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Inspire by Dennis Had Enjoying Vacuum Tube Audio

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  #6531  
Old 08-06-2021, 03:35 PM
Bombadil Bombadil is offline
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Could a worldwide shortage of vacuum tubes be on the way?

https://guitar.com/news/gear-news/pa...re-valve-amps/
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  #6532  
Old 08-08-2021, 12:20 AM
Isaacc7 Isaacc7 is offline
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Default El38 not such a good choice after all?

I saw that the Firebottle KT88 would set the screen voltage and anode voltage lower than the max rating of the el38 so I got some adapters and put them in. They sound phenomenal. But as I read more maybe they aren't a great fit and I'm killing them? Turns out that they require about half of the negative bias of an el34. I'm reading things like this, "EL38 has higher transconductance than EL37, and will require much less negative bias voltage under similar conditions."

I'm told to check if the plates are glowing red but I don't know which part is the plate. The entire inner section is lit up but I don't know if that is the filament or the plate. Wish I knew more about this stuff so I don't blow something up. I've put the 807 tubes back in until I can figure out if this amp is incompatible with the el38. Anyone have some resources I can check and see if running el38tubes is a bad idea? Dennis? Straitwire?
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  #6533  
Old 08-08-2021, 10:21 PM
Isaacc7 Isaacc7 is offline
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Quote:
Originally Posted by straitwire View Post
The 6.3v winding is 6 amps.
Does that mean I could use a 6080/6as7 as the input tube when using 807 tubes as the output?

Sorry for asking so many question but this is all Dennis's fault for making an amp catering to the worst aspects of tube rolling mania! Lol.
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  #6534  
Old 08-10-2021, 10:07 AM
FloridaBoy FloridaBoy is offline
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Quote:
Originally Posted by Isaacc7 View Post
I saw that the Firebottle KT88 would set the screen voltage and anode voltage lower than the max rating of the el38 so I got some adapters and put them in. They sound phenomenal. But as I read more maybe they aren't a great fit and I'm killing them? Turns out that they require about half of the negative bias of an el34. I'm reading things like this, "EL38 has higher transconductance than EL37, and will require much less negative bias voltage under similar conditions."

I'm told to check if the plates are glowing red but I don't know which part is the plate. The entire inner section is lit up but I don't know if that is the filament or the plate. Wish I knew more about this stuff so I don't blow something up. I've put the 807 tubes back in until I can figure out if this amp is incompatible with the el38. Anyone have some resources I can check and see if running el38tubes is a bad idea? Dennis? Straitwire?
The amp is autobias, so you're fine. Below is a link to a pdf version of The Tube Substitution Handbook. You can get a hard copy at Amazon.

https://worldradiohistory.com/BOOKSH...ume-4-1962.pdf

Search A Taste of Tubes. It's a downloadable e-book and covers everything you need to know about tubes. I can't find a link that I can post.

Last edited by FloridaBoy; 08-10-2021 at 10:17 AM.
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  #6535  
Old 08-10-2021, 10:33 AM
FloridaBoy FloridaBoy is offline
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[QUOTE=Analog Addict;1041657]Dennis has been perfecting an upscale version of a pre amp that we have been monkeying around with for the better part of 3 years, and as some of you may already know, is called the LP-71A.

Before I go any further, let me tell you all what Dennis has said about this new design, and I quote...

"Not only is this the best pre amp I've ever designed, but it is the best pre amp I've ever heard"

What more is there to be said?

One of the nice things is that it will run three different types of tubes interchangeably, the 12/112, the 01A and variants, and of course the 71A and its variants. I won't try and describe how it sounds. Let Dennis' comment speak for itself...

I ordered one yesterday.

I wasn't aware that it would also run the 12/112, the 01A and variants, and of course the 71A and its variants.
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  #6536  
Old 08-10-2021, 11:35 AM
bearcity bearcity is offline
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I ordered one yesterday. :

Good on ya. I have on on order as well. Anticipation.
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  #6537  
Old 08-10-2021, 01:52 PM
rmlowz rmlowz is offline
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Congratulations on your new preamp!
I have a question for straitwire if he sees this. When all tubes are made they all supposedly are made to the same spec. If you use tubes (output tube) that are matched within 10% with different construction and manufacture would you use them?
Thanks
rmlowz
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  #6538  
Old 08-10-2021, 02:07 PM
Isaacc7 Isaacc7 is offline
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[QUOTE=FloridaBoy;1042926]
Quote:
Originally Posted by Analog Addict View Post
Dennis has been perfecting an upscale version of a pre amp that we have been monkeying around with for the better part of 3 years, and as some of you may already know, is called the LP-71A.

Before I go any further, let me tell you all what Dennis has said about this new design, and I quote...

"Not only is this the best pre amp I've ever designed, but it is the best pre amp I've ever heard"

What more is there to be said?

One of the nice things is that it will run three different types of tubes interchangeably, the 12/112, the 01A and variants, and of course the 71A and its variants. I won't try and describe how it sounds. Let Dennis' comment speak for itself...

I ordered one yesterday.

I wasn't aware that it would also run the 12/112, the 01A and variants, and of course the 71A and its variants.
Woo! Congrats! Sure it’s going to be an amazing addition. What are you replacing?
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  #6539  
Old 08-10-2021, 03:35 PM
FloridaBoy FloridaBoy is offline
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[QUOTE=Isaacc7;1042931]
Quote:
Originally Posted by FloridaBoy View Post

Woo! Congrats! Sure it’s going to be an amazing addition. What are you replacing?
An LP27a, I really like it but I heard some hum and put my ear to the speaker. It wasn't hum, but I could faintly hear the 45/2A3 amp saying 'I want to be driven by a DHT preamp'. So, I obeyed and contacted Dennis.
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  #6540  
Old 08-10-2021, 03:54 PM
FloridaBoy FloridaBoy is offline
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Quote:
Originally Posted by bearcity View Post
Lee,

Dennis is installing a volume control on the 300b so yes it can be used w/o a preamp. In fact, I recall that is how Dennis listens to vinyl in his home/reference setup. As to what you gain or loose? You will gain clarity and loose gain. With sensitive enough speakers you will be fine.
He's using the phono preamp for gain and controlling volume with the pot in the amp.
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