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September 15, 2019, 10:11:33 PM

Author Topic: Need Help with First Tube Build - WE91 300B Parafeed Derivative  (Read 1383 times)

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Offline EricS

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Re: Need Help with First Tube Build - WE91 300B Parafeed Derivative
« Reply #120 on: September 11, 2019, 08:35:39 AM »
Understood - I agree that exceeding current ratings can end in all sorts of bad outcomes that are best avoided.  I tend to be a fan of the Nelson Pass approach to (over)engineering circuit designs: Wear both a belt and suspenders.  I can arc-weld with the PSU of my 150w Class A solid state amps :)

Is there a compelling reason not to add series resistance to trim the rest of the AC voltage on the filament?  I've been doing lots of searching/reading and haven't found anyone saying that this is a bad idea...
Eric

Haven't electrocuted myself yet...   
There are ALWAYS User Serviceable Parts Inside!

Offline Paul Birkeland

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Re: Need Help with First Tube Build - WE91 300B Parafeed Derivative
« Reply #121 on: September 11, 2019, 09:30:06 AM »
If you split it up as two resistors, I can't see that it would be a problem, but it does feel overly anal to be dialing in rectifier voltage that tight. 
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline EricS

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Re: Need Help with First Tube Build - WE91 300B Parafeed Derivative
« Reply #122 on: September 11, 2019, 01:32:31 PM »
Yep, I absolutely LOVE to futz with and tweak stuff, so I'm definitely guilty as charged!  Besides, isn't the realm of DIY just an endless opportunity to tweak simply because we can?  ;D   On the plus side, now that my prototype is nearly finished and dialed in, I think I might have fewer questions ahead than behind. 

In all seriousness, I do very much appreciate your patience with me while I learn!  I'm REALLY excited for my first opportunity to hear a stereo pair of these amps!
Eric

Haven't electrocuted myself yet...   
There are ALWAYS User Serviceable Parts Inside!

Offline EricS

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Re: Need Help with First Tube Build - WE91 300B Parafeed Derivative
« Reply #123 on: September 12, 2019, 03:49:16 AM »
Here is the final iteration of voltage measurements - I think I'm finished tweaking things and I'm pretty happy with where things are right now!  Overall, the amp is producing about 7.5-8w of output power into an 8R load, which is pretty much in line with the datasheet for the EML 300B mesh tube. 

I think I'll keep my prototype functional and build the second channel so that I'll be able to listen to the stereo pair sooner.

Guess it's time to work my way through those physical/aesthetic decisions that I've been putting off: color choices for the top plate (brass or powder coat black), methods to avoid a million screw holes in the plate, etc.  I'm thinking this is going to be much slower work.

Eric

Haven't electrocuted myself yet...   
There are ALWAYS User Serviceable Parts Inside!