ECP Torpedo III [indexed in first post]

I still seem unable to make these CCS boards test well. I redid one, with new parts and double checked all my connections and I'm getting 0.001 mA. I followed the new graphic, but with no luck measurement wise.

 

Did you check the fuse on your DMM?

 

Some RCA 12AT7 Black Plate tubes are available local to me. Perhaps a good match? Could possibly pick up 4 for around $50.

Edit: sorry just realised these were discussed above. Will the 12at7 be similar to the 12ax7 discussed?

 

I imagine those will be better than the stock tubes at least. 12AT7 works well for the most part. 12AX7 isn't advised.

 

Agreed. The 12AT7 may in fact be the first choice at different tube types to roll into the amp. Gain is similar to the 12AY7 (12AX7 is not) and heater current is the same (12AZ7, 7062, 6829, 6414 is not).

 

Just another note about the cap bypasses -

I tried the Sonicap Gen II 0.1uf 400V that I talked about earlier - don't use them. They took out the excellent bass that seemed to have improved with Doug's CCS boards. So, look elsewhere if you are interested in trying the bypasses.

 

Im collecting tubes while i wait for the cinemags. Got some Mullard CV4024s while i continue the RCA hunt.

 

Hey Doug - just thought I'd check in; any cycles free to work on this mod yet? Just wondering.

 

I installed the mod, and it seems to work well. I don't have any measurements to back things up but it is definitely tighter and cleaner to my ear. Unfortunately, as designed the boards are not ready for general use as they can make contact with some screws and theoretically cause a short. Actually, it is a long shot, but I think it is worth a redesign to make them safe.

Edit: I guess I should explain what's going on here. The output transistors' emitter resistors have been replaced with a constant current source (CCS). In essence, the emitter resistor and the transformer load are in parallel which means that the output must drive both of them. When doing that, the resistors soak up about 1/3 of the output current. The CCSes provide a load that is a couple of orders of magnitude higher than the resistors meaning that almost none of the current is lost. Additionally, they isolate the circuit from the power supply in that the draw on the PS is always the same, regardless of signal making the circuit truly differential. The end result is more output power, lower distortion, and better sound.

 

Very very nice Doug. I'm down for one when you have boards you're ready to let go.

 

Same here. My T3 gets a lot of use, and new mods make me happy.

 

Sounds terrific, Doug.. I'm looking forward to the reworked boards!

 

That looks awesome. If the boards are available when the cinemags come back in stock Ill probably get both.

 

Cinemags should be here very soon Any mod boards will be a while yet.

 

Would the RCA 7062 be too lush/tubey for a SBAF-modded HD650? I'd appreciate some more thoughts on the Amperex 7062, if possible.

For those interested in avery liquid sounding 12AU7, the Tungsram 12AU7 gets my vote. I don't know how it'll sound in the TIII, but I had it in the BH Crack and pimped-CTH and it was a keeper for me. It's got a badass rugged build, too. Plentiful at reliable tube sites and they don't cost an arm and a leg. Break in is a good 50 hrs, IME.

Has anyone tried any other bypass caps?

 

I wouldn't characterize RCA tubes in general as lush, if anything they tend to be more aggressive. My AudioCap Thetas should be in around the end of the month.

 

I read on the T3 page that 12AU7 isn't a good fit for the amp. 12AT7 or 7062 seems to be the current favourite.

 

It is not that it is a poor fit, it is that there is limited gain. For many, that's not really an issue as many sources have more than enough voltage. So it depends on your source, your phones, your listening preferences, and your source material.

 

So if I'm running from a Gungnir Multibit > T3 > HD800S and i enjoy going to a medium loud volume, should I be considering this family of tubes?
EDIT: I am actually just about to purchase some RCA black plate & Amperex 12AT7s

 

Really hard to answer here; you'll just need to give it a try.