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Old 28th August 2006, 05:13 PM   #1
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Default ECC88 Class B

Gentlemen,

I 'm considering in trying out this little amplifier stage, if i have a favourable opinion about it from you(i know it's class B, but if it sounds good as an experience...), as euros are short at this time for custom winding output trannies for "silly" projects.
I'm considering using a transformer as phase splitter for this one, as my stock only has 2 ECC88
Thank you!
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Old 28th August 2006, 05:35 PM   #2
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If 27ma is the idle current, its not class B. Or is that peak current with 2V RMS signal? It may be class AB?
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Old 28th August 2006, 06:10 PM   #3
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I made this schematic from the tables, where it states as being class B... :S
2Vrms for each tube, 4Vrms for full swing.
I just wanted to knwo if it's a safe bet...
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Old 29th August 2006, 11:36 AM   #4
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Personnally i think its a bad idea. ECC88 are unreliable at much about 16mA and only give their best reliability below about 10mA.
Think about using some 5687 or 12b4, both reasonably cheap and hard wearing. The ECL82/86 would be even better bets as you can use plate to plate feedback to get the output impedence really low. All these valve options are cheaper than ECC88's.

What type of mains outputs would you be using ?

How do you plan on doing your phase splitting?

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Old 29th August 2006, 12:48 PM   #5
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Quote:
Originally posted by Shoog
All these valve options are cheaper than ECC88's.
I dunno. The price of ECC88's on ebay are in the basement. Other than Telefunkens, you can get them (even Mullards) for a buck-a-bag
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Old 29th August 2006, 05:27 PM   #6
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Quote:
I dunno. The price of ECC88's on ebay are in the basement. Other than Telefunkens, you can get them (even Mullards) for a buck-a-bag
I hadn't checked recently. Still I don't think the ECC88 would be a good choice.

I thought about how you might approach this and get a good result. If you used 5687's you could probably go self splitting as in the simple EL84 amp on Diy paradise. If using toroidal mains as outputs, place a LM317 in each cathode to keep the current balanced. Could sound really good.

Another approach would be to use the ECC88's as an initial gain stage, put this though a mains toroidal with a step down ratio of about 10:1+1, then put this into a pair of ECL82 with plate to plate feedback and finally into a mains toroidal as the output (though getting one with the right ratio ,might well be impossible). Very cheap to build and potentially an excellent sound. Interstage transformer phase splitting is very high end indeed, and with the step down toroidals work very well in this role.

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