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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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It is currently 04 Jul 2020, 04:31

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PostPosted: 10 Jun 2020, 00:52 
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Joined: 28 Mar 2020, 19:57
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so... I built a stereo oddwatt amp with 6l6 output tubes and I am having a problem My b+ is a bit high at 505v at the 3rd filter stage and 511 at the first filter cap. My power transformer was out of dead twin reverb - 4 6l6 tubes and 5 or 6 9pin 12a?7 tubes. so I assume that it has enough capacity to power my stereo oddwatt...

since it was a newer twin reverb the TP didnt have a center tap.but it does have a bias tap that puts out about 45v

so could I use the bias tap to put about -50v onto my B+ and drop it to around 455v?

thoughts?

thanks in advance
Paul


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PostPosted: 11 Jun 2020, 16:41 
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Joined: 14 Feb 2010, 13:13
Posts: 707
Location: Lisbon, Portugal
Hi Paul!

It doesn't work that way. You need to place a drop resistor on the B+ rail or increase the current one.

Take a look at the schematics found over here.

Cheers!

Miguel


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PostPosted: 11 Jun 2020, 20:33 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
Hi, Are you measuring this without the tubes in place. If so it will be way high. This is a common thing to test power supplies without loads. It will not give correct results.

Good listening
Bruce

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PostPosted: 11 Jun 2020, 21:29 
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Joined: 28 Mar 2020, 19:57
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--- Hmmm

I wish I was testing without tubes - I would have a winner :) my amp without tubes it is even higher - the twin reverb b+ loaded is supposed to be about 460v. it has more tubes and different resistor values,,,

I really don't want to make any more heat than I have to - so any ideas? as you can see I have a regulator for the heaters I guess I could ditch that so I could make more heat inside - I have already perforated the chassis since these photos were taken

the good news is it sound really good- and dead quite - I just dont want to eat tubes and running 500v caps at their max is not good. (I am glad I made the first cap a pair of 350v so I am good till I get to about 650v

Thanks again for such an awesome design...

Maybe it is time to buy a new PT


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PostPosted: 12 Jun 2020, 21:39 
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Location: Arizona, USA
Hi, If you are not doing so, change the power supply to a choke input filter. It will dramatically cut the B+ voltage. Something in the 5hy range (with suitable dc rating) should work. Otherwise you will need a very large power resistor to dissipate the excess voltage and current. I would mount something like that on the outside back of the chassis (insulate the wires to keep from getting zapped). A power FET set as a regulator might work as well. Big heat sink etc.

Good listening
Bruce

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