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PostPosted: 08 Aug 2020, 21:35 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
Hi, The type "D" with the power supply with the 2 LR8s. It also has one LM317 per channel. It incorporates all the newest and best features. This one uses adds a small (8-10v) of positive dc to the grids to balance the tubes. It keeps the LM317 from ever seeing less than about 5-8 volts on its terminals and thus away from the funky stuff it does when there is too little voltage to act correctly as a CCS. A side plus is about an extra 1/2 watt of clean output. IMO the extra complexity in the grid circuit is worth it.

EDIT: You can use either AC or DC heaters the difference in hum and noise is very slight and while measurable it is not audible. Just remember to add the heater lift voltage and not ground any part of the heater circuit.

Good listening
Bruce
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Type D.jpg


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PostPosted: 09 Aug 2020, 03:49 
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Many thanks.


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PostPosted: 12 Aug 2020, 04:19 
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Hello again Bruce, a follow-on question if I may; in your write-up on version 'E' you mentioned concerns over potential failure mechanisms with 'D', do you still have those reservations, and if not, what wattage/type would you recommend for the 1M pot?


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PostPosted: 12 Aug 2020, 21:53 
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Hi, Any part can fail. Fortunately this is very rare in these amps. The concern was mostly if the pot fails any number of odd things can happen. Things like a lot of positive voltage on one tube or the other which would likley cause the LM317 to fail while it tried to keep the current constant but the voltage was excessive. I would be possible to derive the voltage differently perhaaps with a regulated source, but that complicates the design. I goes against my less is more thoughts. So in actual use (in the kits and by folks talking to me) there has not been any of the failures I thought might happen. So, I would not be too concerned. The kits use 1/2 watt controls (trim pots). They appear to be fine and there are numerous sources, just get a good brand. I believe at the moment we are using Vishay ones, but I have personally used some from Bournes as well.

Good listening
Bruce

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PostPosted: 13 Aug 2020, 09:09 
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Thanks again Bruce, that fixes the build for me. I already have the transformers (albeit the power transformer may have to be returned because of paint bubbles) and chassis, with the valves coming next week, and the remaining parts to be ordered for an Autumn build. Will report back then.


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PostPosted: 25 Aug 2020, 09:46 
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Joined: 01 Feb 2015, 13:41
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Location: Athens-Greece
Hello to everyone. Just finished the second EL84PP following Bruce's schematics.

Some material upgrades:
Output transformer with amorphous core made by MONOLITH
V-Cap CuTF capacitors
Audio note tantalum non magnetic resistors
Yamamoto tube sockets
PSVANE tubes
Jensen electrolytics audio grade
Silver wires (signal) and Copper Oxygen free wires (power)

Thank you Bruce for your excellent schematics
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PostPosted: 25 Aug 2020, 20:27 
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Hi, I'm glad to have provided the design for everyone to use. Your build looks nice. Probably some of the highest quality components I've seen used in a Poddwatt. Should be really nice sounding.

Good listening
Bruce

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PostPosted: 26 Aug 2020, 04:22 
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Thanks Bruce. To my ears sounds nice but I am not an expert. However, very soon I will be in a position to run a series of tests with both :
1. Frequency generator and digital oscilloscope
2. Audio analyser Quant asylum QA401
I will upload the test results when available. It is an interesting project to see how can we improve test results with tweaks, materials etc


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PostPosted: 29 Aug 2020, 15:02 
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@dimitris1811 Really nice work. I am new to this group and stumbled across this while researching the Poddwatt.
I live in Germany and wanted to try a tube kit. To date I have restored old 60’s tube radios but wanted to try something with known good parts. I also restore old DUAL and Lenco TT’s so I thought the Poddwatt would be a nice complement combined with a good preamp.


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PostPosted: 01 Sep 2020, 08:50 
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Location: Athens-Greece
Thanks a lot. Working with tubes is always fascinating!


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