Bias question 20th Shiva

[Emg77]

This is my third Shiva and my Eurotubes bias probe will not catch a reading on these amps. Anyone know which pins I should meter to get a current ma reading?

Thanks!

 

[MetalHeadMike]

Interesting, I had a 20th Anny Shiva and used a Eurotubes probe that worked fine.

 

[scottosan]

This is my third Shiva and my Eurotubes bias probe will not catch a reading on these amps. Anyone know which pins I should meter to get a current ma reading?

Thanks!

Pin 8 is on an el34, 6l6, or kt88 is cathode. If your tubes have low current draw then perhaps you have too much bias voltage applied. It's zero through the entire sweep? Have you tried the previous tubes?

 

[steve_k]

This is my third Shiva and my Eurotubes bias probe will not catch a reading on these amps. Anyone know which pins I should meter to get a current ma reading?

Thanks!

Black to chassis ground
Red to pin 4.

 

[scottosan]

This is my third Shiva and my Eurotubes bias probe will not catch a reading on these amps. Anyone know which pins I should meter to get a current ma reading?

Thanks!

Black to chassis ground
Red to pin 4.

The OP is asking.about current draw (mA), not plate voltage (V). Additionally, plim 4 is the screens, which will yield lower voltage readings than the plates eading to a lower than accurate bias calculation using the typical calculation methods. Also, if you are going to use a multimeter instead of a problem, I suggest using the hook clamp probes I'm case you have shaky hands

 

[Emg77]

This is my third Shiva and my Eurotubes bias probe will not catch a reading on these amps. Anyone know which pins I should meter to get a current ma reading?

Thanks!

Pin 8 is on an el34, 6l6, or kt88 is cathode. If your tubes have low current draw then perhaps you have too much bias voltage applied. It's zero through the entire sweep? Have you tried the previous tubes?

Good morning. Thanks for the reply. I did as Steve K referenced in his reply. I grounded at the chassis and probed pin 4 . The reading was 48 mv on both tubes on the same pin. This is with the bias pot bottomed out. As am reading through your reply this is actually the plate voltage? So, really this is giving me 480 V ? Should I be probing pin 8 to get the ma reading? Here is a pic for reference. Thanks in advance!

 

[scottosan]

This is my third Shiva and my Eurotubes bias probe will not catch a reading on these amps. Anyone know which pins I should meter to get a current ma reading?

Thanks!

Pin 8 is on an el34, 6l6, or kt88 is cathode. If your tubes have low current draw then perhaps you have too much bias voltage applied. It's zero through the entire sweep? Have you tried the previous tubes?

Good morning. Thanks for the reply. I did as Steve K referenced in his reply. I grounded at the chassis and probed pin 4 . The reading was 48 mv on both tubes on the same pin. This is with the bias pot bottomed out. As am reading through your reply this is actually the plate voltage? So, really this is giving me 480 V ? Should I be probing pin 8 to get the ma reading? Here is a pic for reference. Thanks in advance!

Probing pin 8 with a multimeter alone is not effective unless you have 1 ohm resistor to measure across. That is what the bias prob is doing. A multimeter alone wont work. If your amp has the 1 ohm resistors between pin 8 and ground it would work. As for pin 4, there should be no change when adjusting the pot. pin 3 is the plates, not pin 4. Pin 4 is the screens and typically lower than pin 3 in most designs becuase you are measuring the voltage after the choke and 1k screen resistors vs pin 3 right of the HT/OT feed.


With the bias probe, are you sure the amp is off standby? I recall the older Shivas stanby is not traditional. B+ is applied but the standby switch liftsntje cathodes from ground. Just a different way to do standby. This can be confusing though because unlike other amps, you will get a played voltage reading even though the amp is on standby, but to current reading