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

[kscwuzhere]

So its not just something wrong with my E80CC?

Definitely not, no tubes are identical. Your e80cc can run at 108V or whatever value you were getting and your crack will sound wonderful but for a couple of bucks worth of experimentation I thought it was worth it to find the correct resistance to run the e80cc tube at the correct plate voltage.

[Strikkflypilot]

I will certainly look into it.  Maybe some resistor sockets of sorts for easier interchangability.

[Paul Birkeland]

So its not just something wrong with my E80CC?

If you have unusually high voltages with the same resistor that is working for the rest of the crowd, you may have a tired E80CC.

[Strikkflypilot]

If you have unusually high voltages with the same resistor that is working for the rest of the crowd, you may have a tired E80CC.

My thoughts exactly. Was supposed to be a NOS and everything.
 
By the way, I have read the 12AU7 datasheets :
http://free-hosting.infodiv.com/audiotube/small_signal_triode/small_signal_triode0018/small_signal_triode0018-01.html
To me, it seems a plate voltage of 100v should be a usual operating voltage, not 75v.
Again, there must be something I do not understand.

[Paul Birkeland]

By the way, I have read the 12AU7 datasheets :
http://free-hosting.infodiv.com/audiotube/small_signal_triode/small_signal_triode0018/small_signal_triode0018-01.html
To me, it seems a plate voltage of 100v should be a usual operating voltage, not 75v.
Again, there must be something I do not understand.

There are literally an infinite number of operating points for any tube.  The plate curves for a tube will reflect this. (They are usually a few pages into the datasheet).

The number on page 1 are maximum ratings.  The 100V rating is an insulation rating. 

[Paul Joppa]

There is a listed operating point at 100v; it's just another example. The example operating points are just that - not recommendations, just examples of the infinite possibilities. In this case, the 100v example is also at zero bias, a point that will have significant nonlinear grid current and is unsuitable for audio. It might reflect use as a vertical deflection amplifier in B&W televisions.

[Strikkflypilot]

Thank You both very much. I feel privileged to learn so much in so brief time!

[onelivewire]

Just dropping in to give some updates on my 5687 experience. Recently I've become fond of kscwuzhere's Amperex 7119, which certainly became less sibilant after burn-in. However, just a couple days ago I received a Sylvania Gold Brand 5687 (Gold Pin variety). With the t1s, this tube is incredible. Easily takes the cake as my favorite tube for t1s. Soft, yet articulate, this tube truly takes away just about all the harsh glare that I find in bad recordings, while sacrificing nearly no articulation. I highly recommend this tube to any t1 owners running this mod.

[Strikkflypilot]

There are literally an infinite number of operating points for any tube.  The plate curves for a tube will reflect this. (They are usually a few pages into the datasheet).

The number on page 1 are maximum ratings.  The 100V rating is an insulation rating.

Some feedback.
Decided another attempt at ordering an E80CC instead of changing my resistors.
Received an unmarked Tungsram where the plate voltages are 78ish and 81ish with 470ohms
On my now heavily hotrodded crack with GEC brown based 6080, I am convinced the soundstage widened, upper mids and treble much clearer and stronger but no annoying sibilance. I use HD580s and am a very happy camper.

[kscwuzhere]

I just received an RCA bronze plate 5687 as research eluded to it's warmth, which was something I was looking for my hd800s. After letting the NOS tube warm up for a couple of hours it has become my new favorite with the hd800s! Sonically, mid bass to mids have become much more lush and sound more whole-bodied and less airy than the 7119. Treble seems to be rolled off a little more than the amperex but is slightly more sibilant (won't surprise me if this goes with more burn in). The amperex 7119 bass is tighter and has an overall quicker presentation than the rca.

For more rock/metal orientated as well as poorer recorded music I find myself preferring the warmer RCA 5687s. Whereas for jazz, electronic and more "tamed" music, I find that the Amperex is my go to tube (particularly enjoy the speed the hd800's provide with these genres).

[jboehle]

Here's a sneak peek at my solution for easy switching between 12AU7, 12BH7, and E80CC tubes. It fits right into the existing resistor holes on the Speedball boards.

With no jumper installed:
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi.imgur.com%2FxdKfJYe.jpg&hash=e66254306896f246eb970b2d2cde994010e2a687)

With jumper installed for 12AU7 operation:
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi.imgur.com%2FGYlebXF.jpg&hash=c8ebfd64aa169c4177f7b3db8bbc0a4e963e280a)

The back:
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi.imgur.com%2FusZwaXp.jpg&hash=2282576145b06ce5fb489d596076d8671d59f515)

I will post more pics once I get the 2nd one made and both installed.

[2wo]

how cool is that...John

[JamieMcC]

Creative solution!

[kscwuzhere]

Here's a sneak peek at my solution for easy switching between 12AU7, 12BH7, and E80CC tubes. It fits right into the existing resistor holes on the Speedball boards.

With no jumper installed:
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi.imgur.com%2FxdKfJYe.jpg&hash=e66254306896f246eb970b2d2cde994010e2a687)

With jumper installed for 12AU7 operation:
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi.imgur.com%2FGYlebXF.jpg&hash=c8ebfd64aa169c4177f7b3db8bbc0a4e963e280a)

The back:
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi.imgur.com%2FusZwaXp.jpg&hash=2282576145b06ce5fb489d596076d8671d59f515)

I will post more pics once I get the 2nd one made and both installed.

Any update with the mod? I'm curious to see the results!

[NightFlight]

Well, I've been sitting on this Rogers(Canadian?) D Getter 12BH7A that I got with a bunch of other stuff about a year ago now   I was digging through my electronics kit, and found some 150ohm resistors so I decided why not give it a go and put them together.

Glad I did.

In a stock SB crack the 12BH7A was sitting in the low 60V on T1 and T2. Dropping R1 to 150Ohm brought up T1 and T2 to ~70V. Acceptable given I just soldered the resistors them straight in without much thought to reverting. Honestly, re-reading this thread from the start tonight indicated to me that I was likely be happy with this choice anyhow.

I gotta say before modification the 12BH7A showed a ton of potential, but was a bit fat in the transients and flabby on the bottom end at ~60V. Bringing the plate up to 70V put this tube in the zone! Still using the stock MJE350s, so I'm hoping their not going to go into runaway with the extra load to dissipate... because I'm not reverting. NOPE. ;-) No sir. I won't like it.

Whole new texture appearing across the spectrum compared to the 12AU7s I've give a fair shake over the last year. I really don't roll tubes that much these days. I may just setup switching because I'm curios about the E80CC, but that's about it. I've read the E80CC sacrifices some bottom end for clarity, so I'm likely prefer this 12BH7A.

Strangely with the 12BH7A I find the RCA 6080WA stock tube totally new. My 5998 has been my staple since I got it - even selling the 412A in favour of this particular 5998. But the 6080 has a midrage texture reveal that is a bit lost on the 5998. Interesting.