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

[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?

 

[Paul Birkeland]

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.

Paralleling diodes doesn't really word, you have to have just one or the other.

 

[kscwuzhere]

Since there may be a chance that the LEDs may be noisy, I want to order a variety of LEDS, should the following be a good selection?

http://www.vishay.com/leds/list/product-81641/

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

http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_334749_-1

http://www.electron.com/led-1.8mm-blue-130lb7c.html

http://www.electron.com/led-5mm-blue-520lb7c.html

Thank you and sorry for the plethora of links!

 

[Paul Birkeland]

The first one is a surface mount part, and you don't want to deal with that. 

I'd suggest just starting with one pair, I haven't yet run into LED's causing issues in this situation unless the circuit is very, very sensitive. 

 

[kscwuzhere]

Alrighty, I'll get those LEDs and toggle switches ordered and update ASAP! Thanks PB

 

[onelivewire]

Can't wait! You guys really kick ass for providing this level of customer interaction. I can wholeheartedly say that I wish all business could make themselves a part of the community with such social outreach. I can't say thank you enough!

 

[kscwuzhere]

Once I get this mod done for the 5687, would I be able to roll the 7119's with the crack too?

 

[Paul Birkeland]

Yes.

 

[kscwuzhere]

Awesome! Onelivewire and I are gonna give this thing a shot once all the parts come in and I'll update the thread accordingly.

 

[kscwuzhere]

Switches/biases have been installed, just waiting for the proper resistors and tubes to come in now! Exciting stuff!

 

[JamieMcC]

Ok well I find myself liking the two 12bh7's that arrived in the post this morning I have been listening to them on the 12au7 setting but am mindful of how well the e80cc sonics improved with the resistor mod once better matched so once again interested in following progress here. 

 

[Loon]

I thought I would join the club and add a three way switch to SB allowing me to select between three resistance values for E80CC 12AU7 and 12BH7.

I checked actual vales for resistance before installing speedball and they came to the expected values.  I inserted both an E80CC and a 12AU7 (don't have a 12BH7 yet) and measured voltages of between 75 and 80 on the correct switch settings.

Listening on the E80CC everything is sweet (switch position off).  On the other two settings there is a horrible hum in both channels that never varies despite changing volume via Submissive or volume pot. 

Did I mess up design, implementation or do I have a dodgy part?

 

[Paul Birkeland]

On the other two settings there is a horrible hum in both channels that never varies despite changing volume via Submissive or volume pot. 

Did I mess up design, implementation or do I have a dodgy part?

Is this with the E80CC or the tubes that those positions are supposed to feed?

This is part of the risk of switching R1's.

 

[Loon]

1.  Tested with 12AU7

2.  Is the hum part of the risk of this mod?  If so, what causes it and why isn't everyone reporting the hum?  If not, what exactly is the risk you are referring to? 

For the record, I will take risks all day if I can learn from them, especially with a bargain amp like the Crack.

 

[Paul Birkeland]

2.  Is the hum part of the risk of this mod?

Yes

If so, what causes it and why isn't everyone reporting the hum?

Not everybody is going to build this the same way.  (There's no manual)

 

[Loon]

Paul, do you and the rest of the staff support modding in our community?

Is there anyone else reading this who is willing to help an idiot and a Loser (ie, me) trouble shoot?

For instance, what are the common causes of hum, how do you determine the cause and how do you eliminate it?