Well it started with a buzz, changed the speaker and it's still there. Held the handle of my screw driver against the 6v6 and it stopped. I noticed the tube vibrated against the handle. Then I seen smoke, melted a small amount of my handle, no big deal. Then I noticed a faint red streak and the 470ohm cathode resistor turning brown. Changed it to a 2 watt cc and the cap along with it. Still have the red streak going down faintly almost like the filament is glowing threw the plate. Voltage coming out of the pt 333v, pin 8 on the 5y3 414, pin 3 on the 6v6 392.
Pt and ot are classic tone. Switched the ot primary to the 5k instead of 8k and nothing changed.
Any help would be appreciated.
5f2a problems
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stretch2011
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stretch2011
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Re: 5f2a problems
Using webers calculator I was running 15watts on the 6v6, replaced the cathode resistor with a 600ohm, raised the plate to 401 and the cathode to 24v. Put the numbers back in the calculator and it brought it to 14watts.
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Stevem
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Re: 5f2a problems
This amp should run the 8k load and it would be a real good move to add a 470 ohm or so screen resistor to the output stage as that is a major flaw in these cheap student amps of yore!
At 14 watts you had better be running a JJ brand output tube or your gonna burn thru them darn fast, remember in a class A stage the tube is dumping that full 14 watts thru it until you play and only then does it transfer some of that wattage to the speaker!
If you hook up a meter set for AC volts across the speaker with the amp at idle what do you read?
At 14 watts you had better be running a JJ brand output tube or your gonna burn thru them darn fast, remember in a class A stage the tube is dumping that full 14 watts thru it until you play and only then does it transfer some of that wattage to the speaker!
If you hook up a meter set for AC volts across the speaker with the amp at idle what do you read?
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Not screaming like the passengers in his car!
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stretch2011
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Re: 5f2a problems
It reads 0 well it wobbles between .000 and .001.
Forgive me for the green question put where exactly should I put that 470ohm resistor?
Also thinking about bumping the cathode resistor up to 680ohms to get it closer to 13watts.
My friend on here suggested putting in a 5r4 to lower the voltage. Also thinking about doing that.
Forgive me for the green question put where exactly should I put that 470ohm resistor?
Also thinking about bumping the cathode resistor up to 680ohms to get it closer to 13watts.
My friend on here suggested putting in a 5r4 to lower the voltage. Also thinking about doing that.
Re: 5f2a problems
Using a 5ar4 will not lower the voltage, but using a Ruby 5Y3 will drop it like a new old stock will. These are great 5y3's.
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stretch2011
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Re: 5f2a problems
I know a 5ar4 wouldn't but a 5r4 would some. I think that's what I'm going to do. I've fiddled with the cathode resistor and it seems like it wants to stay at 14watts dissipation.
Like always I appreciate everyone's advice.
Like always I appreciate everyone's advice.
Re: 5f2a problems
Or 5v4GA. Great tube.
Re: 5f2a problems
Put it right on the pin for the screen, leads as short as you can make them. If space is tight, make it stand upright.stretch2011 wrote:... where exactly should I put that 470ohm resistor?