hyperma 3 Posted April 9, 2020 Report Share Posted April 9, 2020 On 4/3/2020 at 7:09 AM, simmconn said: I'm not sure if I understand your reply. In the Megatron the first stage uses 12AU7, and the second stage uses 12AX7. What do you mean by "provide 24db gain to drive pair 12au7s"? Sorry,the first stage 12au7s to drive 12ax7. Quote Link to post Share on other sites
jamesmking 164 Posted January 20 Report Share Posted January 20 (edited) My apologies if this has been asked before.... As normal my first steps in a build is to get the circuit diagram and reverse engineer the gerbers to check them against each other.... looking at the circuit diagram pdf the decoupling caps have been omitted... fair enough, however 1. the circuit diagram shows a single 150K resistor from the led D3 to ground but the reverse engineer of the gerbers has two 150K resistors in series to ground.... 2. the gerbers seem to have two 330K resistors, one each from the 300V line to anodes 1 and 2 of the 21ax7. These resistors are not on the circuit diagram... here is my reverse engineer with components in pink missing from the pdf: NOTE this circuit diagram has not been checked Edited January 20 by jamesmking Quote Link to post Share on other sites
mwl168 822 Posted February 6 Report Share Posted February 6 Single digit temperature outside. Time to power up this glorious sounding amp. What a treat... 11 Quote Link to post Share on other sites
jose 1,637 Posted February 8 Report Share Posted February 8 I've had it "heating" my home for thee weeks 😁 4 Quote Link to post Share on other sites
jose 1,637 Posted February 9 Report Share Posted February 9 Yesterday, after three years of regular use (from 2018 to now) I measured some voltages for check how my Megatron aged. It is very nice to see that the voltages are still similar to that I did as a reference once finished it. The EL34´s glass have gotten a bit darker with use but otherwise my "baby" is perfect. As an anecdotal detail, my preferred valve for the first stage is still E180CC. 3 Quote Link to post Share on other sites
JoaMat 1,195 Posted February 9 Report Share Posted February 9 2 hours ago, jose said: EL34´s glass have gotten a bit darker like a Gran Reserva 2 Quote Link to post Share on other sites
mwl168 822 Posted February 9 Report Share Posted February 9 6 hours ago, jose said: As an anecdotal detail, my preferred valve for the first stage is still E180CC. That's what I am using in my Megatron as well, Philips E180CC SQ. Very happy with the outcome. 1 Quote Link to post Share on other sites
jose 1,637 Posted February 9 Report Share Posted February 9 Yep, it was a lot of fun looking for a tube with the right* gain for this position. *For us, of course. 1 Quote Link to post Share on other sites
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