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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment. |
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20th Nov 2007, 8:41 pm | #1 |
Retired Dormant Member
Join Date: Nov 2005
Location: Leicestershire
Posts: 20
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FT-102 final compartment
I've been trying to decide how I can check whether the 6146B's are serviceable. This is prompted by the rig going crackle, fizz and leaving me with approximately half of the expected output power.
I've tried all three on an avo vcm MK4 using the data given in the valve data manual (fifteenth edition, 1962) for a 6146. Unfortunately, 6146B isn't listed. Maybe data is listed in a later edition ? http://www.greensgadgets.com/images/6146data.gif The valves are marked Sylvania 6146B/8298A. Under the tabulated conditions I get the following approximate results: Valve 1: Ia=92mA, ma/V = 6 Valve 2: Ia=80mA, ma/V = 5 Valve 3: Ia=76mA, ma/V = 5 From these results, should I consider them to be sufficiently closely matched ? I suspect that these tests are probably of little value because in the transmitter the valves are subjected to a much greater anode volts ? Whilst investigating the problem, I noticed that if I gently tapped the rear panel near where the pb-2354 pcb is mounted, I could make the output power vary as indicated on an external power meter. So I removed the board for inspection. It doesn't show in the photo, but the lower side of the plastic case relay adjacent to the lettering RL01 appeared to be slightly melted or deformed. So I've now replaced the relay with an RS part number 369-472 just to be safe. I also found that the 'Lamp Fuse' has at some time been replaced with the wire and solder blob shown at the top-right of the photo ! I believe the original part looked just like a wire-ended panel bulb, can a standard bulb of suitable rating be fitted, or are original spares still available ? http://www.greensgadgets.com/images/pb2354.jpg Regards Ian |
20th Nov 2007, 10:11 pm | #2 |
Dekatron
Join Date: Feb 2005
Location: St.Ippolyts, Hitchin, Hertfordshire QRA IO91UW
Posts: 3,517
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Re: FT-102 final compartment
Hi Ian,
Yep, thats one of the many iffy relays lurking in an FT102! Use the set as a valve tester - measure voltages around the valve base - cathode, screen, and if you have the equipment, anode volts on each valve. You may well have a capacitor gone down, or one of the screen supplies may be down. As for the fues on the ACo board, I wouldnt really bother! Cheers Sean
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