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In Reply to: Re: 5AR4 tube does not light up posted by Tre' on February 27, 2007 at 08:48:03:
Appreciate your quick response. I am not really a technical guy and would not want to mess around with high voltage! Where do I poke my voltmeter to check the transformer filament winding? I see two pairs of wire-green and orange- coming from the power transformer to the tube base and the solder on the tube base appears to be okay.
Follow Ups:
With the 5ar4 out of the socket put an AC volts meter between pins 2 and 8 counting counter clockwise from the keyway, looking at the top of the socket. When you turn the amp on there will be no high DC voltage. There will be high AC voltage between pins 4 and 6. Stay away from those pins.You should have 5vac the moment you switch on the power. Be careful. Never touch anything with both hands. Put one hand in your pocket.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Okay just poke the volt meter into pin2 and 8 and it reads 5+ volts. Does this means the trans are okay? Thanks.
Yes.With the amp turned off and unplugged from the wall , take a 10watt 1K ohm resistor and a clip lead, connect one end of the clip lead to a ground point on the amplifier chassis and connect the other end of the clip lead to one end of the resistor. With one hand in your pocket, use the the other end of the 1K resistor to "short out" the caps in the amplifier to ground. Touch each cap connection to discharge them. Holding the resistor lead to each connection for 30 seconds. The resistor might get hot. Be careful.
Now that the amp is safe you need to look very close at the solder connections to pin 2 and 8 on the 5ar4 tube socket. If those solder connections look good then you had two bad tubes. Get a new 5ar4.
You should check your old tubes. Put your ohm meter between pin 2 and 8 on the tube itself. For a tube that has good filaments you should get a very low reading. Less than one ohm. If your tubes have bad filaments the reading will be very high. An open circuit.
If your old tubes filaments check OK and the solder connections on the tube sockets look good you might have to tighten the tube socket connectors. This is easy. Take a close look at the connectors down inside the tube socket's holes where the tube pins go. Use a small tool to carefully bend them closer together.
Good luck.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Checked pin 2 and 8 for both tubes and reading were around 0.5ohm. Reheat the joint on pin 2 and 8 and tube socket were all tightened up. Still no luck. The 5ar4 still look and feel lifeless.
I don't have an answer for you. Sorry. If I had that thing on my work bench I would find the problem. Where do you live?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
If you have no experience with high voltage, take this to a technician. This will be easy to diagnose and either cheap or expensive (no in-between) to repair.It could be something as simple as a loose tube socket, which takes about three seconds to fix (just slightly tighten the thing sthat hold the tube pins (whatever you call them). It could also be a cold solder joint (5 minutes) or it could be a bad power transformer (expensive).
It is unlikely that two tubes in a row had open heaters.
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