pmillett TUBE preamp project begins!!!!

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Curran

Well-known member
Joined
May 15, 2010
Messages
88
Hey all- this is a funny little PCB I stumbled apon wjile browsing ebay. This is a two tube preamp build using a Llundahl 7903 1+1+1+1:2+2+2+2 input transformer. I had the 7903 from an OSA preamp of mine that died and never worked right anyway so I bought this PCB and sourced the parts for this build!!!. NOW I have too wait for mouser to get me the last of my goodies BUT I figured I would post a little build thread here for people too check out. Here are some pics and what not. As I move the build along i will post more picks for people to check out!!! here is the link to my facebook........

http://www.facebook.com/media/set/?set=a.10150220686616780.310591.671496779&l=bd69d45bf3

Love and Metal Curran
 
had the tubes n ceramic sockets show up today!!! woo hoo it looks so cool with all of the little things getting laid out on the board!!!
 
I'm interested to see this project unfold! I exchanged emails with Mr. Millett and he seems like a nice, enthusiastic guy.
 
got most of the parts ( only one resistor missed on the BOM, and one parts set that is wrong, which is MY fault) other than that here is the resistor set loaded and soldered on then onto the caps n inductors


http://www.facebook.com/media/set/?set=a.10150220686616780.310591.671496779&l=bd69d45bf3
 
here is the last of the pix before i can fire it up

http://www.facebook.com/media/set/?set=a.10150220686616780.310591.671496779&l=bd69d45bf3

I am waiting for the correct switches and then I can give it a WAAAAA HOOOOO!!!! does anyone out there know how to test an input transformer by the way? I have the Lundahl 7903 in this thing but now i am sweating it working
 
Looking good! I love that first moment. Is it going to work? Catch fire? Very exciting.

Do you have a tone generator? You could put a tone on the input and measure AC on the other side. You could also test continuity on the primary and secondary windings. You mentioned that you took the transformer from a pre that stopped working, but transformers rarely fail, so it should be fine.

Looking forward to seeing the finished project!
 
AAAAAAAAAAAAAAAAHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH HAHAHAHAHAHAHAHAHAHAHAHAHAAHAHAHAHAH
Tube tone preamped victory is MINE!!! all shall bow and worship at the glory of my TOOBZZZZZZZZ!!!!!!! guess what guys, it works!!!!

<object width="400" height="224" ><param name="allowfullscreen" value="true" /><param name="movie" value="http://www.facebook.com/v/10150230074596780" /><embed src="http://www.facebook.com/v/10150230074596780" type="application/x-shockwave-flash" allowfullscreen="true" width="400" height="224"></embed></object>

this is the embeded link to me geeking out on it with my iphone


http://www.facebook.com/media/set/?set=a.10150220686616780.310591.671496779&l=bd69d45bf3

this is the link for the final pics I took of it!!
Still need to do the metal work but I will be using this beast on a session in the studio tonight!!! very very cool. Mr. Millett was very helpfull with all of my questions and info on the build he deffinatley gets BIG UPS from me!
 
Sorry to bump an old thread but I found this guy's web page about a year ago and I finally ordered the PCB from him. Then it dawned on me I wanted something rack mount, so I ordered a 2nd PCB and I am going to put 2 of these in a 2U rack box and build a 2 channel unit.

Maybe I'll start another thread when I get building, but my question for the OP is where did you source the inductors (4 of them) in the metal cans? When I search the part number in his BOM I get inductors that aren't in cans. Does it matter?
 
Ricardus said:
Maybe I'll start another thread when I get building, but my question for the OP is where did you source the inductors (4 of them) in the metal cans? When I search the part number in his BOM I get inductors that aren't in cans. Does it matter?

Probably a non-issue if it's the  equivalent. Also, those blue cans are probably just a protective plastic? Are you worried about magnetic shielding?

Edit: i just noticed those inductors are part of the +48V circuit. Then it's definitely a non-issue.
 
Conviction said:
Probably a non-issue if it's the  equivalent. Also, those blue cans are probably just a protective plastic? Are you worried about magnetic shielding?

Edit: i just noticed those inductors are part of the +48V circuit. Then it's definitely a non-issue.

I was concerned about shielding yeah. The part number are identical on Mouser so it's definitely an equivalent.

Thanks for the reply. My Mouser BOM for this is on the way, and I'll be ordering the Lundahl transformers soon. I plan to balance the output with Sowter 3603's.

I'm not a design engineer, just a builder. I have a friend who is a very good designer/tech and after looking at the circuit he had some concerns about where the gain pot was. Any ideas why?
 
Ricardus said:
I was concerned about shielding yeah. The part number are identical on Mouser so it's definitely an equivalent.

Thanks for the reply. My Mouser BOM for this is on the way, and I'll be ordering the Lundahl transformers soon. I plan to balance the output with Sowter 3603's.

I'm not a design engineer, just a builder. I have a friend who is a very good designer/tech and after looking at the circuit he had some concerns about where the gain pot was. Any ideas why?

Was he referring to the  overall topology? Perhaps he meant the pot before the ECC88 grid. I've heard good and bad in terms of S/N ratio. Actual gain is set in the feedback circuit, though. The pot acts as an attenuator of the input signal. If you're worried, remove it and replace it with a input pad.

I've built several Millett-designs and I really trust his engineering work.
 
Conviction said:
Was he referring to the  overall topology? Perhaps he meant the pot before the ECC88 grid. I've heard good and bad in terms of S/N ratio. Actual gain is set in the feedback circuit, though. The pot acts as an attenuator of the input signal. If you're worried, remove it and replace it with a input pad.

I've built several Millett-designs and I really trust his engineering work.

Yes, now that I remember this is what he said... input pads would be better. I don't think I'm good enough to change the design so I'll build it as is and see what happens.

I'm more concerned about putting a switching PSU in the case with it.

I'd be curious to hear from the original poster, Curran, to see what he thinks of it now that he's used it for many years...
 

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