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August 18, 2019, 08:59:39 PM

Author Topic: Tube Rolling w/Crack  (Read 456749 times)

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Offline cddc

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Re: Tube Rolling w/Crack
« Reply #1980 on: June 18, 2019, 07:19:01 PM »
If one puts feedback around a circuit, a tube like a 6SN7 can be made to work properly.
300Bs in the Crack circuit would be a poorer choice to drive power hungry headphones, especially low impedance ones.


You'd be better off with a Kaiju.

Thats probably more easy as converting Crack for 300b output tubes.

Crack puts out 0.3w into 300ohms i think.

Thanks a lot, PB and Tom!

I was just kidding for sticking a 300B into Crack. It requires heavy modding...way too much for me. ;D

On the other hand, I would love to see Bottlehead to add a headphone jack to their 300B or 2A3 speaker amps if possible. It will definitely increase the amps' use and hence increase sale volumes. You know, Woo's 300B amp WA5 can be used for both headphone and speaker, and lots of other 300B amps too. :)





Offline cddc

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Re: Tube Rolling w/Crack
« Reply #1981 on: June 18, 2019, 07:36:28 PM »
One more question:

I am comparing 2 headphones recently. So I am wondering whether it's okay to plug & unplug headphones into my Crack without having to turn it off?

Currently I turned off my Crack before switching headphones, because I was concerned that the metal part on headphone plug would bridge 2 adjacent sections inside the headphone jack on Crack and would possibly short Crack circuits during plugging or unplugging.

Offline Tom-s

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Re: Tube Rolling w/Crack
« Reply #1982 on: June 18, 2019, 07:43:52 PM »
There's no problem switching headphones with the amp on.
I always plug in my headphones after the amp has warmed up (essentially the same as changing headphones).
This because i roll a different tube almost every day, and before i had a tube tester (to check for internal shorts) i've seen some spark shows during tube warmup.

Edit: Just make a 4 banana/spade to 4 pin XLR adapter. That's what i use for the AKG K1000 headphone and works just fine for now. But i do see your point about the extra headphone connection.
« Last Edit: June 18, 2019, 07:46:04 PM by Tom-s »

Offline Paul Birkeland

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Re: Tube Rolling w/Crack
« Reply #1983 on: June 19, 2019, 04:59:04 AM »
On the other hand, I would love to see Bottlehead to add a headphone jack to their 300B or 2A3 speaker amps if possible.
You can do this with an adapter cable.  This isn't a good idea unless the DC filament upgrade is added to our directly heated amps. 
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline cddc

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Re: Tube Rolling w/Crack
« Reply #1984 on: June 19, 2019, 07:15:33 AM »
There's no problem switching headphones with the amp on.
I always plug in my headphones after the amp has warmed up (essentially the same as changing headphones).
This because i roll a different tube almost every day, and before i had a tube tester (to check for internal shorts) i've seen some spark shows during tube warmup.

Edit: Just make a 4 banana/spade to 4 pin XLR adapter. That's what i use for the AKG K1000 headphone and works just fine for now. But i do see your point about the extra headphone connection.

Greart to hear. Thank you very much, Tom!

That would make switching headphones much easier.

Offline cddc

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Re: Tube Rolling w/Crack
« Reply #1985 on: June 19, 2019, 07:41:41 AM »
You can do this with an adapter cable.  This isn't a good idea unless the DC filament upgrade is added to our directly heated amps.

You are correct, that's why it's hard for users to heavily mod their amps.

I still think it is a good idea to have some official Bottlehead 2A3/300B/845 amps with both headphone and speaker outputs.

Offline Paul Birkeland

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Re: Tube Rolling w/Crack
« Reply #1986 on: June 19, 2019, 09:19:03 AM »
I still think it is a good idea to have some official Bottlehead 2A3/300B/845 amps with both headphone and speaker outputs.
Well, we have the SEX amp.  It's significantly quieter than we could make a 2A3/300B/845 amp and it has speaker and headphone outputs. 

If we put a hole on the Kaiju plate for a headphone jack, then filled it with a plug for the stock kit, we would end up answering the same technical support question over and over again about why the stock amp is noisy on headphones when builders put the jack in without the DC filament board.  I would also want to make it so that the speakers switch off when headphones are plugged in, and that is a significant amount of work as a retrofit item.  We would then be in the awkward position where our majority of users who use these amps with speakers would be on here asking us why there was a headphone jack.  There are also what 2 or 3 pairs of headphones that could make use of 8W? 

We could certainly make an adapter cable with banana plugs on one end and a 4 pin XLR on the other.  Or you could check these out:
https://www.ebay.com/itm/Dyson-Audio-4-pin-XLR-to-Spade-Balanced-Headphone-Cable-Speaker-Tap-Adapter/113437046309?hash=item1a695ff625:g:4jIAAOSwkfxcDXXf
https://www.portentoaudio.it/en/prodotto/adattatore-xlr-4-pin-banana/
http://apuresound.com/v3haec.html

You could also drill a hole in the wood on the Kaiju or Stereomour and install your own headphone jack. 



« Last Edit: June 19, 2019, 01:24:44 PM by Paul Birkeland »
Paul "PB" Birkeland

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Offline cddc

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Re: Tube Rolling w/Crack
« Reply #1987 on: June 19, 2019, 12:11:02 PM »
Ahhh...I saw the challenges making a 2A3/300B/845 headphone amp.  :o

Thanks very much for the explanation and alternative solutions, PB!  :)

Offline L0rdGwyn

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Re: Tube Rolling w/Crack
« Reply #1988 on: June 20, 2019, 06:37:21 PM »
With the appropriate adapter, what would be the feasibility of using a shared cathode 6N7G/6N7GT tube in the Crack + SB (or Crackatwoa in my case)?  Would it be safe to throw in and give it a whirl despite being incorrectly biased?

https://frank.pocnet.net/sheets/127/6/6N7.pdf

Wish I had the knowledge to say, I am slowly but surely teaching myself.  I can see the plate dissipation is double that of a 6SN7, so it seems that should not be an issue.
Keenan McKnight

Offline Paul Birkeland

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Re: Tube Rolling w/Crack
« Reply #1989 on: June 20, 2019, 06:47:33 PM »
With the appropriate adapter, what would be the feasibility of using a shared cathode 6N7G/6N7GT tube in the Crack + SB (or Crackatwoa in my case)?  Would it be safe to throw in and give it a whirl despite being incorrectly biased?

https://frank.pocnet.net/sheets/127/6/6N7.pdf
You would have to use two 6N7s.  15mA and 80V or so of plate to cathode voltage on a 6N7 will give a grid bias voltage of about +10V, which will cause the grid of the 6N7 to draw significant current.  This grid current will throw the operating point of the circuit off significantly!  This might pass music through, but it will be badly distorted and you'd damage the 6N7 eventually.  You'd also raise the output impedance by about 50%.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline L0rdGwyn

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Re: Tube Rolling w/Crack
« Reply #1990 on: June 20, 2019, 07:23:57 PM »
You would have to use two 6N7s.  15mA and 80V or so of plate to cathode voltage on a 6N7 will give a grid bias voltage of about +10V, which will cause the grid of the 6N7 to draw significant current.  This grid current will throw the operating point of the circuit off significantly!  This might pass music through, but it will be badly distorted and you'd damage the 6N7 eventually.  You'd also raise the output impedance by about 50%.

Okay, so I am going to take that as a hard NO, ha!  Thanks, PB.  I hope to get to a point where I can make that determination on my own, not a lot of spare time to do so, unfortunately.  But I do know that a positive voltage on the grid is no bueno.
Keenan McKnight

Offline L0rdGwyn

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Re: Tube Rolling w/Crack
« Reply #1991 on: July 13, 2019, 06:23:03 PM »
Wish I knew how to determine this on my own, but is there any reason putting a Mullard ECC32 in the stock Crackatwoa would be harmful to the amp or the tube?  I would be using a 6SN7 to 12AU7 adapter.  I typically use 6SN7s but I know the ECC32 is not a direct equivalent.  Thanks!
Keenan McKnight

Offline Tom-s

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Re: Tube Rolling w/Crack
« Reply #1992 on: July 13, 2019, 11:12:31 PM »
If my recollection is correct.  With Crack the ECC32 bias will set correctly, with the 475R R1 resistor on the CCS board.
Voltages will be high with the 237R R1 resistor. Plug one in, and measure after 5-10 minutes of warmup.
I'm a happy camper with these tubes. Although i feel money is better saved for a Mainline.

With all this tube rolling. I keep coming back to 12BH7's.

Offline L0rdGwyn

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Re: Tube Rolling w/Crack
« Reply #1993 on: July 14, 2019, 04:23:37 AM »
If my recollection is correct.  With Crack the ECC32 bias will set correctly, with the 475R R1 resistor on the CCS board.
Voltages will be high with the 237R R1 resistor. Plug one in, and measure after 5-10 minutes of warmup.
I'm a happy camper with these tubes. Although i feel money is better saved for a Mainline.

With all this tube rolling. I keep coming back to 12BH7's.

Thanks, Tom, I'll look into it.  I really enjoy the 12BH7 as well.  I recently acquired a pair of Italian Fivre 12BH7 tubes, they sound fantastic.
Keenan McKnight

Online Toad_of_Toad_Hall

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Re: Tube Rolling w/Crack
« Reply #1994 on: July 15, 2019, 03:08:47 PM »
I'll be buying a Crackatwoa in the not-too-distant future and am thinking about suitable tubes.

When I owned the Crack I went nuts on tube buying - WE421A,  GEC 6AS7G, Amperex 7316 etc. I've learned from my misspent youth and am buying many fewer and much, much cheaper tubes based around a theme: Australian made.

Is anyone aware of an Australian made candidate for the output position?