[Mullet]

Might be interested. What kind of prices are we talking? I'm looking to get a few 12BH7 in the near future. I'm local to Leeds electronics, so I might give them a try first. I've been reading that the 12BH7 is better than the 12AU7 and I'm curious to really find out. I can't stop buying tubes. I'm addicted!!! I know this typically belongs in the "tweaks" thread, but other than GE, what are some experiences/impressions? I'd figure that for the most part they'll have the manufacturers house sound ie RCA -- warm and lush; Sylvania -- detailed on top with rolled off bass, etc., etc. I'm looking for a cheaper Tung Sol 12BH7 that doesn't cost $60+.
 
It seems to me that your mystery tube is a rebranded Raytheon or Matsutshita or maybe even Toshiba. My guess is it's Matsutshita that's rebranded. I've read on a few forums that tube manufactured by Matsutshita aren't the highest regarded 12BH7. But that's just a matter of opinion, isn't it?

 

[Garage1217]

I may have a bunch of 12bh7's at home. Will have to check tonight / nos stuff. Still have a few hundred tubes laying around lol

 

[BK_856er]

 
Quote:

Might be interested. What kind of prices are we talking? I'm looking to get a few 12BH7 in the near future. I'm local to Leeds electronics, so I might give them a try first. I've been reading that the 12BH7 is better than the 12AU7 and I'm curious to really find out. I can't stop buying tubes. I'm addicted!!! I know this typically belongs in the "tweaks" thread, but other than GE, what are some experiences/impressions? I'd figure that for the most part they'll have the manufacturers house sound ie RCA -- warm and lush; Sylvania -- detailed on top with rolled off bass, etc., etc. I'm looking for a cheaper Tung Sol 12BH7 that doesn't cost $60+.
 
It seems to me that your mystery tube is a rebranded Raytheon or Matsutshita or maybe even Toshiba. My guess is it's Matsutshita that's rebranded. I've read on a few forums that tube manufactured by Matsutshita aren't the highest regarded 12BH7. But that's just a matter of opinion, isn't it?

$6.40 + tax (no box, test "good").  My two were grey plates, but there were also some black plate and non-A types available.
 
BK
 
 

 

[BK_856er]

I'm finally declaring this one done.  I tested it extensively over the last couple of weeks and it's good to go.  Next week it heads off to Afghanistan with my brother.  I hope to get it to him in the next few days - he's still in the dark about it.  I predict that when he returns in about a year he'll take up DIY and join the head-fi community!
 
I want to publicly thank sachu, jdkjake, mullet and cfcubed for donating key parts - thanks, guys!
 
I've already posted way too many pics of the build progress, but here's a couple more with everything boxed up using jdkjake's killer Pelican.  The little blue box next to the transformer is a USB SkeletonDAC (emergency backup hi-fi).
 
BK
 
 

 
 

 
 

 

[jdkJake]

Bravo Zulu BK!!

 

[cfcubed]

Wow.  Kudos on the build & case up, has a military look about it  What a nice surprise its going to make.  Down the road we'll have to hear how he likes it.

 

[devast]

Hi there!
 
After seeing these wonderful new cths, i've got the urge to finally debug mine (it's been semi-working for a year now)
Can anyone measure the DC offset of his cth, when theres no tube plugged in ? How much should it fluctuate around the output ground ?
I guess my ~ 50-60mV fluctuation (between +30mV and -30mV) is too high, but i need to confirm that, before i start messing with my dc servo
 
Thanks.

 

[Mullet]

I'm not sure that it's too high. I get a reading close to that. Around +/-33mV with no tube plugged in. I'm not noticing anything strange with my amp. What are your issues?

 

[devast]

My issues are the following:
A year ago, i connected sg to og, smoke came out etc, fixed the psu part fine. After that it developed the following problem:
e12 trips ,depending on the volume of the music. It does it with every tube, its channel independent, with or without a load (headphone) connected. Apart from that, at lower volume the unit works perfectly.
Voltages read fine everywhere, i basically replaced the left output stage (transistors) the psu part transistors, the vreg, e12 transistors (except the mpsa14, its hard to source here), i tried it with different op amps.
If my dc offset is fine, then i assume that my output stage is ok.
That means, i'll try replacing the remaining stuff in the e12, particularly the mpsa14 darlington (i recently found a source), and maybe if thats no good, then the 1N4148 diodes.
It uses bom c4s, so that can't be the problem either. I can't think of any other solution... i hope this time it will work.
 
Thanks for the info, Mullet.

 

[sachu]

Make sure your AC line is good. If you are going off of a power strip, maybe try going off of a regulated power strip.
 
Try different wallsockets. In my experience with the CTH and the infamous E12 trips, this could very well be a source of the problem.

 

[cfcubed]

I've a couple ideas in addition to sachu's. 
Seems like you did cover many bases with your repairs/replacements, except maybe those right channel OB transistors & rail splitter parts.  Think I've had toast/smoke trouble twice across all my CTH builds, and they didn't happen due to OG-SG shorting, but were "fixed" shotgun style through replacement of all output buffer & rail splitter TO92s (not e12 parts).  So something to consider (replacing TO92s not already replaced).
Also have you checked your source for offset & tried different sources?
As a sort of last resort you could try shorting your R18 positions & that may get you more volume prior to de-latch.

 

[Mullet]

At what volume level is your CTH e12 tripping? If I go to about 1 or 2 o'clock and have a song that has some thumping bass or a loud transient hit I can get the relay to trip. This is with most tubes as well. With most of my headphones this is pretty darn loud so it doesn't really effect me. If I'm using my AKG K701s then I actually have to go to 1 o'clock to get a decent listening level so I'd have to go to a higher level on my pot to make the e12 trip.

 

[sachu]

I believe this is due to the fact that the E12 is not being used separately for each channel. The main reason however I feel is due to the use of CW multipliers on the power supply. Then again, there is no other way to get  such high voltage levels for the tube bias in such a small package. 

 

[devast]

Thanks for the replies.
 
First, it's tripping with different sources as well. My (usual) sources offset is roughly 10-12mV, but that shouldn't be a problem. It was working fine (at max volume without load connected it did not trip) before i fried it
I think i've replaced all transistors in the rail splitter, and the psu. The +/-12V rail and og is totally stable, (as far as my multimeters accuracy goes).
It might be my 24V 1050mA transformer brick, but that seems to work good as well. Good voltages with or without the cth connected.
@Mullet: Here's the tricky part: it's totattly dependant on the music i'm playing. Some songs trip at 11-12 o'clock, but most can go a bit higher like 1-2 o'clock.
Phones are HD600.
@sachu: i tried it with only one channel connected. The symptoms are exactly the same, even the tripping volume is the same.
I did not touch the heater/tube part at all, and i don't think the problem will be there.
If the e12 mpsa14 / 1N4148 diodes won't solve my problem, i think i'll try to get a new 24V brick.
 

 

[civilmonkey]

Quote:

@Mullet: Here's the tricky part: it's totattly dependant on the music i'm playing. Some songs trip at 11-12 o'clock, but most can go a bit higher like 1-2 o'clock.
Phones are HD600.
 

I have noticed that when using 600 ohm DT880's my CTH e12 trips anywhere from 12 to 2, depending on music.  Luckily for me, the volume is more than sufficient.  Typical bass heavy music with big hits actually trips the e12 less than a song with a full and constant spectrum of mids and bass, say like a live folk/soft rock with a nice drum line, constant bass guitar, and male vocals.