Tube rectifier input capacitance

[regal]

I made a mistake and ran a tube rectifier with a max 60uF spec into a PS with a 150uF input cap. Ran for about 8 hrs before I thought of it, the sound was a little harsh on the bass. Should this be cured by lowerering the cap? Could I have damaged the rectifier tube?

 

[radiostar]

Which rectifier tube do you have?

 

[Sheldon]

The input cap specification assumes a particular value for the resistance of the transformer and any added series resistance. So, without values, it's not possible to know if you've exceeded the rating. But if it's still working, you probably haven't done much damage - yet.

Sheldon

 

[analog_sa]

Could I have damaged the rectifier tube?

Not very likely. QuickSilver were running parallel GZ34 into 330uF for the lifetime of their amps, so 8hrs seems quite safe. Not something i would recommend though.

 

[bigwill]

Don't sweat it, valves aren't wimps

 

[tomchr]

Too high cap usually results in arcing at turn-on due to the inrush current needed to fill the cap. If you didn't have any fireworks in the rectifier, I'd say it's probably fine.

~Tom

 

[regal]

Not very likely. QuickSilver were running parallel GZ34 into 330uF for the lifetime of their amps, so 8hrs seems quite safe. Not something i would recommend though.

This was actually a GZ34 as well, I ordered a 60 uf Can to replace the 150uF electrolytic to be on th safe side.

 

[Arnulf]

You could also add a choke, NTC or fixed resistor ahead of existing capacitor ...

 

[barretter]

Thermistor OK, resistor OK, but if you make it a choke input supply, the output voltage will drop dramatically.

 

[regal]

I think I'm going to add a 60uF cap + 100 ohm resistor then attach to the 150uf PS. PSUD shows this will reduce the ripple 75% and I only lose a few volts.

 

[Sheldon]

I think I'm going to add a 60uF cap + 100 ohm resistor then attach to the 150uf PS. PSUD shows this will reduce the ripple 75% and I only lose a few volts.

If you do that, and I understand you properly, you are adding some series resistance, and some input capacitance. You may be making matters worse. As I mentioned originally, you can't model this supply accurately without knowing your transformer values. You have to measure the primary resistance, secondary resistance, and unloaded voltage over the primary and secondary.

Once you do this you can model accurately. With your accurate model, check the current over your rectifier. If you are using an indirectly heated rectifier, select "soft start" in the psud options. If it exceeds the rating, increase the series resistance or use a smaller cap. You may get away with it if it only exceeds the rating by a little, for a few cycles.

Sheldon

 

[regal]

Thanks for the tips, I wasn't using soft start.

I found that adding a small resistor in series from the rectifier tube to the input cap slowed down the inrush current enough to pass the PSDU test. After I installed it I swear the amp sounded smoother wrt bass hits, may have been some arcing going on on bass drum hits before I added the resistor.