My Grundig Majestic stereo console w/ turntable (150S) sounds just fine at first, whether it's the FM radio or Turntable. But then after 10-15 minutes or so the sound starts going bad. It gets more and more garbled and less clear. The only thing I see while looking at the tubes is it seems to start happening right when one particular tube gets glowing red, red hot. Any ideas? Thanks much.

You should check all of the condensers in the audio section. The ones that go from the 1st audio tubes to the output tubes are probably causing the trouble. However, others that don't cause plates to glow red can cause trouble, too. Your condensers are probably leaky. In order to test a condenser, you must remove it from the amplifier. Connect it to your multi-meter with the meter set to its most sensitive setting (X10,000, or the setting that deflects the needle with your fingers touching the leads). Without touching the meter leads or the condenser leads (your fingers will throw off your reading), connect the meter to the condenser in question. For values over .001 MFD, the needle will swing up slightly (more for higher values) and then fall back down to infinity. For values smaller than .001 MFD, needle deflection might not be visible. Whatever the case may be, if the needle moves up, it must fall back to EXACTLY where it started. If it lingers above the starting point by even the thickness of a hair (millions of ohms), the condenser has unacceptable leakage as far as audio and radio circuits are concerned (it might work okay in a power supply, but might fail in a bigger way later on). Even with condensers smaller than .001 MFD, if they have leakage, the needle will move upward and stay up. Replace all leaky condensers. Tube circuits, especially audio amplifiers, which must pass low frequencies and have high gain, have very high impedance qualities about them. Slight leakage that doesn't even seem like it'd cause trouble will throw off the grid bias enough to cause distortion (cause the tube to work out of its linear area of function), and will cause the tube to conduct excessively. Remember that a less negative, or even worse, positive, grid will make a tube conduct more. When the grid swings positive, it also starts conducting its own current, which is what puts distortion into the audio. The tube will no longer work as a linear valve. Output fluctuation will not match input fluctuation. The heavier current flow will also cause plates to glow red.

Now, I explained the above for your knowledge. You don't necessarily have to test all of the condensers. You can just replace them and be done with it. I strongly recommend that you test each one, though, as a learning experience. You can then find out just which ones were causing the trouble, and why. Then, as a safety precaution, replace all other paper condensers in the radio, including those in the radio (RF) section. You'll have improved performance. Be careful with values. Try to stay close to the originals, especially in the RF section. You do not need to replace ceramic disc or mica condensers unless they actually test bad. I recommend that you test these first, before replacing them, because they don't often fail. It is best, in the case of these condensers, to leave the originals in if at all possible.

Thomas

Thanks, Thomas!
Ok, so I need a multi-meter. Obviously, I'm new to this so I have to buy one and I see on Amazon the prices ranging from 10 bucks to 150.00. Is one that costs 20-30 bucks, ok? I'm looking forward to working on this and getting it working great.

:You should check all of the condensers in the audio section. The ones that go from the 1st audio tubes to the output tubes are probably causing the trouble. However, others that don't cause plates to glow red can cause trouble, too. Your condensers are probably leaky. In order to test a condenser, you must remove it from the amplifier. Connect it to your multi-meter with the meter set to its most sensitive setting (X10,000, or the setting that deflects the needle with your fingers touching the leads). Without touching the meter leads or the condenser leads (your fingers will throw off your reading), connect the meter to the condenser in question. For values over .001 MFD, the needle will swing up slightly (more for higher values) and then fall back down to infinity. For values smaller than .001 MFD, needle deflection might not be visible. Whatever the case may be, if the needle moves up, it must fall back to EXACTLY where it started. If it lingers above the starting point by even the thickness of a hair (millions of ohms), the condenser has unacceptable leakage as far as audio and radio circuits are concerned (it might work okay in a power supply, but might fail in a bigger way later on). Even with condensers smaller than .001 MFD, if they have leakage, the needle will move upward and stay up. Replace all leaky condensers. Tube circuits, especially audio amplifiers, which must pass low frequencies and have high gain, have very high impedance qualities about them. Slight leakage that doesn't even seem like it'd cause trouble will throw off the grid bias enough to cause distortion (cause the tube to work out of its linear area of function), and will cause the tube to conduct excessively. Remember that a less negative, or even worse, positive, grid will make a tube conduct more. When the grid swings positive, it also starts conducting its own current, which is what puts distortion into the audio. The tube will no longer work as a linear valve. Output fluctuation will not match input fluctuation. The heavier current flow will also cause plates to glow red.
:
:Now, I explained the above for your knowledge. You don't necessarily have to test all of the condensers. You can just replace them and be done with it. I strongly recommend that you test each one, though, as a learning experience. You can then find out just which ones were causing the trouble, and why. Then, as a safety precaution, replace all other paper condensers in the radio, including those in the radio (RF) section. You'll have improved performance. Be careful with values. Try to stay close to the originals, especially in the RF section. You do not need to replace ceramic disc or mica condensers unless they actually test bad. I recommend that you test these first, before replacing them, because they don't often fail. It is best, in the case of these condensers, to leave the originals in if at all possible.
:
:Thomas

Go to Radio Shack and buy their $15 to $20 model. It's very small and works quite well. Typically the meters are 20,000 ohms per volt, which is fine for most electrical work. If you want to get picky about grid bias, a vacuum tube volt meter (in working condition) is a must. Typically, though, if you have good tubes, leak-free condensers, and good resistors, grid bias shouldn't be a problem. Someday I'd like to own a VTVM. They're available on eBay for cheap. The trick is getting them working accurately. I may go down that route someday. I currently own a Simpson 260. A friend gave it to me because a resistor fried. They are extremely accurate meters, and are fairly easy to come by (eBay for instance). You can buy a brand new one that looks just like the ones from the 1950s, but a new one costs several hundred dollars. I think that a Radio Shack model is ideal. It's cheap and works almost as well as a Simpson. It also isn't made out of bakelite, so it won't break if you drop it. Both are likely to dislodge the meter movement if dropped, so you are better off breaking a Radio Shack model than a Simpson. I do like my Simpson, though. It's nice. I just have to be extra careful with it because it's so fragile.

If you ever do buy an old meter and the movement isn't always accurate, the movement bearings may need fine adjustment. This is touchy, and you have to know which screw and nut to turn, or you'll throw off spring tension. You can also make this correction for a new meter if you drop it and the needle suddenly gets hung up all the time. However, you may also have a bent or tangled hair spring. This isn't an easy fix unless you're very careful and know what you're doing. All in all, again, the Radio Shack meter is your best option. It's cheap, and can be replaced easily.

Thomas

:Go to Radio Shack and buy their $15 to $20 model. It's very small and works quite well. Typically the meters are 20,000 ohms per volt, which is fine for most electrical work. If you want to get picky about grid bias, a vacuum tube volt meter (in working condition) is a must. Typically, though, if you have good tubes, leak-free condensers, and good resistors, grid bias shouldn't be a problem. Someday I'd like to own a VTVM. They're available on eBay for cheap. The trick is getting them working accurately. I may go down that route someday. I currently own a Simpson 260. A friend gave it to me because a resistor fried. They are extremely accurate meters, and are fairly easy to come by (eBay for instance). You can buy a brand new one that looks just like the ones from the 1950s, but a new one costs several hundred dollars. I think that a Radio Shack model is ideal. It's cheap and works almost as well as a Simpson. It also isn't made out of bakelite, so it won't break if you drop it. Both are likely to dislodge the meter movement if dropped, so you are better off breaking a Radio Shack model than a Simpson. I do like my Simpson, though. It's nice. I just have to be extra careful with it because it's so fragile.
:
:If you ever do buy an old meter and the movement isn't always accurate, the movement bearings may need fine adjustment. This is touchy, and you have to know which screw and nut to turn, or you'll throw off spring tension. You can also make this correction for a new meter if you drop it and the needle suddenly gets hung up all the time. However, you may also have a bent or tangled hair spring. This isn't an easy fix unless you're very careful and know what you're doing. All in all, again, the Radio Shack meter is your best option. It's cheap, and can be replaced easily.
:
:Thomas

:My Grundig Majestic stereo console w/ turntable (150S) sounds just fine at first, whether it's the FM radio or Turntable. But then after 10-15 minutes or so the sound starts going bad. It gets more and more garbled and less clear. The only thing I see while looking at the tubes is it seems to start happening right when one particular tube gets glowing red, red hot. Any ideas? Thanks much.

Hi I have a new grundig 5299. The same thing happened to me. It sounded ok at first. One of my ell80 tube plates would glow red. You need to change all of your wax/paper caps inside. Also change your elecrolytics. I am in the process of changing my paper caps, and none of them have the right capacitance readings when checked on my fluke capacitance scale. I bet one or more paper caps are bad going to that tube.

Didn't I kind of say that already?

:Didn't I kind of say that already?

Yes you did, kind of. I just wanted him to know that someone else with the same German make had the exact same problem. And What I am doing to rectify the problem. No need to be a smart ***

Thanks, guys. I really appreciated the responses. I'm feeling more confident I can get this sounding great.