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 Post subject: 6146B Amp
PostPosted: 19 Jul 2009, 23:39 
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Joined: 19 Jul 2009, 18:29
Posts: 14
I inherited several (ok, 6) 6146B tubes from my dad (along with some 12AU7s, 12AT7s, 12AX7s, etc). He used them in his HF amp. Since I'm not into RF ( although I have a Tech license) I thought I'd try my hand at a stereo class A amp ( single drive or possibly push pull) with constant current cathode drive (ala LM317).

I don't see a search ability and have spent a few hours looking at previous thread without seeing anything related to the 6146. However I have seen reference to them elsewhere being used for 100W amps in push pull so they should be good for 20-30W in single ended drive.

Has anyone done a design based on a 6146 output?

I'm rusty at tube theory since they abandoned it when I went in the NAVY in 76. I've started reading up on it though (I'm an EE from Clemson in 81 and familiar with solid state theory, but they didn't teach tube theory by the time I went to college.)

Passed up a foot locker of tubes 20 years ago since they were "Obsolete". Damn, the missed opportunities of youth. Lots of 12A-7 series, 807s, etc.

Glad to see all the work being done with tubes now days. Some really nice construction projects in here.

I've been wanting to get back into tube design for 20 years, but never got around to it till a friend at work told me he had a guitar amp with hum. I offered to replace the filter caps and one thing lead to another and now here I am.

Steven


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 Post subject: Re: 6146B Amp
PostPosted: 20 Jul 2009, 04:03 
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Joined: 04 Oct 2008, 11:29
Posts: 375
Location: Chillicothe, Ohio
Hey Steven! Welcome to the forum!

You have a tough one there. The 6146 family of tubes aren't very commonly used in high fidelity audio circuits, it seems. I'm sure there are ways to do it if one is knowledgeable enough. Here's link to a short discussion about this tube.

http://music-electronics-forum.com/t7241/

Cheers, Greg


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 Post subject: Re: 6146B Amp
PostPosted: 20 Jul 2009, 23:02 
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Joined: 19 Jul 2009, 18:29
Posts: 14
Thanks Greg.

I'll continue doing research.

I'll admit right off that it isn't the best tube for an audio amp, but I'd like to do one any way. The fact that it is referenced as a P-P audio amp tube gives me some hope.

Steven


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 Post subject: Re: 6146B Amp
PostPosted: 21 Jul 2009, 03:56 
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Joined: 04 Oct 2008, 11:29
Posts: 375
Location: Chillicothe, Ohio
The 6146 has the longest page of data I've seen on the NJ7P database. Might be a good tube to go with. Sounds as though it's very versatile.

http://www.nj7p.org/Tube4.php?tube=6146

I have about 6 or 8 of these myself. If you find something, please post it here.

Cheers, Greg


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 Post subject: Re: 6146B Amp
PostPosted: 30 Jul 2009, 22:03 
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Joined: 19 Jul 2009, 18:29
Posts: 14
If you go down to page 11 of :

http://www.clarisonus.com/Archives/Trans/Acro55.pdf

You will find a 100W amplifier design using 6146 tubes. The screen feedback is interesting in that it is ultrlinear, but not at a 40-45 (43)% tap. It uses a seperate set of windings with a screen supply of +220V and a B+ of 725V for the plate supply.

I suspect finding a set of transformers at anyting less than my 401K will be difficult.

I've come up with a nice supply of tubes in the form of a dead Tektronix 545 with Type CA and Type L plug ins.

If I can't get it going, I'll canabilize it for sockets and tubes. Some are matched sets of 12AU6s, 12AT7s, 6AK5s etc.

6AK5 PPP Ultralinear?

I hate to disassemble it, but I did save it from the junkyard.

Steven


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 Post subject: Re: 6146B Amp
PostPosted: 02 Aug 2009, 11:45 
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Joined: 02 Aug 2009, 10:47
Posts: 1
I know that there are not many audio amplifiers described with 6146 tubes, but its is no problem to use schematics for 807 instead as they are more or less the same tube eventhough 6146 are more modern. 6146A have less anode dissipation, (25W) than 807, (30W) and 6146B have a bit higher, (35W) but other characteristics are very similar and if you look at the electrode structure it is also very similar. As 807 6146 have the same problem for audio use in that max screen grid voltage is low and therefore it is not well suited for high power ultralinear applications.

I used 6146 tubes in one of my first audio amplifiers that where designed for 807, the only thing I needed to do was to change the sockets, see here http://www.tubetvr.com/pushpull.html

Another idea is to use schematics for 6L6 as this is essentially a 807 without top cap and also 6L6 is therefore similar to 6146, however beware of the screen voltage as some 6L6 variants have higher max screen voltage.


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 Post subject: Re: 6146B Amp
PostPosted: 02 Aug 2009, 12:04 
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Joined: 28 May 2008, 21:53
Posts: 4577
Location: Winnipeg, CANADA
Hi tubetvr, welcome to the forum.

I was just going through your website and found some good info on the 6C33C tube. Thanks for sharing.
Cheers

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 Post subject: Re: 6146B Amp
PostPosted: 08 Aug 2009, 22:47 
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Joined: 04 Jun 2008, 20:59
Posts: 3963
Location: Arizona, USA
Hi, I love innovation and creative thinking, I was late getting into this thread so please excuse me. There are some issues with the original thoughts. A pair of 6146 can certainly deliver at least as much output as a pair of 6L6GCs. I would, as others noted, base a design on them. The parameters are close enough. Now the wrinkle. If you use a LM317 as a CCS in the cathodes, you force the amp to operate in class A mode. This severely restricts the output. It will generally fall in the 25-30% range related to the total input power. So if you run a pair at 125ma (via the CCS) and at about 450 volts you should expect around 15-18 watts. This is not a horrible thing, as the sound quality in class A is excellent. You can push them a little higher if you don't care about tube life. I like to keep my stuff at or below 80% max dissipation. If you want the higher power levels, I suggest you go to fixed bias with each tube being adjustable independently. This will give the max output and still have quality sound. In that mode something on the order of 55 watts is possible.

Good listening
Bruce

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 Post subject: Re: 6146B Amp
PostPosted: 19 Aug 2009, 22:50 
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Joined: 19 Jul 2009, 18:29
Posts: 14
The Acrosound 350 uses a separate screen winding on the transformer for 100W amplifier with 6146s. This is because the 6146 has a max grid 2 voltage of 250V but a plate max of 600V.

I got to wondering if it would be possible to use a transformer with a 40% screen tap, and capacitively couple it to screen 2, and then resistively bias the screen with a 250V supply?

I can see a possibility of a resonance caused by the inductance of the transformer and the coupling capacitor, but it might be possible to use a large capacitor (1uF or greater) and push this down low enough to not matter.

Any thoughts on this?

I tested my 6146s today and have several that are better than 90% spec (Mercury 1000 Gm). A co-worker said he had some I could have for free, so I'll see what they measure out at.

Steven


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