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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: 27 Jun 2011, 16:27 
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Joined: 06 Jun 2008, 18:23
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Location: Australia
Thanks for the info. Bruce. I do like the 6N1P and would only gang plates in the case where it will be driving the SS stage.

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PostPosted: 18 Aug 2011, 21:27 
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Joined: 17 Jan 2009, 18:30
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Location: Victoria,BC, Canada
A couple of shots of my Poddwatt- it's a good-sounding little amp. Thanks, Bruce!
Attachment:
podwatt_1.jpg


Attachment:
poddwatt_2.jpg

Power transformer was 'right at the limit' supplying the B+ current, so I added a separate filament transformer to take some load. Output transformers were from a Heathkit SA-2 originally. An eBay seller had parted out the amp.

Chassis was from my used/junk pile. I cut the top out and pop-riveted an aluminum plate on and added a bottom plate.
Ends and knob are black cherry, oil finished. Hammertone black paint- hides lots!


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PostPosted: 18 Aug 2011, 22:04 
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Looks good and the sound?

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PostPosted: 18 Aug 2011, 22:26 
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mwhouston wrote:
Looks good and the sound?

That's about as detailed as I get...sorry!
For PRAT, black soundstage, etc etc you need another guy! :D


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PostPosted: 18 Aug 2011, 23:33 
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Have you put a CRO on it? I know Bruce is a big fan of the tubes for good sound.

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PostPosted: 18 Aug 2011, 23:46 
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mwhouston wrote:
Have you put a CRO on it? I know Bruce is a big fan of the tubes for good sound.

Looking in my Oz to Canuk translation guide..... :mrgreen:

CRO='scope ?
as in: square wave response?

I think I did that but didn't get pics. I'll re-do.......


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PostPosted: 19 Aug 2011, 00:36 
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CRO = Cathode Ray Oscilloscope. Function generator generally produce sine and SQR waves.
Not just square wave response but max power into 8 and 4 ohms sine wave at 1khz
Frequency response (upper and lower -3db points)
SQR wave at 100hz, 1khz and 10khz at 1w into 8 ohms (pictures please)

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PostPosted: 19 Aug 2011, 01:03 
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Location: Victoria,BC, Canada
Don't know if I can get all that info for you - I'll have a look tomorrow.
How do I get the -3dB measurement?

How much power should I be getting out of this thing? And do I just measure AC voltage across 8 ohm load resistor, then calculate power?
EDIT:
Well, I hit my files and did a bit of reading (it's been a couple of months since I completed the amp). Apparently, I should be getting about 5 watts out into an 8 ohm load. I measure 4.5 volts across the 8 ohm dummy load resistor with my HP bench DMM, with a 1v 1000Hz sine wave input and volume 'wide open'. This works out to 2.5 watts? And it is clipping anywhere above about 1 o'clock on the volume control (100k pot), with a 1v input.

So I think I need to dive into it and do a few more measurements?


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PostPosted: 19 Aug 2011, 10:20 
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Hi, Nice build. I like the wood knob. The actual performance should be measurable, but difficult to compare to the originals as different transformers were used. Most configurations I have measured deliver about 5 watts RMS per channel. Response with the specified transformers is from right at 25 to past 21K within one db. Usually much better than that. Upper -3db point is typically 40KHZ, Lower about 15-18HZ. Distortion is less than 1% at 1 watt and about 2% at 5 watts. I have determined that some of this is driver tube dependent. If you use the 5751, the NOS ones (generally Phillips or Sylvania) tend to have higher distortion below 100HZ and slightly better above 5K. The new Sovtek ones are more consistent across the whole range and are my personal choice of all I have heard. Generally these amps are very clean and detailed with a easy to listen to quality. Quite good on sensitive speakers. I spent a little time listening to mine just yesterday (to compare a "retro" build of it with 6SL7s and 6V6Ss). On my Martin Logan Vistas it put out enough sound to be fine for anything but seriously loud music. At high volumes it overloads cleanly, but can't deliver. No surprise. BTW, the 6V6 version is slightly less powerful (still enough on the Vistas for casual listening) and a bit toward the warm side overall.

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PostPosted: 19 Aug 2011, 17:46 
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Thanks Bruce. Nice to hear the Sovteks are the best. Good to find a tube which is reasonanbly priced and not NOS. I have an EL84 build in mind for the far distant future. It will be SE. Gio has a good cct. on his site using an EF86 driver. I heard some old Quad amps with EF86 drivers. The owner claimed they gave the amp a punch and drive not normally found with other driver tubes. As I said "One Day".

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