5E3 V1 Voltages

[mayburyds]

Hi,


Need some advice again please!


Had a problem with the socket on V1 and a lose pin 6.


After replacing the faulty socket I measured the voltages on pin 1 & 6 and they read about 100vdc with all the controls at zero, if that makes any difference. After playing for about an hour I turned down the controls to zero and checked the voltages again and they were up to around 125vdc.


Is this normal or should they be static?


I do have a VRM kit installed and the amp sounds ok.


Any thoughts appreciated.


Cheers.

[Willabe]

VRM? 

[mayburyds]

Sorry, it's a VVR kit from Trinity amps for varying the b+ voltage.

Cheers.

[Paul1453]

When something doesn't seem right to me, I try to look at the circuit and components involved and try to figure out if things are operating within their parameters.

Pins 1 & 6 are your plates, and they are supplied voltage from the PS through the plate resistors.
Resistors can drift, but 25% change would be outside of specifications.
Resistors also tend to decrease in resistance when they get hot.
If your VVR hasn't increased 25% then I wouldn't expect the V1 plate voltages to increase 25%.

So, what's next?  Well the tube right?
If the tube was conducting more current when it was cold,
there would be a bigger V drop across the plate resistors,
and the plate voltages would be lower.

If when the tube warms up it starts conducting less current,
there would be less V drop across the plate R's and higher V on pins 1 & 6.
If there are voltage numbers on the schematic, are your voltages within +/- 20% of that?
If things sound good, and your numbers are within that 20% range then I wouldn't worry about it too much.

You could try to swap that tube and see if you get the same results.     

[mayburyds]

Thanks for the reply. I'll swap the tube tomorrow and check the voltages.

Cheers.

[HotBluePlates]

... After replacing the faulty socket I measured the voltages on pin 1 & 6 ... After playing for about an hour I turned down the controls to zero and checked the voltages again and they were ...

Does the amp sound good?

If so, it's probably fine. A 25v increase at that plate (if your plate load resistor is exactly 100kΩ) just means a reduction in tube current of 25v/100kΩ = 0.25mA. That could be normal tube drift, especially if these are new tubes.

[mayburyds]

Amp sounds fine and the tubes are about a year old.

I'll try another tube just to see if it makes a difference.

Thanks.

[mayburyds]

Hi,


Measured the voltages cold this morning and they read 100vdc. Left the amp cooking for an hour and remeasured the voltages which again read 100vdc.


But when I adjusted the VRM/VVR control down and then back to full the voltages went up to around 125vdc. I kept the DMM attached and the voltage gradually dropped back down to around 100vdc after about a minute or so.


So, I now understand why I get different voltages and I guess it's the amp settling down after the change in voltages due to the VRM/VVR adjustment.


Many thanks for the replies and help, much appreciated.


Cheers.

[Paul1453]

It is always good to learn the little intricacies of our amp's circuits!

Especially if we implement mods to the original design.