Modifications to run e80cc/12bh7a/5687 for Crack+Speedball

[onelivewire]

I wonder if anyone with this mod will actually use the 235 ohm switch position.  With this mod, is there any 12AU7 tube that is superior to the E80CC?

I still preferred my ECC82 to the E80CC when I installed the mod, it was simply a gateway to the 12BH7 for me. I'd say that these results are very dependent on your other equipment - E80CC is an excellent tube for the hd650s, but not my t1s (IMO).

[JamieMcC]

I wonder if anyone with this mod will actually use the 235 ohm switch position.  With this mod, is there any 12AU7 tube that is superior to the E80CC?

I still preferred my ECC82 to the E80CC when I installed the mod, it was simply a gateway to the 12BH7 for me. I'd say that these results are very dependent on your other equipment - E80CC is an excellent tube for the hd650s, but not my t1s (IMO).

Interesting I am very pleased with the mod with my T1's and use the E80cc for roughly 90% of my listening. 

[Hornet900]

Yeah I liked the e80cc at first but now I'm finding it a bit to much , It has  bit more detail but its brighter and gives me ear fatigue to quick with my hd600s
I like a smoother warmer sound and going back to 12au7 sounds better for me    I will try it again tho 

[Hornet900]

plus i get more volume control with the 12au7

[JamieMcC]

I will disconnect my pio capacitors and try it running with just the mkp films tomorrow, I did spend some time today swapping between my 12au7 and e80cc types today its very close but defiantly prefer the e80cc in my set up. A whisper more dynamic and revealing.

Running gec 6as7g brown base power tube

12au7's inputs rolled today

RCA
Tung Sol black glass
Tung Sol JTL
Mullard 4003 box plate

 

[kscwuzhere]

I will disconnect my pio capacitors and try it running with just the mkp films tomorrow, I did spend some time today swapping between my 12au7 and e80cc types today its very close but defiantly prefer the e80cc in my set up. A whisper more dynamic and revealing.

Running gec 6as7g brown base power tube

12au7's inputs rolled today

RCA
Tung Sol black glass
Tung Sol JTL
Mullard 4003 box plate

You should definitely try rolling with the 12bh7a. I got a chance to listen to onelivewire's set-up the other day and his T1's are a new beast with the Sylvania 12bh7as, seriously. The detail and dynamics of the e80cc is definitely all there with the 12bh7a but the 12bh7a is much more forgiving and has a larger soundstage (width and depth). Imaging also improved significantly with the T1's!

[onelivewire]

I'll just add my 2 cents, though ksc pretty much laid out my feelings. The 12bh7a at the proper resistance is not as bright as the e80cc, and definitely has the same level of imaging and dynamics, which was lacking from 12au7s. I couldn't handle the obvious sibilance in lesser recordings that came with the e80cc + T1s. The e80cc matched the 650s very well though.

I just finished installing a 3 way switch to let me run the 12bh7a, e80cc, or 12au7s, so I can try to do a direct A/B with the former 2 tubes soon.

On another note, the MJE5731As are in the mail, too! I've been looking at the 5687 pinout, and here are the differences I see between that and the 12bh7/au7 pinout:
12au/bh7
1 - Plate (2)
2 - Grid (2)
3 - Cathode (2)
4 - Heater (2)
5 - Heater (1)
6 - Plate (1)
7 - Grid (1)
8 - Cathode (1)
9 - Heater (2/Midtap)

5687
1 - Plate (2)
2 - Grid (2)
3 - Cathode (2)
4 - Heater (2)
5 - Heater (1)
6 - Cathode (1) [Redirected from stock pin 8]
7 - Grid (1)
8 - Heater (Midtap)  [Redirected from stock pin 9]
9 - Plate (1) [Redirected from stock pin 6]

So pin 8 must go to 6, 9 must go to 8, and 6 must go to 9.

I realize I may have displayed that poorly, but does it seem to be correct? If these are the only changes necessary for the 5687, couldn't these three leads go through some 2-way on-on switches, with the biasing LED on it's own switch between pins 6 & 8? It seems previous 5687 modders used blue LEDs to achieve a different bias, which I'm guessing would eliminate 12au7s and the lot for tube rolling - but it seems the 5687 could run just fine with the stock HLMP6000s? Sorry for all the questions!

[Paul Birkeland]

Yeah, that will get the pinout to be correct. 

For the 5687 to reach 75V on the plate with 1.5V LED's on the cathode, you'd need to run 20mA of plate current! (The stock 12AU7 is about 3mA). 

12mA of plate current and just over 2V of bias on the 5687 makes for a more reasonable operating point. 

[kscwuzhere]

Yeah, that will get the pinout to be correct. 

For the 5687 to reach 75V on the plate with 1.5V LED's on the cathode, you'd need to run 20mA of plate current! (The stock 12AU7 is about 3mA). 

12mA of plate current and just over 2V of bias on the 5687 makes for a more reasonable operating point. 

In order to achieve this bias and install it on a switch so that we can roll the crack with the 12au7, should we replace both the 1.5V Red LEDS on A3 and A8 with 2V Blue LEDS (being on A3 and A6 instead) or just one of the LEDS? Thank you PB!

[Paul Birkeland]

You would need a switch to swap out both LED's on the tube socket to something else. 

This gets a little bit beyond the bounds of what should be switchable on an amplifier, if you go far enough down this trail, you'll turn your Crack into a tube tester.

[kscwuzhere]

You would need a switch to swap out both LED's on the tube socket to something else. 

This gets a little bit beyond the bounds of what should be switchable on an amplifier, if you go far enough down this trail, you'll turn your Crack into a tube tester.

What LEDs should we switch it out with? Would the following LED be okay?

http://www.digikey.com/product-detail/en/HLMP-CB1A-XY0DD/516-2275-1-ND/2428165

[Paul Birkeland]

That LED would work with about 5mA of plate current.  (~175 Ohm R1)

One thing to note, that LED will be effing bright.  I wouldn't hesitate to spray them with black paint (mask the leads) before you install them.

[Paul Joppa]

LEDs are highly variable in their voltage even if they are said to be  the"same color". They are also quite variable in how much noise they generate, and in their dynamic impedance. The LEDs we use seem to be (so far - knock on wood!) fairly quiet and fairly repeatable. We haven't measured or otherwise tested other LEDs, and the specifications for most LEDs give a wide range of voltages and no noise data, so the specs are no real help.

[kscwuzhere]

Would installing these LEDS in series with a switch or in parallel with a switch allow us to achieve the correct plate voltage? Otherwise we'll just have to chance it with some LEDs.

[jboehle]

Are there any other desirable Speedball part changes when swapping the MJE350 for MJE5731A other than the transistor facing the opposite way?