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

[kscwuzhere]

The cans I listen to most often are Sennheiser HD800. My music tastes are quite varied although I tend to gravitate towards jazz or vocals. Classic rock, rock, some classical, most types of jazz, new age, hip hop every now and then. It's easier to say that I don't typically listen to rap, opera, or country.

On the way are NOS tung-sol 5687 and RCA 5687. In my repertoire of input tubes:

12AU7: RCA long black plate, Westinghouse, Sylvania (stock), RCA clear tops (currently in my MC240)
5814: CBS-Hytron (angled D-getter), GE
12BH7: Sylvania, RCA (currently in my MC240)
Mullard CV4003

My output tubes:
GE 6080 (stock), Sylvania GB6080, Mullard CV2984, Tung-sol 5998

My favorite input tubes are the Sylvania 12BH7 and CBS-Hytron 5814. For output I like the 5998 and GB6080.

I run the Hd800s too! My fav combination of all time is the Bendix 6080wb slotted cross columns with either the Amperex 7119 PQ or the RCA 5687. They jive really well with the hd800s. The Amperex 7119 is my go to for jazz, or anything not quite as brutal as heavy progressive rock or some metal in which my RCA 5687 is my go to. The bendix outshines the GEC 6as7g, WE421a, and tungsol 5998 with the HD800s imo, the data retrieval is unmatched.

 

[Maxhawk]

Two of my 5687 tubes arrived today. With 138 ohms I'm running 74.5 volts, so I also can use the same resistor for 5687 and 12BH7 (didn't actually measure 12BH7, but assumed 138 was the proper value based on what I read here).

Wow this 5687 runs hot. I'm showing 180F with an IR thermometer vs 125-130 for all the other tube flavors.

My initial impression is better imaging, well controlled bass, maybe a more luscious/liquid midrange. This is with my Gold Brand 6080.

 

[Maxhawk]

Well, I decided to go the extreme route and made a new speedball PCB to accommodate a switch and various resistors to support 3 different bias points. I didn't feel comfortable with the taped switch and wanted something neater.

Here's the bare PCB:

Stuffed with parts:

Installed in place of the dual PCBs:

The fit wasn't perfect (had to dremel the screw holes a little as I didn't realize the 3rd standoff would interfere), the pads for some of the parts are on the small side, the holes for the diodes are too big, but it worked first try. It's also slightly simpler requiring only one input (B+) and one ground.

I just got my Tungsram E80CC tube in today and I'm listening to it with a Bendix graphite plate 6080 as I type this. The E80CC and 5687 both sound better than the various 12AU7. I'll have to switch back to the CBS-Hytron 5814 at some point since I recall liking it a lot too, as well as the Sylvania 12BH7.

 

[Paul Birkeland]

Good stuff!

 

[mcandmar]

Very nice layout, love the symmetry of it

 

[kscwuzhere]

incredible!!

 

[Strikkflypilot]

Very cool!

 

[NightFlight]

The fit wasn't perfect (had to dremel the screw holes a little as I didn't realize the 3rd standoff would interfere), the pads for some of the parts are on the small side, the holes for the diodes are too big, but it worked first try. It's also slightly simpler requiring only one input (B+) and one ground.

Interesting. I'd love to know what tools/service are required to create a custom PCB for low scale count like that. A very clean solution. I believe the original PCB was one piece like this as well... correct me if I'm wrong, I saw a single PCB for the C4S circuit for the input tube on a Crack previously on here and prefer the look.

I assume the third stand-off you refer to is the middle one that mounts the C4S for the output tube. My first thought would have been to notch out space for it on the long edge rather than the two screw holes. Is there room for that? From the photos it looks possible.

 

[Maxhawk]

Interesting. I'd love to know what tools/service are required to create a custom PCB for low scale count like that.

There are numerous companies on the net that will create boards from your gerber files in small volumes at affordable prices. Some companies offer free software to allow you to create boards, but I haven't tried them since I have Orcad schematic capture & layout.

I assume the third stand-off you refer to is the middle one that mounts the C4S for the output tube. My first thought would have been to notch out space for it on the long edge rather than the two screw holes. Is there room for that? From the photos it looks possible.

Notching out the top would work too. You just need to keep away from the bottom side trace that carries B+.

 

[Maxhawk]

In order to wire this mod to run the 5687 you're going to need 2 dpdts and the following leds and transistors:

http://www.digikey.com/product-detail/en/HLMP-CB1A-XY0DD/516-2275-1-ND/2428165 - blue LEDS for 5687

Is your amp silent when using the 5687?  I substituted the above referenced LED with a different one with identical Vf (@20ma) but 2 orders magnitude lower luminous intensity, and although my voltages are right where they should be, I get a very faint hum when no signal is present. The hum is there with 3 different 5687 tubes, so I figure it could be the LED since I've seen mention of noisy LEDs before. The amp is dead silent when switched to use with 12AU7.

 

[kscwuzhere]

Is your amp silent when using the 5687?  I substituted the above referenced LED with a different one with identical Vf (@20ma) but 2 orders magnitude lower luminous intensity, and although my voltages are right where they should be, I get a very faint hum when no signal is present. The hum is there with 3 different 5687 tubes, so I figure it could be the LED since I've seen mention of noisy LEDs before. The amp is dead silent when switched to use with 12AU7.

I get no hums whatsover, its black as can be.

 

[Maxhawk]

I've made another PCB to clean up my 5687 switch. It helps to clean up the implementation shown here because you no longer need multiple wires to certain connections. I haven't installed it yet because I don't have any more of the solid core wire that came with the kit, and I usually end up breaking one or more of them because the solid core doesn't like to be bent more than once. I'll install it once I have extra wire on hand.

 

[kscwuzhere]

Beautiful work my man! I know what I'm gonna do now.

 

[Tom-s]

Any updates? I wish i could make a PCB myself.
Everybody still in love with their 5687 or got something better?
Deciding on pin-out switch mods.

 

[Rhok]

I just tried out a 12BH7A and love it, however, voltage at T1/T5 are low, 50, and 53 - considering replacing the R1 resistors for lower resistance to bring the voltage up - one question (that may have been answered already, sorry if it was):

Is it unsafe to run it at low voltage? what is the danger if so?

 

[Paul Birkeland]

Is it unsafe to run it at low voltage? what is the danger if so?

It's not unsafe, but that voltage biases the 6080 in the Crack, and if this voltage is too low, the tube will not be properly biased, and you won't get optimal performance out of the amplifier.

 

[Rhok]

It's not unsafe, but that voltage biases the 6080 in the Crack, and if this voltage is too low, the tube will not be properly biased, and you won't get optimal performance out of the amplifier.

Understood, I'll wait until I get my new headphones to see if I still like the 12BH7A as much as I currently do before making any changes.

Currently running HD 650's, in the mail a HD 800 S is on the way.

You guys are fond of the HD 800's from what I've seen around, any interest in the new variant?

 

[Finkä]

Hello from Switzerland

First, i want to say thank you to the pioneers of this topic (especialy kscwuzhere,onelivewire, Snarii, and Maxhawk) and of course thank you to the Moderators in this Forum. With the information in this thread i was able to create (let create) two pc boards to handle the diffrent voltatges on t1 and t5 and to switch between stock and 5687/7119 tubes.

Here some pictures with a lousy smartphone cam:

Hm... in this picture the blue light shines like a house with freaky christmas decoration. In reality its not that intense.

As you can see (or not) i drilled a hole in the chassic plate to fix the small pc board. Spontaneous i was not able to get some nylon standoffs therefore i did it that way. I would not recommend this, because when you or someone else switch between the stock/5687 mod accidentally you could possibly break a tube. In my case the amp is far away from strangers hands and the switch is behind the input tube, so i got that goin for me

A note to the post #211 from maxhawk.  On the small pc board to switch between stock/5687 there is a solder joint named B+. On the big pc board and on the two small ones of the the speed ball uprgrade the B+ solder joints are connected to 2U. But in my understanding this solder joint should be connected with T1 (1U). It was a bit confusing for me

Best regards

 

[Tom-s]

Another 5687 switch board here.
Really like this this tube (Amperex 7119 PQ), lush, big soundstage with loads of details.
Worth it IMO.
All three (5687, 12bh7 and e80cc) are special sounding tubes in there own way.
Nice flavors or "sound seasoning" compared to the standard 12au7's.

 

[guildenstern]

I'm hoping one of you technically savvy forum members can help. On Head-Fi I bought a modded Crack from a BH forum member -- great build and very enjoyable sound. What I can't get from the builder is a clear explanation about which way the switches should be set for 12AU7 and which way for E80CC. Here are pictures of the resistor switch assembly he devised, taken by the builder of the amp. If you can use these pictures to deduce the proper switch positions for 12AU7 vs E80CC, I would appreciate it. Especially if you can explain in "for dummies" terms (as I readily confess I am). Thanks in advance.

6SN7,12AU7 =( T1 75V / T2 76V )-very happy with this  ;D
E80CC=( 85/86V )
12BH7A=(55/57V )

Thank you Sir !!