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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 Mar 2018, 09:26 
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Joined: 23 May 2016, 19:39
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Just a little update. The transformers are taking a long time to process and ship from Edcor.
The plus side is it gave me plenty of time to pick at the small things. Should be wired up by the end of the week with the LM317K, TO-3 mounting kit and probe posts on the way.


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PostPosted: 06 Mar 2018, 09:16 
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Joined: 03 Sep 2017, 19:19
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Kevin Mitchell wrote:
Just a little update. The transformers are taking a long time to process and ship from Edcor.
The plus side is it gave me plenty of time to pick at the small things. Should be wired up by the end of the week with the LM317K, TO-3 mounting kit and probe posts on the way.

Looking good. Do you end up making a revised turrent board layout? Where is the 220k to 1k resistor mistake you spoke of?


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PostPosted: 06 Mar 2018, 16:21 
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Joined: 04 Jun 2008, 20:59
Posts: 3854
Location: Arizona, USA
Hi, The amplifiers continue to amaze me. I am using a pair as my main ones. The speakers I am using are quite efficient (96db/w) and the Poddwatt/Mini-Watt amps do an excellent job. The areas that are good for tinkering are changes in the coupling capacitors (I am using Audyn True Copper Caps at present), and tube rolling. Mine use JJs at the moment. Russian 6P15PEV are nice as well but you need to connect pins 3 and 6 together.

Good Listening
Bruce
Attachment:
Silver Mono Block E.jpg


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PostPosted: 06 Mar 2018, 17:35 
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Joined: 26 Feb 2018, 18:21
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Thanks for your help Bruce.
I wasn't concerned about negative feedback per se. I guess what I would like help with is how to set the Poddwatt up by eliminating the preamp section entirely. I really like the sound of the amp, and would like to retain as much as I can of that sound for the high frequency section in a bi-amp.


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PostPosted: 06 Mar 2018, 18:41 
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Location: Arizona, USA
Hi, There really is no preamp section. The Poddwatt is really a stereo power amp with a slightly more than average gain. Typical gain in power amps is for 1 volt of input to give full output, the Poddwatts will usually do full output with about 0.3 volts of input signal. The 5751 is a voltage amplifier that provides the gain and signal level necessary to drive the output tubes. If you remove it you will need to find a way to obtain about 15 volts of drive for the output section. It certainly can be done, but few line stage preamplifiers can do this well. There is no reason to remove the driver stage anyway. Just use one of the inputs on the amp (if you have more than one) and feed it from your main preamp. I do something similar with my system. I use a pair of the mini-blocks as power amps. Really no different from 1/2 each of a Poddwatt. Just no input selector and no volume control. A fixed 100K resistor to ground in place of the volume control. I use a modified Forewatt to drive them. The arrangement works great. I am a very picky person when it comes to sound quality and things like hum and noise (..there is none). With speakers in the 96db/watt range any hum or noise would be clearly audible.

Good listening
Bruce

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PostPosted: 07 Mar 2018, 06:46 
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Joined: 23 May 2016, 19:39
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thedecline wrote:
Kevin Mitchell wrote:
Just a little update. The transformers are taking a long time to process and ship from Edcor.
The plus side is it gave me plenty of time to pick at the small things. Should be wired up by the end of the week with the LM317K, TO-3 mounting kit and probe posts on the way.

Looking good. Do you end up making a revised turrent board layout? Where is the 220k to 1k resistor mistake you spoke of?

The fix is shown in the power board of the layout with the filament label. Per the V2C schematic you'll see the 220k in the power supply section is tied to ground and I guess it should go to where the 4.7k resistors are connecting to the 1K 1W resistor as the user eshazen has suggested in their layout and revised schematic.

I did revise the bottom board but it was simply splitting it and cutting out the LM317 section so I could use the chassis mount LM317K with those resistors off-board as well. To note... The PIO (green) caps were a bit larger than expected so I ended up using smaller poly ones in their place.


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PostPosted: 07 Mar 2018, 16:04 
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Joined: 03 Sep 2017, 19:19
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Kevin Mitchell wrote:
thedecline wrote:
Kevin Mitchell wrote:
Just a little update. The transformers are taking a long time to process and ship from Edcor.
The plus side is it gave me plenty of time to pick at the small things. Should be wired up by the end of the week with the LM317K, TO-3 mounting kit and probe posts on the way.

Looking good. Do you end up making a revised turrent board layout? Where is the 220k to 1k resistor mistake you spoke of?

The fix is shown in the power board of the layout with the filament label. Per the V2C schematic you'll see the 220k in the power supply section is tied to ground and I guess it should go to where the 4.7k resistors are connecting to the 1K 1W resistor as the user eshazen has suggested in their layout and revised schematic.

I did revise the bottom board but it was simply splitting it and cutting out the LM317 section so I could use the chassis mount LM317K with those resistors off-board as well. To note... The PIO (green) caps were a bit larger than expected so I ended up using smaller poly ones in their place.

Ahh I never saw that particular schematic. The versions I was going off didn't have that error. Any reason to go with the additional filter stage on the power board rather than the LR8 regulators?


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PostPosted: 08 Mar 2018, 08:46 
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Joined: 23 May 2016, 19:39
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thedecline wrote:
Ahh I never saw that particular schematic. The versions I was going off didn't have that error. Any reason to go with the additional filter stage on the power board rather than the LR8 regulators?

I went with the most recent schematic which was the one on page 54 where Bruce also explains some advantages of using the LR8N setup.

I didn't go with that configuration due to simplicity. I'd omit all integrated circuits in the Poddwatt if I could. I like oldschool things. But efficiency is most important. So I try to find my middle ground. It's the spirit of DIY. I'll consider changes in time with close observation as I use the amp. This is all a learning experience for myself.

I had the thought of designing a PCB where I would use the most efficient/modern configuration. But this being my 2nd tube amp build I feel more comfortable with point-to-point soldering where troubleshooting would be less of a hassle.


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PostPosted: 26 Mar 2018, 22:36 
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Joined: 23 May 2016, 19:39
Posts: 12
Today I had received the transformers. I couldn't help myself but to finish things up and turn it on. I feel anticipation got the best of me wiring the night away... and to my amazement everything seems awesome so far. It sounds lovely. I'm proud of this one and very thankful for such design to be out there for those who decide to build one of their own.

KM


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PostPosted: 27 Mar 2018, 09:42 
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Joined: 09 Oct 2012, 19:43
Posts: 318
Location: Vancouver Canada
Kevin did you do your own silk-screen for the writing on the front cover or did you send out?


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