Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => AmpTools/Tech Tips => Topic started by: spud on May 25, 2010, 11:05:13 am

Title: RK/CK sub box
Post by: spud on May 25, 2010, 11:05:13 am

Hey guys, 

Haven't posted here before or if I did it's been so long that I don't remember - anyway, I'm in the process of building my own take on a RK/CK sub box.  My plans are here: 

http://s252.photobucket.com/albums/hh7/spudjds/Builds/MISC%20Projects%20and%20Ideas/RK-CK%20Box/ (http://s252.photobucket.com/albums/hh7/spudjds/Builds/MISC%20Projects%20and%20Ideas/RK-CK%20Box/)

Has anyone built or bought one of these?  Weber sells them but mine is a little "enhanced" - I added bypass switching, a larger pot (10k 5w) and binding posts/test points so you can add whatever values of cap/resistor you want outside of those available.  The caps on the rotary are low voltage (50v -100v) so it would be primarily for pre-amp use but with the binding posts and the bypass switch, it could be used for PA as well or the PSU if needed.

I'm still waiting on some of the caps - had most just needed the last 2 (33 and 68 uf).  I'm going to put it into an RS box I have - 6 x 3. 

Any input/comments/ideas would be appreciated. 

Jim

Title: Re: RK/CK sub box
Post by: RicharD on May 25, 2010, 12:22:48 pm

I would suggest another 12 position switch in lieu of the pot and use standard resistor values.  I have built 2 cap decade boxes, 1 for coupling and 1 for cathode bypass.  Here are their values  (all uF):

A.  .56, .22, .15, .1, .047, .033, .022, .01, .0047, .0033, .0022, & .001  (630V)

B.  .56, .68, 1, 2.2, 4.7, 6.8, 10, 15, 22, 35, & 100  (25V)

Title: Re: RK/CK sub box
Post by: spud on May 25, 2010, 12:31:35 pm

Thanks - That's a good idea but I was thinking that the pot could dial it in well - I guess having to deal with measuring the value afterward  might be a pain.  I know that a 10k is pretty big but it was what I could find at the time - weber uses a 5k but I would think 2.5 would work ok too.  I have another 12 position so it's doable -

What values did you use for the resistors on the rotary?

Thanks -

Jim

Title: Re: RK/CK sub box
Post by: RicharD on May 25, 2010, 11:01:39 pm

I haven't built a resistor substitution box yet.  I probably should.  I'd REALLY like to have a power resistor substitution box that ran from 10 ohms to about 5K at 10 watts.

Here's 3/5th of a true decade box.

Title: Re: RK/CK sub box
Post by: spud on May 26, 2010, 01:54:51 pm

That is pretty comprehensive - I guess I'd be more interested in "typical" RK values - 820R, 1.2k, 1.5k, 2k...etc. 

Thanks - I'm going to see if can come up with a list of 12 "typical" values for my 2nd rotary.

Jim

Title: Re: RK/CK sub box
Post by: HotBluePlates on May 27, 2010, 11:50:43 am

Need 820 ohms? Just engage the switch connecting the 1st rotary switch in Buttery's diagram.

Need 1.2k? Engage the 1st and 2nd switches, select 1k on the second, and you get your choice of 1.22k or 1.27k. Or you could round down and go for 1.15k.

But all that would require the individual rotary switches to be wired in series; the diagram shows them wired in parallel. But that's an easy change to make once the switches are in-hand.

Title: Re: RK/CK sub box
Post by: RicharD on May 27, 2010, 05:08:56 pm

>the diagram shows them wired in parallel.


oops!  I knocked out that drawing way too fast.