10-29-2023, 06:25 AM
Hello everyone, Some progress has been made with this set but perhaps not with the musings which follow.
I mentioned , I think , that it does actually go - only with some distortion and the volume is down.Where is the distortion and low volume ? Which side of the volume control? Well, the probe on the Eico Signal Tracer placed on the top of the volume control delivers a big fat distortion free (relatively !) signal to the tracer speaker so I'm picking the problem lies with the transistor audio amp section.There be dragons for me!The power transistor is screwed to a cast metal section of the chassis (it gets remarkably warm -that part of the chassis acting as a heat sink )with two screws with a peculiar top - not Philips ,square or normal or any of the other "tamper proof" screw heads we get nowadays but with a screw I have read about in ads in "Radiocraft" whose chief merit seems to have been speed of assembly. The slot in the head is like a circle with two little opposite facing arcs cut out. No doubt someone will recall the trade name for these screws.
I do not have a screwdriver that fits this head,nor can I easily fabricate one. But I'm getting ahead of myself here. It may be that this transistor is fine and will not need removal.
So - back to getting the board out. The board sits in the chassis like a file in a filing cabinet drawer , the front of the " drawer " being the dial and push buttons. The board is located in four dimples in the bottom of the "drawer". At the top, as mentioned it is held in by a u-shaped bar , bolted on one side and soldered on the other . Bolt removed and iron and soldering wick applied and two tabs bent down and the bar which has held this board captive for 61 years is released.Does the board pop out ? No. The wires which connect the board to the other components are too short to allow the board to be lifted out.So a lot of cutting and tagging and pictures and notemaking will be required before the transistor section can be comfortably measured and assessed and hopefully repaired . It can be done but it will take time.
One gets the impression Mr Motorola might have got the actuaries in when designing this radio."Well,boys,how long will these 12 volt valves last in car radio service?Uh huh - that long eh? And the transistors?Not so sure but probably ...Hmmm. Okay, our pick then is the sets will outlast the car in normal service so there will be no servicing or warranty issues so yes, go ahead ,build the sets and it wont matter that the boards are barely seviceable."
Perhaps I've watched Madmen or Suits too much.
But here we are 61 years later wrestling with this set ,trying to get it to go properly , while surrounded by electronic devices of a capability and sophistication unimagined that long ago. Did bronze age men pick up stone age tools, re -sharpen them and run after woolly mammoths? And will the breakthrough for artificial intelligence have come when we discover a robot playing wistfully with a screwdriver inside a 1930s Zenith?
Time I went to bed!
I mentioned , I think , that it does actually go - only with some distortion and the volume is down.Where is the distortion and low volume ? Which side of the volume control? Well, the probe on the Eico Signal Tracer placed on the top of the volume control delivers a big fat distortion free (relatively !) signal to the tracer speaker so I'm picking the problem lies with the transistor audio amp section.There be dragons for me!The power transistor is screwed to a cast metal section of the chassis (it gets remarkably warm -that part of the chassis acting as a heat sink )with two screws with a peculiar top - not Philips ,square or normal or any of the other "tamper proof" screw heads we get nowadays but with a screw I have read about in ads in "Radiocraft" whose chief merit seems to have been speed of assembly. The slot in the head is like a circle with two little opposite facing arcs cut out. No doubt someone will recall the trade name for these screws.
I do not have a screwdriver that fits this head,nor can I easily fabricate one. But I'm getting ahead of myself here. It may be that this transistor is fine and will not need removal.
So - back to getting the board out. The board sits in the chassis like a file in a filing cabinet drawer , the front of the " drawer " being the dial and push buttons. The board is located in four dimples in the bottom of the "drawer". At the top, as mentioned it is held in by a u-shaped bar , bolted on one side and soldered on the other . Bolt removed and iron and soldering wick applied and two tabs bent down and the bar which has held this board captive for 61 years is released.Does the board pop out ? No. The wires which connect the board to the other components are too short to allow the board to be lifted out.So a lot of cutting and tagging and pictures and notemaking will be required before the transistor section can be comfortably measured and assessed and hopefully repaired . It can be done but it will take time.
One gets the impression Mr Motorola might have got the actuaries in when designing this radio."Well,boys,how long will these 12 volt valves last in car radio service?Uh huh - that long eh? And the transistors?Not so sure but probably ...Hmmm. Okay, our pick then is the sets will outlast the car in normal service so there will be no servicing or warranty issues so yes, go ahead ,build the sets and it wont matter that the boards are barely seviceable."
Perhaps I've watched Madmen or Suits too much.
But here we are 61 years later wrestling with this set ,trying to get it to go properly , while surrounded by electronic devices of a capability and sophistication unimagined that long ago. Did bronze age men pick up stone age tools, re -sharpen them and run after woolly mammoths? And will the breakthrough for artificial intelligence have come when we discover a robot playing wistfully with a screwdriver inside a 1930s Zenith?
Time I went to bed!
