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Concept for 4P1l Tubes
http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=6133
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Author:  gofar99 [ 27 Jan 2018, 11:12 ]
Post subject:  Concept for 4P1l Tubes

Hi Everyone, I would like to hear some thoughts on a concept for design of a single ended pentode (U/L) 4P1L amplifier. It seems to me based on some initial testing (call it monkeying around if you want) that the heater circuit for DH tubes can cause a number of undesired problems. It seems as if two DH tubes are on the same heater circuit interactions between them and the power supply will occur. I test bed set up a push-pull oddwatt style amp using a pair of these tubes and found that not only did the slave not function well, that the driven tube was both sourcing and sinking the audio into the heater circuit. Certainly not desireable. So I decided to try the tubes with a single ended circuit. There are many...but my thinking went to what if the heater circuits had a common ground. Then interactions might not occur. This would save having to have duplicate heater supplies as well. The problem there is the need for fixed bias. Not really an issue though. My inquiry is about using two DH tubes on the same supply. Opinions....?

The partial schematic is for a stereo amplifier. Points H1 and H2 go to the output tubes in each channel. Grounding the heater center tap on both tubes is thought to eliminate the need for cathode resistors, cathode capacitors and allow for for both tubes to share the same heater supply without interaction between the tubes or heater supply. The actual heater supply is floating.

Any thoughts,

Good listening
Bruce
Attachment:
4P1L SEP UL Concept.jpg

Author:  gofar99 [ 28 Jan 2018, 09:05 ]
Post subject:  Re: Concept for 4P1l Tubes

Hum? No thoughts?

Good listening
Bruce

Author:  Geek [ 28 Jan 2018, 17:44 ]
Post subject:  Re: Concept for 4P1l Tubes

Hi Bruce,

After "monkeying" with DH tubes, I found that using a CCS for each tube solves a multitude of issues.

Cheers!

Author:  gofar99 [ 29 Jan 2018, 16:42 ]
Post subject:  Re: Concept for 4P1l Tubes

I have considered that, but it won't get around using a single heater supply on two different channels. That was the idea to ground the center point of the heaters. Then interactions between the tubes might be non-existent. I was hoping someone would have a definitive answer on if it would work. In absence of that I will try it in a test bed and hope for no smoke. :firefighter:

Good listening
Bruce

Author:  Geek [ 30 Jan 2018, 03:22 ]
Post subject:  Re: Concept for 4P1l Tubes

gofar99 wrote:
....but it won't get around using a single heater supply on two different channels....Then interactions between the tubes might be non-existent.


In theory, as long as you stay in class-A, you're OK. But turn up the volume into cutoff and all bets are off :sick:

Author:  Soundbrigade [ 30 Jan 2018, 03:38 ]
Post subject:  Re: Concept for 4P1l Tubes

There's a guy, called Azazello who on the forums Diytubes and Diyaudio has published constructions with the 4P1L tube. He sent me, btw, a bunch of those to test and to show his gratitude for inviting him to my place a few years ago, when he also showed up with one of his 4P1Ls. We also attended a DIY-meeting in Gothenburg together and his small amp did impress.
The 4P1L is supposed to be a very nice tube when it comes to sonic qualities.

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