Well got my tranies from Edcor in and got her built and it's alive! Really does sound fantastic! She's a very heavy girl - more than I thought she'd be .. that's some heavy duty iron (35lbs in Edcor iron). I build them fast as I get caught up in doing this and don't even take a break or eat .. it's an illness - have to learn to go slowly and walk away. Love the 300B sound- it's my 3rd 300B ive'd owned and its tops - Thanks for all you do for our community! it's an excellent design! I did not do the copper ckct board on bottom of power trans - do have a small rubber spacer that lifts it up maybe 2-3 millimeters - everything worked out of the gate - needed no trouble shooting - voltages spot on - dead silent-no hum, Just an excellent amp!!! will probably be adding the amp meter also.
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Awesome build Danny!
Just thought if anyone is also going to do this - the Triad F-313X 6.3vac 600ma needs to look like this with the resistors as there is no center-tap. Also I believe the 12BH7 is a much better sounding tube than the 12AU7's.The 12BH7 requires 600ma where as the 12AU7 needs 1/2 or 300ma- if you prefer the 12AU7 I'd get a 300ma transformer but you will not be able to run the better 12BH7 tube. Another thing - either way you will need to get a transformer for the heaters as the one in Skunkies just has enought to cover the 6SN7's so you can't tap into that. You can follow my RC combo for your B+ as there is enough juice in the 200ma power transformer - 1/2 the 12BH7's draw only 2.25ma each in this circuit or 4.5 ma total - most of the juice feed the 300B's mine draws 79.5ma each or almost 160ma total. Just thought I'd throw all this out there if some are not up to the math on what's needed. On another note - been running the amp everday and it's truly a fantastic sounding amp- everything works so well together and the output transformers sound as good or better than the high end ones with the 300B tube. Thanks Skunkie!!! your awesome!
All really great info Danny - thanks for sharing!!
just wanted to share my thoughts on volume pots - myself I prefer the log type they have indents when turning -- if you measure these with the other type these they are dead on accurate balanced each side and I never had a problem finding my "perfect" volume- discovered using these restoring vintage amps/receivers as they are also the only ones you can find with "loudness tap" pins- the ones I got were from China and probably not Alps but they are quality made and accurate and been using them for years - never had a problem. I also have a few dozen of the small mounting boards - because I always hated wiring these up with out them. -
If anyone wants to do the same 4s preamp to Skunkie's 300B - Match made in heaven. Before I went ahead with this I tried with my standalone 4s I built for use with my Dynaco ST-70 and it sounded fantastic .. mind you I have a slightly weak line source in with my dac so this really fits the bill for me.
well I did it ... It's fantastic ! ! ! ! ! ! ! added the 4s universal preamp into it ... it rocks! Glad I did it. In the pic I don't have the bottom on yet and the black thingy in the middle is a vent - found some stainless black vents for a 3/4" hole on amazon 10 for $5 and added a nice blue led power light to match the Edcor's. If anyone else is intrested in doing the same- need to swap 100K volume pot for a 250K -add a small transformer for your 6vac- I used a small Triad F-313X -600ma- heater- went with the 600ma because I like to run the 12BH7A in the 4s preamp and I added a load resistor-a 47K off the b+ with a 22uF 450V to grn for power to get the 250V needed. It's been kicked up a notch ... well worth it in my humble opinion.
just a thought .. don't want to screw up a good thing- was thinking I like the sound and headroom with that 4S universal preamp feeding the 300B - the simple simple one and seeing it even lowers the THD .. What if I got a very small hammond 500ma 6,3v for a 12AU7 and a simple 2 resistor voltage divider for the 250V B+ and punched another hole in chassis and wired her up like this?? it would be a very easy preamp add on? Thoughts?? If she gets any heavier I'll need a dolly to move it.
just for grins tested THD on my old Distortion Analyzer... tested as is and thru tube preamp .. got very respectable readings for a 300B- what was really weird for me was when I used pre amp i got even lower thd readings at lower wattages. other than higher line Vrms in driving the input- testing I used pre - (had the amp pot all the way up) maybe because the driver stage in the 300B is getting a hotter signal- more amplification taking place proir to the 1st 6SN7? also don't have the 1K resistor at the pot to the grid, other than that it's the exact schematic. Just an intresting tidbit.
Update... After a couple days listening Iam really happy with how this project turned out. Having another 300B amp with lundhal output transformers I can honestly say this one sounds as good or better- Skunkie's amp might even beat my other 2 in the bass dept - no need for a sub either - the Edcor's really match up good with the 300B tube. Wonderful amp!!