Noisy Eros

[juanfz]

Hi:
I have been using my Eros for a long time, but suddenly there's a  Hmmm noise from the right channel and it increases as volume goes up.
I thought it could be a failure tube so I replaced all tubes, but the noise hasn't disappeared.
The amp is Ok. there isn't any noise when connected to other components or when the Eros is disconnected from it.
I have tried disconnecting the turntable from Eros but the noise is still.
What should I do to diagnose what's wrong with my Eros.
Regards,
Juan

 

[Paul Birkeland]

How are the DC voltages? 

 

[juanfz]

Hi Paul:
Thank you for your prompt answer.
I have measured the C4S board's DC voltages, the results are shown below.

                  Left                        Right
KReg        1.9 VDC                    0  VDC
bReg        98.6 VDC                99.8 VDC
OB          97.7 VDC                98.4 VDC
bA              0  VDC                    0  VDC
IA          224.5 VDC                220.9 VDC
OA        152.5 VDC                152.4 VDC

All LEDs are lit on each board.
Regards,
Juan

 

[Paul Birkeland]

Kreg being 0V on the right would tend to mean that the EF86 on that side is near death or the STP that feeds terminals 4/5 on that 9 pin socket isn't well connected.

If you swap the EF86s, do the voltages stay the same?

This seems tough to believe because your bReg and OB voltages are what we would want to see, suggesting that the EF86 is functional and the servo under its cathode is doing its job.

 

[juanfz]

Hi:
I swapped the EF86s tubes and the voltages are:

                  Left                        Right
KReg        1.7 VDC                    2.0  VDC
bReg        100.6 VDC                100.6 VDC
OB          99.4 VDC                98.9 VDC
bA              0  VDC                    0  VDC
IA          224.4 VDC                220.9 VDC
OA        152.2 VDC                151.4 VDC

I re-swapped the tubes to their initial positions and found similar DC voltages as the first measurement except for the Kreg voltages: Right Kreg 1.9 V  Left Kreg 1.6 V  .  I assume something was wrong during the first measurement.

 

[Paul Birkeland]

How about the DC voltage on the +6.3V pad on the power supply board? 

For something like this, the things I would look at would be loose hardware or loose solder joints primarily since your voltages are looking good.

 

[juanfz]

Hi:
DC voltage on the +6.4  pad on the power supply board is Ok. it's 6.4 V
I don't notice any loose hardware but I'm going to resolder most of the solder joints.