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Old 10th November 2008, 02:49 AM   #1
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Default Making component choices (6V6/EL84 PP)

Hi,
I'm trying to design and build a push pull amp using either 6L6s or EL84s. I'm trying to narrow down parts to buy so that I can do some prototyping and testing.

Power transformer:
Will 275-0-275 get me a rectified B+ of 300 volts?
What current rating should I aim for? If I knew exactly what I wanted to build I could calculate it, but as I'm kind of going to be designing as I go I can't do that. What current rating do I need?

Output transformers:
6V6/EL84s have an 8k or so output impedance, eh?
Are the Edcor transformers a good deal?
http://edcorusa.com/products/transfo...p25-ms-8k.html
Yay?
Are those honestly worth the price increase from these?
http://edcorusa.com/products/transfo...pp15-8-8k.html

It seems the former can go 50 Hz lower and has multiple impedance taps. I don't think I really need multiple impedances though anyway.

Thanks!
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Old 10th November 2008, 03:20 AM   #2
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Buy Edcor's model CXPP25-8-7.6K or its 4 Ohm equivalent, depending on the speakers you use.

The cores of the little $20 trafos will saturate from the NFB induced LF error correction signal.

Allow for at least 150 mA. of B+ current. The "El Cheapo" voltage doubler PSU very comfortably supplies 200 mA., while holding costs down.
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Old 10th November 2008, 03:29 AM   #3
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Thanks.
Btw, could you link me to the El Cheapo? I keep hearing things about it, but all the links I find are dead.

Thanks!
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Old 10th November 2008, 03:40 AM   #4
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Default Re: Making component choices (6V6/EL84 PP)

Quote:
Originally posted by rockgardenlove
If I knew exactly what I wanted to build I could calculate it, but as I'm kind of going to be designing as I go I can't do that.
In my opinion "designing it as I go" is not the proper way to build an amplifier unless you are very experienced and have a lot of parts at your disposal. All amplifiers are a carefully chosen set of compromises. You would be much better served to decide on that power level (tubes) you want and next choose a circuit that you like. Then proceed to acquire the parts needed. It's easier and better that way.

Quote:
Are the Edcor transformers a good deal?
Are those honestly worth the price increase from these?
Yes, they are a good deal. And yes, the price difference is not unfair since it's a bigger unit with more iron, copper and labor in it's makeup.

Victor
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Old 10th November 2008, 04:02 AM   #5
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The "El Cheapo" SAGA is here. Get your waders on!
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Old 10th November 2008, 04:09 AM   #6
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Default Re: Re: Making component choices (6V6/EL84 PP)

Quote:
Originally posted by HollowState


In my opinion "designing it as I go" is not the proper way to build an amplifier unless you are very experienced and have a lot of parts at your disposal. All amplifiers are a carefully chosen set of compromises. You would be much better served to decide on that power level (tubes) you want and next choose a circuit that you like. Then proceed to acquire the parts needed. It's easier and better that way.



Yes, they are a good deal. And yes, the price difference is not unfair since it's a bigger unit with more iron, copper and labor in it's makeup.

Victor
Thanks for the reply. I actually am going to design the amp first really, it's just that I want to have the power supply so I can build the preamp stages or whatnot first and test them with my scope.
Cheers
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Old 10th November 2008, 10:58 AM   #7
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Default Re: Re: Re: Making component choices (6V6/EL84 PP)

Quote:
Originally posted by rockgardenlove
...it's just that I want to have the power supply so I can build the preamp stages or whatnot first and test them with my scope.

If you build the AF amp and phase inverter before the finals are constructed, the supply voltages will be higher than in the finished product. That might interfere with whatever testing you were planning to do.
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Old 10th November 2008, 12:33 PM   #8
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Good point, thanks for the post. I guess I'll probably have to build a different version of the PSU then testing the preamp. Cheers!
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Old 10th November 2008, 12:44 PM   #9
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So, how does the Hammond 370 HX sound?
275-0-275
200 mA
6.3 v, 5v filament taps

That looks right to me. The price is 110 though.

The 370 FX is the same except for a 150 mA current and a 90 dollar price tag. But yeah. Maybe I should design the circuit first so I can figure out the current draw...

Cheers!
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Old 10th November 2008, 01:52 PM   #10
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Take a look at the Allied 6K56VG.
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