• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Telefunken 2430 Opus Resistor Burnout

numinous

Member
2013-04-14 6:40 pm
Hi everyone. I have a Telefunken 2430 valve receiver which has given me much listening pleasure over the years. It went into storage for a time after a house move; after I unpacked it, it was working fine but I noticed it had collected quite a bit of dust/dirt and used an air duster to clean it -- big mistake because after that I had a persistent and annoying hum from both channels. After much cleaning and replacing of valves, the problem persists; however, after the last attempt at trouble-shooting, a resistor on the amplifier board burned out. Because of the way it's burned up, the colour coding is gone - it's placed below an ECC83 valve.

I was wondering if anyone could help me identify this resistor so I can replace it. I haven't switched it on since. I know very little about electronics and have basic soldering skills. There are no specialist hi-fi shops near me. I have attached a photo:



Thanks for any help. I'd really like to salvage this if I can. Is this resistor really fried, or can I take a chance on switching it on?
 

numinous

Member
2013-04-14 6:40 pm
Hi Frank, thanks for your reply. There are four electrolytic caps beneath the output transformer - I've noticed that they seem to be quite leaky as they're old paper caps - the problem with that is that the paper is so faded I can't read the values. Thankfully I do have the spec sheet on PDF. Also those caps are very hard to get at because of the way the amp is constructed - quite a lot of disassembly and wire-cutting - I better take a lot of photos before I start.

So I'm looking at replacing those caps, and that resistor?
 
The resistor overheated for a reason. I'm guessing that one or more electrolytic capacitors have shorted. You should replace all electrolytic caps.

Hello Frank

That's not so easy in the 2430.

Example: The 4 Electrolytics 100µF in the Power Supply are combined in one housing! It's nearly impossible to get a spare part.

Best regards
Michael
 
Hello Frank

That's not so easy in the 2430.

Example: The 4 Electrolytics 100µF in the Power Supply are combined in one housing! It's nearly impossible to get a spare part.

Best regards
Michael

4 Separate caps under the original cap perhaps ??

Ce manufacturing has some newly manufactured can caps so does FT i they have the exact i dont know.

The nearest in size and value with some added caps in parallel works to.

If perfectly original isn´t a must.
 

numinous

Member
2013-04-14 6:40 pm
Hello numinous

For your convenience I attached the schematic diagramm.

When i'm back home in the evening, i will have a look at my own Opus 2430 to tell you the right value of your burned resistor.

Best regards
Michael

Hi Michael, thanks very much - I'm not sure where the resistor is located on the schematic so if you can give me the value it would be a big help. I'll log on later and take a look.
 
Hello numinous

I'm at home now and just had a look at my Opus.

Your Photo, is that the corner of the PCB that you can see without removing the whole Assembly?

The resistor on the left side of your Photo is 1 Megaohm, 5% - Brown, Black, Green and Gold. This is the resistor from Grid to Ground.

The burned one is the kathode-resistor of the ECC83, 2,2 Kiloohm, 5% - Red, Red, Red and Gold.

If this resistor burned, then there is a serious Problem. Someone has to measure the voltages in the NF-Part and the Power-Supply!

Best regards
Michael
 

numinous

Member
2013-04-14 6:40 pm
Hi Michael, thanks very much for taking the time to get that information for me. Yes, the part of the board is at the very bottom left, below the lower ECC83 valve near the edge of the board. The other thing I wanted to ask is - is there a specific wattage for that resistor?

I'm sorry to hear it means there's a serious problem as my experience of electronics is very limited. I will have to ask around and see if I can find someone more qualified than myself to measure the voltages.

My original plan was to replace the resistor and if it worked, all well and good; if not, to seek other help. I love this receiver so much that I'm willing to work at it.

Many thanks - if you have any further ideas or information, they will be gratefully received, and I will keep this thread updated on my progress.
 
The other thing I wanted to ask is - is there a specific wattage for that resistor?

Hello numinous

Please have a look at the schematic diagramm on the first half of the ECC83. There has to be 120V on the Anode and 1V on the Kathode measured against Ground. The resistor from Kathode to ground determines the current, that flows through the tube.

I=U / R so 1V / 2200Ohm = 0,00045A = 0,45mA

And that is exactly the value from the schematic printed on top of the tube-symbol. Power rating is:

P=U x I so 1V x 0,00045A = 0,00045W

So every resistor with the normal power rating of 1/4W or 1/2W is good enough.

And now you can see yourself that something goes really wrong there, because you need way more current through the resistor to burn it down.

Best regards
Michael
 

numinous

Member
2013-04-14 6:40 pm
Hi Michael, thanks for working that through for me and explaining it so well. I see there is something very wrong.

I have asked around and there's a friend of a friend who undertakes repairs of this kind, being an electrician, so I've decided to ask him to take a look at it rather than have myself damage it further. So someone who is qualified will be looking at it next - I've printed the schematic you provided, so I will pass that onto him.

I will also ask him about the hum which appeared after I used to air-duster to clean it - I'm not sure why that would have happened.

I'll keep you updated. Thanks again for your help. :)
 
Hello numinous

I really hope he can fix it, this little radio is worth to be kept. Prices on ebay are rising for many years now.

Opus was the name for the Top-range of radios from Telefunken beginning with the Opus 49 in 1949, only 4 years after the war.

Opus 49 9M65WLK Radio Telefunken Deutschland TFK, build

The 2430 was one of the last radios with tubes, only the next model 2550 also had tubes and after that Telefunken goes for solid-state devices.

Opus 2430 Hi-Fi Radio Telefunken Deutschland TFK, build

Opus 2550 Hi-Fi Radio Telefunken Deutschland TFK, build 1964

Best regards
Michael
 

numinous

Member
2013-04-14 6:40 pm
Hi Michael, I hope you're well. I just wanted to update you on my progress - I got the receiver back from the electrician yesterday. The blown resistor has been replaced, and also two capacitors. It is working well, though with a couple of small drawbacks:

There is a still a slight hum in the left channel - the electrician said this hum seemed to swap between channels upon removing the casing. He checked the grounding but couldn't find any problem. The hum is not very intrusive.

On the FM range all channels tune perfectly, except that one I listen to most - BBC Radio 3. I'm making arrangements to get a better aerial. But it is strange because it tuned perfectly to that channel before it went for a service.

At any rate, I'm very pleased that it's working at all; I'd like to thank you again for your help as I don't think I would have had the nerve to go to the engineer without your schematic and comments. :)