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PostPosted: 10 Mar 2018, 08:55 
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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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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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PostPosted: 23 Nov 2020, 10:57 
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Joined: 16 Feb 2016, 19:45
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Location: Boston, USA
I'm looking for a good amp to build for the bedroom. I built an original poddwatt several years ago and I'm very happy with it. I was thinking of this "budget" model, partly to save a bit of money and partly to do something a bit different.

How does the performance compare with the original EL84 version? Maybe it's not worth the cost savings.

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PostPosted: 23 Nov 2020, 11:22 
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Hi, Within the power limits it is quite good. The sound is very much like the Poddwatts. It seems that the configuration makes them all sound similar. Anyhow it should do fine for you use. Pretty much any output tubes can be used. I used the 12A6 tubes as they were cheap and easy to get. 6AQ5s and 6V6 would be good alternatives. and are often cheap too. BTW I paid under $3 each for the 12A6s from the wholesale side of Antique Electronic Supply (the wholesale side if you can go that way is CE Distributors). I expect they have more but now likely at slightly increased cost. BTW they are where I and Oddwatt get most of our tubes. Great service and trustworthy. You might also look at the Junk box amp project. Rather similar and also great sounding.

Good listening
Bruce

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PostPosted: 23 Nov 2020, 11:25 
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Thanks very much for the advice and tips. I'll check out the AES wholesale side. Whatever I build, I'll post details and photos on the forums. Happy Thanksgiving!

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PostPosted: 23 Nov 2020, 20:02 
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Question about power transformer ratings. In the original Poddwatt, the power tubes are set at 83mA per channel or a total of 167mA, plus the SRPPs few mA. You use a full-wave rectifier with capacitor load. Referring to the handy Hammond cheat-sheet: http://www.hammondmfg.com/pdf/5c007.pdf they suggest that I(DC) = 1.00 x I(Sec)(AC). So with some margin I would think one might want about a 250mA rating. Is this correct reasoning?

On the original Poddwatt schematic you suggest a 360VCT @ 100mA for the PT. The Edcor "kit" includes an XPWR236 which is rated 360VCT @ 250mA (just what I estimated above). So is the 100mA a typo, or am I missing something? Maybe the 100mA was for one channel originally.

Looking at your "Budget poddwatt" you suggest a 400VCT @ 70mA transformer on the schematic, while I would think one might want more like 225-250mA.

Thanks for your patience with all these questions!

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