After many months of use I noticed when listening at higher volumes the sound was a little crunchy. The next time I went to play I decided to pull the cover and see if anything was obvious. I noticed c6 was on its way out-brown ooze had begun to collect at the top, After I pulled that cap I found resistor R6 had been running way too hot. I had a Mills 12 in there and it got so hot as to bake the pads. When I measured it cold it was still in spec.
I had a 5 watt Vishay 10K resistor I wired in using the leads of R7 and R5.
When I first built this amp I was padding down the HV center tap by adding a 100 ohm power resistor. I have since been running without the resistor and find the 300-310 volts seem to give better sound, or at least more punch.
I am using a XPWR093 edcor transformer.
I am a little gun shy and have been at this all day. I started back from step 1 doing checkouts. The problem is with a rectifier in I have 2.5 volts to the heaters of the 45's and checking the voltage at r30 I turn it off as I start to see volts over 450.
I have thermistors in the amp so I can watch the climb.
I know when the 45's get installed and bias current is aplied the voltage will drop. Any word of wisdom from the good folk here would be appreciated.
Walt
I had a 5 watt Vishay 10K resistor I wired in using the leads of R7 and R5.
When I first built this amp I was padding down the HV center tap by adding a 100 ohm power resistor. I have since been running without the resistor and find the 300-310 volts seem to give better sound, or at least more punch.
I am using a XPWR093 edcor transformer.
I am a little gun shy and have been at this all day. I started back from step 1 doing checkouts. The problem is with a rectifier in I have 2.5 volts to the heaters of the 45's and checking the voltage at r30 I turn it off as I start to see volts over 450.
I have thermistors in the amp so I can watch the climb.
I know when the 45's get installed and bias current is aplied the voltage will drop. Any word of wisdom from the good folk here would be appreciated.
Walt
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My XPWR093 edcor transformer with no tubes installed is measuring 307 volts and this is with 100 ohms added to the center tap. The spec for the transformer is 250-0-250 and previous tests indicated 265 or therabouts. I am working on memory here so you know how that goes.
Should the transformer be suspected? I checked last night and I shut the amp down after voltage reached 450 volts.
Should the transformer be suspected? I checked last night and I shut the amp down after voltage reached 450 volts.
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