It's Here! and it is Beastly

[Paul Joppa]

Since I don't have any post in this thread, I must have asked for voltages in another thread. I don't recall why I asked for that - too many posts under the bridge, plus a weekend spent throwing acres of driftwood logs back over the bulkhead.

[drewh1]

Ah. Makes sense.  My apologies. You were helping me set up the Eml's meshplates in the thread titled use of bias probe. I thought it would make sense to continue it here.   I want to set up correct voltage for the meshplates

[Paul Birkeland]

Thanks Ed!

Paul J - After letting things settle in a bit and setting hum pots etc, I measured final voltages.

both filament voltages are  5.25
63u  - 72.1
33u -  72.8

c2 -  429
B2 - 428


If I measured correctly, I come up with 30.8 watts? I am guessing the voltage on pin 2 is not the way to measure plate voltage?
 Looks like the filament voltage is perfect if I need an additional 5%. Will the DC Regulator take it down to 5 V, thus leaving me with low filament voltage?

The voltage the plate sees is the plate voltage minus the DC voltage at the top of the 1K resistor.  For one side, this is 429V-72.1V, so 356.9V.  Current through that tube is 72.1mA, so plate dissipation is about 26 Watts.

Your filament voltage is within 5%, which is great.  The regulator will regulate to 5V (at a tighter tolerance than 5%).  I'm not sure what you're asking when you mention low filament voltage.  Low filament voltage for a 300B is going to be more like 4.5V.

[drewh1]

Paul - thanks for that explanation. I knew I was missing something.

So - EML Mesh draws 1.4 amps so, 5.25 volts on 1.2 amps (sovtek tube) would be more like 5 volts on the EML. Does the DC regulator (not yet installed) provide 5V independent of current? if so I that is perfect for the EML. Spec is 5v +/- 4%

26 amps is the maximum plate current for the EML. It would be better to have it at 24, recommended is 22.  But it all looks workable with no modification. However, if I wanted to bring it down, what would be the best option?

That leads me to a follow up question - I might be moving in with my GF  .  House voltage there is 119, mine is 125. How much does a difference in AC voltage affect the output voltage of the transformer? Might be just right if it reduces the voltage a bit.

BTW - I appreciate all the time you are taking to respond!

drew.

[drewh1]

I'm sorry - 28 is the maximum current. 26 is within operating range.

[Doc B.]

It would be very impressive to see 26 Amps of plate current through an EML tube. I think you probably mean 26 watts.

For what it's worth, after all of this discussion I put my EMLs in my Kaiju and ended up going back to EHs. Thought the EMLs were not as open sounding in my system. YMMV, TANSTAAFL, WYSIWYG.

[Paul Birkeland]

So - EML Mesh draws 1.4 amps so, 5.25 volts on 1.2 amps (sovtek tube) would be more like 5 volts on the EML. Does the DC regulator (not yet installed) provide 5V independent of current? if so I that is perfect for the EML. Spec is 5v +/- 4%

You might see something like 5.2V on the EML's, PJ would probably have a more educated guess, but in any case, you can just plug them in.  I could have sworn a few months ago that the EML spec was +/- 4%, this is getting pretty tedious to keep up with.

It would be better to have it at 24, recommended is 22.  But it all looks workable with no modification. However, if I wanted to bring it down, what would be the best option?

Western Electric specs 36 watts as the maximum plate dissipation for the 300B, with some suggestions in application notes that you can go as high as 40.  The ultimate question here is why a manufacturer would call a tube a 300B when it can only dissipate 22 Watts.  There are many amps commercially available that have been manufactured over the last 20 years that run at over 30 Watts of dissipation, so this seems pretty unusual.

Are you running the 300B mesh?  The operating point that you measured and posted is one that is recommended on the EML website for the 300B mesh, so I wouldn't adjust it at all.

That leads me to a follow up question - I might be moving in with my GF  .  House voltage there is 119, mine is 125. How much does a difference in AC voltage affect the output voltage of the transformer? Might be just right if it reduces the voltage a bit.

You'll still be on the correct transformer tap.  You might see something like 4.95V instead of 5.25V, and there would also be a slight reduction in plate dissipation. 

[drewh1]

Great! Thanks Paul - I don't have the Mesh Plates yet, should have them by the end of the week.  I am measuring everything with Sovtek's.  Gonna plug them in and listen when I get them.

I am learning a lot from this project and really appreciate the detailed answers.   Also, really loving the Kaiju - you guys do a great job in design and support.

drew.

[drewh1]

Just installed the DC regulator.  Dead quiet, can't hear anything with ears right upmto speakers.  Now have 4,91v on the filaments.

[drewh1]

It looks like I will be out of spec on the filament voltage with the .51 resistors and the DC regulator.

So based on the specs of the EML drawing 1.4 amps, I calculate I need .45 ohm resisters to bring the voltage up to 5V spec.

6.3 - 5 = 1.3   1.3/1.4 = .92  .92/2 = .46   

correct?

[ebag4]

Just installed the DC regulator.  Dead quiet, can't hear anything with ears right upmto speakers.  Now have 4,91v on the filaments.

Hey Drew, anxious to learn if you perceive any difference in the music vs AC other than the lower noise floor.  Please post a pic as well, I would like to see what it involves.

Thanks,
Ed

[drewh1]

I got the DC heater even though I have terribly inefficient (92db) speakers  . Paul suggested it because EML recommends using it on their tubes. For my budget, these tubes are expensive, so I am being very careful about getting things right.  I did a lot of research on the debate about sound. Like many things in audio there is little agreement.

Here is a quote from the Emissions Lab site on providing power to EML tubes  "Use DC filament heating. AC heating will not sound better, because these will hum, and there is nothing better sounding about that." 

I did some critical listening late last night and could not hear any differences. The hum was noticeable even on my speakers so I think it is a good call.

Bottom line, it is an easy build: very simple circuit board and a couple of wires, and it is not very expensive for what you get. I would recommend it.  Sorry I don't have a picture. If you send me your email by PM, i'll send you a copy of the manual.

drew.

[fullheadofnothing]

Could you quantify "noticable"? I.e. do you mean if you put your ear up to the speaker, you can hear a little hum in a quiet room, or do you mean that it is audible from the listening position. Also, what were you seeing on the hum balance measurement?

Please do not offer distribute manuals (or any portion) without permission. A large portion of kit cost is the time and effort of writing these manuals; they are the property of Bottlehead, and we do not take that lightly.

[drewh1]

Hi Josh. Apologies about offering the manual. I wouldn't have except that Ed is already a kaiju customer .  at any rate it did not happen

The hum was apparent with ear to speaker and barely audible in a dead quiet room. I listen nearfield at 9ft away. Hum pots were at 4 to 8
mv if I remember correctly. Speakers are dead quiet now.

[Paul Joppa]

It looks like I will be out of spec on the filament voltage with the .51 resistors and the DC regulator.

So based on the specs of the EML drawing 1.4 amps, I calculate I need .45 ohm resisters to bring the voltage up to 5V spec.

6.3 - 5 = 1.3   1.3/1.4 = .92  .92/2 = .46   

correct?

More precisely, you should include the 0.1A through the hum pot. Assuming the EI tube is drawing exactly 1.2 amps (it's probably close but not exact), that's 1.3 amps total. Adding the resistor drop to the measured 4.91 volts, I get 6.236 volts from the filament supply as seen at the tube - the 0.064v difference from the target 6.30v is probably lost in the wires. Using 1.5 amps for the EML plus hum pot, I get a target of 0.412 ohms each. This can be done by paralleling the 0.51 ohm resistors with 2.14 ohms each. 2.2 ohms is close enough and readily available. A half watt rating is adequate, though I'd spring for 1-watt resistors. Might as well get some 2.0 ohm and some 2.4 ohm resistors at the same time in case you want to adjust further.