Hi everyone,
I finally received the transistor from Audio Research. I have to say that their customer service leaves a lot to be desired. After installation it it seems that my voltage problems are cured. 450 volts going into the transistor 250 volts coming out and no smoking resistors or blown fuses. I am getting a signal in the audio section. However I am still getting a hum from both speakers. Played around with the tubes a little and if I pull either V10 or V5 the hum is greatly diminished and barely audible. Doesn't matter which one. Again I am baffled and unsure of how to proceed. Any help would be greatly appreciated.
Thanks,
WILD1
I finally received the transistor from Audio Research. I have to say that their customer service leaves a lot to be desired. After installation it it seems that my voltage problems are cured. 450 volts going into the transistor 250 volts coming out and no smoking resistors or blown fuses. I am getting a signal in the audio section. However I am still getting a hum from both speakers. Played around with the tubes a little and if I pull either V10 or V5 the hum is greatly diminished and barely audible. Doesn't matter which one. Again I am baffled and unsure of how to proceed. Any help would be greatly appreciated.
Thanks,
WILD1
Hmmmmmmmmmmmmmmmmmmmmm...
Both channels?
50/60 Hz or 100/150Hz?
Variable or constant with volume control setting?
Same with inputs open or shorted?
Both channels?
50/60 Hz or 100/150Hz?
Variable or constant with volume control setting?
Same with inputs open or shorted?
Well I had a reply Sy hit submit and lost the whole damn thing. Lets try it again.
Yes the hum and music are heard on both channels. As far as the frequency I am a little unsure what you are asking. Duh. If you mean the power source it is 110 volt 60 Hz. If you mean the hum I do not have a scope to look at it. I could probably get one if necessary. I would say that the volume control is not effecting the hum. There seems to be a lot of scratchiness to the volume control which I had not noticed before. There is a switch which changes the output signal from 30 db to 12 db. This definitely effects the hum. The hum is there whether there is a source hooked to the input or not.
Yes the hum and music are heard on both channels. As far as the frequency I am a little unsure what you are asking. Duh. If you mean the power source it is 110 volt 60 Hz. If you mean the hum I do not have a scope to look at it. I could probably get one if necessary. I would say that the volume control is not effecting the hum. There seems to be a lot of scratchiness to the volume control which I had not noticed before. There is a switch which changes the output signal from 30 db to 12 db. This definitely effects the hum. The hum is there whether there is a source hooked to the input or not.
OK, so we know that at least one stage is pulling current out of the wiper of the volume control, which the new scratchiness is a screamin' indication. That should be a strong clue where to look, and a clue that the regulator pass transistor didn't jump, it was pushed.
You also know that the hum comes from a stage before that gain control.
You can generate 60 and 120Hz tones easily with your computer so that you can match the hum to the frequency- it's an important diagnostic. There's a lot of online apps for tone generation, and if your computer speakers are too dinky for 60Hz, you can use headphones.
Sy,
Was checking voltages to those tubes and I am only getting 208 volts from the transistor I replaced . I went back and checked at the transistor and I am only getting 208 volts from the source [the input is the drain] and gate leads. Could of sworn I was getting 250 volts yesterday after installing it which is still not the 275 volts I should be getting. Could this make a difference?
Was checking voltages to those tubes and I am only getting 208 volts from the transistor I replaced . I went back and checked at the transistor and I am only getting 208 volts from the source [the input is the drain] and gate leads. Could of sworn I was getting 250 volts yesterday after installing it which is still not the 275 volts I should be getting. Could this make a difference?
No that isn't it . I guess I should of stated that at the drain [input] of the transistor I am getting 457 volts. That is a little high it should be 410 volts.
Hello Sy,
I downloaded an app for tone generation. The hum is definitely a low frequency. Lower than 50-60 Hz. I am a little confused with your statement of one stage pulling current out of the wiper of the volume control and that the transistor didn't jump it was pushed. Could you explain these two comments?
I downloaded an app for tone generation. The hum is definitely a low frequency. Lower than 50-60 Hz. I am a little confused with your statement of one stage pulling current out of the wiper of the volume control and that the transistor didn't jump it was pushed. Could you explain these two comments?
Good morning,
Well I woke up thinking about the discrepancy in voltage readings from when I replaced the transistor and yesterday. 208 volts versus 250 volts. Then I remembered that the first measurement was done with tubes outs so I pulled the tubes out and checked it. Lo and behold 250 volts [still not the 275 volts it should be]. What does this mean? I haven't a clue. Could this low voltage to the plates cause the hum? Again I haven't a clue. With my limited knowledge it does seem to me that the amp is struggling to regulate the plate voltage. Which makes me think that the op-amp UP OP175 might be damaged. I replaced 10 of these on a set of ARC M100s it is not fun. This one is tucked underneath the volume control. I say lets take a vote. All those in favor of pulling it say aye. All those against pulling it say nay. Seriously though I would appreciate some opinions on whether I am barking up the wrong tree.
Well I woke up thinking about the discrepancy in voltage readings from when I replaced the transistor and yesterday. 208 volts versus 250 volts. Then I remembered that the first measurement was done with tubes outs so I pulled the tubes out and checked it. Lo and behold 250 volts [still not the 275 volts it should be]. What does this mean? I haven't a clue. Could this low voltage to the plates cause the hum? Again I haven't a clue. With my limited knowledge it does seem to me that the amp is struggling to regulate the plate voltage. Which makes me think that the op-amp UP OP175 might be damaged. I replaced 10 of these on a set of ARC M100s it is not fun. This one is tucked underneath the volume control. I say lets take a vote. All those in favor of pulling it say aye. All those against pulling it say nay. Seriously though I would appreciate some opinions on whether I am barking up the wrong tree.
You are measuring the DC voltage of the B+ at 250volts. Switch your meter to AC and see what kind of ripple you have there.
Now this is after the transistor tubes out. Measuring AC voltage my meter kind of bounces around from 1.6 to 3.5 volts. Thing is as far as DC voltage I cannot really get a constant voltage. Right now with tubes out I am getting 240.6 volts. As I install the tubes the voltage drops down to the 208 volts.
Yup op-amp or one of those little zeners cooked. Look up the zener voltage using the part number and see what they measure. Example ZD1 is 1N4740A which is a 10 volt zener.
I had an op-amp left over as well as a machined socket from the rebuild on the ARC M100s. Called Mouser and talked to one of their Techs and he assured me that it could replace the op-amp in the LS5. After replacing it there was no change. I am not into replacing parts in this power supply circuit until I finally hit on the problem. I would really rather narrow down the problem first. There are quite a few zenyrs there and with my limited understanding of op-amps I do not really have a clue as to their purpose. If anyone can kind of clue me in about their purpose or steer me to the one that might be causing this problem it would be greatly appreciated. Or if someone feels that the problem is somewhere else I am open to suggestions. Meanwhile I think I will order the correct op-amp.
Thanx,
WILD1
Thanx,
WILD1
Hi.My friend has a problem on LS5 MK3.He says there are 3leg to220 case item which connected in the middle of output tubes and ground and they are marked green and white.We think it is for limiting current.Anyone knows which part are they? They contacted Audio research and they sent them to92 transistors which does not work well there.
Has anyone met same problem?
Has anyone met same problem?
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