Tube Rolling

[TurbOSquiD77]

Hello everyone and happy holiday!

Starting my Crackatwoa build today. Can I roll these tubes? I did in the Crack but just wanted to double check for use with it's big brother.

Svetlana 6AS7G/6H13C "Winged C"
Philips Miniwatt ECC82 made in Heerlen , Holland, 1962.

https://i.imgur.com/2RWRxxZ.jpg
https://i.imgur.com/SjBE6OD.jpg


Any suggestions you think would be fun to try with the shunt voltage reg. tubes?

Cheers! 

[Paul Birkeland]

The allowable tubes are identical between the Crack and Crack-a-two-a.

For the shunt reg tubes, I tend to use 6005's.

[kritpoon]

The allowable tubes are identical between the Crack and Crack-a-two-a.

For the shunt reg tubes, I tend to use 6005's.

For rolling the Shunt reg tube, would the effect of the overall sound be as pronounce as rolling the input and power tube? Thank you

Krit.

[Doc B.]

In general rolling the shunt reg tube is audible but much more subtle than rolling the signal tubes. Probably something best tried for yourself rather than relying upon opinions.

[kritpoon]

In general rolling the shunt reg tube is audible but much more subtle than rolling the signal tubes. Probably something best tried for yourself rather than relying upon opinions.

Thanks Doc. I don' have crackatwoa yet, just gathering some info. Since its on my next to purchase list, after I experiment on mod on my Crack to see how each mod effects the sound. I am lerning so much and its so much fun! I am proud to say that I am bottlehead addict now.

[TurbOSquiD77]

Is it okay to run a GE 12BH7A in the Crackatwoa? I'm also using the 6AS7G from above, and just recieved GE 6005/6AQ5W's

How about for the E80CC?

I'm unsure how to decipher the modifications needed to run various tubes, as most of the posts about tube rolling are for the Crack. I shall continue my studies. lol. If someone could point me in the right direction for popular tubes, input and power, it surely would help the initial struggle.

Thank you - all help is appreciated!

[TurbOSquiD77]

Actually, I might have an explanation for why the 12BH7A wouldn't be a direct replacement for the 12AU7. If you find anything incorrect, or something that could be explained more effectively please advise...etc. Pulled this from datasheets, but I noticed some numbers were not shown for certain tubes.

12AU7 - Vf 6.3 Volts / If 0.3 Ampere
CV4003 -    Vf 6.3 Volts / If 0.3 Ampere

ECC82 - Vf 12.6 Volts / If 0.15 Ampere - Tapped heater also permits operation at 6.3V 0.3A.  (I do not understand why, but I currently run this tube with the 6AS7G both pictured above)
12BH7A -    Vf 12.6 Volts / If 0.3 Ampere - Durch Heizfaden-Mittenanschluss auch Betrieb mit 6.3 V und 0.6 A möglich. Google translate: By filament center connection also operation with 6.3 V and 0.6 A possible. (I do not understand why)

Other specs:
Plate Voltages, Current, and Resistance
Grid Voltage
Amplification Factor
Transconductance


Links for more info on the following questions are much appreciated Forum threads and other stuff. It's tough to find a needle in a haystack, especially when it's a specific needle like the C2A. Wait, the Crackatwoa is an amplifier - not a needle. Anyways.....

What would be the correct way to go about calculating if a tube type will work with the stock Crack/Crackatwoa? How about modded (output caps, TwoQuiet, and in use with other input/power tubes)?

What justifies if a tube is within an allowed range of value in order to be used without further modifications?

What tube specifications are most important to pay attention to? Although, I'm sure all of them influence something....

I could insert the tubes I'd like to use, do a full voltage/resistance check from the manual, and compare that to values of the stock tubes.
Seems logical, but after the tests I would not know where to make adjustments. I can spend some time on it and post all values if need be!

Is there a standard way to implement changes needed to run tubes of certain specs? (the resistor at location X needs to be changed if the voltage at location Y is  +/- outside optimal range...etc.)

I will spend time learning basic circuitry, but I was wondering the order in which power flows through the amplifier.....
Example: Power comes in, goes to [object/location/terminal], then goes to [object/location/terminal]....etc.
Would this be an effective way to troubleshoot/adjust component values?
Example: Location X voltage too high, so replace the resistor just before it to decrease voltage at location X.

I'd like to implement switches, like some Crack builders have, to allow use of different tubes.
I'd also like to implement a switch allowing me to change between 2 separate sets of output capacitors. Or just make connectors and need to power off, disconnect/connect them, power on.

Definitely liking this project - just a bit 
Pics soon!

Thank you

[Paul Birkeland]

The 12BH7 and E80CC will work in the C2A, but the two R1 resistors on the small PC board will need to be swapped out with 470 Ohm parts. 

Filament voltage isn't a constraint on the driver tube, there's a bit of headroom on that winding.

As far as what will and won't work, the first consideration is whether the tube in question is pin compatible.  For instance, the 6CG7 is electrically a drop-in substitute for the 12AU7 in the C2A, but its pinout is different, so you would have to rewire the socket to get it to work.

The next consideration is the overall operating point.  If you look at the plate curves and see where the 1.5V grid bias line hits 3.5mA, how close are you to 75V?  If you are off one way or the other, then current has to be adjusted.  In the C2A, since it is shunt regulated, there is a bit of a limit to how far you can adjust current one way or the other, though this shouldn't be much of an impediment ultimately due to the range of plate current generally needed for these small dual triodes.

The last consideration is gain.  Just because a tube is pin compatible with a 12AU7 and can be made to produce the appropriate plate voltage doesn't mean it will be a good fit in the circuit.  For example, a 12AX7 with 0.5V of bias an 0.75mA of current will make the appropriate plate voltage to work in the Crack, but the extra 16dB of gain will be a nuisance.

-PB

[TurbOSquiD77]

Thank you Paul.

These cool?
http://www.mouser.com/ProductDetail/Vishay-Dale/RN55E4700FB14/?qs=sGAEpiMZZMtlubZbdhIBIEq9S5QvvTQUOPhdG1TlS6g%3d

Description seems incorrect - they are indeed 125 mW (1/8 W) by part number.


I've found this:
http://db.audioasylum.com/cgi/m.mpl?forum=bottlehead&n=119635

"This comes up periodically. We use specifric resistors in specific places for specific reasons.
Carbon composition is the best for low inductance, which is important in grid stoppers which are effective at hundreds of MHz. They are noisy, but only if they have DC current through them, and the noise is proportional to the resistance. So as grid stoppers (no current) and as plate stoppers (small resistance, and located after the first signal amplification stage so that noise is 30dB less important) they are OK. In both applications, drift of the resistance is not important.

Plate resistors are usually metal film, which is generally very quiet even with DC current, and they are also readily available in 1% or better precision. They do have a bit of inductance, but it's not significant at audio frequencies. We also use them in the RIAA equalization network, where precision and low noise are important. We avoid them when small amounts of inductance are important.

Wirewound is the quietest, but usually has the most inductance. We us them in power supplies where the small inductance helps isolate diode switching transients and power line RFI noise.

Metal oxide is noisy and usually imprecise, but they are very sturdy (withstand voltage transients and momentary overloads without damage) so they make good power supply bleeders where the large parallel capacitance can shunt the noise to ground.

Hope that helps! "

Could you briefly elaborate on the physical locations of where resistor types function best?
[Resistor Type] = [Circuit Section] = [Physical Part - C4S Boards, sube sockets, RIAA network...etc.]

If you look at the plate curves and see where the 1.5V grid bias line hits 3.5mA, how close are you to 75V?

Could you elaborate on this? Basically follow the 1.5V grid bias line until 3.5mA and see what voltage you're at?
Does this apply to input tubes only? Or power as well? Is the driver tube considered the input or power tube? I'm guessing power, but the word "input" throws my understanding off.

This info, in addition to studying circuitry, greatly aids in the initial learning process.

-Regards 

[Chris65]

These cool?
http://www.mouser.com/ProductDetail/Vishay-Dale/RN55E4700FB14/?qs=sGAEpiMZZMtlubZbdhIBIEq9S5QvvTQUOPhdG1TlS6g%3d
Description seems incorrect - they are indeed 125 mW (1/8 W) by part number.

Vishay Dale RN55 are in practice rated up to 0.5W as they derated for military usage. The commercial equivalent is the CMF55.
Yes, they are nice, I use them extensively.

[Paul Birkeland]

Could you briefly elaborate on the physical locations of where resistor types function best?
[Resistor Type] = [Circuit Section] = [Physical Part - C4S Boards, sube sockets, RIAA network...etc.]

Grid stoppers are connected to the tube grids.  You can look at the datasheet for each tube to see which pins are grids.  If you stick with metal film you're pretty much safe for just about anything you may run into (other than high power, where there tend not to be metal film resistors big enough)

Could you elaborate on this? Basically follow the 1.5V grid bias line until 3.5mA and see what voltage you're at?

Yes, the C2A driver circuit has a fixed bias voltage of 1.5V (the LED) and a constant current source set at about 3.5mA. With these two numbers, you can look at a tube's plate curves to see what plate voltage you'd get with 1.5V of bias an 3.5mA of current.

Does this apply to input tubes only? Or power as well? Is the driver tube considered the input or power tube? I'm guessing power, but the word "input" throws my understanding off.

In the C2A design, this applies to the 12AU7 (you could call it a preamp or driver tube, it is not the power tube, the 6080 is the power tube).

[TurbOSquiD77]

Vishay Dale RN55 are in practice rated up to 0.5W as they derated for military usage. The commercial equivalent is the CMF55.
Yes, they are nice, I use them extensively.

Nice! Thank you. So that's a yes on the RN, CN, or either? I'm guessing either, but I want to be sure that if I'm ordering a 125 mW (1/8 W) resistor, that is what I'm getting.

Closest CM I can find is CMF55470R00FKR6 (1/2 W 470 ohms). Though, I read somewhere that wattage isn't quite that important. True, or only in some cases?

Yes, the C2A driver circuit has a fixed bias voltage of 1.5V (the LED) and a constant current source set at about 3.5mA. With these two numbers, you can look at a tube's plate curves to see what plate voltage you'd get with 1.5V of bias an 3.5mA of current.

Helps a ton! How might I apply this to the power circuit?


Where should I take measurements from if (after replacing the R1 resistors on the low current C4S board with 470ohm 1/8W) I'd like to insert a 12BH7 or e80cc and test to ensure all is well?


Thank you   

[Paul Birkeland]

Closest CM I can find is CMF55470R00FKR6 (1/2 W 470 ohms). Though, I read somewhere that wattage isn't quite that important. True, or only in some cases?

You can use Ohm's Law to determine this.  3.5mA passes through 470 Ohms, P=(I^2)*R, so P=(0.0035^2)*470, so the resistor will dissipate 0.005 Watts of power, and for long life, we would want a resistor that's rated for at least 0.015 Watts of power.  So a resistor that's rated for at least 1/60th of a Watt will work (for this position at least).

Helps a ton! How might I apply this to the power circuit?

That's quite a can of worms.  You really should leave this alone.  Trying to alter the operating current of the output stage can have adverse effects on the operation of the amplifier, and the presence of the shunt regulator means that the whole amp would need to be redesigned if this is messed with.  Additionally, there are very few dual triodes with enough transconductance to offer the low output impedance available with the 6080.

Where should I take measurements from if (after replacing the R1 resistors on the low current C4S board with 470ohm 1/8W) I'd like to insert a 12BH7 or e80cc and test to ensure all is well?

OA and OB on the small center C4S board.

[TurbOSquiD77]

You can use Ohm's Law to determine this.
That's quite a can of worms.
OA and OB on the small center C4S board.

Sounds good to me, and thanks for explaining. 

Good to know about the power circuit - I shall not touch! *Imagines Gandalf

Just threw a Tung Sol 5998 in the C2A. Loving it  sounds more airy and detailed.
New sound due to the higher transconductance? The amp seems to have higher gain - louder all around (running Beyer T1.2's and HD6XX/50's). Also have DT-990 600 Ohm's but don't use as often.

[TurbOSquiD77]

OA and OB on the small center C4S board.

I've replaced the R1 resistors on the low current board with 470 Ohm Dale's.

Here are my voltages (the numbers on the right are mine):

Tubes:
Tung-Sol 5998 (also grabbed voltage of OA and OB on Low board, and OB on High board with the 6080 in place for comparison.)
GE 12BH7A
GE 6005's

OA and OB on Low Current C4S are half of what they should be.
OB on the High Current C4S is low as well.

Terminal Voltage (DC)
Low Current C4S
IA 150V   150v
OA 60-90V  35.1v Damn near the same with 6080
KregA 3-6V   5.42v
bRegA 150V   150v
IB 150V  148.9v
OB 60-90V   36.3v  Damn near the same with 6080
KregB 3-6V  5.45v
bRegB 150V  148.9v

High Current C4S
IA 190V 193.2v
OA 150V  148.9v
bA 0V  .1mV
IB 0V   0-3mV
OB 90-110V  51.4v  68.5v with 6080
bB 150V   148.9v


Thank you!

Travis