Tube Rolling w/Crack

[Grainger49]

I would like to see a beginners guide to tube rolling.  I dont have a background in electronics so most of this is foreign to me.  

Paul Birkeland's explanation covers most of it.  If you buy a tube with the exact same tube number you are fine.  

This is a quote from the Product Page, "And of course you can tweak to your hearts content tube rolling different 12AU7 and 6080/6AS7 variants."  What Doc means is that there are "equivalent" tubes out there.  Some are a drop in replacement, like the CV4003 Mullard is exactly the same as a 12AU7 but sounds nicer.  Others are very similar but won't work for some reason or another.  In the case of the 6DJ8/6922/7308 that is used in the Seduction the Russian 6N1P is the same except it needs more current for the heater.  Using it in the Seduction will either blow the fuse, we hope, or burn out the heater winding in the transformer, we hope not.

Look two posts above yours, I suggest that usable tubes like the CV4007 be listed as a "Sticky" for each product.  That would take the guessing out of it.  And maybe I will start a thread that others can correct and add to and Doc can make it a Sticky.  

The OP, Dr Toobz could collect the equivalents for the crack and edit ("Modify") his first post for the Crack.

For the input tube, the 12AU7 I have a list of tubes that I believe are usable equivalents.  I do not know that all use the same or lower heater current, a common problem is higher current.  But this is a start for the 12AU7:

12AU7(A)(WA)
ECC186
ECC82
ECC802(S)
E8025
E82CC
CV4003
CV4122
CV491
5814(A)
6189(W)(WA)
6680 (WL6680)
6067
7489
7316

I will be happy to correct this list if anyone can help.

 

[tdogzthmn]

Has anyone tried using a Western Electric 421A?  I saw some for sale but they are quite pricey. 

 

[jrebman]

How about the 5670/2c51?  Will this tube work in the amp if the front socket is rewired?  I don't have a pinout chart so I can't tell if it is the same as a 6cg7.  I also don't have access to the curves so I can't tell if any changes to bias would be needed at the 75v operating voltage.  I realize there will be 5 dB more gain, but is there anything else I should be considering?

Thanks,

Jim

 

[Paul Birkeland]

You could indeed use this tube, but it would be easier to do with the Speedball upgrade. If you're planning to go that route, I can post the R1 value for the driver C4S boards.

Honestly, I'd go for the 5687 instead.

 

[mrarroyo]

A good site to find information on tubes and their equivalets is: http://tdsl.duncanamps.com/tubesearch.php

 

[jrebman]

Thanks, Paul.  If you can post the resistor value, that would be great as I may just give this a try at some point.  I only thought of the 5670 because I have a few of the super nice, 1950s Ericsson/simens gold pins and no 5687s in house, and no money to buy more tubes right now.  Any particular reason for one over the other?  The interelectrode capacitance values of the 5670 seem decent to me.

Marroyo, I do use that site, but I'm blind so the graphs and graphical pinouts are of no use to me, but the TDSKL page often gives me links to other html pages where the electrical data is published in text.  I still haven't found one that identifies pinouts though.

Thanks anyway,

Jim

 

[ironbut]

Hey Jim,
The pin assignments for the 5670 are;

1-heater
2-cathode (2)
3-grid (2)
4-plate (2)
5-shield
6-plate (1)
7-grid (1)
8-cathode (1)
9-heater

Heater-6.3V, 350mA

Class A
plate voltage 150V
cathode bias resistor 240 ohm
amplification factor 35
plate resistance 6400 ohm
transconductance 5500 micromho
plate current 8.2 milliamperes
grid current -8V (Ib=10 milliamperes)

 

[Dr. Toobz]

Ok, here's a theoretical question, just out of curiosity: is the lowly 6AS7 and its many variants we're playing around with like a sort of indirectly-heated twin 2A3? I remember somebody claiming someplace else that a 6AS7 is similar to two 6B4's, or at least close. 6B4's are the octal version of the 6A3, which is a 6-volt heater version of the 2A3. Correct? So, might a 6AS7, the lowly regulator tube now finding use in many headphone and P-P amps, actually be an indirectly-heated cousin of the 2A3? This tube certainly sounds a lot better than it has a right to....

(One problem I found, though, is that the 2A3's mu is higher than the 6AS7, which I think is around 2, correct? So,maybe distant cousins....).

 

[Dr. Toobz]

I've started to compile a list of tubes on the original post as a reference. Would you guys who actually know something about tubes double-check it for accuracy, and PM me with any additions/corrections? There's one input tube, for example, that I left off, the ECC80, as I don't know if it's a drop-in replacement or needs the heaters rewired (don't have specs handy ATM).

 

[Paul Birkeland]

Wow, the 5687 does indeed look like an interesting tube to try.  Of course, the pinout is different, so that has to be addressed first.  After that, I would change the R1 on the green PC boards to 52 ohms.  This will set the forward current to around 15ma, and should keep the plate voltage around 75 volts.  Of course, 150-75=75 volts across the CCS, then .017A*75v=1.275 watts, so use a small clip on heatsink for each transistor (it won't require anything significant). 

The 5687 has similar gain to the AU7, and the extra plate current should really sweaten the sound!  Based on the extra current drawn, I would go to a CLC power supply at the same time to ensure that the B+ rail stays up over 150v.

 

[jrebman]

Steve, thanks very much for that information -- that helps a lot, but also tells me that a dpdt won't exactly work to switch between 12au7 and 5670 configurations.  Oh well, at least now I have the info for future reference.

-- Jim

 

[jrebman]

Hi Paul,

Now, that sounds tempting.  I still plan to try the stock config first, but I'm thinking the additional current drive would be nice with the 650s for a bit more detail...  perhaps.

Thanks again,

Jim

 

[Paul Birkeland]

Yeah, I think it really comes down to taste.  Doc loves his 12AU7's, and I totally understand that when we cue up tape and listen.  PJ is pretty into 6SN7's (as is Ed Fallon), and in PJ's case I think it's reflective of his preference for musicality.  In my case, I might go for a 6414 or something like that, except that gain is an issue, so wiring for 5687's or ECC99's seems like a good choice. 

Putting in a switch for the filaments seems easy enough and like a good plan.  With  the Speedball installed, you should be able to switch between 6CG7/6FQ7, 12AU7, and 12BH7 without tremendous voltage mismatch between the driver tube and the output tube.

 

[jrebman]

Yes, it really does all come down to personal taste, and that's why I at least originally wanted to have the ability to use the 6cg7 (and because I have a few very nice examples of those on hand), but also because I too really like the musicality of the 6sn7 even though I do find that the ability to render dynamic contrasts to be high on my preferences list and the 6sn7 is really not the ideal tube for this.  On the other hand, (and I see you anticipated my next questions) is that with the direct coupling and no cap between driver and output, dynamic contrasts are much better than in cap coupled amps anyway.

So, all these unknowns and experiments to be done, but at least with my original plan to have a switchable filament arrangement, I can play with enough variations to keep me happy for a while and not worry about putting undue stress on the amp.

This is the kind of thing that makes BH kits so much fun!

-- Jim

 

[Dyna Saur]

Hey Jim,
The pin assignments for the 5670 are;

1-heater
2-cathode (2)
3-grid (2)
4-plate (2)
5-shield
6-plate (1)
7-grid (1)
8-cathode (1)
9-heater

Heater-6.3V, 350mA

Class A
plate voltage 150V
cathode bias resistor 240 ohm
amplification factor 35
plate resistance 6400 ohm
transconductance 5500 micromho
plate current 8.2 milliamperes
grid current -8V (Ib=10 milliamperes)

If you are re-wiring the driver 9 pin socket for 5670, then it will also be compatible with 2C51 and the ever popular and lovely WE 396A.

If 12BH7s are to your liking, then the 6GU7 is the 6V filament near equivalent, just wire the filament power to pins 4 and 5 and leave 9 open. Same pinout as 6CG7 / 6FQ7.

 

[levlhed]

With  the Speedball installed, you should be able to switch between 6CG7/6FQ7, 12AU7, and 12BH7 without tremendous voltage mismatch between the driver tube and the output tube.

12BH7's come highly recommended to me as suitable 12AU7 subs.  With Speedball you're saying there'll be no concerns?  Would a particular model of output tube be better suited for use w/ a 12BH7?

 

[Paul Birkeland]

With the Speedball a 5-10v difference in driver plate voltage won't really affect the output tube.

 

[Natural Sound]

Yeah, I think it really comes down to taste.  Doc loves his 12AU7's, and I totally understand that when we cue up tape and listen.  PJ is pretty into 6SN7's (as is Ed Fallon), and in PJ's case I think it's reflective of his preference for musicality.  In my case, I might go for a 6414 or something like that, except that gain is an issue, so wiring for 5687's or ECC99's seems like a good choice. 

Putting in a switch for the filaments seems easy enough and like a good plan.  With  the Speedball installed, you should be able to switch between 6CG7/6FQ7, 12AU7, and 12BH7 without tremendous voltage mismatch between the driver tube and the output tube.

Sorry if this has been asked before. Isn't the 12SN7 the same as a 6SN7 with different heater voltages (12V vs 6V)? Wouldn't this make a more suitable replacement for the 12AU7 since the filament voltage is the same? 12SN7's tend to be a lot cheaper too.

 

[jrebman]

The actual filament voltage in the Crack, as in the s.e.x. amp (same power transformer) is 6.3v and you can run some of the 12v tubes on this by running the heaters in a parallel, rather than serial configuration.

Hope this helps,

Jim

 

[Dyna Saur]

12SN7 has a 12.6 volt (only) filament, it is not tapped like the 12AU7 or 12BH7 which allows those tubes to run on either 6.3 or 12.6V.      Crack would need a 6SN7 (and an enlarged chassis hole to accomodate the octal socket.  "Hole Shrinkers" in reverse, anybody ?  ;^)  Yah, they're called Greenlee Punches ;-)

FWIW, though it doesn't really mean anything useful  for "The Crack", there is also an 8SN7.    Like my erstwhile experiment with the 8CG7, it will work, but gain will be low, and sound "subdued" as the operating voltages will be skewed from the 8CG7's reduced emission.

/ed B