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Old 17th September 2012, 08:14 PM   #1
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Default 6V6 amp question

Hi all,

As you can see I am quite new to this board. I recently completed a 6V6 amp based on one of Poindexter's designs (I have attached a picture). I am very pleased with the sound, but am going to upgrade a few components to see (and hopefully hear) any effects. I am going to start with the coupling caps - I used sprague 'orange drops' in this one, but recently purchased some Mundorf silver supremes, which Poindexter recommended in his implementation guide. My question is, I have two values I can use, 0.33uf which is in the original plan, or 0.47uf. I am wondering if the higher value will bring any benefit at all? I ask because I read somewhere that higher coupling values may improve the bass response to a point. Thanks for your input.
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Old 17th September 2012, 08:22 PM   #2
Salas is offline Salas  Greece
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Hi and welcome to the forums. There is no picture to be seen, the attachments interface needs press ''go advanced'' under the posting window, then roll down. Maybe it was too big a file, see max allowed near each file type on the attachments interface. Maybe you need to re-size.

P.S. As for your question, many can elaborate and Poinz is a member too. You need attach or link the schematic if its free-share for defining such questions though.
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Old 17th September 2012, 10:20 PM   #3
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Default thanks Salas

Picture resend - it appears to be within size guidelines:

Attached Images
File Type: jpg amp4.JPG (736.2 KB, 177 views)
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Old 18th September 2012, 01:40 AM   #4
Salas is offline Salas  Greece
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Nice organic box. If in your shoes I would go with the 0.33uF as recommended because on 100K grid resistors 0.47uF will not make any big response difference, only it will be bulkier, plus this is a design with a detailed parts guide as I read so its better you follow Poindexter's values exactly since he had blended his tone with those materials and values carefully. Only keep oil carrying Mundorfs as much away you can from heat sources. Also try Tungsol reissue 6V6s at a point maybe.
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Old 18th September 2012, 03:13 AM   #5
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A circuit diagram would be good.

You could try the bigger caps as an experiment. If it sounds like a chugging motorboat, switch it off immediately and revert to the smaller caps. If not, listen and see what you think. Something with a range of instruments and heavy bass, with loud bits.

The chances are that the caps are correctly specified to fit in with the rest of the design. No larger than necessary is usually best for coupling to the output stage. The bass roll-off should have been optimised with a particular output transformer in mind. If your transformer is capable of supporting bass lower than the design expected, it will be possible to modify it. However, the coupling caps are just one frequency-controlling element amongst several.

Basically, you should ensure that the combination of output valves, transformer and speakers doesn't get lower bass than it can handle without causing unacceptable distortion and possible oscillation.
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Old 18th September 2012, 08:22 AM   #6
disco is offline disco  Netherlands
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Creative casing. The high pass (filtering low frequencies) is normally a function of the output transformer, as the most delimiting unit in the amplifier. Coupling caps can be too small so they come in to play, as can be catode bypass caps. This is not a good practice as it will bundle phase shift with the OPT (output trannie). Here I've put some theory behind the calcultation of the bypass cap which I unfortunately gave the name of Low Pass Filter, what should have been HPF.
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