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Modifications to run e80cc/12bh7a/5687 for Crack+Speedball
- Thread starter kscwuzhere
- Start date
JamieMcC
New member
I used just some ordinary 470 Ohm 0.25w Metal Film resistors £1.19 free delivery for 10 at that sort price its a throw away mod if you don't like it just stick the old ones back in. My original ones came out quiet easily just heated up one lead at a time and pulled it out with some forceps once the solder melted.
http://www.ebay.co.uk/itm/120531828406?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649
http://www.ebay.co.uk/itm/120531828406?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649
kscwuzhere
New member
serpent68 said:
For my HD650s, it really tightened up the bass (after a/bing it with against the 237ohm, I found the old resistance to make the bass noticeably muddier) ,slightly improved the imagining/instrument separation and soundstage definitely widened.
onelivewire
New member
Can anyone just confirm the 200ohm net resistance needed for the 12bh7? I haven't seen anybody put this on a switch yet and just wanted to make sure.
onelivewire said:
You'll have to smoke it and see... The 12BH7 curves aren't well enough resolved to really make a good estimate of what the current should be at 1.5V of bias to get 75V on the plate.
As R1 drops, the plate voltage will increase. I might try something around 100 Ohms first. You can run the amp with a 12BH7 plugged in and no 6080, then adjust the resistance of R1 till you see ~75V. If you have a few different 12BH7's, you can then swap them all in the socket to confirm that they are all in the appropriate range.
Depending on how much current you end up running, a small heatsink or a beefier transistor may be a good idea.
kscwuzhere
New member
Caucasian Blackplate said:
How should I go about installing a small heatsink, (where on the board would i do this)? Which transistor should I replace with a beefier one to run the 12BH7A with the proper resistance?
Start by determining the R1 that gives the correct plate voltage.
onelivewire
New member
Alright, time to order a pack of resistors and start trying! Would testing these using some 21" alligator leads be alright just for multimeter purposes? I realize the leads are far too long for listening purposes, but would they be alright to keep the solder/unsoldering time down in testing?
NightFlight
New member
I would just use a pot in the right range to dial in what you want. Then measure it when your done.
onelivewire
New member
Haha well, I went ahead and threw the 470ohm resistors we had in parallel to each other to get about 160ohms with 3, and about 117 ohms with 4.
@160ohm
T1: 64.7V
T5: 69.5V
@117ohm
T1: 79V
T5: 75V
I'm about to give this a listen. I did add some ~1.5" leads in order to tack on resistors, so hopefully that doesn't make itself too obvious of a bottleneck.
Edit: Plugged in, this thing sounds crazy! Bass extension, detail retrieval, soundstage are all the best I've heard on the t1, even though the treble can be a bit more cutting than the Mullard ECC82. I must say though, the tubes are getting extremely hot with this setup, even after just 10 minutes or so of play. What can be done heat sink / transistor wise to fix this while still allowing for stock resistance use?
@160ohm
T1: 64.7V
T5: 69.5V
@117ohm
T1: 79V
T5: 75V
I'm about to give this a listen. I did add some ~1.5" leads in order to tack on resistors, so hopefully that doesn't make itself too obvious of a bottleneck.
Edit: Plugged in, this thing sounds crazy! Bass extension, detail retrieval, soundstage are all the best I've heard on the t1, even though the treble can be a bit more cutting than the Mullard ECC82. I must say though, the tubes are getting extremely hot with this setup, even after just 10 minutes or so of play. What can be done heat sink / transistor wise to fix this while still allowing for stock resistance use?
Looks like 147 Ohms would be a sweet spot.
This is about 6mA, which in an MJE-350 being cooled by air will give a temperature rise of 75C beyond whatever temperature is under the hood of the Crack. The MJE-350 has a maximum heat rating of 150C, but will eat itself in your case if that temperature goes beyond ~130-ish.
IIRC, the temperature measurements that we have seen have been between 30 and 40C, so adding 75C to that still leaves you in safe territory. Replacing the MJE-350's with MJE-5731A's (they face in the opposite direction) would decrease the temperature rise to ~47C, which gives a much higher safety margin (and longer life most likely).
This is about 6mA, which in an MJE-350 being cooled by air will give a temperature rise of 75C beyond whatever temperature is under the hood of the Crack. The MJE-350 has a maximum heat rating of 150C, but will eat itself in your case if that temperature goes beyond ~130-ish.
IIRC, the temperature measurements that we have seen have been between 30 and 40C, so adding 75C to that still leaves you in safe territory. Replacing the MJE-350's with MJE-5731A's (they face in the opposite direction) would decrease the temperature rise to ~47C, which gives a much higher safety margin (and longer life most likely).
onelivewire
New member
Alright, I think I'll put some MJE-5731ag's on order, as it seems that the "a" variants aren't very available. When installing these, will the back still butt up to the heatsink in the same way, even given that "they face in the opposite direction" or will some orientation changes need to be made?
I plan to test these numbers with a Sylvania 12bh7 that I have coming in tomorrow, and then committing on the proper resistors to get a 3-way switch running properly for the e80cc, 12bh7, and 12au7
I plan to test these numbers with a Sylvania 12bh7 that I have coming in tomorrow, and then committing on the proper resistors to get a 3-way switch running properly for the e80cc, 12bh7, and 12au7
Hornet900
New member
So guys if I wanted to try the E80cc tube I should "our its best" to replace my 237 ohm resistors with the 147 ohm ones for the lower voltage? I don't intend to install a switch just yet ..I'll try the tubes out for sound 1st.
I received some E80cc tubes today but haven't tried them yet.
I received some E80cc tubes today but haven't tried them yet.
onelivewire
New member
The E80CC's need something along the lines of 470ohms across R1, which is why many of us have been replacing R1 with a 470ohm and putting a second 470ohm on a switch in parallel, so when switched on, the resistance totals 235ish, and both resistances are usable. The 12BH7's are the dual-triode tubes that we're finding require a resistance of ~147ohms.
onelivewire said:
Butt up to which heatsink? These transistors go on the smaller PC boards, they do not go in place of the TIP50's on the bigger PC board.
onelivewire said:
Yeah, this is the difference between just plugging any old tube in and actually sitting down and figuring out what needs to be done to properly operate said tube.
I don't understand the question about heat and the stock resistors.
Paul Joppa
Moderator
For what it's worth, ever since we had problems with the early Foreplay III upgrade and the Paramount, I have designed for a maximum chip temp of 100C and assumed 60C under the hood - so a 40C maximum temperature rise.Caucasian Blackplate said:
That's a good reference, thanks for the reminder. It seems like an MJE-5731 should be OK on most line voltages. (I calculated for a drop from 200V to 75V, which is worst case scenario)
