ECP Torpedo III [indexed in first post]

My source is metrum musette. I have done voltage checks in the past on my bottlehead crack. I'll be extra careful and do as you said.

Where do I start for measurements?

Edit.
Or maybe I would be better off sending it to tomb if its too difficult.

 

I trust you're not solely judging this with an unmodded HD800, does this also occur with your 650's?

 

The first thing to check is the resistance of the plate loads (R23, 24, 25, 26) and the resistance of the emitter resistors (R19, 20, 21, 22) -- do this with the amp powered down, unplugged, and drained.

If those check out, then we need to see if the voltage is correct - there are spots to check that near C2. If that's OK, check that the CCS in the tube tail is pulling the correct current. To do that you need to check the plate voltage with the amp on. I'll draw a diagram in a bit.

 

Or, shoot some pics of your Torpedo - detailed enough to let us see the parts on the PCB - top and bottom. Maybe there's something simple that we can spot.

 

So received the 12AZ7's tubes... and @TomB was right. Very nice tubes and cheap too! Still need to burn in ofc but so far the impression is that they're definately a step up from the stock tubes. Sound nice and balanced less bright yet still detailed and no sibilance that i sometimes detect on the stock tubes.

Edit: All aboard for goosebump city...

 

Has anyone ordered parts from Symphonicas Audio? The Amtrans I'm looking for (100K ohm / 2W) are out of stock at PartsConneXion and HiFi Collective only has one left (I need four for the TIII). Symphonicas Audio has the Amtrans I need and the site looks legit (they've got a B&M storefront, too).. but it's China/HK and that region of the world is fairly infamous for fake parts, big and small.

 

You could try http://www.acoustic-dimension.com/ had good dealings with that site in the past.

 

It looks like you can order directly from the mfg in Japan too...

http://www.amtrans.jp/hpgen/HPB/entries/54.html

 

Have you calculated the power rating you need?

 

I haven't.. I'm just going off the BOM specs for the resistors at R23-R26 (and what other users who've used the Amtrans in that position have used, i.e. @MortenB & @bazelio).

 

I'll have to go back and look but I think it worked out to 1W, so 2W made sense. Mine get quite hot. I suppose the idea with the epoxy filling is to radiate heat outward. And if so, it does do that!

 

If I remember correctly dsavitsk mentioned at some point, that the plate load resistors must be rated at minimum 400V DC. Maybe you can confirm dsavitsk?

The Amtrans 0.75W are rated at 350VDC
The Amtrans 2W are rated at 500VDC

I choose the 2W Amtrans because 2W is specified in the BOM and I'm not a fan of choosing lower spec components than the designers choice. And also because (I think) 400VDC rating was mentioned.

 

Thanks for the vendor recs, fellas. I ordered the six Shinkoh tantalum resistors (1/2W, 1K3 Ohm) from PcX and four Amtrans AMRG resistors (2W, 100K ohm) from Acoustic Dimension. Both vendors were terrific in terms of customer service. I chose the least expensive shipping options from both vendors (shipping to the US).. the total for the Shinkoh order was ~USD$25 & the Amtrans order was ~USD$28.. very reasonable for these 'boutique' parts, IMO.

 

Cool, hopefully you will think they are worth the money and the effort

 

The Great T3 Tubeup went down! @philipmorgan @brencho @drfindley stopped in for the festivities. I had a great time with these great folks, and learned a lot. I'm a bit tired - because we absolutely tube rolled the crap out of these T3s - and so will quickly summarize the festivities and learnings. I'm sure the others can fill in some greater detail as desired...

After taking a scenic route on bikes to a courtyard encircled by roach coaches with live acoustic music for dinner, we got down to business. Equipment involved was a Gungnir Multibit, 3 ECP T3's, modded HD650s, modded HD800s, and a Shitt source switcher. Toward the end, a Jensen isolator and Laconic Night Blues Mini made cameos. Great stuff.

The three T3's involved were configured as follows:

T3(A): Cinemags, Mundorfs
T3(B): Cinemags, Mundorfs, CCS boards
T3(C): Cinemags, Mundorfs, CCS boards, AMRG R23-R26, electronic choke.



First order of business: Determine whether a choke and 4 AMRG resistors make a difference. For this we compared T3(B) to T3(C), both tubed with Brimar 6060s. Again, skipping details, the unanimous determination was that yes, absolutely, there is a positive difference and one that is as or possibly more significant than any delta from tubes (minus a pair of shitty Philips tubes that belong in the landfill). For a parts cost of about $60 bucks (choke + 4 resistors + shipping), I think we all agreed it's a no-brainer. My own personal opinion now is that this is a required upgrade. Warm up the iron, bust out the solder wick, and just git her done!

Second order of business: Roll through a crapton of tubes with our favorite T3 - which was T3(C) - and compare notes. Oh man, so many tubes... Let's see if I can remember them all... Telefunken 801S, Amperex 12AZ7A, Valvo 6201, Amperex/Dario 7062, Brimar 6060, GE 12AZ7, Telefunken ECC83 in EI boxes, Amperex Bugle Boy 12AX7, JJ ECC83, maybe others that I've forgotten. A pic:



Results (others will have to chime in as they desire to provide listening notes as I'm just going to cut to the chase):

I believe we all ranked the Amperex 12AZ7A at or near the top, but felt it's definitely a better tube for the HD650 than the HD800. Please correct me if I'm wrong here, too. Further, I believe drfindley and I both had the Amperex 12AZ7A and the Brimar 6060 as #1 and #1a with the HD650, but maybe in reverse order. Both brencho and philipmorgan had the Valvo 6201 in their top 2 or so I believe. And interestingly I don't believe any of us had the most expensive pair - the Telefunken 801S - in our top group. For me they'd be middle-top somewhere. Based on these results, we're now interested in obtaining a variety of 12AZ7s and rolling through just that tube family. Incidentally, I also now think I like the HD650 better in general than the HD800 (modded). Is that supposed to happen?

Third order of business: Determine if CCS boards make a difference. We used T3(A) and T3(B) here. Actually I think I was too fatigued to participate in this one, but brencho and drfindley seemed to eventually conclude that, yes, they make a difference that is somewhat subtle or minor. However the preference is for the amp with CCS boards.

Lastly, we all took a listen to the Laconic Night Blues Mini. My takeaway: there's a surprisingly elegant sound produced by this $300ish tube amp. I was thinking, geez, 3 transformers, 4 tubes, $300 - it's gotta have some serious sound quality issues. But it simply did not. Now, it's not necessarily a proverbial "giant killer" IMO, but if there's another $300ish amp out there that sounds like the Laconic Night Blues Mini, then I'd like to know what it is. And what a shame that they simply refuse to export these gems to the USA.

And that's about it - bed time for me!

 

Good stuff guys! 12AZ7'S really are the shit

 

EPIC ! Thanks so much for the terrific comparisons and information, fellas!

 

Yes, epic Thanks guys..!!!

And perfect that you got the chance to make a comparison between a T3 with Amtrans plate load resistors with one with the standard resistors. I have been waiting for someone to get a chance to do that. This confirms that these resistors are a big improvement.. Great stuff and a no brainer for sure.

EDIT:
The improvement in sound is even bigger with the ''full resistor package'' I have described earlier, but the plate load resistors are the most important / makes by far the biggest difference. The e-choke on the other hand seems to make little/no improvement in SQ in the T3. The fully differential circuit with the high ripple rejection works really well and it seems like improvements of the PS ripple performance is of little importance. It would still be very interesting to lower the output impedance of the PS as mentioned earlier by Dsavitsk.

 

@MortenB we were definitely wondering what contribution - if any - the choke itself had. Of course we didn't have a soldering iron on hand to make a determination.

On the resistor package, I'd actually be tempted to go with Amtrans in the other signal positions as well, if the R values were available. I'm not sure if there's any magic to the Shinkoh/Amtrans combo, or if we'd experience similar improvement with Amtrans across the board there. Lastly, I've got the Rike's on hand now. I'm thinking I'll get around to doing those this weekend, and be done for a while.

What this experience made all of us realize was that as good as the T3 is, there's still notable room for relatively inexpensive SQ improvement. No more writing off T3 plate resistors as audiophoolery. ;-)

 

It's the resistors that gives the improvement in SQ. I have now tried swapping the e-choke for the resistor, and I can't say that I can hear a difference with the e-choke. Maybe I hear a slightly cleaner sound? Or maybe I make this up because I know the power supply is cleaner with less ripple? It's marginal, or not there at all. Try for yourself. I still like to have cleaner power, so the e-choke will stay.

The only way you can know what resistors sounds best to you is to try different ones and listen. Both the Amtrans and Shinkoh are top class resistors with a powerful, natural and slightly warm sound. The Amtrans a bit more bass heavy, the Shinkoh a bit more transparent. You can also opt for something like Vishay Z foil to get the most neutral and transparent resistors of them all. Just try, listen and choose what you think sound best. That's what voicing is about and these are not expensive parts.

But again: The improvement in SQ is not as big in those other positions, so you might also find less difference in sound between different good sounding resistors. With the plate load resistors the differences are kind of magnified.

I'm not sure what you mean when you say, ''if the R values were available''. Hifi Collective seems to have 190 of the 1K / 0,75W Amtrans in stock. So if these are what you want, they seem to be available:

http://www.hificollective.co.uk/catalog/amrg075330-075w-amtrans-amrg-resistor-p-7168.html