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Raphael Audio EL84

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audiorado

Member
Joined 2009
#1
For sale some old but good pcbs from kit to build el84 tube amp. This pcbs are with ecc82 input tube and 4x el84 output tube per chanel.I bought this some years ago and used this amp for about 4 years in my second system.You only need to put your own psu with piwer trans and coupling caps and the amp will work. This pcbs are old, maybe from around 1995,but in still goid shape, there are maybe some 2 or 3 bad traces but you can repair this without a problem. I also have original output transformers from this kit from Welter. Verry good transformers good up to 50 watts. The pcbs were upgreded with Takman carbon film, metal film resistors and input resistor is from amtrans. There are on each chanel one mundorf 20uf mkp psu cap for last cap in psu for input tube. I used el84 heaters with AC and input tube with Coleman reg. Price would be 200 eu plus shipping or best offer. The output trans are verry bigg and havy. I can also put for the buyer my 4 year old el84 output tubes from JJ and a pair of input tubes from tungsram.More info ower contact. I also have original Elektor magazine in which the project is explained step by step.
 

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#11
According to the original article, it's 775mV with the 10k/100R NFB voltage divider and ECC82's as the small signal tube.

Anyway, I don't see the necessity of coupling cap C2. Just for ECC 82/12AU7 there are many examples around with slightly different component values that allow to omit it.

Best regards!
 
#12
The 775 mV surprises me. It would think that this means that there's hardly any feedback going on.

The gain of the first stage is 15 x at best. The phase-splitter has no gain. The EL84's need about 9 Veff for full power. So that would give a sensitivity of 600 mVeff without feedback being applied from the OPT to first stage. Or am I missing something?
 
#15
Regarding NFB, Frank Raphael, the article author, states that with ECC83's input sensitivity would be about 350 mV for full drive (32 W output power) as well as increasing NFB, which is possible, would result in some sterile, lifeless sound. After all, one has to ask then if he really was after HiFi?

Note that the 330 pF capacitor across the 10k NFB resistor matches with his original Raphael transformers. The Welter's in this offering most probably aren't bad either, but probably need the compensation adjusted accordingly.

Best regards!
 
#18

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