The tubes do light up. Does that exclude any possible faults? I've checked the anode voltage of the ECC83 and it's alright (around 130V). I've tried measuring the other pins but those all gave a voltage of 0 (I only tried by touching the black cable of the multimeter to ground and the red cable to each pin).
How can I check the contacts in sockets?
How can I check the contacts in sockets?
Well, I am afraid I am with DF96 here. I'd suggest you get a bit of electronics experience first, before attempting to tackle this repair. Having the tubes light up doesn't really tell you anything, and it is likely that any fault may be hard to locate exactly.
Whenever I restore an old radio, it usually takes a while until I have located all the issues. Frequently it is a case of fixing one problem, only to have another raise its ugly head. You need to have a bit of experience with schematics and understanding how the equipment you attempt to fix is working, before you have a good chance of success. Randomly poking around is unlikely to get you anywhere, except possibly in the morgue.
Whenever I restore an old radio, it usually takes a while until I have located all the issues. Frequently it is a case of fixing one problem, only to have another raise its ugly head. You need to have a bit of experience with schematics and understanding how the equipment you attempt to fix is working, before you have a good chance of success. Randomly poking around is unlikely to get you anywhere, except possibly in the morgue.
I'm going to agree with the rest of the chorus... don't do much more until you read a bit and have some idea what all this stuff is. Like the difference between AC and DC for starters.
It's all online or in books.
I'm going to disagree on the tubes vs. caps being faulty percentage wise, but it is irrelevant to this OP's issues. It is sufficient to say that both frequently fail.
I'M GOING TO ASK AGAIN: WHAT ARE THE SYMPTOMS WITH THIS UNIT???
After posting and thinking about it, the problem could be as simple as an RCA plug not being plugged in... or the speakers not being connected, etc...
The one thing you could do, if you read the sticky on safety as suggested is to make voltage measurements and compare them to the typical operating conditions for the given tube as found in a tube manual. That will teach you something. If you don't slip and short stuff out, or to ground, or put ur fingers in it, there is no harm in it. It may reveal a bad operating condition...
_-_-bear
PS. you also need to learn how to solder and desolder...
It's all online or in books.
I'm going to disagree on the tubes vs. caps being faulty percentage wise, but it is irrelevant to this OP's issues. It is sufficient to say that both frequently fail.
I'M GOING TO ASK AGAIN: WHAT ARE THE SYMPTOMS WITH THIS UNIT???
After posting and thinking about it, the problem could be as simple as an RCA plug not being plugged in... or the speakers not being connected, etc...
The one thing you could do, if you read the sticky on safety as suggested is to make voltage measurements and compare them to the typical operating conditions for the given tube as found in a tube manual. That will teach you something. If you don't slip and short stuff out, or to ground, or put ur fingers in it, there is no harm in it. It may reveal a bad operating condition...
_-_-bear
PS. you also need to learn how to solder and desolder...
I have some basic knowledge to test some of the parts. I know the difference between AC and DC. And yes, I can solder and desolder.
Like I said:
I do get a slightly amplified sound (barely hearable) along with the buzz.
There are no RCA plugs or anything. This is a tube pre-amp inside a Hohner Cembalet. Here are some pics of my Cembalet:
As you can see, the original (mono) output was a long cable coming out of the unit with a DIN-plug (this is not from the original build, someone has messed with it before I bought it). I already replaced it with a jack output.
So far I've had the exact same symptoms on both the DIN and jack-plug, so the problem does not lie there.
Like I said:
I do get a slightly amplified sound (barely hearable) along with the buzz.
There are no RCA plugs or anything. This is a tube pre-amp inside a Hohner Cembalet. Here are some pics of my Cembalet:
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
As you can see, the original (mono) output was a long cable coming out of the unit with a DIN-plug (this is not from the original build, someone has messed with it before I bought it). I already replaced it with a jack output.
So far I've had the exact same symptoms on both the DIN and jack-plug, so the problem does not lie there.
Last edited:
Ok, buzz, low amplification.
You need to measure the B+ voltage and look at the voltage both as AC and DC. The DC should be about 250vdc +/- (the voltage can vary quite a bit, but somewhere below ~300v is likely). THEN you read the AC on the same voltage point. Ok?
You can find the B+ on the filter caps.
This will tell you IF you have excessive ripple. <---what is ripple?
Ripple is excessive AC voltage on a DC supply.
IF you have excessive AC voltage (ripple) THEN you probably have bad filter caps.
However, you can also get excess ripple if you are drawing WAY too much current. That can happen if there is a leaky coupling cap going to the grid of a tube, causing it to conduct way too much.
SO, IF you find this condition (you are likely to do so) then pull the tubes one by one and check the result... if the ripple drops then you have identified the section that is drawing too much current. Otherwise you replace or bypass the bad filter cap or filter cap section.
Now, as I suggested BEFORE go through the preamp section and measure the voltages on the PINS of the TUBES. Compare to the values shown in a tube manual. After you do this a few times, you'll see a trend, and a substantial difference between expected and measured values will be apparent. Report back if this happens.
The FIRST thing to check is if the GROUND on the "jack" whichever one it is is connected to the chassis. Measure it with an ohmeter. It should be ZERO.
Also be sure that the chassis of the preamp is also connected to the ground of the piano.
NOW, check to see that the WIRE from the piano GUTS that goes to the preamp is actually connected to the input of the preamp electrically. That means finding the solder point in the GUTS and the solder point in the preamp (it is usually connected with an RCA plug so the preamp can be removed for service) and checking the continuity with an ohmeter.
The other thing to try is to solder or clip lead a temporary jumper from the input point to ground - this sets the input to ZERO, if the hum stops then, you have a problem that is NOT in the preamp.
Do all this, and then you'll have something to work with. Ok then?
_-_-bear
PS. If you can't handle this, then you can't fix it yourself. Suggest you find someone locally with some electronics background. Consider a college, electronics repair shop, ham radio club, etc... as possible places to ask.
You need to measure the B+ voltage and look at the voltage both as AC and DC. The DC should be about 250vdc +/- (the voltage can vary quite a bit, but somewhere below ~300v is likely). THEN you read the AC on the same voltage point. Ok?
You can find the B+ on the filter caps.
This will tell you IF you have excessive ripple. <---what is ripple?
Ripple is excessive AC voltage on a DC supply.
IF you have excessive AC voltage (ripple) THEN you probably have bad filter caps.
However, you can also get excess ripple if you are drawing WAY too much current. That can happen if there is a leaky coupling cap going to the grid of a tube, causing it to conduct way too much.
SO, IF you find this condition (you are likely to do so) then pull the tubes one by one and check the result... if the ripple drops then you have identified the section that is drawing too much current. Otherwise you replace or bypass the bad filter cap or filter cap section.
Now, as I suggested BEFORE go through the preamp section and measure the voltages on the PINS of the TUBES. Compare to the values shown in a tube manual. After you do this a few times, you'll see a trend, and a substantial difference between expected and measured values will be apparent. Report back if this happens.
The FIRST thing to check is if the GROUND on the "jack" whichever one it is is connected to the chassis. Measure it with an ohmeter. It should be ZERO.
Also be sure that the chassis of the preamp is also connected to the ground of the piano.
NOW, check to see that the WIRE from the piano GUTS that goes to the preamp is actually connected to the input of the preamp electrically. That means finding the solder point in the GUTS and the solder point in the preamp (it is usually connected with an RCA plug so the preamp can be removed for service) and checking the continuity with an ohmeter.
The other thing to try is to solder or clip lead a temporary jumper from the input point to ground - this sets the input to ZERO, if the hum stops then, you have a problem that is NOT in the preamp.
Do all this, and then you'll have something to work with. Ok then?
_-_-bear
PS. If you can't handle this, then you can't fix it yourself. Suggest you find someone locally with some electronics background. Consider a college, electronics repair shop, ham radio club, etc... as possible places to ask.
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