Bottlehead Crack

@Jeb great work, man.. totally concur with you on the E80CC tube.. I'll take it over virtually any 12AU7 in the 'proper' Crack + SB. By 'proper' I mean a BH Crack who's resistors are setup to handle the E80CC's tube optimally. Did you look into the small board w/ a switch that some gents over on the BH forum fashioned? It allows you to run three different types of tubes with resistors/values (and whatever else) that are optimized for each 12v tube type that the BH Crack can handle (i.e. 12AU7, 12BH7, E80CC). I really encourage this as I've heard a BH Crack + E80CC with the switchboard it sounded phenomenal.

 

@MoatsArt - I agree, perspective is always good. For me, the desire to accumulate fancy stuff is just as alive and well in DIY as it is in buying manufactured equipment. It just takes more time & effort and involves more swearing at the soldering iron. Crack + Speedball sounds great and there's not necessarily any compelling reasons to go beyond that unless there's a desire to squeeze out the last drops of performance from the Crack, and/or have fun and learn about the changes that component upgrades can have in a simple circuit.

You make the good point that not every mod will bring about a positive change for everyones tastes. Plus, although there is usually great help available on the BH forum, the modder has to accept that they are heading out into the wilderness somewhat.

@FlySweep - I am digging the E80CC. Somehow most of the 12AU7s seem a bit rough around the edges now - in comparison. Even the Mullard CV4003 which I always considered to be smooth as hell.

How does one go about getting a switchboard ? I guess you have to submit a PCB design and have it made. I've never done this before. Would anyone have a design or could offer some help with this ?

If not, I might just optimise it permanently to E80CC parameters.

 

I am looking for an input tube to replace the stock 12AU7 (I got a stock 12au7a that has no name on it), I want a quality tube but not one of those high price boutique ones. I also might get a power tube maybe the 6080 tung-sol.

Reading your posts I think the Telefunken 12au7 is right for me, but then is the E80CC tube is really that good that you'll mod the resistors to incorporate it?

 

Some people like the E80CC and others not so much.

I like the Telefunken 12AU7 and it would lean towards the more even & neutral end of things - as much as that can be said about the Crack. If that is the direction you're looking to steer things then the E80CC would be worth checking out.

I don't really have a huge problem with the stock tubes but the Speedball/Mods exposed some minor frailties in the 12AU7s as a whole. The E80CC sounds more controlled & less grainy to me. But I would advise to maybe avoid it if you prefer something warmer and softer. Otherwise, it should be a fairly cheap experiment to try, if you can pick up an E80CC for around £20 on eBay before deciding if you want to make any permanent changes or implement some kind of switchable resistance solution.

 

What resistance do you need to use/switch out for the e80cc to work? What power tube are you using?

 

I haven't implemented any resistance/switching modifications yet.

This thread on the BH forum covers the changes people have made, which ranges from just switching out the Speedball R1 resistors, to adding 2 small switches, or using a new custom speedball board with an integrated switch. All the information is here:

http://bottlehead.com/smf/index.php?PHPSESSID=nhomqrkd847dbs9gsankb0cel7&topic=5989.15

I am using a Tung-Sol 6AS7 as power tube.

 

I ordered a telefunken e80cc used old stock tested good. Also a nos tung-sol 6080. I also got the 470ohm resistors.

Also have you guys tried adding a shunt voltage regulator like the cracka2a? I was thinking about adding a voltage regulator to my crack but not sure what to do. Buying crack2 might be an option if bottlehead ran another sale. But I like the smaller size of the crack more.

K&K has a shunt voltage regulator kit that can probably be used in the crack. http://www.kandkaudio.com/other-kits/

 

What are SNR and THD measurements on the Crack?

 

Better than yours.

 

The measurements are way too good though it was a modded out crack with a choke. So yeah, better than yours.

http://www.superbestaudiofriends.org/index.php?threads/bottlehead-crack-measurements.124/

 

I don't understand the toxic reactions to a question, but the Crack seems to measure okay. Considering that it's a low-end tube amp.

 

Are you asking to be banned from the Internet?

 

So, after looking into the swtichmod a bit more I got in contact with Maxhawk to see if I could get hold of one of the custom switch-PCBs that had been mentioned in this thread. I discovered that he had also designed a neat little PCB that allows the Crack to be internally switchable to use the 5687 (and 7119, I think) tube variant. (Please remember, all switching is done when the amp is OFF, caps are discharged and the mains power is disconnected).

Here are the boards when they arrived:





In case anyone doesn't know what these are:

1) The larger switchboard replaces the 2 stock smaller Speedball boards. It uses a switch & combinations of resistors in parallel to keep the driver tube plate voltage in the sweet-spot when using the 12AU7, E80CC or 12BH7 variants. The stock metal tab MJE-350 transistors are also replaced with MJE5731A, which I understand from the BH forum allow a slightly higher safety margin in terms of the operating temperature & longevity of the transistor. (note these face the opposite direction to the stock ones)

2) The 5687 tube has a different pin layout than the 12AU7 so involves rewiring much of the nine-pin socket to the second little PCB so you can use the switch to select between the 2 different pin layouts. At the same time the switch also swaps between the stock HLMP-6000 red LEDs and some beefier Blue LEDs which are used to bias the 5687, which requires more plate current.



Fitting:

The new speedball switchboard just slots in perfectly where the 2 stock ones come off. 4 More holes in the top-plate were required for the 5687 PCB. I had to raise this on taller 40mm standoffs to clear the headphone jack and give me room to work.

Here they are populated and mounted.




My understanding is that if the driver tube plate voltage is too high, the operation of the 6080/6AS7 in turn may not be optimal. Measuring the plate voltages with and without optimisation and listening to the results was an interesting experiment. The new resistors bring all the driver tube plate voltages into the 75V range whereas before they had been over 100V (E80CC) and somewhere in the low 50s (12BH7. )


Listening:

I don't want to go on about tubes too much. But for me it was a worthwhile tweak to get the amp running optimally for the ones I like. These mods should not be seen as a way to open the door to excessive rolling (which is rightly discouraged around these parts) but as a way to get the best out of the tubes that you like, if those happen to be the ones that the Crack wasn't really designed for in the first place. Some people still prefer the 12AU7s, so it's just a matter of preference.

In the case of the E80CC, with the correct resistors, the sound is slightly less forward, more balanced and less jagged. I can hear a little more depth, decay and extension throughout. These are my favourite aspects of the Tung Sol 6AS7 and I wonder if what I am hearing is the output tube operating in its sweet spot.

I'd previously thought that the 12BH7 was a bit dull, rounded and boring and, although it still seems quite laid back to me, it too has a little more balance, separation and feels somewhat less congested now. This actually became quite an enjoyable tube

In terms of the level of improvement I would say it is similar to many of the other mods - subtle but worthwhile.



5687

The 5687 is a funny one. It's nice. I would say it has most in common with the 12AU7 but has noticeably wider staging and depth than every other tube I've heard in the crack. A great all-rounder but might lose a tiny bit of ground to the E80CC in impact and bite.

E80CC & 5687 are my favourites.


The Blue LEDs for the 5687 are bright as hell. A dab of black paint on the LEDs may be in order.



.

 

I chose a different LED than the one specified in the BH thread. I used a HLMP-KB45-A0000 which is only 30 mcd versus 9600 mcd for the HLMP-CB1A-XY0DD suggested by kscwuzhere. Both have the same Vf and current specs so I figure the bias would be the same.

Re: E80C vs 5687 -- have you tried the comparison with different output tubes? Been running a Bendix slotted graphite plate 6080 for the last few months and for me, the 5687 beats out the E80CC in all respects. I seem to recall that your E80CC is a T-S? I'm on a Tungsram.

 

Maxhawk do you still have more of those switch mod boards? I would like to get one.

 

Nice. I'll give the Bendix/5687 a listen sometime. I didn't get too deep into exploring different combinations as I wanted to keep the variables to a minimum while testing the new set-up, otherwise I find I begin to lose my mind somewhat. One of the nice things for me about the 5687/E80CC is that there are so few options out there so it keeps things simple.

My E80CC is a Philips. My research suggests only Philips-Holland and later Tungsram manufactured these tubes. Any labelled Mullard, Telefunken, Valvo etc seem to be rebrands from those factories.

I'm definitely impressed with the effects of having the tube voltage optimised though. Great job on those pcbs. lol I should have checked about the blue LED luminosity. Oh well, at least there's no mistaking when my amp is on!

 

I snipped out the stock rectifiers and just replaced them with Cree Schottky diodes - some of the guys had mentioned this mod earlier on in the thread.

The board from parts connexion is tiny! The metal tabs on the diodes carry very high voltage so I knew I wouldn't sleep well unless the pcb was mounted securely on standoffs, just as other people have done. So, 3mm holes as close to the corners as was possible. That still left the mounting screws pretty damn close to the pads, so nylon screws seemed like a good idea. 25mm standoffs.

Here's the bits & bobs ready to go for around £10




installed, tested & ready to listen:




Extreme caution must be practiced when doing live voltage tests and working around those metal tabs and make sure your mountings are well placed and secure. Some people said to heat shrink them, but Doc said probably better to let them breathe. I also think I need to get a temperature reading in the case to make sure my wax bypass cap isn't going to shit the bed.

1/2 a day elapsed before fitting the board so I can't go overboard on the sonics but I've been really impressed with all the upgrades to the power-supply and this one is no exception. I feel the amp is a slightly less congested, quieter and blacker in the background. I also notice a bit firmer, deeper, more authoritative bass.

Apparently the Schottky diodes have no reverse recovery spike so may well be quieter but I'm not sure there is anything concrete to back-up my other claims about the bass and separation?

That's the final mod & the end of the line for me. No more space!

Listening now with the 5687 and its all sounding not too bad. Not too bad at all.

 

I put the crack back in and I like some things about the crack more than the torpedo III it has a fuller sound to it, it is more natural sounding and the treble is smooth and non fatiguing. It kind of makes me want to sell the torpedo III and crack, to get the mainline.