Tube Rolling w/Crack

[cddc]

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.

[Tom-s]

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.

[Paul Birkeland]

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. 

[cddc]

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.

[cddc]

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.

[Paul Birkeland]

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. 

[cddc]

Ahhh...I saw the challenges making a 2A3/300B/845 headphone amp. 

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

[L0rdGwyn]

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.

[Paul Birkeland]

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%.

[L0rdGwyn]

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.

[L0rdGwyn]

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!

[Tom-s]

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.

[L0rdGwyn]

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.

[L0rdGwyn]

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?

Hi Toad - saw your post on HF as well.  I have never seen an Australian-made 6080 or 6AS7G, no output tube compatible with the Crack actually.  I have seen some 6SN7s floating around that could be used as inputs.  Unfortunately, what you had before are truly the best!  But prices are only going up and availability going down.  There are of course good sounding outputs for not a whole lot of money, like the Tung Sol 7236 or RCA 6AS7G black plate.  If you can find them, there are some very good Japanese 6AS7G tubes out there for very little money, usually.

[cddc]

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!

Please ignore...my bad....ECC32 instead of ECC82....I thought you were asking about ECC82 which is an European version of 12AU7.