Head-Fi.org › Forums › Misc.-Category Forums › DIY (Do-It-Yourself) Discussions › Cavalli Compact Tube Hybrid (CTH) Tube & Tweak thread.
New Posts  All Forums:Forum Nav:

Cavalli Compact Tube Hybrid (CTH) Tube & Tweak thread. - Page 30

post #436 of 672
1/8/10 at 11:55am
Thread Starter 
Forgot to mention, before running out & getting 6F8G to 6CG7 adapter + 6F8Gs note that I had to revert from incorrect/non-BoM coupling caps (Sonicap 1uf gen I w/0.22uf gen II bypass) to WIMAs for reliable CTH/e12 latch w/6F8Gs.

I've noticed a relationship between "massiveness" of coupling caps and time-to-1st-latch and, possibly, latch sensitivity. All tubes I've tried other than 68FGs, and there've been a lot, were rock-solid & fine w/numerous coupling cap combos in CTHs using 8/2009+ BoM. Just a heads-up that one may need to reduce sensitivity of CTH's e12 to achieve reliable latch w/6F8G depending.

Note to marketers of designs lacking muting delay + offset protection: Please do not use this & other CTH/e12 discussions as promotional material. IOW, think its unwise to assume your customers see delay + offset protection as a downside of a design. Hated to have to say this, but as crazy as it seems there have been a few thinly-veiled jabs @ designs w/delay + offset protection in these forums. Yes, offset protection can sometimes be a nuisance as it does its job of protecting your cans... Much like paying any insurance bill
Reply
post #437 of 672
1/8/10 at 8:33pm
Quote:
Originally Posted by cfcubed View Post
but as crazy as it seems there have been a few thinly-veiled jabs @ designs w/delay + offset protection in these forums. Yes, offset protection can sometimes be a nuisance as it does its job of protecting your cans... Much like paying any insurance bill[/I]
That does sound pretty crazy. Not only is it illogical, but practically why would a 20 - 30 second turn on delay be a problem with tubes? Tubes need to heat up before they can perform properly. I would think that most audiophiles would want to wait a least a few minutes before they start playing music.

...and I have to say again: I love this amp! I end up selling off a lot of equipment just because it seems unreasonable to have so many amps/dacs/headphones but this one is a keeper.
Reply
post #438 of 672
1/8/10 at 9:02pm
Thread Starter 
Quote:
Originally Posted by rds View Post
That does sound pretty crazy. Not only is it illogical, but practically why would a 20 - 30 second turn on delay be a problem with tubes? Tubes need to heat up before they can perform properly. I would think that most audiophiles would want to wait a least a few minutes before they start playing music.
The jabs I was referring to, and could try to find if they've not been edited out, had more to do w/offset protection AFAIR (don't think muting delay advantages can be debated). They mostly occurred in the first few months of CTH release when we were having issues w/a few CTH build's e12s staying latched. Although some of this was due to issues in the builds themselves, we tweaked CTH-e12 implementation resistors to better guard against this.

I felt it had to be said since those involved w/CTH development want to maintain full & clear disclosure but there are risks involved in doing so. IOW, if there was danger of a proper build of this design damaging connected sources or cans we'd likely not have released it. And if it had already gotten out, or the risks were implicit in the design, you'd see big, bold warnings noting the dangers & instructions for avoiding them. Often & everywhere.

Enough said there I think, my hope/bet is the request has been digested
Let's try not to come back to this. Too much CTH good stuff to discuss
Quote:
Originally Posted by rds View Post
...and I have to say again: I love this amp! I end up selling off a lot of equipment just because it seems unreasonable to have so many amps/dacs/headphones but this one is a keeper.
Thanks again for expressing this. If people around here knew the many amps you've built & heard, they'd know the real weight your statement carries
Reply
post #439 of 672
1/9/10 at 3:50pm
Quote:
Originally Posted by cfcubed View Post
So, after seeing a couple tubes were tried in CTH that had other than 6.3v & 12.6v heater and found to work & sound good, knew there was nothing keeping the design from directly supporting more heater voltages.

Nothing but a few more resistors & a way to switch among them.

Calculated (ideal) R3H values for various heater voltages:
Votage / R3H (ideal)
4.2v / 3.3k
5.6v / 5.8k
6.3v / 7.4k
7v / 9.3k
8.4v / 15.1k
9.4v / 23.3k
12.6v / <none>
Finally got around to fitting this mod and have run into a problem.

After fitting the voltage switch checked to make sure the heater voltages were all what they should be and they are all low.
4.2v / 2.98v
5.6v / 4.35v
6.3v / 5v
7v / 5.63
8.4v / 7.01v
9.4v / 8.12v
12.6v / 11.38v
So anything between 1.22v & 1.39v low.

Have the two wires from the switch connected were R3H was and have jumpered H1 & H2 which seems to be the correct way to hook this up. All other voltage measurements are correct and it is working. I don't know what my heater voltages were before as I have never checked them so not sure if this is a new problem or if they have always been low.

I did also change L2H to a 1.1amp version and increased the size of C1/2H could these changes have anything do do with it?

It looks like I need to raise the voltages by about 1.3v to bring them all up to the level they should be. Looking at the schematic changing R1H should do this, but how do I calculate the value required?
Reply
post #440 of 672
1/9/10 at 5:14pm
Thread Starter 
It is possible that the changes/upgrades affected the final heater voltage(s).
I bet we can get them within a few %s of targets by a change in the "reference" resistor - R1H.
It was correct to jumper H1/H2 & have the rotary substitute R3H values (or easier jumper R3H & wire R3H rotary to H1/H2).

I'm curious what load you are using. I'd try a tester 6.3v tube for all Vs <= 7v and a 12.6v tube for >7v settings. Need a realistic load to tune the values.

Think it would be good to get your 12.6v setting fixed first and that may bring the others in line. So with your "R3H switch" set to open/infinite resistance, we'll be adjusting R1H's value.

The standard R1H = 9.31k, start by checking its value. Then raise its value, by adding <= 1k or so in series, until you attain 12.6v heater (+/- 0.1 or so) for the tube. Pwring up/down between trials & double-checking R1H for each. If/when that is set recheck the other voltage settings.

Let us know how it goes. BTW, AFAIR only wiatrob has done this mod.

Edit: It's important to have some resistance for the R1H/R3H combo - not let both go open/infinite. That could make the switcher output its max based on input V.
Reply
post #441 of 672
1/10/10 at 11:26am
Thread Starter 
Quote:
Originally Posted by Forte View Post
It looks like I need to raise the voltages by about 1.3v to bring them all up to the level they should be. Looking at the schematic changing R1H should do this, but how do I calculate the value required?
So while having my coffee this AM I ran National's SIMPLE tool for this... Asking for 12.6 + 1.3v to be generated, it suggested 10.2k - looks like adding a 1k to your 9.3k R1H will do the trick.
Not important, but curious what your 1k R2H measures since if its off that could cause the unexpected values.
Reply
post #442 of 672
1/10/10 at 11:38am
Are you guys typically using R18 ?
Reply
post #443 of 672
1/10/10 at 2:47pm
Thread Starter 
I always use 56R -> 100R there. Found 100R is generally best all-around as it compensates better for higher-Mu tubes & normal sensitivity cans.
If using w/very low efficiency cans, e.g. orthos, might want < 56R or even short. Anyone using such phones could chime in.

We are really just looking for the lowest R18s that make the amp nicely usable (e.g. decent vol pot range).
Reply
post #444 of 672
1/14/10 at 12:59am

Two JHS 12AU7 Sylvania Vacuum Tubes NOS Black Plates

Two JHS 12AU7 Sylvania Vacuum Tubes NOS Black Plates - eBay (item 320471678191 end time Jan-13-10 19:14:11 PST)

I just picked up these two tubes on ebay. I just happened to be window shopping (or is that monitor shopping) on ebay for tubes and saw this auction about to end. The final bid was at $13.50 so I said what the heck I'll throw $15 bucks up there. Sure enough, I ended up winning.

Since there are two tubes, if someone wants to trade send me a PM.
Reply
post #445 of 672
1/14/10 at 2:49am
using 100ohms, tried a bunch from 0 - 150 and 100 seems to be a good balance.

Quote:
Originally Posted by regal View Post
Are you guys typically using R18 ?
Reply
post #446 of 672
1/16/10 at 7:15pm
Quote:
Originally Posted by keyid View Post
using 100ohms, tried a bunch from 0 - 150 and 100 seems to be a good balance.
Mine also appears to be 100 ohm, based on the color bands (Wiatrob built it). My most sensitive 'phones are custom Klipsch X10's, and the least sensitive are modded YH3 orthos. It seems to be a good value for that wide range of cans.

Regarding the Raytheon 6GU7 that many of us are using: It's still one of my favorite tubes, but I've been having synergy issues with it because it seems to excite the high frequencies quite a bit. It makes my custom X10's too bright. And if I'm using an internal sound card as a source it is too bright on all headphones. (I only do that if I'm at work and the battery is dead on my MP3 player. Like today.)

So, I've been using a Mullard 12AU7 a lot lately. It has perfect frequency balance and great detail, but doesn't excite the high frequencies. Which seems to be perfect for sources or phones that don't need any additional treble. (I think I called it "boring" in an earlier post. "Mellow" might have been a better word. Mellow does not always mean boring.)
Reply
post #447 of 672
1/19/10 at 5:21pm
I just got a couple of (unmatched) Sylvania 12au7s. I'm trying to find out a bit more about them. They both have black plates and a square getter.

The printing on the tubes are slightly different. One tube has green printing. It says "JHS 12AU7, Made in USA, Sylvania" across the front. Written vertically to the right are the numbers "409". 12AU7 is also printed in smaller numbers near the top on the back.

The other tube also says "JHS 12AU7, Made in USA, Sylvania" but the printing appears to be white (it's more faded so it's hard to tell). It has 406 printed vertically and also at the top is 12AU7 with the additional code below it J3T.

Does anyone have any idea what JHS, 409, 406 or J3T stands for?
Reply
post #448 of 672
1/19/10 at 7:00pm
Quote:
Originally Posted by erikzen View Post
I just got a couple of (unmatched) Sylvania 12au7s. I'm trying to find out a bit more about them. They both have black plates and a square getter.

The printing on the tubes are slightly different. One tube has green printing. It says "JHS 12AU7, Made in USA, Sylvania" across the front. Written vertically to the right are the numbers "409". 12AU7 is also printed in smaller numbers near the top on the back.

The other tube also says "JHS 12AU7, Made in USA, Sylvania" but the printing appears to be white (it's more faded so it's hard to tell). It has 406 printed vertically and also at the top is 12AU7 with the additional code below it J3T.

Does anyone have any idea what JHS, 409, 406 or J3T stands for?
JHS is a government agency indicator. It means they were manufactured for use by the US government. And the black plates in Sylvania tubes indicate they are probably from the 1950's. I'm guessing based on the info at Joe's Tube Lore:

AudioAsylum.com -- Joe's Tube Lore

How do they sound?
Reply
post #449 of 672
1/19/10 at 7:18pm
Quote:
Originally Posted by barleyguy View Post
How do they sound?
I had them delivered to my office. Heading home now. I'll post impressions later.
Reply
post #450 of 672
1/20/10 at 12:53am
Popped one of the Sylvanias into the amp tonight. With the Denon MD5000 DEs, I wasn't thrilled. The highs seemed a bit too rolled off, midrange was flat, and although there was a lot of good, deep bass, it did not compare to the the Amperex 8416 PQ. If I want lots of bass the Amperex brings it but it still has some slam and punch.

Switched to the Grado HF-1s and this is a much better match. It fills out the bottom end nicely, with some punch and the highs sound good, if a bit grainy. This tube is a much better match for Grados.

Edit: After a couple of hours, the tube sounds a bit more open. Bass is a little tighter. Highs are a bit more extended and the soundstage is much more tube-like.
Reply
New Posts  All Forums:Forum Nav:
  Return Home
Head-Fi.org › Forums › Misc.-Category Forums › DIY (Do-It-Yourself) Discussions › Cavalli Compact Tube Hybrid (CTH) Tube & Tweak thread.