clear as it should be. Can be be because of the higher voltage ?

2) The output valve is not the original EL84, but the american version 6BXX (i forgot to write it down. It Glows very bright, is this a problem ?


3) The ECC81 which drives the EL84 Equivalent GLOWS very brightly when powered on but becomes normal. Is this valve on the way out ?

Will see what else turns up after running it for a few hours..

David

[cathoderay57]

Hi David, often the Grundigs were designed to work with a mains transformer primary voltage of 220v AC. Not sure what you are operating on in Oz but probably worth measuring your mains carefully with a suitably rated AC voltmeter. If you are +10 or +20v above 220v that won't help. Similarly measure the valve heater AC voltages and see how much in excess of 6.3v (with all the valves running) you have got. You might be able to solve any overvoltage heater and HT simply with a 10W series resistor in the mains input line starting at 100R and working up at least until the heater voltages are closer to the mark. The HT is not too critical so long as the peak voltages of the electrolytic smoothing capacitors are not being exceeded. If they are, then increase the HT dropper to 200R. The ECC81 bright-up at start is fairly common and nothing to worry about. Cheers, Jerry

[simpsons]

Grundig radios supplied to the UK and Australian market differ from their European cousin to cope with the 240 volt mains supply and this is clearly shown on the back cover.

Where it is a modified 220 volt radio, the thread on this site "Grundig 3028 220 volt to 240 conversion" will help you. It says place a 82 ohm resistor in series with the mains supply. The exact value might differ for the 3060 but not much. The modification shown includes how to mount it.

I am not sure if the distortion you hear would be caused by over running the radio but the valve heaters will not be too happy.

Once the mains input side is right, then should distortion still be evident, try to narrow down the problem by using the radio as a tuner or amplifier.

The most common problem is leaking af coupling capacitors. My schematic only shows values not component references so I can't be more specific.

Alternatively, should the AVC not work properly, then this will show up when used as a tuner.

Chris

[julie_m]

If the new rectifier has a lower forward voltage drop than the original, then you will need to add a resistance in series to compensate for this. It makes no difference whether this be on the AC (transformer) side or the DC (capacitor) side.

[Chris55000]

Hi!

In all probability the valve you tried is probably 6BW6 which I'm surprised produces any sound as pin 9 on this is the beam–plates and G2 is pin 8 – in any case it would be substantially under–biassed, hence low volume & distortion!

The correct GB for the EL84 is –7.3V, but you can also use more economical 'EL41' conditions by using a cathode resistor of 180 ohms and reducing Vg2 to 210V – Mullard specify this operation to reduce h.t. current and heat dissipation in smaller sets, the Regentone ARG77 uses a 220 ohm cathode resistor with Va 240V, Vg2 245V and this works very well with only 40mA h.t. current!

(If the chassis is wired the valve holder would have been rewired I presume!)

6BW6 pinout :– 1 i.c., 2 g1, 3 k, 4 h, 5 h, 6 i.c., 7 a, 8 g2, 9 b.p.

Va 250V, Vg2 250V, Vg1 –12.5V, gm 4.5mA/V, Rk 270R, Ra 4500 ohms, Pout 4.5W (10% D), Pa 9W, Vh 6.3V, Ih 0.45A

The opt. load for an EL84 is 5600 ohms so you might get away with an EL84 transformer (45:1 to 3 ohms for 6BW6), but the main objection is you'll lose a lot of a.f. gain!

EL84s are starting to be affected by "audiophoolery" prices, but the Russian 6P14P is a direct EL84 substitute you might get more cheaply!

Chris Williams

PS!

I agree totally with Julie M's advice – my experience with Continentals is that the h.t. and heater voltage is often much higher than it ought to be on UK power supplies – I'd add 82–120 ohms 5–7W in series with the primary of the mains transformer then add enough resistance in the bridge's positive lead to give 275V rectified o/p at the reservoir electrolytic – you don't need more than that!

PPS!

The American EL84 equivalent is 6BQ5 by the way – if that's what you have you're fine – others are N709 GEC/Osram & 6P15 Mazda!

I believe the 6CH6 video o/p pentode works very well as an EL84 substitute if the base is rewired – pinout same as 6BW6 except pin 9 is g3!

[Phantomrose1999]

Thank you all for taking the time to post your informative comments,

The EL84 replacement is the american 6BQ5, as there are no wiring changes.

As mentioned above, i did measure the "GB for the EL84 is –7.3V" voltage and it was over 10v, due to the higher supply

I will measure the heater voltages and add a 100 ohm in the mains circuit to get the heaters to the correct voltage, then see if the HT needs reduction.

Back to work, hope i get time next weekend..

PS: The power switch has stopped working on Sunday so no chance to do anything until that is fixed.

This will be a nice match for my TK920/3D, i think they are of a similiar vintage.

[TowerRadio]

Are you measuring the HT with a digital meter? The voltages on the data sheet were probably taken with an analog (AVO 7 ) meter.Les

[Phantomrose1999]

Onto the next phase:

I have added a 100ohm 10W in series with the 220v primary and the main HT is around 280v so am happy with that. The 10W is dissipating bit over 6W, so it get a bit hot.

I used it as an amp, with the turntable input driven from my laptop with two 10K resistors to combine the stereo output into a mono and the sound with just the big speaker was great !!

Now to the problem of AM and FM distortion and low volume.

FM does work, but its not great. Distortion is less compared to AM

AM is squealing, strong signals (one) seems to be somewhat better than weak signals which sound like SSB.

So i investigated around the EBF89, and found the anode voltage was around 90, schematic says it should be 190-219v. ah this is good.

Checked all surrounding resistors and found a non-original one, where R18 1K should be. One one side of it, the HT rail at 250, after it 90v. Removed it and it was 41K ohms. See attached photo, i cant work out what it is supposed to be. Every time i touched the 90V anode with my digital multi-meter the weak AM signal stopped.

So i put a temp 1K (actually a 10K pot, wound down to 1K) and then i got about 211v on the anode of the EBF89, which is close to the spec, BUT both AM and FM were now DEAD !! no reception at all.

Unfortunately i shorted the anode and blew the 10K pot, will get a real reistor in the morning, as its midnight here in melbourne aus.

Any ideas why reception would be dead when EBF89 had the correct anode voltage ?

Other points
The EBF89 has a 6DC8 installed
The ECH81 has a 6Aj8 installed
The EAA91 has a 6AL5 installed
The EL84 has a 6BQ5 installed

All seem to be pin compatible from an internet search.

The magic eye EM34 is not bright, and does not move when tuning, there is a very faint glow. Can this be causing the IF section to fail ? may try removing it and see if it helps ??

Schematic attached, and photo of mystery R18

Back at it Sat morning with a new 1K resistor.

[Phantomrose1999]

I installed a new 1K resistor and all valve voltages are good, except the ECC81, which i have opened a new thread for.

There is still a very bad sequeak off station on AM, and on SW there is static towards one end of the dial and just silence towards the other end of the dial.

Suspect the whole AM IF needs to be aligned..

[Radio Wrangler]

Originally Posted by Phantomrose1999

Suspect the whole AM IF needs to be aligned..

Not yet. Decent sets hold their alignment quite well. Unless someone has been in there before and done some random core-twiddling, leave alignment until you're sure you've sorted all the failed components.

Watch the AGC voltage as you tune it across a few stations to see if it's alive.

Do stations turn up about the right place on the dial?

A scope and sig gen help in tracking distortion through the stages.

David

[crackle]

SW is likely to need a nice long wire aerial, have you got one plugged in.
I would also check the voltages around the OP valve to see if it needs replacing.
If the valve is worn out then it may not be conducting well and that will reduce the current on the HT making ALL the voltages seem high.
I would check the voltage between the grid and cathode, pins 2 & 3.
Checking the the voltage across the cathode resistor and working out the current will give a rough indication if the valve is conducting as it should.

Mike

[Phantomrose1999]

Well, it went from making a noise to being totally dead on AM and FM !! both were working prior to what i did.

I removed the 6Aj8 and inserted a real ECH81, which caused a "bang" and after i lost both AM and FM.. though i seem the hear the IF of AM, the FM side is totally dead..

So taken a few steps back.

[Phantomrose1999]

Well, i got AM back. It could be the AGC malfuncitoning, as the distortion does sound like a station that is too strong over loading

Also it squeals very strongly, while tuning, until i am 100% in the middle of the station, then the squealing stops. Weak stations, i can only hear the squeal, but stronger ones do stop the swueal.

There are really no caps left to change apart from the small clear ones in the RF section.

Whee is the AGC circuit in the schematic please ?

[Phantomrose1999]

I posted a video of the whistling, anything off station has very strong whistling, exactly on station has sound, but its not totally clear, its distored like the AGC is not working. I think if i can find the cause of the whistling i will also fix the distortion....

https://www.youtube.com/watch?v=b28isBYZJiI

Any ideas where to look ? No more caps to change, all voltages are ok, except the ECC81 where one anode is much higher than the other. Another thread posted.

i really want to finish this... any suggestions appreciated

[crackle]

I normally associate that sort of effect with poor screening of the Frequency changer and IF valves, are there any aluminium valve screens missing? I would also check the decoupling of the HT & screen supplies for each valve, maybe C32 C35 C49 C50.

Mike

[ms660]

Aka the screaming abdabs, oscillating at the IF, that beats with the signal which is at the IF, hence the whistle (the difference frequency) when you go off tune either side.

As Mike said, check AGC, HT feed and screen grid de-coupling etc and any valve screening connections.

Remember that the IF amplifier is a tuned grid tuned anode oscillator waiting to happen.

Lawrence.

[Phantomrose1999]

I have changed EVERY cap except the big filtering 50uf/50uf ones. All volages in the IF stage are close, just a little high.

Can you please tell me where the AGC components are please ? This is the only thing left. Usually after a re-cap, this problem is gone, but not so now.

Notes:

Only other point is it takes a very long time to actually hear any AM, way longer than any other set i have had.

The ECH81 has been replaced with 6Aj8, i tried to install a real ECH81 and it seems to have damaged the FM, There was a small bang, and the FM no longer works. Checked all FM voltages at the valve and its good, check the continuity of the main FM Switch and its also good.

The EBF89 has been replaced with a 6DC8.

The set came with all USA equivalents.

[crackle]

I think C86 47nF is on the AM AGC circuit, which I believe comes from pin 7 on the EBF89. There is a 820k resistor in series before it goes to switch 14c and then to the grid of the ECH81.
But I may be wrong.
Mike

[ms660]

Originally Posted by Phantomrose1999

Can you please tell me where the AGC components are please ? This is the only thing left.. Usually after a re-cap, this problem is gone, but not so now.

It's hard to make out the component reference on the copy schematic I'm looking at but the AGC de-coupling capacitor is the 47nF that's connected between the anode of the AGC delay diode and chassis (junction of R10 and R69)

EDIT: Post crossed.

Lawrence.

['LIVEWIRE?']

I've discovered that, although these files cannot be opened via Foxit Reader, they will open via 'TWINUI', and agree with Mike 'Crackle' and 'ms660 'Lawrence' about the AGC circuit