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PostPosted: 10 Mar 2018, 08:55 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
Hi, I gather from your questions you plan to build the 832 amp. It will work, but IMO all the others are better. The 832s look cool, but really don't perform as well as other tubes. The common cathode is an issue as well. In order to accurately balance the sections you will really need to use the scheme in the latest Poddwatts. That is applying a small (adjustable) positive voltage to the grids. The budget Poddwatt IMO clearly sounds better than the 832 one. Depending on your needs I would actually build a typical Poddwatt with EL84s. It probably has the nicest sound of any small amp I have encountered.

On the questions though, I would not use a choke....none is needed so why bother. It would need to handle at least 200ma. The resistors are a sort of fail safe in the circuit . It will protect the amp from major damage, the AC mains fuse might not trip early enough to do this. It seems wonky, but in practice it works. Typical resistors of that type and size are not well matched...good in this case. So if there is a tube failure the excess current will cause one to overheat before the other and fail, resulting in the second one failing. I considered using an 80 ohm and 120 ohm resistor pair for even quicker action. (that will work well BTW) A fuse there would be an issue as it would have to be big enough to not fail all the time but not so big as to never fail. Plus it would not provide the CRC filtering of the resistors. A single 50 ohm 10 watt resistor in series with about a 500ma slow blow fuse would probably be OK. All resistors are 1/2 watt except the 100 ohm ones in the power supply for a Poddwatt 5 watt ones are OK. All capacitors in the power supply are rated at 350 volts. The small electrolytic in the driver stage is 25V, any capacitors across heaters are 25 v, the coulping capacitors need to be 200 or more. The X2 is a standard value of 275-310VAC.

Good listening
Bruce

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PostPosted: 10 Mar 2018, 22:56 
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Joined: 22 Feb 2018, 14:20
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Thank you for your helpful reply. I need to gather my priorities, however you have opened other options for the selection process.
Bruce


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