Crack;Bottlehead OTL

[TylersEclectic]

Recently got the 6SN7 adapter and Tung Sol 6SN7GTB tube… I think I like it a lot…now to find a cover for the adapter lol

It is dead silent with no music except at Max volume... already sounds great with no break in. Very excited for this

 

[cebuboy]

Been wondering to ask, can the stock power supply handle the extra current needed to run the 6SN7?

 

[Paladin79]

I certainly hope so, I have been running one for a couple years now, as has my son, and one employee and a few friends.

When I say running one, I mean one variation of the 6sn7 or another. I have run dual 6J5’s and 7A4’s single triode versions that each require half the filament current of a 6SN7. I have run 7N7’s, the loktal version of the 6SN7 as well.

I run the same tubes in a Schiit Vali 2 that normally draws about 450 milliamperes of filament current but can handle the higher current for the 6SN7.

My favorite single tube is the 6N8S 1578 Melz (6sn7 equivalent), you have to be very careful which version you buy and they can be pricey because they are highly sought after. They sound very different than your normal RCA, Sylvania or Tung Sol so they may not be for everyone.

 

[TylersEclectic]

I certainly hope so, I have been running one for a couple years now, as has my son, and one employee and a few friends.

When I say running one, I mean one variation of the 6sn7 or another. I have run dual 6J5’s and 7A4’s single triode versions that each require half the filament current of a 6SN7. I have run 7N7’s, the loktal version of the 6SN7 as well.

I run the same tubes in a Schiit Vali 2 that normally draws about 450 milliamperes of filament current but can handle the higher current for the 6SN7.

My favorite single tube is the 6N8S 1578 Melz (6sn7 equivalent), you have to be very careful which version you buy and they can be pricey because they are highly sought after. They sound very different than your normal RCA, Sylvania or Tung Sol so they may not be for everyone.

I have always liked your custom builds and the look of them! I especially like the VU meters!

 

[Paladin79]

I have always liked your custom builds and the look of them! I especially like the VU meters!

Thanks for your kind words. Here is a Crack with one of the 6sn7's. I will be testing around 20 of them as part of a challenge I am involved with. I have help though.

 

[Tom-s]

Been wondering to ask, can the stock power supply handle the extra current needed to run the 6SN7?

Crack's heater winding on the PS is designed for 3.5A total current. It's designed with all the needed headroom to accommodate tube rollers abuse. The 6080/6AS7 uses 2.5A (or 2.4A for 5998, 7236). This leaves +-1 amp for the driver tube.

On a hot day, even with higher current "6SN7 equivalents" like ECC32 (0.9A) and a Bendix 6080WB for the output, Crack takes this abuse perfectly.

So a normal 6SN7 (0.6A) won't be a problem.

Anybody know who designed Crack?

How i remember it, is that Crack was based on an older OTL schematic. Reworked by the guys at BH for optimal headphone performance.
It's probably been a team effort, where based on the original design different drivers, and bias options passed through selection before settling on the 12au7 direct coupled, led bias setup OTL. Maybe this is a good question to ask on the BH forum.

I will be testing around 20 of them as part of a challenge I am involved with. I have help though.

You've got my attention, do tell us more about that challenge!

 

[Paladin79]

Ok the challenge. Sealed within this PVC pipe is a 6SN7 tube, only the pins stick out. Top, and all sides are well sealed and the pipe is vented. A friend in North Carolina has bet me a steak dinner with a big bottle of wine (he hates GE tubes), that he will pick a GE at the very bottom of whatever tubes I send him, (all 6sn7 equivalents). Each tube is numbered 1-8 but after he does the listening and I tell him what the tubes really are, we can change the numbers, send them on to other friends and they can try to figure out which tube is which. No bets involved with them. I own in excess of 200 6sn7 tubes and will do a lot of listening to make it as hard as possible but I will send him tubes with similar emission so they sound at or near their peak. Tubes may well include RCA, Sylvania, Ken-Rad, Melz, Foton, Marconi, Hytron, Mullard, etc. I will make every effort to insure a tube was not built by another company and re-branded. I have CBS tubes like that, some are obviously GE, others are made by Sylvania I believe. No tubes will be harmed and when all is done I can recover them. I am including many of the tubes my friend knows and loves, 1953 Foton with ribbed plates, tall body 7n7's (a loktal equivalent of a 6sn7), Melz 1578 etc.

If anyone wishes to try this themselves down the road, PM me and I will see about sending the tubes your way. If nothing else, it may be a chance for you to hear some black glass and grey glass tubes from the 40's compared to some more modern tubes.

I should note I am testing this in a $100 headphone amp, just in case the wax melts I am not about to take a chance with another amp lol, no offence to Schiit.

 

[SilverEars]

How i remember it, is that Crack was based on an older OTL schematic. Reworked by the guys at BH for optimal headphone performance.
It's probably been a team effort, where based on the original design different drivers, and bias options passed through selection before settling on the 12au7 direct coupled, led bias setup OTL. Maybe this is a good question to ask on the BH forum.

I'm curious because I'm wondering what else has the designer of Crack and the speedball has also designed?

 

[JamieMcC]

I had always thought the Cracks conception was down to Paul Birkelands (PB / Caucasian Blackplate) I think he also does/did some custom design work as well as there are a few posts about online.

 

[SilverEars]

It is an amazing amp, either if you built it or had it built. No shame, as I paid a pro, and could not be happier.
The amp has speedball added and an Alps Blue Velvet pot, and is top notch.

That looks well built. Whoever built that seems to be very detailed oriented.

A good build is important with this amps because the solder-joints must be soldered with good amount of solder. Building one of these I realized how important well soldered joints are for proper sound out of these amps.

 

[attmci]

Crack's heater winding on the PS is designed for 3.5A total current. It's designed with all the needed headroom to accommodate tube rollers abuse. The 6080/6AS7 uses 2.5A (or 2.4A for 5998, 7236). This leaves +-1 amp for the driver tube.

On a hot day, even with higher current "6SN7 equivalents" like ECC32 (0.9A) and a Bendix 6080WB for the output, Crack takes this abuse perfectly.

So a normal 6SN7 (0.6A) won't be a problem.



How i remember it, is that Crack was based on an older OTL schematic. Reworked by the guys at BH for optimal headphone performance.
It's probably been a team effort, where based on the original design different drivers, and bias options passed through selection before settling on the 12au7 direct coupled, led bias setup OTL. Maybe this is a good question to ask on the BH forum.



You've got my attention, do tell us more about that challenge!

You' better not using the 6SN7GT with a pair of 6bl7/6bx7.

The 6bl7/bx7 are the most suitable power tubes for a Crack. Don't know why they are not using these.

I highly recommend the other Tom to make a Crack to use these tubes. We may have to move the power tube socket away from the transformer.


Paladin79

 

[audiowize]

You' better not using the 6SN7GT with a pair of 6bl7/6bx7.

The 6bl7/bx7 are the most suitable power tubes for a Crack. Don't know why they are not using these.

I highly recommend the other Tom to make a Crack to use these tubes. We may have to move the power tube socket away from the transformer.


Paladin79

We will be looking forward to the release of your 6BX7 OTL amp!

You will find that a 6BX7 is about twice the price of a 6080 and far less common. The heater cathode insulation on a 6BX7 is also inferior to a 6080, so be careful where you use them! There are also a great many negative reviews of paralleling triodes. How do you ensure that one half of the 6BX7 isn't drawing 90% of the current and the other half 10%? Under these conditions you lose the assumed benefits of the paralleled triodes in the first place and you're better off with a single tube. If you want to provide 6BX7s with matched triode sections, then you will take an expensive and somewhat uncommon tube, then throw a large number of them away because they have poorly balanced sections.

An additional complication is that the higher mu of the 6BX7 will push the operating point of the 6BX7 in a Crack close to where it will draw grid current and seriously impede the performance of the amp. This is improved a little bit by using a second tube, but at the same time (assuming each tube shares current equally) you will run into cutoff very quickly. I think you'd swing less than 3.5V RMS before distortion got ridiculous into a 300 Ohm load, that's terrible! Using a single 6080 that number is more like 17V RMS, but clearly that's not the right tube to use right?

While you might love the way this sounds and think that everybody's amp should sound like this, that viewpoint is poorly supported by empirical standards. I have no doubt that it sounds a lot different than a 6080.

 

[attmci]

We will be looking forward to the release of your 6BX7 OTL amp!

You will find that a 6BX7 is about twice the price of a 6080 and far less common. The heater cathode insulation on a 6BX7 is also inferior to a 6080, so be careful where you use them! There are also a great many negative reviews of paralleling triodes. How do you ensure that one half of the 6BX7 isn't drawing 90% of the current and the other half 10%? Under these conditions you lose the assumed benefits of the paralleled triodes in the first place and you're better off with a single tube. If you want to provide 6BX7s with matched triode sections, then you will take an expensive and somewhat uncommon tube, then throw a large number of them away because they have poorly balanced sections.

An additional complication is that the higher mu of the 6BX7 will push the operating point of the 6BX7 in a Crack close to where it will draw grid current and seriously impede the performance of the amp. This is improved a little bit by using a second tube, but at the same time (assuming each tube shares current equally) you will run into cutoff very quickly. I think you'd swing less than 3.5V RMS before distortion got ridiculous into a 300 Ohm load, that's terrible! Using a single 6080 that number is more like 17V RMS, but clearly that's not the right tube to use right?

While you might love the way this sounds and think that everybody's amp should sound like this, that viewpoint is poorly supported by empirical standards. I have no doubt that it sounds a lot different than a 6080.

https://www.head-fi.org/threads/2359glenn-studio.600110/

 

[audiowize]

https://www.head-fi.org/threads/2359glenn-studio.600110/

You linked me to a thread with 1800 pages and didn't mention anything about why...

 

[m17xr2b]

https://www.head-fi.org/threads/2359glenn-studio.600110/

Crack and Glenn have nothing in common, different input design, different output design, different PSU configuration and most likely different operating points.
The crazy tube configs that can be used in the GennOTL cannot be used in the Crack