GK-71 op points

Andrew · Post by **Andrew** » Tue Jul 30, 2013 6:49 pm

I had a friend bring a laptop round to my house, the original supply had died so he'd bought a replacement one from e-bay; as soon as the switcher went on to charge up the battery, our ADSL connection went down

It was so repeatable it was scary! I made him put it in a tin box....

IslandPink · Post by **IslandPink** » Tue Jul 30, 2013 9:29 pm

Dell supply will light the GK-71 OK if helped by a CL-60 thermistor in series with the filament . After it's been on a couple of minutes, the thermister takes about 1.3V off the total voltage, so I reckon it has about 0.45 ohms resistance . You still get 18.0V across the GK-71 which should be OK - I think that's what Andrew I. ran them at.

Picture below .
It's interesting that the Dell ( 90W ) supply hesitates about 1.5 to 2 seconds before anything happens. Not sure if it normally does this. The Sony one came on immediately .

After half an hour, the Dell supply is quite warm, but no worse than the Sony 100W supply . Confirms it's a very efficient unit .

jack · Post by **jack** » Tue Jul 30, 2013 11:04 pm

Looking at the model of Dell laptop PSU you have there, a bunch of these had a habit of spontaneously combusting and were subject to a product recall...

The dangerous PSUs had 3 part numbers (09364U, 04983D or 07832D) and that the AC adapter was manufactured by Delta Electronics in China(CH) or Thailand(TH).

Just a thought...

IslandPink · Post by **IslandPink** » Tue Jul 30, 2013 11:15 pm

Thanks for a warning, Nick , but doesn't look to be one of those ( I will make a note of those numbers though ) .
It has more info on it than most people could shake a stick at eg. :
PA-10 Family
PA-1900-02D
09T215
'Dongguang Lite Power 2nd Plant'
etc, etc, etc .

slowmotion · Post by **slowmotion** » Wed Jul 31, 2013 6:42 am

Be interesting when you find out how it sounds?
Compared to the regular stuff?

IslandPink · Post by **IslandPink** » Wed Jul 31, 2013 7:56 pm

Jan, do you mean how the GK-71 sounds compared to 'regular' valves ... or how the SMPS supply sounds relative to a 'regular' supply ?
I'm more likely to be able to give you the first piece of info, rather than the second !

slowmotion · Post by **slowmotion** » Wed Jul 31, 2013 8:34 pm

I was thinking you would maybe get a feeling if SMPS supplies were usable for heating filaments or if there would be problems with noise or bad sound?
Just curious, I guess.

pre65 · Post by **pre65** » Wed Jul 31, 2013 8:40 pm

The general feeling is that SMPS filament supplies can work well.

andrew Ivimey · Post by **andrew Ivimey** » Wed Jul 31, 2013 10:43 pm

I use 18 volts at 6 amps smpsu because the fan doesn't switch in. If I use 20 volts the fan switches in & out and if I use 22 volts, where its is gorgeously bright (I can read my Kindle or remove a cat's appendix by it) the fan is on continuously.

The quality of sound doesn't change significantly.

There is a difference however with the 833 which, to me , is a raw, rough and ready swpsu. I think it is this heater supply that sounds rough and I need to work on it to improve the supply - over to Philip whose 833 sounds rather nice actually. My 833 sounds raw, rough and ready, his does not; he has an improved swpsu unit and over to you Phil, to explain how. It might be just the odd smoothing cap or two.

pre65 · Post by **pre65** » Wed Jul 31, 2013 10:59 pm

Yep, my 12v SMPS has two lots of RC to bring it down to 10v.

I've got it set up to scope the heater supply, but I've lost my little book that tells how scopes work.

Paul Barker · Post by **Paul Barker** » Thu Aug 01, 2013 7:43 am

andrew Ivimey wrote:I use 18 volts at 6 amps smpsu because the fan doesn't switch in.

Take this in the context of someone who promotes filament starvation.

Thoriated tungsten valves should not be starved or over heated. There is a very fine window of operation outside of it on the high side results accelerated end of life. Filament on the low side causes loss of capability which may be recovered by running the valve hot for a while, but in the end will reduce valve life, restoration will be short lived.

It is in your best interests to heat a TT filament exactly right.

andrew Ivimey · Post by **andrew Ivimey** » Thu Aug 01, 2013 8:41 am

No, I don't promote filament starvation, never had ... and I note what Paul says about thoriated tungsten but as I can't really hear any difference in the heater voltages varying between 18 and 22 (as my spec sheet for GM70 recommends) then I am not going to worry, given how wonderfully cheap these (GK71s too) are.

I could add silent fans (then I'd run them at 22 volts) but I'm lazy!

IslandPink · Post by **IslandPink** » Thu Aug 01, 2013 6:06 pm

This business of the switch-on current surge : do we think it's important ?

Last I remember of the debate, it seemed to be the risks were due to the filament flexing in the B+ voltage ( if the B+ is already on ) when you put the initial high-current pulse into there while the filament is cold - this being due to the magnetic field of the filament interacting with the high-voltage field .
If the B+ ( in my case ) comes up more slowly than the filament, is there still a risk on filament lifetime ? I'm thinking more in terms of the Copper GM70's which are more expensive to replace than GK-71's or graphite GM70's .

andrew Ivimey · Post by **andrew Ivimey** » Thu Aug 01, 2013 9:49 pm

Surely its safest to warm through the heater long before the HT comes on or cathode stripping or/and surge pulses can only do harm?

Post by **Nick** » Thu Aug 01, 2013 10:01 pm

andrew Ivimey wrote:Surely its safest to warm through the heater long before the HT comes on or cathode stripping or/and surge pulses can only do harm?

If you had a cathode

I personally think the twisting moment of the long filament in the B+ field is the biggest problem for high voltage DHT's

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GK-71 op points

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