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the CTH (Compact Tube Hybrid) Rev A thread... - Page 4

post #46 of 536
3/25/11 at 4:58pm

I have some questions about the mechanical fastening of the PCB and supporting the tube socket.

 

1.  Given that the PCB can slide foward to backwards, do people use a standoff or something, potentially bolted through the bottom of the case?  Last time I did something like this I just screwed a few small screws in the track which the PCB slides to wedge it in place, but I wondered what other solutions are.

 

2.  I read most of the previous CTH thread and it seemed like few people support the tube socket.  Maybe I missed a post or so, but wouldn't you be worried about flexing the PCB over and over as tube's are rolled?  I tend to over engineer things, but I would plan on some kind of support underneath the socket.  Thoughts?

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post #47 of 536
3/25/11 at 6:44pm


 

Quote:
Originally Posted by civilmonkey View Post

I have some questions about the mechanical fastening of the PCB and supporting the tube socket.

 

1.  Given that the PCB can slide foward to backwards, do people use a standoff or something, potentially bolted through the bottom of the case?  Last time I did something like this I just screwed a few small screws in the track which the PCB slides to wedge it in place, but I wondered what other solutions are.

 

2.  I read most of the previous CTH thread and it seemed like few people support the tube socket.  Maybe I missed a post or so, but wouldn't you be worried about flexing the PCB over and over as tube's are rolled?  I tend to over engineer things, but I would plan on some kind of support underneath the socket.  Thoughts?

 

1.  I built mine in the longer Hammond case and put a Bantam DAC in the rear which holds it in place nicely.

 

2.  Should not be a problem. The board is quite narrow and well supported in the BOM Hammond cases, after two years of almost daily use and constant tube rolling I have had no problems.  If your still worried you could bolt a short nylon spacer to the bottom of the case under the tube to give additional support. 

 

 

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post #48 of 536
3/25/11 at 6:51pm
Quote:
Originally Posted by BK_856er View Post

Any others [tubes] to consider to capture a broad spectrum?


 

I'd recommend Amperex 6922 PQ if you're willing to spend the money.  Another great option that is very affordable are GE 5814a ...if you want to spend some more then RCA 5814a.

...and you gotta have at least one actual 12au7...

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post #49 of 536
3/25/11 at 8:39pm

 

Quote:
Originally Posted by rds View Post

 

I'd recommend Amperex 6922 PQ if you're willing to spend the money.  Another great option that is very affordable are GE 5814a ...if you want to spend some more then RCA 5814a.

...and you gotta have at least one actual 12au7...



Thanks for the suggestions.  Quick spot-check shows the PQ to be out of my budget for now.  Is there any significant difference between the 5814a and 5814?  I think I remember reading something in my multi-hour crash course last night, but the memory is fuzzy...

 

BTW, got all my CTH parts today - wow, that is one impressive bag of parts for such a small amp!

 

BK

 

 

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post #50 of 536
3/26/11 at 5:16am
Quote:
Originally Posted by BK_856er View Post

Thanks for the suggestions.  Quick spot-check shows the PQ to be out of my budget for now. <snip>

 

BTW, got all my CTH parts today - wow, that is one impressive bag of parts for such a small amp!

tubes -  IMO the Amperex you already have may have a presentation similar enough to its pricier cousins (PQ, 8416), so if you think you need > the 3 tubes you have I'd go for something different.  This is opinion, but if I had the tubes you do & wanted a 12au7 class tube a bit different I recommend a Siemens circa early 60's.  The chrome/silver plate is a premium variant & my favorite alongside the PQ/BB/8416:
http://www.head-fi.org/forum/thread/398839/a-very-compact-hybrid-amp/285#post_5461087

 

parts - Yes about 160 in a 3" x 5" space and a pretty tight fit in the small/std hammond.  One reason I was going to recommend against trying to jam a DAC in with it.  Recommend a "cable" DAC  build for that.  After I bundle things I often come around later to wishing I hadn't.  Better/different things come about, etc.  E.g. a couple years ago you'd have been looking @ little cap-coupled DACs instead of the ones you are. 

BUT it's hard to argue against the great little combo a CTH/DAC makes, so we make our choices:)


Edited by cfcubed - 3/26/11 at 5:20am
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post #51 of 536
3/26/11 at 11:57am

Thanks, cfcubed - will keep that stuff in mind.

 

I'm comtemplating upgrading the C4 coupling caps from the get-go if I can get some in time.  I understand the BOM piece is a good performer, but I guess I have upgrade-itus.

 

What is the pn of the larger square Wima that I see in some builds??

 

Mouser pn for the BOM piece is 505MKS2.22/11/10 (so tiny!)

 

Audience Auricap is 0.22uF / 400VDC 0.5 x 0.6" (~$13/each)

 

Sonicap Gen II is 0.22uF / 200VDC 0.27 x 0.73" (~$3/each)

 

BK

 

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post #52 of 536
3/26/11 at 6:21pm
Thread Starter 

BK_856er,

 

If I was putting a DAC in the same case I'd definitely not use the BOM case or even the longer Hammond case. The longer case is tight enough as it is. However, it depends on I/O components that you choose to use though. If you were using 1/8" jacks and a RK097 on the front instead of a RK27 and 1/4" jack then that would give you more room. Also, if you wanted RCAs that would also cramp things a bit on the back. The best way to do this is go with 1/8" jacks on the front along with RK097. Then skip out on the fuse and RCA jacks on the back. That way you just have a power switch, USB for your DAC, air wired DC jack, and Heater switch. Are you going with 4 heater voltages? That NKK switch takes up a bit of space as well. Overall, if you want to accomplish a lot I would take a look at that case that cfcubed is using for his Fancy CTH. It looks to have space on the sides of the CTH board that would allow for a DAC.

 

Civilmonkey,

 

With regards to your worries about the PCB and it needing more support. It fits snuggly in the BOM case. The tube socket is fine too. The only thing that I'm thinking of doing is getting one of those socket savers like cfcubed uses. I hear it's a PITA to change out a tube socket if one goes bad.

 

Perhaps, Forte can let us know if he thinks a socket saver is required for tons of tube rolling.

 

I've got a whole list of tubes and thus far I'm liking a bunch of them. Siemens ECC802S, RCA 6CG7 Clear Top, Raytheon 6GU7 Japan, Telefunken ECC82 Smooth Plates, Sylvania Gold Brand 5814A gold pins to be specific. There are tons of others that are good as well. Tonight, I'm auditioning 4 different 4BZ7 tubes. So far I'm liking them the least. They seem to be a little shrill. And the bass seems a tad bit muddy. Perhaps, this is partly due to using my KSC-75s with this amp. I'll switch over to my K701s for comparison.

 

 

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post #53 of 536
3/27/11 at 10:54pm

Thanks, Mullet.  Will see what I can squeeze in there as far as a tiny DAC goes, and if it won't fit I'll do the "cable" version.

 

It looks like this mouser Wima would fit in the optional RevA larger 10mm lead spacing for C4:  505-MKS4.22/100/10P

 

I think I'll pick up a couple to try.

 

BK

 

 

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post #54 of 536
3/28/11 at 6:12pm
Thread Starter 
I already posted this in the group buy thread.

Something came up with one of our group buyers. So we have one board available. My only request is that the PCB goes to someone that hasn't built a CTH before. Who ever PMs me first gets the board. Good luck!
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post #55 of 536
3/28/11 at 7:35pm

Hey Mullet, how about this guy:)   He's been asking & think it'd be his 1st CTH (<<<  And he has one now, so still one more PCB avail AFAIK):

Quote:
Originally Posted by Lil' Knight View Post

Missed the group buy :( Anyone has a spare board that you could sell me? Would appreciate a lot.


Edited by cfcubed - 3/29/11 at 3:23am
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post #56 of 536
3/30/11 at 12:32am

I finished populating the board today and everything is progressing nicely.

 

- Need to wait for my "special" coupling caps to arrive before power-up.

 

- My ceramic tube socket is a little larger total diameter than the ones shown on p1, resulting in a small amount of interference with C1R.  Nothing a few minutes with a dremel can't solve.  Is there a preferred tube socket for this build?

 

BK

 

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post #57 of 536
3/30/11 at 3:59am


Quote:

Originally Posted by cfcubed View Post

BTW a crafty builder might try installing 120R or 150R R18s plus a DPDT switch that optionally shorts the positions.  Note though the R18s are "embedded" into the OB circuit, so I'm unsure of the impact (if any) of long leads on their pads..



For a test, I was able to put a piece of 26 awg SPC through the top side of the PCB for R18, then gentle wiggle a SIP socket also through the R18 location.  I haven't soldered it yet but that will be my plan.  I can run the wires from all R18 positions to a DPDT as receommended to short the positions.  I'll report back once it's tested out.

 

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post #58 of 536
3/30/11 at 3:14pm
Thread Starter 

Civilmonkey,

 

Can you post pics of this when you're done so I can see what everything is supposed to look like? I might try and do this for my 2nd build. I'm finding that my in-ear phones aren't liking the BOM R18 100 ohm resistors that much and I could use 150 ohm resistors. I only get the volume up to maybe 7 or 8 o'clock before the volume is too loud. I'm also hearing  some noise and static. I'm leaving the 100 ohm resistors in on my first CTH for good.

 

BK,

 

What caps did you get? Wiatrob sent me some of those green Russian PIOs. They look like they might be a pain to solder in. I'm wondering how they compare to the Wimas I'm currently using in my CTH. Not sure if they're the BOM ones because I acquired them from cfcubed.

 

On another note here's an observation that I noticed. Sometimes when I take 2 fingers, my thumb and middle finger, and rub them along the length of the CTH, I can feel friction or energy. I measured this with my DMM and I'm getting a reading of .007 VDC. After taking the reading the friction goes away then quickly comes back after a minute or so. Interesting...

 

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post #59 of 536
3/30/11 at 3:17pm
Thread Starter 

Also, no more boards left...

 

Lil' Knight and meltdown100 got the last two.

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post #60 of 536
3/30/11 at 6:29pm


 

Quote:
Originally Posted by Mullet View Post

On another note here's an observation that I noticed. Sometimes when I take 2 fingers, my thumb and middle finger, and rub them along the length of the CTH, I can feel friction or energy. I measured this with my DMM and I'm getting a reading of .007 VDC. After taking the reading the friction goes away then quickly comes back after a minute or so. Interesting...

 



You're probably having charge build up on your case.  It should be grounded for safety, and this will solve the issue you mention.

 

Here's how I did it:

IMG_2104.jpgIMG_2108.jpg

 

fyi the other white wire goes to the pot (to stop hum when you touch the volume knob) like so:

IMG_2107.jpg


Edited by rds - 3/30/11 at 6:32pm
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