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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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 Post subject: Re: 6V6 PP amp
PostPosted: 24 Oct 2019, 17:26 
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Joined: 23 Feb 2017, 02:02
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The main thing about chockes is for the simulated caluclations to work, the core must not saturate
Real life the most filtering transformers saturate and you do not get the filtering effect


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 Post subject: Re: 6V6 PP amp
PostPosted: 13 Feb 2020, 12:16 
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Joined: 06 Oct 2015, 22:05
Posts: 41
and so it begins:
Attachment:
temp.jpg


I've been hearing about Greenlee punches for years and they really are great.


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 Post subject: Re: 6V6 PP amp
PostPosted: 13 Feb 2020, 22:33 
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Joined: 13 Jan 2018, 21:33
Posts: 353
Location: australia
Looks like a cool project. I used the stepped drill for the holes and worked ok. Your greenlees would be way more accurate I'd guess. Good luck.

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 Post subject: Re: 6V6 PP amp
PostPosted: 14 Feb 2020, 11:27 
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Posts: 41
The stepped bits are nice too. I used that for the holes for the wires from the transformers that I did last night.

I stumbled on a single used greenlee punch for sale at a really good price that was the exact size for the tube sockets. For me it was nice because it took the fear of going one too many notches down the stepped bit.
Now I just need a rectangular punch for the iec power connector. I keep telling myself that this time I will go slow and do a clean job of that one


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 Post subject: Re: 6V6 PP amp
PostPosted: 14 Feb 2020, 17:13 
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Joined: 13 Jan 2018, 21:33
Posts: 353
Location: australia
invaderzim wrote:
The stepped bits are nice too. I used that for the holes for the wires from the transformers that I did last night.

I stumbled on a single used greenlee punch for sale at a really good price that was the exact size for the tube sockets. For me it was nice because it took the fear of going one too many notches down the stepped bit.
Now I just need a rectangular punch for the iec power connector. I keep telling myself that this time I will go slow and do a clean job of that one


I recall @Gio posted a few years back he used a Klein nibbler even on a steel chassis. I looked and couldn’t find one or a compatible in Aust . I used a strip nibbler which got me part of the way followed by a couple of hours of filing. Got to be a better way. than that though.

easy search: viewtopic.php?f=14&t=4547&p=50310&hilit=klein#p50310

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 Post subject: Re: 6V6 PP amp
PostPosted: 24 Feb 2020, 11:29 
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Joined: 06 Oct 2015, 22:05
Posts: 41
I wish I had a larger chassis for the build. It looked big until I got everything mounted and now things are quite close and there isn't enough room underneath for a nice layout to be easy. And I need it to be as easy as possible ;)

It is 8 x 12 and the 10 x 17 seems to be a much more commonly used size.


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 Post subject: Re: 6V6 PP amp
PostPosted: 28 Mar 2020, 18:13 
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I finished the amp and fired it up to a high pitch scream from both channels and no music.

I double and triple checked all the wiring and didn't find anything that was off. I checked the grounds and grid stoppers.

I checked the hand-written wiring notes that came with the output transformers to make sure I had the right side for ground on them and it was but as a long shot I reversed them and the scream went away but the volume level is really low.


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 Post subject: Re: 6V6 PP amp
PostPosted: 28 Mar 2020, 18:58 
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Joined: 01 Jun 2013, 09:05
Posts: 985
Hi,

First guess feedback problem.
Its probably out of phase,
Take a look at the 6SL7 cathodes one has the FB on it, the other has a capacitor.

Swap the feedback connections on the output transformer as a quick test.
Check the capacitor and feedback connections on the 6SL7.

The more involved way if you want to keep the Gnd on the C and the FB on the 16 ohm tap is to swap over the output tubes connections from one side of the output transformer to the other. But you obviously need to move the Ultra linear tap so its on the same side as the correct tube.

Regards
M. Gregg

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 Post subject: Re: 6V6 PP amp
PostPosted: 29 Mar 2020, 05:20 
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Hi,

As you know the gain is set via the 100K anode load and the 1K cathode resistor to ground via the output winding.
The other side is again 100K anode load via 100 ohm to 1K to ground via the output transformer.
The AC gain is increased via the 100uF cap from the cathode to ground.

So if everything is as it should be but the gain is to low you could connect the feedback to the 8 ohm tap instead of the 16 ohm.
This will reduce the FB and it should have more gain.

Make sure the output tube cathodes have their ground between the 47uf and 47K resistor.

Regards
M. Gregg

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 Post subject: Re: 6V6 PP amp
PostPosted: 29 Mar 2020, 20:27 
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Joined: 06 Oct 2015, 22:05
Posts: 41
Thank you for the detailed tips M. Gregg.

I got it working, and it sounds better on speakers that weren't blown by the squealing sound. It still seems a bit low on power based on the estimated 10 watts that was shown as it is quieter than my SE 6L6GC amp but it does sound quite nice and is more compact.


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