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 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

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PostPosted: 05 May 2010, 12:06 
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Joined: 03 Aug 2008, 20:22
Posts: 386
Location: Denver, Colorado
A great source to find 12AU7 tubes is on eBay, since you are not looking for a pair, you can find some older used tubes from organs and even vacuum tube volt meters. The average price is about $2 for a batch of used organ tubes, usually sylvania, rca, baldwin.

Rogers


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PostPosted: 05 May 2010, 12:59 
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Joined: 31 Dec 2008, 15:34
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Hi Todd ( and others ).

You'll have to give your build time to break in ....several hours, days, weeks before it sounds right.

About tweaks, try some better input caps ( MKP ), ex. Audyn Caps, Vima or Phillips. Output caps, try ex. Panasonic, Nichicon or Frako. All named caps aren't expensive.

12AT7 ( and 12AX7 ) doesn't work proper for this build, so keep the 12AU7 in the socket.

You also asked for headphones. I use the NP-100v12 build for my Sennheiser HD650 and Phillips SHP-8900 and it all sounds great together. ( SHP-8900 = 100 $ headphones ).


Last edited by KrammeAcoustics on 05 May 2010, 13:19, edited 1 time in total.

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PostPosted: 05 May 2010, 16:38 
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Joined: 04 May 2010, 07:33
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How important is it for the bias voltage to be exactly 1/2 of the input? I cannot get it to go that low.
KrammeAcoustics wrote:
About tweaks, try some better input caps ( MKP ), ex. Audyn Caps, Vima or Phillips. Output caps, try ex. Panasonic, Nichicon or Frako. All named caps aren't expensive.

Where do you like to source your caps from?

Todd


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PostPosted: 06 May 2010, 06:57 
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Todd wrote:
How important is it for the bias voltage to be exactly 1/2 of the input? I cannot get it to go that low.

It's important to get it adjusted half the supplyvoltage, to get the best possible soundquality.
I can regulate my trim.pot lower than 5 V. I can't explain why you can't get it lower. With use of a trim.pot with 3 pins, two of the pins will have to be soldered together ( 1 and 2 or 2 and 3 ), as mentioned before in this thread, did you do that ?
Image

Todd wrote:
Where do you like to source your caps from?

Mouser, Parts Express or RadioShack ...name it. Gio and Rogers has already made a BOM ( bill of materials ) where to order parts: http://diyaudioprojects.com/Solid/12AU7-IRF510-LM317-Headamp. ( The Mouser parts looks good ).

If you ask me, i like these as output caps, found on Ebay: http://cgi.ebay.de/Nichicon-Muse-KZ-470uF-50V-Audio-Tuning-amp-upgrade-/150416610011?cmd=ViewItem&pt=Audio_Zubeh%C3%B6r&hash=item23058752db
And these as input caps, also from Ebay: http://cgi.ebay.de/AUDYN-CAP-MKP-QS-2-2-F-AXIAL-/310191230773?cmd=ViewItem&pt=Lautsprecher_Selbstbau&hash=item4838d68f35


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PostPosted: 06 May 2010, 12:17 
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Joined: 28 May 2008, 21:53
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Location: Winnipeg, CANADA
Hi Guys, on the BOM we only have bi-polar electrolytic types. We should add some polypropylene types that will fit on the boards so builders will have a few options to choose from. Feel free to shoot me some product numbers and I will add them to the page.
Cheers

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PostPosted: 08 May 2010, 06:34 
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mxweas wrote:
So I heard some clipping and decided to check those pots again. At 100% resistance its only brought down to about 9v. I'm using the exact trim pots linked in the tutorial from mouser. Though the trim knob faces sideways for some reason. Any Ideas?

roggom wrote:
Just one more thing about the pot, you did wire it as a variable resistor, the center pin should be shorted to either the #1 or #3 pin. Other things could be recheck the value of the resistor for the LM317 should be 10 ohms and verify the pinout of the LM317 as well. There are a couple of variation I have seen out there.

I was indeed measuring the wrong side of the resistor. I'll check it again later this weekend. How do you suggest I go about checking the pinouts of the LM317? Just look for which pin has a regulated voltage?


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PostPosted: 08 May 2010, 11:54 
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Location: Winnipeg, CANADA
Here is the pinout for the LM317 voltage regulator.
You want to check at "Vin" which is connected to the "Source" pin of the MOSFET. in this circuit.
Cheers

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PostPosted: 09 May 2010, 02:00 
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Joined: 26 Oct 2008, 13:48
Posts: 70
Location: Central California coast
Hi All:

I like the idea of adding the CCS. :sing:

I haven't built my Roggom hd ph amp yet, got side tracked with FM tuners and a great jazz station - KRML 94.7 [www.krmlradio.com]. But, I also picked up a Knight 12-in-1 experimenters kit from the late 50's at an antique store.

So what, 'e says mate! Well, let me plant a bug in yer ear - This "kit" uses the 12K5 low voltage pentode. Yep, uses 12.6V on the plate... :idea:

Happy experimenting!! :headphones:

8>) MIke
Are they REALLY airwaves?


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PostPosted: 09 May 2010, 04:45 
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Joined: 25 Apr 2010, 03:14
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Hi

First of, my compliments on the amplifier. I've built one in about 2 hours, and it drives my headphones (one 32R and another 300R) with complete ease. After testing it I came to the conclusion that the sound card in my computer doesn't perform well at low volume (I was testing the amplifier without a volume control), but that's beside the point.

I, too, had a problem biasing the tube (it wouldn't go below 7.*V on either channel). I ended up using 2 39K resistors in series + a 10K trimmer for one channel, and 2 39K resistors in parallel + a 10K trimmer on the other channel. (This using a JJ 12AU7 tube). I also tried a 12AX7 (Electro-Harmonix) and it works fine (didn't test it for too long, since I've already set up the bias for the 12AU7 tube).

I think that it might be a good idea to substitute the 10K trimmer with a 100K one for some tubes, otherwise some rework (like I did) is required to bias them properly (which is fine if the amplifier is used with only one tube, but for tube rolling a potentiometer/trimmer is better since tubes will bias differently).

Some pictures:
Link to gallery

Regards


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PostPosted: 09 May 2010, 16:23 
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Joined: 20 Apr 2010, 02:04
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Roggom, I'm using 10k trim pots, should I be using 100k trim pots?

I've tried looking at the voltage on them and one side has constant 12.6v and this remains at 12.6v regardless of what the trim pots are set at. The other side however will decrease as I adjust the trim pot, but my 10k trimpot will only bring it down to 9.12v. What am I doing wrong?

Thanks,
Max


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