Rectifier Tube Arcing - Has Rectifier Tube Quality Declined?

[Grantorino]

For those experienced - have you observed rectifier tubes arcing when powering up, at the moment the standby switch is flicked?
I have observed a 5AR4 rectifier consistently arc on startup. Two flashes, a second apart. The second arc sends a signal through the speaker. see the gif.

Perhaps I would not be otherwise concerned, but this amp previously suffered a failed rectifier tube. A modification was made to reduce stress on the rectifier. Swapping the C1 (47uF) and C2 (22uF) positions.

Does arcing inherently damage a tube?

-update- The rectifier tube had failed. The manufacturer recommends bypassing the use of the standby switch to avoid current spikes. They have also suggested that the quality of rectifier tubes has declined considerably in recent years.

Thank you.

[johnfromcyrene]

I put in a stand by switch and had arcing on mine. I had to remove the stand by switch and replace the tube. Not sure why this happens or how you prevent this.

[Lekky]

Not sure why this happens or how you prevent this.

It could definitely happen if the standby switch was wired between the rectifier tube and the reservoir cap. Putting the standby switch after the reservoir cap, or removing it completely, is a better solution with tube rectification.
Schematics and info on Valve Wizard's page about standby switching: https://valvewizard.co.uk/standby.html

[acheld]

If you post a schematic, we can give better advice.

Arcing is always a problem.  The question is -- is it the tube, the circuit design, or a fault in the circuit?

Since this is not the first time, there is a problem somewhere.

[Grantorino]

The Sovtek tube is toast. It was in place four weeks.

A newly fitted JJ rectifier tube does not arc.

 

Arcing is always a problem.  The question is -- is it the tube, the circuit design, or a fault in the circuit?

Since this is not the first time, there is a problem somewhere.

Thank you. I am inclined to agree.

[pdf64]

It's weird how people carry on using a standby switch even when with a moment's reflection, it would be clear that its use is causing significant problems.

[Grantorino]

It's weird how people carry on using a standby switch even when with a moment's reflection, it would be clear that its use is causing significant problems.

Thanks PDF - this is a salient point, as although the manual for the amplifier recommends the usual start-up procedure (1 minute warm-up in standby), having now spoken to the manufacturer, he recommends bypassing the standby switch altogether, leaving it always on.

[Grantorino]

Not sure why this happens or how you prevent this.

Putting the standby switch after the reservoir cap, or removing it completely, is a better solution with tube rectification.
Schematics and info on Valve Wizard's page about standby switching: https://valvewizard.co.uk/standby.html

Putting the standby switch after the reservoir cap will help prevent the current spike at switch-on, but will not prevent rectifier failure during operation. This would require changing the first filter cap to handle over 500V and i'm told would result in an audible 'pop' through the speaker when engaging the standby switch.

[Grantorino]

-update- The rectifier tube had failed. The manufacturer recommends bypassing the use of the standby switch to avoid current spikes. They have also suggested that the quality of rectifier tubes has declined considerably in recent years.

What is the consensus here on the quality, robustness and consistency in rectifier tube manufacturing in recent years? The manufacturer states that since the conception of the amplifier (approximately 8-10 years ago), the quality of rectifier tubes has declined considerably and this is the reason for repeated rectifier failures in this amplifier.

They have floated the idea of replacing the rectifier altogether with a transistor-based plugin device, such as the Copper Cap by Weber.

Any thoughts on this subject would be interesting to me.

Thanks again.

[stratomaster]

Reply #2 identified the issue and the remedy. 

Has rectifier tube quality declined over time? Probably, maybe even most likely, but that's irrelevant as there are plenty of recently produced rectifier tubes operating just fine in better implementations of standby.

[Grantorino]

 
Has rectifier tube quality declined over time? Probably, maybe even most likely, but that's irrelevant as there are plenty of recently produced rectifier tubes operating just fine in better implementations of standby.

I would say it is relevant to a customer without technical knowledge, that has purchased an expensive amplifier to play, where the manual tells him to warm up the amplifier in standby before every use.

When considering the cause of a failure in such an amplifier, whether it be the circuit (including standby position), or a weak rectifier tube, this does become a consideration.

I don't disagree about bypassing use of the standby switch altogether.

The quality of rectifier tubes is relevant to me and I have an interest in any thoughts on the matter, having now spoken to tube suppliers and tube amp manufacturers about the issue.

If the Sovtek factory is in Saratov, Russia, which just yesterday was being hit with drone strikes, the factory is certainly at risk. Not to mention the men from the factory floor being seconded into the military.

If, for example, a Vox amplifier blows four Sovtek rectifier tubes in quick succession, but runs well with a JJ tube, what does that suggest to you? (an anecdote relayed to me by a tube suppler).

In the specific case of the amplifier I am working on, I think it would be prudent to measure the heater and HV secondary pins of the rectifier, to see exactly the voltage demands placed on the tube.

I think it's all relevant...

[pdf64]

Adding back up silicon diodes stops arcs and hence shorts developing, keeps the valve rectifier operational,  perhaps until it loses emission.
https://www.premierguitar.com/the-immortal-amplifier-mod
The silicon diode voltage rating needs to be higher than RG Keen advises though, 1kV is insufficient unless the winding voltage is <550V AC.

[Grantorino]

Adding back up silicon diodes stops arcs and hence shorts developing, keeps the valve rectifier operational,  perhaps until it loses emission.

Thank you PDF.

 I had discussed this with the manufacturer. Their concern was that the if the rectifier tube shorts, the diodes allow continued operation of the amplifier - the protection diodes essentially become the rectifier -  but with a lower voltage drop, resulting in a large increase in plate voltage.

Their preferred fix was actually to fit a solid state plugin rectifier device, such as the copper cap by weber.