[ChrisX]

Dsavitsk would have to answer that, but my guess is yes.  If they're my tubes, please let me know and I'll replace them with something better matched.

 
That was one pair of the kit indeed. Thanks for the offer but I plan to use the 6J6 only for initial setup and I'm going to switch to E90CC anyway, so the tubes are ok for me.
 

We tend to use DC matching as a proxy for AC matching, but who knows whether this is a reasonable thing to do for any given tube. The easiest way to check yours would be to play a 60Hz tone and measure the AC output from both channels with a multimeter (even cheap meters can measure 60Hz reasonably accurately.) That should give you an idea how mismatched your tubes are. And truth be told, tube matching is not that important here. They'd have to be way way off be before you'd hear much of a difference..

 
Thanks for the idea about AC matching. I will try to match the best pair of my 5-pack of E90CC this way. I assume that this will give more useful results than matching with my very simple Sencore tester. I have access to a good multimeter so maybe I can also measure at higher frequencies. But first I will make the proposed measurement with the 6J6 mentioned above to get a feeling about the relation between DC and AC mismatch.

 

[dpump]

Since some of you report that E90CC tubes should be quieter than 6J6 tubes, I decided to do a comparison. In my new Torpedo I had only used Philips and Telefunken E90CC. Although I have a number of different 6J6 from the older Torpedo I used to have, which I sold before the E90CC was discovered, I tried the Sonotone 6J6 in my new Torpedo.
 
I could tell no difference in the slight hum I hear with the Sennheiser HD 800-both the Sonotone 6J6 and the Telefunken had the same amount of hum. There was some difference in sound between the tubes. The Sonotone had a little more bass-it was warmer and more rounded in the bass. As far as the midrange, there was very little difference, with the Telefunken having a little more detail. The highend was a little more prominent on the Telefunken, but this was probably because of the lighter bass response. I still prefer the Telefunken as it seems to be a little quicker, but the Sonotone was surprisingly good. The Sonotone was mentioned a while back, I think in this thread, as being a favorite of several people. The guy I sold my older Torpedo to also prefered it. I could be happy with the Sonotone if the E90CC wasn't available.
 
Maybe putting the E90CC in an older Torpedo without the diode/snubber cap/choke/diode updates would result in lower noise. In my new Torpedo I heard no noise difference. As Tomb has said, the E90CC is generally a more microphonic tube than the E90CC. The Telefunkens in my amp are pretty microphonic-plugging or unplugging phones or contact with the case will cause ringing that takes a few seconds to subside. Not really a problem when listening, but more microphonic than most 6J6 tubes. As TomB said, the E90CC wasn't designed to be an audio tube. Just my 2-cents-YMMV.

 

[tomb]

 
Since some of you report that E90CC tubes should be quieter than 6J6 tubes, I decided to do a comparison. In my new Torpedo I had only used Philips and Telefunken E90CC. Although I have a number of different 6J6 from the older Torpedo I used to have, which I sold before the E90CC was discovered, I tried the Sonotone 6J6 in my new Torpedo.
 
I could tell no difference in the slight hum I hear with the Sennheiser HD 800-both the Sonotone 6J6 and the Telefunken had the same amount of hum. There was some difference in sound between the tubes. The Sonotone had a little more bass-it was warmer and more rounded in the bass. As far as the midrange, there was very little difference, with the Telefunken having a little more detail. The highend was a little more prominent on the Telefunken, but this was probably because of the lighter bass response. I still prefer the Telefunken as it seems to be a little quicker, but the Sonotone was surprisingly good. The Sonotone was mentioned a while back, I think in this thread, as being a favorite of several people. The guy I sold my older Torpedo to also prefered it. I could be happy with the Sonotone if the E90CC wasn't available.
 
Maybe putting the E90CC in an older Torpedo without the diode/snubber cap/choke/diode updates would result in lower noise. In my new Torpedo I heard no noise difference. As Tomb has said, the E90CC is generally a more microphonic tube than the E90CC. The Telefunkens in my amp are pretty microphonic-plugging or unplugging phones or contact with the case will cause ringing that takes a few seconds to subside. Not really a problem when listening, but more microphonic than most 6J6 tubes. As TomB said, the E90CC wasn't designed to be an audio tube. Just my 2-cents-YMMV.

Many thanks for your impressions!
 
Yes, the Sonotone is a fine example of the 6J6.  There are others - the USN JAN comes to mind.  That said, I guess we'll have to agree to disagree.  IMHO, the E90CC is significantly superior - as you say, more high-end detail and definitely quicker.  Also, I suspect that the extra bass you're hearing in the Sonotone maybe emphasized by greater noise.*
 
It may still depend on the headphone, too.  I have been tracking the noise for several years now, and know exactly where and how to hear for it.  I don't have HD800's, but with E90CC's I cannot hear the noise with any of my phones (HD600's, HF-2's, etc.).  If you use a PC as your music file source (many of us seem to do that these days), this can affect the Torpedo if it's too close.  At my previous residence, I think I had the Torpedo way too close to the PC.  I could barely detect the noise with some headphones, even using the E90CC - but I can't at my new residence.  I know from previous experience that the Torpedo can easily pick up transformer flux from adjacent devices and resonate with increased noise: other stereo equipment with transformers, wireless phones, wireless cable router, etc. - the PT in the Torpedo will pick them all up if it's too close.  A good separation distance and the use of all of the tweaks + E90CC tubes should reduce any noise to zero in most cases.  The HD800 may be different, though.
 
* I prefer to use the term "ripple" or "noise" to describe the sound when it was easily heard in the past (pre-tweaks and E90CC's).  "Hum" almost always refers to 60Hz line frequency noise caused by poor transformer application or other power-related issues.  That was never an issue with the Torpedo - it was at 180Hz, and we suspect was caused from oscillation of the heater rectifiers and was magnified by their proximity to the power transformer.  That's why one of the major tweaks incorporated general purpose diodes instead of the super-fast-switching Schottky's that were originally used.  The addition of the snubber caps also help to fight any oscillation that might be produced.  As Dsavitsk immediately realized when KG suggested this cause, there is no reason at all to use high-performance rectifiers just to power the tube heaters.

 

 

[OJNeg]

Okay, just ordered the Torpedo kit + some extra goodies. Excited to get soldering!

 

[ChrisX]

  Thanks for the idea about AC matching. I will try to match the best pair of my 5-pack of E90CC this way. I assume that this will give more useful results than matching with my very simple Sencore tester. I have access to a good multimeter so maybe I can also measure at higher frequencies. But first I will make the proposed measurement with the 6J6 mentioned above to get a feeling about the relation between DC and AC mismatch.

 
I have finished the Torpedo build today. As said before I first measured the slightly mismatched 6J6 by looking at the output. Test setup was output switch set to high, 330 Ohm load resistance. As mentioned before, the DC voltage at C11/C12 was 128 V at the left, 144 V at the right channel. With a 2 Vpp sine wave at the inputs and the pot full open I measured 2.82 V left/2.99 V right ACrms at 50 Hz, 2.90 V/3.07 V at 500 Hz and 2.33 V/2.5 V at 5 kHz (the scope confirms the slight differences) which results in a channel imbalance of about 0.4 - 0.5 dB, so as Dsavitsk stated before not much to worry about.
 
Kudos to the Telefunken E90CC. I have bought a NOS 5-pack of these tubes, the first two I picked showed 101 (whatever, maybe percent) on my Sencore tester on all 4 systems, so I didn't even check the remaining 3 tubes. These two tubes in the Torpedo show both 105 V DC at C11/C12, AC output shows 2.39 V/2.39 V (50 Hz), 2.42 V/2.42 V (500 Hz), 2.44 V/2.43 V (5 kHz). So they match perfectly. Furthermore these pair of tubes shows no microphonics, while one of the 6J6 (JHS Sylvania) did.
 
These results show that DC matching is valid for a good AC match in this setup.
 
The amp is totally quiet, for initial listening I used my 600 Ohm AKG K240. I was really satisfied with the sound, only drawback is that the gain of the amp is just sufficient with these headphones (listening position of the pot between 3 and 4 o'clock), but as seen above the E90CC is slightly less efficient than the 6J6. I didn't test with other cans yet (and unfortunately also won't be able to do so in the next days).
 
BTW: Maybe this is the first Torpedo running with SMD caps? I used Kemet 500 V C0G 1206 types.
 
.

 

[FishHead]

Ordered a Torpedo for when I get back to the States. Since I could not decide on a cap I ended up buying a variety:rolleyes:. While researching them there was some discussion (vcap) on how the cap should be oriented. Ie the outermost foil connection should be connected to B+. Does this recommendation apply to a parafeed design? Which way is B+?

 

[tomb]

Ordered a Torpedo for when I get back to the States. Since I could not decide on a cap I ended up buying a variety:rolleyes:. While researching them there was some discussion (vcap) on how the cap should be oriented. Ie the outermost foil connection should be connected to B+. Does this recommendation apply to a parafeed design? Which way is B+?

B+ is the opposite direction of the output transformers and headphone jack.

 

[FishHead]

Thank you very much. I will post my impressions on the caps over time once I am up and running. Would you like to keep the content here or start a Torpedo Cap rolling thread? I have seen cap threads get a little crazy. Not that tHose who build Torpedos are anything but very sane pedestrian sort of people.

 

[tomb]

Thank you very much. I will post my impressions on the caps over time once I am up and running. Would you like to keep the content here or start a Torpedo Cap rolling thread? I have seen cap threads get a little crazy. Not that tose who build Torpedos are anything but very sane pedestrian sort of people.

JMHO, but I'd prefer to keep it sane and somewhat pedestrian.

 

[OJNeg]

Ok then...I've spent the last month enjoying this amplifier immensely. Construction was a cinch for me. And it's absolutely gorgeous sitting on my desk (w/ no top cover

)
 
I ordered 5 pairs of tubes from Beezar with my kit. 6J6A (Japan, UFO), 6J6W (RCA, Mid Sq), 5844 (GE), 5964 (GE, Top Halo), and the E90CC (Telefunken). I just read through the entirety of this thread and I'm surprised with how well my own impressions of the different devices match with others'. Specifically TomB's post back on page 5. From my own notes:
 
'Phones: Senn HD600, Ety ER4S
D/A: AMB gamma2
Other amplification: AMB CKKIII
 
6J6A:

1. Definitely the most dynamic tube of the bunch. Can swing high and low without compression in either direction
2. Guitars are very engaging without being overly aggressive
3. Very top end is a bit less present, can seem dull with certain instruments
4. Instruments have a great fluid quality, but vocals seem to be lacking the last bit of clarity I'm used to
5. Soundstage is well differentiated but not what I would consider "expansive"
6. Very natural and organic timbre with things like hand claps, also more 3D spatially
7. Comments: Very good. Easy to listen to and engaging. Things are looking good for this amp.

5844:

1. Kinda boring sounding
2. Less detailed, less fluid
3. Bit grainy?
4. Comments: Not impressed, what I would consider a downgrade from the 6J6A. TomB mentioned this one had a "exaggerated midrange", but I hear it just as poor sounding and lacking extension in both directions. This tube kinda sounds like what the others tubes sound like when they're not warmed up yet. I keep waiting for this tube to kick into gear, but it still sounds unrefined regardless. Didn't end up spending much time with this little guy.

5964

1. More similar to 6J6A than 5844
2. More spacious and longer decay than 6J6
3. Bit softer and less dynamic than 6J6
4. I feel the bass on the 6J6 is more dynamic, solid, and better differentiated (in terms of pitch)
5. Comments: A valid sidegrade to the 6J6A I suppose. While it ups the fluidity of the amp, it does take away a certain level of microdetail and sharpness in return for a more diffuse presentation. I spent a lot less time with the 5964 than the 6J6A, which says something I guess

E90CC

1. Oh snap! Leagues different than any I've tried so far. More forward presentation and more microdetail!
2. This tube does a better job of letting the music portray it's own character rather than impart its own. It simply lets the pacing/atmosphere/emotion through better. I know that sounds like BS and you're probably rolling your eyes, but that's just the best way I can put it. You could say that this device is less colored than the others in a sense.
3. More analytical with regard to electric guitars (6J6A preferred to be fluid)
4. This device seems like it's faster at tracking the input signal and recovering information in the treble. Even compared to solid-state amps
5. Comments: This tube is definitely on a different level compared to its smaller brethren, as TomB said. It takes the technicalities of this amp up a few notches. You could say it's a bit leaner sounding in the bass and mids (than the 6J6A), but it's not really brighter or anything. Meaning, it's not increasing gross detail by boosting the treble, it's just inherently more detailed it's own. The only concrete drawback of this device would be that I feel it renders a slightly artificial texture compared to the 6J6A. This is outside of the lean-ness or increased detail, it's just that instruments sound less organic and natural in terms of texture (not timbre, if that makes any sense). A small niggle that I noticed.

 
Overall, this amp holds its own against my CKK. It is a touch warmer than the CKK throughout the the spectrum (regardless of tube choice) and has less top-end presense, but this is definitely not an uber-tubey, syrupy, drown-in-warmth sort of valve amp. It's accurate and balanced, while delivering big images and digging deep into the music. It has absolutely zero harshness in itself, but will render it if it's on the recording. At this point, the E90CC's get most of my listening time, but I'll put in the 6J6A's if I want to rock out to some metal and crank the volume.
 
I have yet to try the 6J6W but I'd suspect them to be fairly similar to the 6J6A's. I also have a pair of Jantzen CrossCaps on the way so we'll see if those make any tangible difference for me. Might also try the Mundorfs or ClarityCaps eventually.
 
Big thanks to TomB and Doug for making this amp available!

 

[tomb]

Many thanks for that fine review!

 

[FishHead]

I thought I would post some build impressions for V 1.02. I brought the project over to Dubai as something to do when it is 105 outside at 8 pm.

The box and packing was excellent and made the trip quite nicely. My biggest issue was my Hakko 936 promptly blew a fuse from the voltage change. :mad: The spec sheet clearly said it was ready for 240 v. Not even close and the internal fuse was soldered in! Well, I got a cheap voltage converter and fixed the fuse (don't ask). Up and running!

Pulled out the clearly labeled bags and started slinging. I would recommend updating the build pictures because they are outdated. I had put in d12 and d14 first and later figured they were originally the LEDs that are in the tweaks section. I am doing fine because the silk screen is great and it was clear what to do even without the build instructions. Between the clearly labeled bags and board screening no real issues exist.

My only niggle is that a few of the back side pads are so small that it is difficult to get a medium size iron head in there to get a good heat transfer. I found it quite easy to fill the r7 hole when soldering r6. Same with r8and 9. Remember to flux the solder wick before use and all will be fine.

My impression so far is that this is an easier project than the Mini-Max. It is certainly easier than the AMB y2+. I am enjoying the project and will probably bore you with more posts as I go.

 

[FishHead]

Pic of D12 and D14. Hopefully in the right direction.

 

[tomb]

Pic of D12 and D14. Hopefully in the right direction.

Yep - those are correct.
 
Don't forget the SMD snubber capacitors on the back side under D5, D6, D7, and D8.  Those are not labeled with silkscreen at all.  There are no other SMD parts in the build, so hopefully - that's self-explanatory.

 
I will try to update the website/build thread when I get a chance.  I've always wanted to detail the hardware as well - it is not trivial.  There are a few key points with the hardware:

1. Bolt on the IEC inlet to the back plate and PCB before soldering it to the PCB.  This ensures that everything lines up with the case.  It also establishes the proper slot.  Once the backplate is bolted to the IEC, there's only one slot the PCB will fit in.  This is clear on the existing website.
2. Black washers go on the back plate - two for the IEC inlet, one for the screw that secures the RCA jacks.
3. The Flat-head Socket Cap Screws are the case screws and the tiny Bondhus hex wrench is used for those.  I include the Bondhus hex wrench for every kit/build now, because removing the case lid is required to change out 6J6-type tubes and it makes everything easier.  (E90CC's are tall enough that tube rolling with them does not require taking the lid off.)
4. Washers are needed under the tabs of the choke to get a good mount on the PCB.
5. The safety ground is a PITA, but absolutely needed for safety.  Be sure to scrape off the anodizing around the hole on the inside of the case bottom.  The only way I've made this work is to bend the wire in such a curve that the lug lines up with the hole in the PCB.  Line it up with the screw hole in the case bottom, and fish through a socket head cap screw (3/8" long) from the top hole in the PCB and through the lug hole and the case bottom hole.  If you hold the case sideways, the screw should stay on the end of a socket wrench while you're fishing.  Luckily, I always use 22 ga Teflon SPC for hookup wire - it's stiff enough that it holds its shape when bending.  That makes things easier in terms of lining up the holes and screw.
6. The rubber bumpers are absolutely required or the standoff/grounding screws on the case bottom will be scraping on your desktop.     

 

[tomb]

OK - I've updated a couple of pages to reflect the new PCB V1.02:
Torpedo Layout
Torpedo Board
 
Also, I added a new construction page that takes care of much of the above, especially the black anodized case and special hardware:
Torpedo Black Case and Hardware Tips