The Vintage Altec Codex

[junker]

A cheap digital multimeter isn't a bad idea... I have a reasonably-priced Fluke.

[grantray]

Looks like 10.5uf caps aren't that in demand these days. At least not on Parts Express or Parts Connexion... Eek. Is it better to move up to 11uf or go down to 10uf?

I guess I should start scrounging eBay for those NOS Russians.

[junker]

The tolerance of the stock caps is 10% so 5% off isn't the end of the world... maybe not audible but MBGO in that size are only a couple bucks. The MBG-CH...or especially the the KBG-MN low (100-400v) are really good. The 4 is way more important the then 10.5 btw - inline to the horn!

[grantray]

Originally Posted by junker

The tolerance of the stock caps is 10% so 5% off isn't the end of the world...

Roger that. Then, if I don't locate 10.5uf caps, I'll up the capacity to 11uf.

And thanks for the tips on a good solder station and multimeter. I've got a cheapo soldering iron from Radio Shack that's been decent, but I'm ready for something a touch better if I'm going to be building anything masquerading as a quality component.

[junker]

I do something like these KBG-MN pack of 4 and use your multimeter to pick the two with the highest values:

http://www.ebay.com/itm/Electrically...%257Ciid%253A1

http://www.ebay.com/itm/2x-4uF-400V-...sAAOSwqu9VJ8kZ

[junker]

I had to update the first one to MBG-CH because there aren't any KBG-MN in 10uF. Those are matched very closely...

[grantray]

Originally Posted by junker

I do something like these KBG-MN pack of 4 and use your multimeter to pick the two with the highest values

Those 4uf KBG-MN caps are only a pair, sadly. Not 4x. But I might snag 'em anyway. Any idea how they compare to 200v or 400v 4uf Mulcaps?

[junker]

Yah, I had a 4 pack on there before editing. But they were only 1.0 not 10. - there aren't any of the KBG in 10.

The 4's are exactly what the schematic calls for. Low voltage is okay for this app and smaller and break in faster. 400 is okay too if you want.

As far as other caps go I'm going to stay out of that... You could look here if you are thinking about some other film caps. I've had Mundorf Supremes before.

http://www.humblehomemadehifi.com/Cap.html

[grantray]

Originally Posted by junker

As far as other caps go I'm going to stay out of that...

Ha. I was only asking in case shipping from Bulgaria for the KBG-MN caps is expensive and takes forever to get to SF. Definitely not interested in going down the rabbit hole that eventually leads to $400 capacitors

I've been sketching, and I think I've got the board mostly laid out. But the schematic doesn't include the L-Pad, when, obviously, there's a big L-pad sticking out the back of the cabinet. Is it placed in the middle of series for the 20 and 25 HF resistors, or is it simply anywhere after the 4uf capacitor before heading out to the horn?

[junker]

Okay yah gotcha!

R1 and R2 is the variable resistor in the path to the horn, and the parallel (to ground) is what works with R1 to attempt to keep the impedance seen more flat. It's the horn level control.

This is where the big 16 ohm L-Pad comes in and just replaces all that. Trust me on this one this is what you want to start with... Using two fixed R for those 0-25 "x" & (20+(25-x) is where you will bang your head getting it dialed in for level. And those damn resistors sound so different... to the point where you are using different values with different types of resistors. I have lots of time with Vishay z-foil, Mills MRA 5 and 12, Duelund, and Allen Bradley 2w)... So different. I'd probably do an L-Pad with another iteration, or maybe Ohmite Brown Devils R like stock if I went to do another iteration

L-Pad is the best way to present a 16 ohm load across a wide adjustment range. Done. Then if you want to try to go more pure replace this with an auto former in the future.

Those USSR caps are soooo good for the money. Don't let the low price throw you off. Yes, they get you back some on the shipping but price those caps with shipping to even something as staple as Munforf Supreme (which sound detailed and spatial but lacks bit in organic liquid textures. WPIO is the way to go there. KBG-MN does it for 1% of a Duelund CAST. Yah they probably aren't quite as good with the copper but they are really good and for the money it would be stupid to not do em. Look up a 4uf Duelund Cast on Part Connexion... hahaha