Tube Rolling w/Crack

[Paul Birkeland]

With the Speedball, the 12BH7 will function in the circuit, but it changes the operating point of the 6080 pretty dramatically.

I'd remove the red LED's on the 9 pin socket and replace them with 1.2K resistors (1/8W is plenty) to bump up the bias a bit, and bring the plate voltage up to ~90V (with the Speedball).

-PB

[Pepper]

With the Speedball, the 12BH7 will function in the circuit, but it changes the operating point of the 6080 pretty dramatically.

I'd remove the red LED's on the 9 pin socket and replace them with 1.2K resistors (1/8W is plenty) to bump up the bias a bit, and bring the plate voltage up to ~90V (with the Speedball).

-PB

Thanks for the great info! You mentioned that it'll change the operating point of the 6080, but if I have a Tung Sol 5998 in, would I still be advised to make the modifications you mentioned?

[Paul Birkeland]

Yes.

[Kris]

PB,

You said "with the Speedball", do you suggest to do similar mod to stock Crack if I want to try 12BH7 tube?
How about 6SN7 that I'm currently using to drive  Chatham 2399 with my stock crack? Does 6SN7 change the operating point of the 2399 as well or is it going to after I install Speedball?

Please respond.

Thanks,
Kris

[Aeolus Kratos]

PB,

You said "with the Speedball", do you suggest to do similar mod to stock Crack if I want to try 12BH7 tube?
How about 6SN7 that I'm currently using to drive  Chatham 2399 with my stock crack? Does 6SN7 change the operating point of the 2399 as well or is it going to after I install Speedball?

Please respond.

Thanks,
Kris

I would like to know this too, I'm using 2399 in my speedballed crack as well. Does 6SN7's change the operating point of the 2399?

Thanks,
Kratos.

[Kris]

Kratos,
I think PB is on vacation right now, so it may take him a while to respond.

[Pepper]

I'm thinking of putting a VT-231/6SN7 to replace the 12AU7 using a 6SN7 to 12AU7 adapter. I heard there does not have to be circuit modifications for the stock Crack, but I'm wondering if I need any circuit modifications if I have the Speedball installed?

Thanks!

[adamct]

No.

[w0lfd0g]

I have discovered another tube combo that I am digging at the moment:

Output: Tung Sol 7236
Driver: Siemens & Halske ECC82 silver plate

I find it to be more aggressive (and less warm) than my GEC 6AS7G + Mullard ECC80 combo, but tight, clear and an awesome sound stage. 

Does anyone know if I need to make any alterations to the circuit to optimise the Crack for the 7236?  I can't imagine it sounding much better than it does atm. 

If alterations are required for this combo, I am considering building another kit just for kicks and giggles.  One for each of my favourite tube combos.

Cheers

Nathan

[Aeolus Kratos]

I'm thinking of putting a VT-231/6SN7 to replace the 12AU7 using a 6SN7 to 12AU7 adapter. I heard there does not have to be circuit modifications for the stock Crack, but I'm wondering if I need any circuit modifications if I have the Speedball installed?

Thanks!

Hi Pepper,

No, you won't have to do any mods if you want to use a 6SN7 in your Crack.

You can check my review here:
http://www.bottlehead.com/smf/index.php/topic,4679.15.html

Best,
Kratos.

[lior.amsalem]

Hi all 
Finally pulled the trigger on 5998 today (ordered from http://www.vacuumtubes.net/), hope to feel the excitement again like all the past upgrades (sb, output caps, dac upgrade, etc...)

wish me luck 

Lior

[Aeolus Kratos]

Hi all 
Finally pulled the trigger on 5998 today (ordered from http://www.vacuumtubes.net/), hope to feel the excitement again like all the past upgrades (sb, output caps, dac upgrade, etc...)

wish me luck 

Lior

Hi Lior,

Nice! I bought my Chatham 2399 from vacuumtubes.net too. My Chatham has some bits of glass inside, but it works perfectly fine so it does not bother me very much. The 5998 is absolutely great, although I still think it's a little bit expensive.

Good luck with your purchase and happy listening!

Kratos.

[Paul Birkeland]

Hello Gents,

Yes, I was out in the middle of nowhere (Wyoming/Montana).

With the stock Crack and the 12BH7, I would recommend:

2.5V bias
5mA current
75V plate

The 2.5V of bias and 5mA of current means a pair of 500 Ohm cathode resistors in place of the LED's.
Getting 75V on the plates from the raw power supply means the 22K plate load resistors should become 17K, with a 2W rating.

-PB

[Kris]

Many thanks Paul for explanation.
Also, can you please post your answer to second part of my original question about 6SN7 tube? Does the 6SN7 change operating point of the 2399 or maybe it's going to after I install Speedball?

Thanks in advance,
Kris

[Paul Birkeland]

The 6SN7 will function with the stock parts.

-PB