Hi everyone,
I am working on the recap of an Eico ST 70 tube amplifier. The amp is in working order. It sounds good to my taste, even there is a slight 60hz and 120hz noise. That's why I have checked through the power supply section, filter caps et cetera. I measured the DC voltage at Pin #8 of the Rectifier tube GZ34. The result is approximately 460 VDC. According to the schematics, it should be only 440 VDC. Others points in the power section also checked, and the result was also approximately 20 VDC higher than stated on the schematics.
Rectifier tube changed, speakers connected or not, the voltmeter always reads 460 VDC. The power transformer seems to be in good working order, because i turn it on for a few hours without problem, no excessive heat.
Could you please help me to identify the cause of this problem ? I will try to attach later the schematics. The original file is too large to upload on this forum.
Thank you for your help !
Hughie
I am working on the recap of an Eico ST 70 tube amplifier. The amp is in working order. It sounds good to my taste, even there is a slight 60hz and 120hz noise. That's why I have checked through the power supply section, filter caps et cetera. I measured the DC voltage at Pin #8 of the Rectifier tube GZ34. The result is approximately 460 VDC. According to the schematics, it should be only 440 VDC. Others points in the power section also checked, and the result was also approximately 20 VDC higher than stated on the schematics.
Rectifier tube changed, speakers connected or not, the voltmeter always reads 460 VDC. The power transformer seems to be in good working order, because i turn it on for a few hours without problem, no excessive heat.
Could you please help me to identify the cause of this problem ? I will try to attach later the schematics. The original file is too large to upload on this forum.
Thank you for your help !
Hughie