Dual-Mono Akai M8 Amp Build

cubby01 said:
Kegger likes him a 6EJ7 :yes: ;)

I didn't pay enough attention to the earlier PS post in the thread...is B+ in the same neighborhood with both circuits? Also are you reusing the OPTs? Looks like it from the pics. A little surprised Kegger didn't persuade UL OPTs?

Having one of these M8's myself I would like to know like to know what improvements are expected and, then once you've got it running, ultimately perceived by replacing the M8 Circuit with this new one? (gain, bandwith, bottom end, dynamics, stability, whatever)
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Yes he does, because they can be swapped in for many different types! I picked up a few EF184 tubes in 2008 having no idea what they were.


sssmokin99 said:
Interested as well. Ive got a Roberts 770x with a transport that is pretty well used up and amps that seem to be pretty much ok (slightly less gain on right channel). And beyond giving pots the deoxit tx, Ive done nothing yet. Curious if make and model of tube will make a huge difference.

Another Roberts 770x was my first good piece of stereo equipment. Used, very used it was, but worked great and got me hooked on R2R tape. Sold it at some point and this one is a different, slightly earlier one. The quality of build is still impressive to me, thats for sure....

Are you other gentlemen starting with "operating" units, or having to fix it before , uh, improving????

Fun, regardless...
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I've never heard these amps in their stock form--I bought them without their tubes + pulled from their players from another AKer at the last AK Fest. I was originally going to rebuild the circuit in a new chassis, but Kegger convinced me otherwise, and after chatting a bit he designed a circuit for me :D


nerdorama said:
If it's a typical cathode resistor bypass, it is in the signal path. All of the AC in that stage down to the bypass frequency (usually below 10Hz) will go through the cap. The resistor sets the DC bias. I'm guessing about your circuit, so I may be off base.

John
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Oh bugger, I need to do more reading on the topologies of these things. Thanks for the heads-up. The cap is in parallel with a resistor and it a 10v rated part.



Thanks for following along, guys.


Philip.
 
jaymanaa said:
The power cord is in the signal path. :music:
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Yea yea yea... :music:


Stalled for now--bought 3k resistors when I needed 30k parts, and the way I've laid out the circuit, they need to go on before I can put other parts on over top of them. :no: D'oh!

I guess I'll have to switch to another project for now... :sigh:


**note to self, swap out the 100k 1/2W resistor with the 2W part**
 
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Well darnit that sucks.. :(

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As to the cathode bypass caps, just bypass them with like a 1-5uf film cap as well. :thmbsp:
(there not as "critical" in the cathode of the output section)
 
Kegger said:
Well darnit that sucks.. :(

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As to the cathode bypass caps, just bypass them with like a 1-5uf film cap as well. :thmbsp:
(there not as "critical" in the cathode of the output section)
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10-4 Kegman :banana:

I also just realized that I ordered 100k resistors in 1/2W and 2W flavours, but installed the wrong one. :sigh:

Is it cool if I post your schematic?
 
It's your work of art! (which I deeply appreciate!)

To people who've been PMming me, here's what Kegger designed for my to build:

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Been a while since I've seen that schematic. ;)
(I was glad it fit your requirements on this build)

You'll have to let us know how she sounds when you get er runnin. :smoke:
 
Merry New Year!

Ordered the resistors I need last week, but store got my address wrong on the invoice (no street number?!) and it might take a while to get across the city to me (45min~1h by car, or $0.72 by post), also caught a wrong part installed (1/2W vs. 2W part, oops!), other than that nothing new.

School's spooling back up again, and this will be on hold before I can get the power supply finished.

Stay tuned for Summer 2013!
 
Resistors arrived! Got everything soldered + bolted up, but on my way out now. Photos tomorrow!

Also, I forgot to wire the heaters! WooOOoOOoo....... :sigh:
 
OK, so I know we talked about this (EF184 on the 0.6A heater and EL84+6CA4 on the 1.8A heater), but since I haven't built-up the power supply section yet, would it be beneficial to get DC on the heaters?
 
Young mr. thefragger man, wire the dang heaters up and listen to the dang thing. :D ...you can worry about DC later if you want, would probably only even consider doing it on the EF184 and unless you heard it with AC fils first you won't know that DC was even an improvement. Get crackin' :).
 
cubby01 said:
Young mr. thefragger man, wire the dang heaters up and listen to the dang thing. :D ...you can worry about DC later if you want, would probably only even consider doing it on the EF184 and unless you heard it with AC fils first you won't know that DC was even an improvement. Get crackin' :).
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Yes Sir Mr. Cubby01 Sir, the power supply top plate still needs some machining before I can build it up, sadly. I need to buy a milling machine when I get my own place :scratch2:
 
No worries, just another pushy voyeur here. ;) Nice job so far.

thefragger said:
I need to buy a milling machine when I get my own place :scratch2:
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Oh yeah, start hitting the DIY CNC sites :yes:. I started down that path many years ago but never got past analysis paralysis and moved on to something else. Wish now I'd actually done it as it would have paid for itself several times over.
 
cubby01 said:
Young mr. thefragger man, wire the dang heaters up and listen to the dang thing. :D ...you can worry about DC later if you want, would probably only even consider doing it on the EF184 and unless you heard it with AC fils first you won't know that DC was even an improvement. Get crackin' :).
Click to expand...

Now that's some dang good advice.:thmbsp:
 
Partied, home now. No heaters yet!

Also, a little bit of the OPTs are past the bottom? Glad I'm adding feet! (the power transformers will be worse!)


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That really looks nice,different.I wonder if the top plate will radiate enough heat to keep the transformers cool,I don't see any vents in the bottom.
I didn't see it at first Biamp? 4 Channel?
 
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Not really any need for DC heaters on an indirectly heated tube amp.

Just keep wiring away and getter fired up..:thmbsp:
 
s-petersen said:
That really looks nice,different.I wonder if the top plate will radiate enough heat to keep the transformers cool,I don't see any vents in the bottom.
I didn't see it at first Biamp? 4 Channel?
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I didn't think about the transformers getting hot, but there will be 3/4~1" feet when it's all done. Stereo amp, single-ended. The other opening is for the power supply.


Kegger said:
Not really any need for DC heaters on an indirectly heated tube amp.

Just keep wiring away and getter fired up..:thmbsp:
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I read on another board that for the EF184 I'd want DC. Eh, whatever. Got the heaters wired up. Went to start working on the power supply and then found that the plates need more metal work, and a way to affix the iron to the plates, etc...


Please don't hate me. It turns out the shielded wire I used is stranded silver... I can't see any copper on the cross section, so might be pure? I don't know, I guess the engineer wasn't joking when he said it cost $16 a foot when they bought it. (yes, I found it in the trash)



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