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

[Stanshall]

I don't know if anyone else has mentioned but this resistor mod has also completely removed the zero volume hum.

Also, really rather surprised but quite delighted to hear the audible improvements. As with most upgrades to the Crack, it's 'just the same but more'. Nothing I've done has removed or fundamentally altered the qualities of the amp, it just keeps opening out and stretching a little further in every direction.

 

[onelivewire]

I don't understand the question about heat and the stock resistors.

I just wanted to make sure these new transistors on the small speedball boards will work just fine with everything else in "stock" configuration, which seems to be the case.

I wanted to throw this out there to anyone thinking of playing with the 12bh7's too- I just grabbed a vintage Sylvania 12bh7 to check the operational differences against a Tung-Sol 12bh7, and got the following readings:

@117ohm, w/SYLVANIA
T1: 64V
T5: 69V

So it seems the proper resistance definitely changes between these 12bh7 tubes.
That all said, the soundstage on my t1s has never been so massive and three-dimensional with any other tube.

 

[Paul Birkeland]

That all said, the soundstage on my t1s has never been so massive and three-dimensional with any other tube.

Try retrofitting for the 5687.

 

[onelivewire]

Just threw in a couple more resistors,

@93ohm, w/SYLVANIA
T1: 74.8V
T5: 70.8V

Try retrofitting for the 5687/

I'm intrigued - any recommended branding? I'll try and scoop one of these up for play. Would resistance be the only mod needed for this dual-triode as well?

 

[Paul Birkeland]

I think you could run 10mA on the 1.5V LED, but you'd want the MJE5731A for that.  Do also note that the 5687 has an annoyingly different pinout, so you'll have to do some work there as well.

 

[serpent68]

I finally installed the 470 ohm mod and am very pleased with the result.  Bass is more controlled and the mids are more detailed and dimensional.

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?

When using a 6AS7G (with E80CC), should the switch remain at 470 ohm or changed to 235 ohm?

 

[Paul Birkeland]

When using a 6AS7G (with E80CC), should the switch remain at 470 ohm or changed to 235 ohm?

The switch is to optimize the plate voltage of the E80CC, so if the E80CC is plugged into the amp, the 470 Ohm resistor should be there.

 

[Loon]

Just had a crazy idea.

I wonder if it would be possible to put a voltage regulator between the anode of the input tube and the grid of the cathode follower, setting the output voltage at 75V.  This would provide a steady bias to the 6080 at the level required by the circuit. 

As I understand it, the voltage into the regulator would need to be greater than the sum of the output voltage and the voltage drop across the regulator.  This in turn would require revision of the operating point of the input tube.  I wonder if a plate load could be chosen that would

1. Result in a linear operating point for 12AU7 (and variants), 12BH7 and E80CC
2. Result in a plate voltage that met the requirements for running the said regulator

If this could be done, you could swap input tubes between these three families without having to turn off the amp and flip switches: Tube rollers heaven.  Wonder how much it would cost to implement.

Does anyone have any thoughts to add.  Do you think it is possible?

 

[Paul Birkeland]

I wonder if it would be possible to put a voltage regulator between the anode of the input tube and the grid of the cathode follower, setting the output voltage at 75V.  This would provide a steady bias to the 6080 at the level required by the circuit. 

Voltage regulators have low impedance and require capacitors at the input and output. Therefore, you would be shorting all the signal to ground at the plate of the 12AU7, and the grid of the 6080.  On top of that, the regulator will work its butt off to null out any signal present at the input from appearing at the output. 

The plate voltage of the driver tube can move around without a whole ton of consequences, it's when it goes down into the 50's or up past about 90V that things may get out of whack.  Being obsessed with getting exactly 75V is neither particularly healthy for one's psyche nor a concomitant to getting better sound out of the Crack.

 

[Loon]

Told you it was a crazy idea! 

Thanks for the learning experience.

 

[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.