emud: Emud Rekord Senior 60 - I'm lost!

Hi there! This forum is always so helpful and I'm hoping someone can help me again!

Fiftenn years ago I restored an Emud Rekord Senior 60....lovely radio, really sounds wonderful with classical music especially. Full recap, retube (several had shorts), replaced out of spec resistors, etc. About 5 years ago it bit the dust and as I was moving/getting married/had a kid in those last 5 years, I've not had a chance to look at it since. So taking some time to resurrect it now.

When it died... I just turned it on, while warming up there was a bright pulsing flash & pop just behind the glass near the volume pot. I course I immediately turned it off and didn't power it on again until I started working at it recently. I've done necessary switch cleaning, etc. I found one resistor (R38 I believe) had blown in the area behind the volume pot. I replaced that.

The radio will power (lamps and tubes light), but no sound whatsoever. The only inkling of sound I get is a very faint "pop" when switching bands. I did take some measurements on B+ voltages, both high...at V7 (EZ80) checking about 380v instead of 280v, and at V5 (EL84) checking 380v instead of 270v. I've poured over the connections looking for shorts. Aside from liffting resistors, I'm lost on what this could be. Anyone have an idea where I can start? Thank you!

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Hello Mr. Phelps,

I looked at the scheme and I think it's important to know which resistor exactly you changed and which value you used - I'm in doubt with "R38" because there is only little powr to expect there.

If the anode voltage is that high it means there is no current flowing, so I would expect R37 (150 ohms) or R39 ( 1k) went dead. You could check the anode voltage of the other tubes: if there is any it will be R37 if not ot will be R39...

Unfortunately - if it is R39 you have to check also C56 (we call that an "Aü-Killer" because if it has a short the output tranformer can be destroyed) - so hopefully that didn't happen. After the repair I would recommend to connect C56 not to ground but to the output transformer where R39 enters - just because imho nowadays it's cheaper to loose a tube or a resistor and not the transformer if the capacitor goes bad ...

Good luck and regards,

D. Consales

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Regarding C56, it can be a good idea to connect a flame proof resistor of a few kohms in series with it, then the resistor will burn and get open circuit in case of a short in the capacitor. Note that the DC working voltage of this capacitor has to be at least twice the radio's B+ voltage. Y2-approved safety capacitors are also safe to use in this position even if they are just marked with 275 VAC.

Check if the output tube is drawing current by measuring the voltage drop across its cathode resistor R37.  It could also be interesting to measure the heater voltage to see if it is 6.3 VAC as it should or if even that voltage is too high.

And, just to avoid drawing any false conclusions, make sure that your multimeter is within calibration. Many digital multimeters have a tendency to give too high readings when the battery is running out, in some cases even before the low battery symbol is lit.

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Hallo Mr. Forsman,

that would be an option - but also changes it's function whilst the connection to the output transformer has not influence on it's function. For audio frequences it doesn't matter if you go to gnd or to the transformer.

Kind regards,

D.Consales

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Thank you gentlemen for your fast responses! As you can see, I don't have much time to work at this as I have a young family. I did take some time this afternoon and look into your suggestions.

Mr. Cosales, I did infact replace R38 as it was blown out with a 100k Ohm 1/2w resistor. Obviously that's not the culprit.  I did tested the plate of EL84 (showing around 380v) and EABC80 (~28v), which led me to R37 as you suggested. I clipped a leg and it's testing 208ohm so obviously out of tolerance. I'm going to order a replacement and try that, but before I do...would a 1w or 2w be suitable for that replacement? The old one is rather large so I'm speculating it's a 2w but hard to tell.

In my original recap of the radio I had already replaced C56 with an orange drop. Would you still recommend it's replacement?

Thank you gentlemen!!

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I would use a 2W resistor although 1W would also be sufficient. The power at the resistor is about 0,3 watts - but it has to handle that the whole time. so a physically bigger resistor is better imho ...

Regarding C56: not replacing but rewiring, connecting it to the output transformer (where R39 is connected) rather than to gnd.

Regards,

D. Consales

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Hello again gentlemen!

No luck thus far, I replaced R37 and no change. Still nothing, pilot lamps will glow, tubes heaters light, but no functionality. Also no function on magic eye tube. I still get faint pop when switching bands, so the amplifier portion is at least somewhat working. I tried connecting a record player to the phono & tape inputs, and did get very faint signal/sound with that. I'd never tried those inputs before so I have no benchmark to test against.

I'm suspecting C55 maybe the problem (circled in green in photo). I stumbled on this one that I missed in the original recap, and it looks like it may have some electrolytic at the anode end. Thoughts?

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C55 shorts R37 for audio frequency. If its capacity is too low the gain is low(er). But that would not explain the high anode voltage. Also if it where short there would be no negative g1 - so current would be high (and anode voltage low). Did you check the g2 voltage at the EL84 ? Is the EL84 OK ?

Otherwise I have no more ideas now ...

Regards,

D. Consales

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Hello again gents, checking back in...it's taking me several days between times at the bench.

I replaced C55, it was bad, however still no improvement. I'm getting very very slight hum that trims with the volume pot, so I know the amp portion is at least somewhat working.

I checked the heater voltage at pin 3 on the EL84, and it's only measuring 1.4v instead of 6, so I'm wondering now if it's something upstream of the EL84 not supplying proper 6v voltage. I think that explains no output whatsoever from the Magic Eye EM80 which I know is good (tested). Not sure how this explains the 380v at the plate of EL84 tho. Any additional ideas?

Thank you gentlemen for your time and thought!

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Pin 3 is the cathode of EL84. The voltage there is determined by the voltage drop across the cathode resistor, which in turn depends on the current through this resistor and the tube's cathode current which will be the sum of anode and screen grid currents.

Possible causes of the low voltage could be either a weak tube, a too low screen grid voltage or that something shunts a bit of the current away from the cathode resistor (for example a wiring short or a bad decoupling capacitor across the resistor).

Try the EL84 from this set in another radio and look if it works properly with correct voltages around the socket with that tube.

Make sure that your multimeter is correctly in calibration, compare the readings at least at all DCV ranges, with another multimeter.

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Unfortunately I don't have another radio that takes that tube to test it in, otherwise I would've done that. When I first repaired the radio some 15 years ago, I replaced all the tubes as I then had no way of testing them and a few were bad. I have the original EL84 and have tried it in the set, but same operation. Do you suppose the EL84 went bad again? I'm willing to try and replace it again. 

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Check all the voltages. It's unlikely the EL84 is low emission already.

The g2 must be near HT. If too low a voltage the EL84 is turned nearly off and you get high anode voltage. A low g2 voltage also reduces gain. The g2 is sometimes used for gain control on RF or IF tubes/valves that have a sharp cff so don't work with AGC via g1.

Check value of cathode resistor when power off. If gone high or open circuit the anode volts are high.

Is EL84 brightly lit? if not check socket if voltage is about 6V to 6.5V AC.

Unplug EL84 and check voltages at top of socket. The g1 and cathode should be zero. Check g1 resistance and cathode resistance to 0V/Chassis from top of socket. If g1 socket is poor or there is no resistor (gone higher than 1 or 2 M) then the g1 is  pulled negative by "space charge" from cathode and anode volts is high. Sockets can go high resistance. Some switch cleaner and a needle file smaller than pin on EL84 can be used.

The radio or other device with a valve can actually be used as a tester if you know the voltages. The G1 can be varied with a 1M  pot from cathode to 0V with wiper to grid. The G2 can be varied but this is tricker as the voltage and current is higher. If the cathode resistance is known then the volts on it / resistance = sum of Ia and Ig2.

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You can short g2 to HT.
Note a leaky cap on g2 on ANY valve lowers the voltage and thus gain.

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Ok, think I might've found something telling.

All of the tubes light a proper glow, the EL84 is particularly bright (probably double the brightness of the other tubes). However, I get no voltage at the heater pin (pin 4) on ANY of the tube sockets, with or without tubes in. I suspected the transformer, so quickly tested with my old Dim bulb tester, but it seems to be fine, no apparent opens, and no visible issues. I'm a little more confused now, unsure how these tubes would light without voltage to the heaters.

EDIT: Disregard this...my meter was mistakenly set to DC instead of AC. Continuing to test.

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Okay values for EL84 as of now:

G2: 39.2vDC

G1: -5vDC

K/G3: 1ish/0vDC

A: 370vDC

If I'm understanding you correctly, G2 on the EL84 should be at roughly 250v, is that correct?

The resistor at Cathode should be good (I replaced R37 with a 150ohm 2watt resistor), and replace C55 there as well.

I've checked continuity between the tube pins and socket, no issues there it seems.

Any ideas? Thank you Michael!

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So with only 39V on g2 the EL84 would be almost off. Check whatever is on that pin and wiring to main HT side of output transformer.

If all else is exhausted, disconnect what is pin 3 (g2) and wire that pin direct to the HT side of the output transformer (not the anode side)

The EL84 is brighter, see current rating of tubes.

The problem is certainly the low g2 volts.

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Thank you again Michael for your quick reply!

Ok, think I've found something interesting. The HT coming from power transformer is 295vAC at the transformer, as well as pins 1 & 7 of the EZ80 (V7).

However, off pin 3 of the EZ80 the voltage is 380vDC, similar to anode of EL84 (pin 7). Those should be aboug 100volts lower, roughly 280vDC. I've tested the EZ80, no shorts and good emission. Swapped with another EZ80 and same operation.

However in all of this I noticed that part of the filter capacitor for C52 was replaced with 8uf instead of 4uf as per the schematic. Could this be what's causing all this? Any other ideas? 

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Look at the schematic and follow the HT voltage all way from the cathode of EZ80 to screen grid of EL84, to see where the big voltage drop occurs. Either it could be an almost open circuit for example in R39 or in the output transformer's humbucking winding, or it could be that something draws too much current from the HT rail supplied by R39. For example high leakage current in the filter electrolytic, or a short in any of the tubes supplied from that rail or any of the 5 nF decoupling capacitors.  In case of a short somewhere in the RF or IF circuitry, you will be able to find it by checking if any of the series resistors supplying the various stages (R12 etc)  becomes hot or if there is a big voltage drop across it.

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The high voltage is because the EL84 isn't taking much current due to having only 39V on g2. The EZ80, and 4uF vs 8uF is irrelevant.

The problem is only having 39V on the g2 of EL84. As a test, disconnnect whatever is connected to that pin and connect g2 with an insulated wire to HT. The HT volts will drop a lot if the EL84 is then working.

If the g2 is now DC HT volts (more than 200V DC), you can examine why it was only approximately 39V, perhaps a wrong connection, bad connection, faulty transformer etc.

On the schematic I have (not export version) the main smoothing caps are possibly 2x 50uF. The main HT from EZ80 (280V) goes to a tap on the output transformer and one connection is anode and the other is HT for the rest of the radio (250V) including EL84 g2. The voltages will be higher because the EL84 isn't taking current.

An AC voltage of 295V will give about 417V with no load at all, so 380V is reasonable. Later when the g2 supply fault is found, we can examine why the volatage is a little high, but it will much lower when the EL84 is taking proper current (maybe more than 20mA?). The EL84 is practically turned off by the low g2, thus HT current is very low.

If you are using USA 115V (it's certainly not 110V), check what voltage it really is (my 230V grid electricity varies from 240V to 260V) and set the mains voltage tap. My schematic has 119, 130, 150, 180, 220V, but likely the "export" version is different. 

However the higher voltage is not the problem on the EL84. The problem is having less than 150V on g2, the 39V is far too low. It should be over 220V DC on this radio.

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Thank you for the very detailed explanation Michael, that makes sense to an old dog like me :)

Want to make sure I'm pulling the correct legs here. According to this pinout, the G2 of EL84 is pin 9, not pin 3...correct?

If that is correct, I've pulled the leads going to pin 9 and jumpered that to HT from EZ80. No change in operation except a louder (and now uncontrolled) hum from the speaker. Voltages at EL84 are now:

Pin 2 (g1): 43mv dc (yes, mv)

Pin 3 (k, g3): 9vdc

Pin 4/5: 6vac

Pin 7 (a): 403vdc

Pin 9 (g2): 306vdc (jumpered to HT from EZ80)

• EL84_base_diagram (15 KB)

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OK, yes, pin 9 is g2 and 3 is cathode. Maybe I looked without glasses/

That's good. Shows EL84 works.

So, the HT line from output transformer to rest of radio is missing. Find out why. Start at primary of o/p transformer with no power to check the winding between HT and g2/ radio HT is the similar to HT to anode resistance (unlikely to be the same)

Then look at HT volts of supply to each anode.

I can't see how the EL84 anode is now higher than HT.

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For clarification as I continue these tests, should I leave EL84 shunted directly to HT or restore the connections at pin 9?

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Measure the voltage at the HT rail after R39 (and also at the point between the output transformer and R39.  Look at if the voltage raises when you remove the tubes one after another (except for the rectifier tube EZ80).  Also, check resistances of R39 and the humbucking winding in the output transformer.

As the HT rail after R39 supplies several parts of the radio, the fault can be almost anywhere, not necessarily near the output valve EL84.

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As Torbjörn, writes, the fault is the secondary HT that feeds all the radio and EL84 g2, so it doesn't matter what you do with the EL84. The EL84 can even be unplugged to stop the hum.

Actually I just downloaded the export version of the schematic. The Europe version schema I had does not have R39 1K. It is the most suspect part. Check voltage either side of it with EL84 on original wiring, or unsolder one end and measure resistance (with power disconnected).

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Well I hope you're all ready for a good laugh...

Two nights ago...FOUND THE FAULT AND FIXED THE RADIO! After tracing the secondary HT all over the radio, I simply could not find any spot that didn't have continuity back to R39, voltages were all low on anodes, and I kept landing back at R39 as Michael mentioned as the most suspect part.

I'm proof that it's a bad idea to work on these late at night, I just KNEW I replaced R39 a couple weeks back. While looking all around R39 I noticed the bands and thought "gosh, that's odd for two resistors of same rating to share a leg. And then it hit me...this is the wrong value. I'd replaced R39 thinking it was R38 with a 100k, and it was choking the HT everywhere, which explained why EL84 (and nothing else) wasn't coming on.

I swapped it out with an appropriate 1K and everything fired right up! Going thru and double checking voltages, everything is looking good so far. AM band is weak, and SW is intermittent but I'm receiving some stations on both. FM is quite loud and good sensitivity, tho slight out of alignment. I don't have a scope and haven't done an alignment before, but I can live with it.

A few things to do yet:

- Replace R39 with 1/2 or 1w resistor. I only had a 1/4 watt and it's running hot, the bands are already discolored.

- Swap the 3rd leg of C52 with a 4uf as rated and see if that doesn't straighten things up all around.

- R27 is flaky & will replace. Eye-tube (EM80) is acting a little odd, not affecting operation.

But all in all, things are looking much better! I'll report back if the AM reception improves after swapping C52.

But I wanted to thank you gentlemen so very much for your time and thought on this for me. I very much appreciate your expertise and sharing your knowledge! I hope this thread will be helpful to others, I come back to things I've posted in the past just to jog my memory. Thank you Michael, Torbjörn, and Daniel so much!

Moral of the story...WORK IN DAYLIGHT HOURS & NOT LATE AT NIGHT! :D

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Use five off 4k7 resisrors in parallel for approximately 1K.

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