Flip69
Active Member
I just finished a partial restoration of an HF-85. Coupling caps replaced with Russian PIOs. Multicap can replaced with new electrolyitics under the chassis. New RCA jacks. New tubes. New two-prong power cord. With regard to inputs, I kept the Aux A, Aux B, AM/FM, and Phono inputs. I kept the preamp out and tape/line out. I did not use the Mic and Tape inputs. I did not remove the Mic or Tape wires from the unit. I simply snipped them off of the old RCA jacks, covered the ends with electrical tape, and left them there. I checked a random sample of the carbon resistors and ceramic caps. They all tested within spec. So, I kept them. I did not do anything with the phono RIAA, e.g., I did not move it off the selector assembly, change any of the resistors or caps, etc. All I did was remove the phono signal and ground wires from the old RCA jacks and attach them to the new RCA jacks.
I tested the unit using a Dynaco ST-70 amp, an AR XA turntable, and an iPhone for testing the the two Aux inputs. The Aux A and Aux B sections are dead silent and sound great. I have not yet attached a tuner. However, the unit is silent when nothing is attached to the AM/FM inputs, the selector nob is set on the AM/FM settings, and the volume is turned up. The Mic and Tape sections are noisy (static) when nothing is attached, the selector nob is set on Mic or Tape, and the volume is turned up. Is this just the way it is because I am not using those sections? Would the noise go away if I removed the Mic and Tape wires and hardware from the selector nob?
I am getting a ground hum on the phono channel. I believe it is a ground hum because it goes away under certain circumstances. I attached an extra wire to the bridge between the two ground terminals on the phono RCA jacks to do some testing. If I have one hand on the unit, and move the end of the wire to the front corner of the unit near the selector switch, the hum goes away. The end of the wire does not even need to be touching the chassis. As soon as I take my hand off the unit, the hum returns. So, I appear to be serving as the ground in that scenario. I can also reduce the hum, if not make it go away entirely, by touching the wire to certain bolts on the chassis, but not all of the bolts. I do not have any grounding wire running between the HF-85 and the AR XA.
As previously noted, I am using the original ground wire for the phono jacks. I am not sure if i should run a new ground wire, run an extra ground wire to some other point on the chassis, or do something else. I have read a lot of threads about ground hum. I am new at this and still find the topic confusing. I read the words but do not necessarily grasp the concepts. I would appreciate your observations, suggestions, and advice.
I tested the unit using a Dynaco ST-70 amp, an AR XA turntable, and an iPhone for testing the the two Aux inputs. The Aux A and Aux B sections are dead silent and sound great. I have not yet attached a tuner. However, the unit is silent when nothing is attached to the AM/FM inputs, the selector nob is set on the AM/FM settings, and the volume is turned up. The Mic and Tape sections are noisy (static) when nothing is attached, the selector nob is set on Mic or Tape, and the volume is turned up. Is this just the way it is because I am not using those sections? Would the noise go away if I removed the Mic and Tape wires and hardware from the selector nob?
I am getting a ground hum on the phono channel. I believe it is a ground hum because it goes away under certain circumstances. I attached an extra wire to the bridge between the two ground terminals on the phono RCA jacks to do some testing. If I have one hand on the unit, and move the end of the wire to the front corner of the unit near the selector switch, the hum goes away. The end of the wire does not even need to be touching the chassis. As soon as I take my hand off the unit, the hum returns. So, I appear to be serving as the ground in that scenario. I can also reduce the hum, if not make it go away entirely, by touching the wire to certain bolts on the chassis, but not all of the bolts. I do not have any grounding wire running between the HF-85 and the AR XA.
As previously noted, I am using the original ground wire for the phono jacks. I am not sure if i should run a new ground wire, run an extra ground wire to some other point on the chassis, or do something else. I have read a lot of threads about ground hum. I am new at this and still find the topic confusing. I read the words but do not necessarily grasp the concepts. I would appreciate your observations, suggestions, and advice.
