Tube Rolling w/Crack

[Paul Joppa]

The circuit calls for two triodes. You are asking about using four triodes. What circuit are you thinking of - are they paralleled, or something?

 

[attmci]

Yes. They are paralleled for Elise or Woo amp. There a lot of discussions going around at Head-fi. A number of people who have those amps report very good results with multiples of the 6BL7 compared to the 6AS7 type tubes.

The circuit calls for two triodes. You are asking about using four triodes. What circuit are you thinking of - are they paralleled, or something?

 

[Paul Joppa]

Thanks - that helps me understand the question. What follows below is a discussion of just the technical issues, which I hope is helpful. Direct personal experience is going to be more significant - so give it a try and report your results, and we'll all benefit.  :^)

The 6BL7 and 6BX7 are rated for 12 watts total dissipation, but up to 10 watts on one triode as long as the total is 12 watts. So for amps that need more than 6 watts dissipation per channel, you would need two in parallel. Crack only dissipates about 2.3 watts per triode so that is not an issue, though it may be with other amps.

The other thing that paralleling two triodes does is double the transconductance (which cuts the source impedance feeding the phones in half). The 6080 has the same transconductance per triode as the 6BL7, but the 5998 has nearly twice the 6080 transconductance. So a paralleled 6BL7 is roughly equivalent to a 5998 in that parameter. I suspect that is the main reason for the audible difference.

There are also (moderate) sonic negatives associated with paralleled triodes, at least to some people, so a good 5998 might be expected to have the edge - but they are expensive, hard to find, and the selection has been picked over for many years. You pays your money and you takes your choice.

 

[attmci]

Thanks again for the reply.

Now the question is if the Crack can handle the ~3A heat current of the due tubes need.

Thanks - that helps me understand the question. What follows below is a discussion of just the technical issues, which I hope is helpful. Direct personal experience is going to be more significant - so give it a try and report your results, and we'll all benefit.  :^)

The 6BL7 and 6BX7 are rated for 12 watts total dissipation, but up to 10 watts on one triode as long as the total is 12 watts. So for amps that need more than 6 watts dissipation per channel, you would need two in parallel. Crack only dissipates about 2.3 watts per triode so that is not an issue, though it may be with other amps.

The other thing that paralleling two triodes does is double the transconductance (which cuts the source impedance feeding the phones in half). The 6080 has the same transconductance per triode as the 6BL7, but the 5998 has nearly twice the 6080 transconductance. So a paralleled 6BL7 is roughly equivalent to a 5998 in that parameter. I suspect that is the main reason for the audible difference.

There are also (moderate) sonic negatives associated with paralleled triodes, at least to some people, so a good 5998 might be expected to have the edge - but they are expensive, hard to find, and the selection has been picked over for many years. You pays your money and you takes your choice.

 

[Paul Joppa]

Sorry I missed that! The PT-3 power transformer spec is a maximum of 3.5 amps RMS. That winding is the most highly stressed one, so I cannot recommend exceeding it even though the high voltage winding is lightly loaded. No 5687s, and I'm leery of the 6SN7 used with pairs of 6BL7/6BX7.

 

[attmci]

Great.  So the spec is the same as the newer PT-5 and PT-7 confirmed by the designer of the transformer.  8) 

Sorry I missed that! The PT-3 power transformer spec is a maximum of 3.5 amps RMS. That winding is the most highly stressed one, so I cannot recommend exceeding it even though the high voltage winding is lightly loaded. No 5687s, and I'm leery of the 6SN7 used with pairs of 6BL7/6BX7.

 

[Paul Birkeland]

You could try the paralleled 6BL7 tube adapter in the Crack-a-two-a, which uses a different power transformer that isn't going to be bothered by the additional current demand on the heater winding.

 

[Paul Joppa]

Great.  So the spec is the same as the newer PT-5 and PT-7 confirmed by the designer of the transformer.  8)

PT-5 has a 9-volt winding rated 2.8 amps RMS; PT-7 has a 6.3vCT winding rated 4.0 amps RMS.

 

[savant]

How are these tubes and what config should I use with the Sennheiser HD650 ? And how much these tubes worth ?

What upgrade should I be going for first ?  Below are the seller comments

I have built this amp as carefully and meticulously as I can. The circuit is noise-free and all voltage readings are within spec.

A high quality Alps RK27 volume pot has been installed instead of the supplied, which has much better low volume tracking. The output capacitors have been installed on leads for easily upgrading to PIO or film capacitors.

The box is finished in "liquid amber" wood stain and clear polyurethane varnish. I will admit the varnish is not 100% smooth in places and could do with another coat. The chassis plate and transformer bell housing is finished in high-temperature rated matte black.

The following tubes are included:

Power:
RCA 6AS7G (x2)
Svetlana 6H13C (x2)
Telefunken 6080 (this one is a rebranded Sylvania)
Unfortunately all bar the Telefunken have slight microphonics

Input:
RCA 12AU7 (x2)
Phillips Miniwatt 12AU7
Brimar 12AU7 (x3, all different plates)
Electro Harmonix 12AU7

 

[FairDinkum]

Hey gang long time no see! I built my Crack/speedball in September 2014 and only now have I tried the almighty Tung Sol 5998. O.M.G! Totally worth the hype! Now, has anyone paired that with the Genalex Gold Lion 12AU7? I'm using the Senn HD650.

 

[Colin]

We do understand your question, and the answer is still not to use the adapter, but rather to plug a single 6BL7 into the 6080 socket.

Iam still confuse for this. So we can directly change 6080 eith 6BL7? Any change for the sircuit? I have read some article we must seperate the jumper from pin 4 & 5 then run a wire to them from pin9. So all wire that connect to pin 4 & 5 must be disconnect(open the solder)?

Sorry for this newbie question.

 

[howzz1854]

hi guys, i recently just started trying a different output tube, after 1.5 year of Crack ownership.

i ordered the so much talked about 6H13C winged C Russian tube and tried it with my new HD800S purchase. surprisingly i wasn't all that impressed. there "may" have been a bit more spaciousness, but i don't know if i am dreaming, but i felt like quite a bit of clarity and crispness and cleaness is lost compare to my stock Crack 6080. overall the Russian 6H13C just feels smokier and less precise than the stock 6080. when i switched back to the stock tube, it sounded more engaging and exciting. in terms of spaciousness/soundstage, i am not sure. it might be the same or the Russian tube might be bigger in space, but i am not really sure.

now the problem is, i can't for the life of me find out what my stock tube is. i know it's a 6080 variant. but i can't seem to find any info on it other than that it arrived with my crack in a bubble wrap and it only has a small marking of "FKHK USA" on the glass.

i took several pictures and hoping that some of you pros can help me identify. i would like to order a few more of this stock tube for backup and use it as a baseline.

 

[mcandmar]

Thats very odd, not come across one of those before.  With the triple mica supports i would have said its a 6080WA or WB ruggedized version, and the white base is common for Raytheon tubes.

 

[howzz1854]

oh my... does that i mean i have one of the kind 6080. lol.

i tried googling but couldn't find ANY info about the markings...

 

[lth1]

Pretty sure it is a Sylvania 6080 WB, the white base Raytheon looks nothing like this tube.

 

[howzz1854]

Pretty sure it is a Sylvania 6080 WB, the white base Raytheon looks nothing like this tube.

Thanks Lee!

how positive are you about this. i did a google for Sylvania 6080WB and it does seem pretty close. but sometimes it's hard to tell when people don't take close-up pictures.

either case, thanks for chiming in.

and if anyone else can confirm that'll be even greater.

 

[lth1]

I have 5 Sylvania 6080 WB and one Sylvania 6080 Gold Brand, they are identical to your tube, except the Gold Brand has .25" taller glass.  Guts are identical.  The Sylvania 6080 also have numbered pins.

 

[howzz1854]

I have 5 Sylvania 6080 WB and one Sylvania 6080 Gold Brand, they are identical to your tube, except the Gold Brand has .25" taller glass.  Guts are identical.  The Sylvania 6080 also have numbered pins.

thanks!.

looks like i'll order 2 or 3 of those for backup. my current stock tube has clocked in about 2k hours roughly.

 

[lth1]

You need to purchase a better sounding tube instead of spending your money on a Sylvania 6080 WB.  The only 6080 style tube that sounds close to the 5998 is the 7236, it is a computer grade 5998A tube shaped like the 6080.  The 6520 is another wonderful sounding tube but you should be saving your money for the Tung-Sol 5998 or Chatham 2399, same tube.   

 

[mcandmar]

What he said.  I thought the Sylvania GB 6080 was the best of the US made 6080's, but i think the UK made variants are better.  The 5998 family is another ball game though, just unfortunate the prices they go for these days.