Filament voltage

[Doc B.]

I don't think we have anything to offer beyond the suggestions that have already been made. You say the tube is operating within tolerance. Sounds like things will be just fine.

[Fred_P]

You say the tube is operating within tolerance.

I do not really think I said that. I only reported some figures, and concluded that there was an improvement.

Sounds like things will be just fine.

That remains to be seen.
I ordered an automatic voltage regulator, I will report the results when it arrives.

[Paul Birkeland]

In theory they are a nice idea, but do you have any concrete model on mind?

http://www.ebay.com/itm/MASTECH-2KW-TRANSFORMER-VARIAC-2000VA-0-250V-220V-INPUT-/361281710618?pt=LH_DefaultDomain_0&hash=item541e116a1a

Take an IEC power cord and cut it in half, then wire each half into that variac.  You can dial in your filament voltage to 2.500000 volts with such a tool.

[Fred_P]

Thanks for the hint, that looks like a viable alternative.
Based on your suggestion, I managed to find the same product also on amazon.de for faster delivery.

In the meantime, I have already ordered an APC line-r 600VA which is due to arrive tomorrow.
It comes with a user selectable 220/230/240V setting, and it should be able to compensate for +/-10% fluctuation.
I will give it try to see if it is a keeper. Otherwise I will return it and order the variac instead as you suggested.

Thanks again

[Fred_P]

The APC unit has arrived today.

Unfortunately, the 220/230/240V switch on the back of the unit does not have any effect whatsoever on the output voltage.
What goes in, goes out independent of the switch setting, at least if the input voltage is stable (233V in this case)
(the measurements were not done while idling, but with the amp connected, and the unit was shut down each time before changing the setting)
This means that the device is useless for my purpose, and will be returned.

Today I have purchased the proposed variac in ebay, it should arrive by Saturday the latest.
When it arrives, I will implement the proposed changes and see how it fares.

[Fred_P]

The variac from ebay arrived today. I installed the cables and tried it out. (I am yet to add a fuse, but it is fine for now.)
The mains voltage was almost exactly 230V this evening, so I measured the filament voltage, and dialled in the nominal 2.50V.
Only downside is that the unit smells terribly, but I hope the bad smell will go away soon.

Thanks to Grainger for the idea, and to PB for finding the specific model on ebay.

Fred
 

[Paul Birkeland]

Yeah, we have a variac similar to that in the lab.  They are painted, then wrapped in plastic maybe a little too early, and the paint solvents stick around.  After a week or two, you'll find that the smell has dissipated.

-PB