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

[TheCoolDoc]

Just installed the Tungsram E80CC alongside a Sylvania 7236 (replaced 237's with 470 Ohm Resistors on the A and B boards) and my background hiss was immediately gone (faulty 12AU7 I guess). It sounds glorious.

I still get crackling at high volumes, but I don't play at those insane volumes anyway so it's all good.

One question, I was only supposed to replace those resistors, correct? 1 237 resistor on A and B? Nothing else?

[Paul Birkeland]

One question, I was only supposed to replace those resistors, correct? 1 237 resistor on A and B? Nothing else?

Yes.

-PB

[Maxhawk]

Thanks to Snarii's diagram of kscwuzhere's mods, I've modded mine using a DPDT switch for the bias current and 4PDT to switch between 5687 and 12au7 wiring topology. The DPDT switch allows me to switch the current on both channels simultaneously.

The resistors I used are 470 ohm in the off position for E80CC. 475 ohms in parallel for 12AU7, and 196 in parallel for 12BH7. I'll have to do some measurements with the 5687 to see if I can get away with 138 ohms.

I'll likely regret it long term, but I epoxied the 4PDT switch to keep it firmly in place since I didn't want to wait for the special tape I ordered, which happened to arrive today that I used for the DPDT. I was worried about the adhesion of run-of-the-mill double-sided tape when used in a high temperature environment, so I bought 3M VHB 5952 tape, which withstands up to 250F long-term exposure. At $15 for 1/2" x 5yds it was on par price-wise with the better stuff Home Depot carries. And 3M does not publish maximum temperatures for the consumer-grade stuff, they only spec application temperature.

I'm running a Sylvania 12BH7 at the moment which sounds even better when biased properly. My Tungsol 5687's will be here this week and I'm hoping to be wowed based on the reviews I've read.

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi.imgur.com%2FsDWfrixl.jpg&hash=7fd81ae88b3b0a2a1583433aa4f8beae058d4097)

[kscwuzhere]

Thanks to Snarii's diagram of kscwuzhere's mods, I've modded mine using a DPDT switch for the bias current and 4PDT to switch between 5687 and 12au7 wiring topology. The DPDT switch allows me to switch the current on both channels simultaneously.

The resistors I used are 470 ohm in the off position for E80CC. 475 ohms in parallel for 12AU7, and 196 in parallel for 12BH7. I'll have to do some measurements with the 5687 to see if I can get away with 138 ohms.

I'll likely regret it long term, but I epoxied the 4PDT switch to keep it firmly in place since I didn't want to wait for the special tape I ordered, which happened to arrive today that I used for the DPDT. I was worried about the adhesion of run-of-the-mill double-sided tape when used in a high temperature environment, so I bought 3M VHB 5952 tape, which withstands up to 250F long-term exposure. At $15 for 1/2" x 5yds it was on par price-wise with the better stuff Home Depot carries. And 3M does not publish maximum temperatures for the consumer-grade stuff, they only spec application temperature.

I'm running a Sylvania 12BH7 at the moment which sounds even better when biased properly. My Tungsol 5687's will be here this week and I'm hoping to be wowed based on the reviews I've read.

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi.imgur.com%2FsDWfrixl.jpg&hash=7fd81ae88b3b0a2a1583433aa4f8beae058d4097)

Beautiful modding! What headphones are you driving? What kind of music do you listen to? I've tested a lot of 5687/7119 varieties on many different headphones with my mod, I could potentially have some recommendations depending on your headphones/music choice.

[Maxhawk]

Beautiful modding! What headphones are you driving? What kind of music do you listen to? I've tested a lot of 5687/7119 varieties on many different headphones with my mod, I could potentially have some recommendations depending on your headphones/music choice.

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.

[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:
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi.imgur.com%2FA5d69jSl.jpg%3F1&hash=63ee2c6e4bffcdf166031be3f923b2ba33ea20c3)

Stuffed with parts:
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi.imgur.com%2FR31SnPZl.jpg&hash=2c835e653f50a5070e200d22fe37c4bf9b22fabb)

Installed in place of the dual PCBs:
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi.imgur.com%2F1kGMm0ll.jpg%3F1&hash=0d654c43411f70e72e5a3a5d655d5625708346fc)

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+.
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi.imgur.com%2F3rpOBbql.png&hash=9ebd020be347327f6a2b312fb5a2a94a55712dab)

[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.