Need Advice: Old Airline/Valco Amp

[Jaurr]

About 6 months ago, I found a 1966 Airline (Montgomery Ward) 62-9032 amp at the Goodwill for $5.99. It is just a small 5 Watt amp with a simple circuit; similar to a late 50s/early 60s Fender Champ (5Y3 - 6V6 -12AX7). I have finally gotten around to fixing-it-up.

My father owned a TV/Radio sales/repair shop when I was growing-up (1960s). I worked in the store when I was still in elementary school, so I have some experience with electronic gear from that time period. However, it has been a long time, and I would appreciate advice from any electronics wizards on these boards.

I found a schematic for a Gretsch 6150 Compact (mid 1950s-1968). The circuit seems to be exactly the same as my Airline except that my Airline has a tone control/circuit and the Gretsch 6150 doesn't. I suspect my airline has the same circuit as the Gretsch 6151 Electromatic Standard (mid 1950s), but I can't find that schematic online (only the 6151 Compact Tremolo). Evidently, these amps were made by Valco.

One wire from the AC cord is soldered to the fuse; the other wire to the ON/OFF-volume control switch. The wires from the T 3036 transformer are soldered to the opposite terminals on the fuse and switch. There is a red wire with a white stripe running between the fuse and the 5Y3 plate. The ON/OFF pilot light is also soldered to terminals on the fuse and switch.

I am planning to replace the old AC cord with a three-prong cord due to safety concerns. I am wondering if I should just attach the green wire on the three-prong cord to a transformer bolt; solder the the black wire to the fuse and the white to the switch.

Or, should I attach the green wire (from the 3-prong cord) to one of the transformer bolts; the black wire to the fuse (same terminal as the current AC cord); and the white wire directly to a transformer wire (I will disconnect the transformer wire from the fuse). I will then run a wire between the fuse and the switch; leaving a transformer wire soldered to the other terminal on the switch. If I choose this option, I need to re-wire the pilot light switch which is soldered between terminals on the fuse and switch.

My other question concerns the filter capacitors. This amp has one of those capacitor cans. The values on the can are 10-450, 10-450, 20-450. This circuit was designed for 117 volt household current. The wall voltage in my place is running about 122 volts. Not a big difference, but I was wondering if I should up the capacitor values a bit to buffer the circuit from the slightly higher voltage. I might need to replace with higher values anyway due to availability issues. How high would you go (volts-mfd.)?

The capacitor in the tone circuit is .05mfd/400 volts. What would you recommend as a replacement?

I know this isn't brain surgery, but I like to be careful. I really like these little, 5-watt, tube amps since I just play at living room volumes.



http://www.notecannons.com/schematic...h6150_767w.jpg

[loudthud]

It looks like the wire that goes from the fuse to the 5Y3 socket connects to the 0.01uF ceramic cap, the other side of the cap goes to the chassis. The terminal on the 5Y3 socket is just used as tie point, it does not connect to the 5Y3. This is the so called "Death Cap". The cap and wire should be removed, you don't need it with a three wire line cord. Current safety standards connect the fuse and switch on the hot side of the line, the black wire in the line cord. The white or neutral wire form the liine cord should go straight to the transformer. The green wire from the line cord should attach to the chassis with it's own screw, nut and lock washer not used for any other purpose.

Edit: The switch being on the volume control will tend to inject hum into the audio. Keep the switch wires as far from the pot wires as you can. You may have to install shielded wires to the pot or install a separate switch to lower the hum.

[Jaurr]

Thanks, Loudthud. That is just the sort of advice I was looking for. You are right about the red wire and capacitor. One leg of the capacitor is soldered to a ground terminal on the metal mount of the 5Y3 socket. I was scratching my head looking at that red wire wondering why it came right off the fuse to the 5Y3. I didn't even notice the leg of the capacitor attached to chassis ground. I guess I didn't think this amp had a "death cap," since it lacks a ground switch. It was also right there in the schematic. I will remove the red wire and capacitor as you suggest.

You also gave me an idea when you suggested adding an on/off switch. Maybe I should remove that pilot light and put a toggle switch through that hole. I wonder if they make switches with built-in pilot lights. Or, maybe I can just find one with the printed words (ON -OFF). I will also change the volume pot and use a dedicated bolt for a crimped ring terminal on the green wire.

[tboy]

I guess I didn't think this amp had a "death cap," since it lacks a ground switch.

Two wire power cords didn't have polarized plugs when that amp was made; the "ground switch" was accomplished by pulling the plug out of the wall socket and re-inserting it the other way.

[Jaurr]

Two wire power cords didn't have polarized plugs when that amp was made; the "ground switch" was accomplished by pulling the plug out of the wall socket and re-inserting it the other way.

I grew-up in old houses (built 1900-1920s). No grounds on the wall sockets; threaded glass fuses (sometimes people would place pennies behind them if they didn't have a replacement handy); metal appliances and power tools without much insulation; old radios with a "hot chassis." I don't remember many problems. I guess we were lucky.

My dad received shocks at his TV store over the 30 years he was in business, but it was usually from high voltage and low current. One time he was knocked-out flat on his back, when he woke-up he went right back to work at what he was doing - like nothing happened. He always made sure he had insulation beneath his feet or seat; and kept one hand away from potential electrical paths. My older brother enjoyed chasing me around with big capacitors when I annoyed him - still don't know if they were charged or not.