Cavalli Compact Tube Hybrid (CTH) Tube & Tweak thread. - Page 24

I'll have to look around, it seems so random. I do love the wee thing though so I will persist.

6n6p

I've been spending some quality time with the Russian 6n6p, after a small heatsink upgrade this weekend. The word for this one would be "impact". It has a tight low end, and listening to it is like having a kick drum in my head. And it's really really fast. The transients are crazy fast. It does have a little bit of high end roll off, probably starting at 12K or so. But it still has plenty of high end detail, just recessed a bit. For trance and rock (listened to REM, DJX2, Muse, and A Perfect Circle), it has an amazing amount of impact. Caught myself giggling while listening.

Note: (for anyone who's not a regular to this thread) Running the 6n6p needs a 1 amp capable CTH. (1 amp chokes, 200V coupling caps, a 40 VA wall wart, and sufficient heat dissipation.)

yep, the 6n6p is really good in the CTH as is the 6cg7 and 6h30. I think these are the best tubes for my tastes, I just got another 6h30 in the mail and it looks like a new tube (not NOS) and unfortunately it seems to be the most microphonic tube I've come across. I really need to get some dampers.

You could go for a 6h30-DR (the "Supertube"). It shouldn't need dampers because it has support bars up and down the length of the entire grid. The sound has the best low end detail of anything I've heard. That was my favorite of Wiatrob's tubes. Unfortunately, they are expensive.

yeah, I have a set of 6h30pi Golds which are nice and quiet, but this one is really bad even though it's a Pi supertube.

Strange. I thought the design of that one would prevent microphonics. I wonder if it had a rough trip from Russia or something.

Oh, how did the beasty tube experiment work out?

still waiting for the tube to arrive
should be fun

Tube structure cannot prevent microphonics, but can help minimize it -I just flicked the 6H30 (heresy?!?!) on my CTH and it rattles - but it never makes noise when subjected to normal desktop vibration, plugging in cables, etc...

this does. plug things in... zzzzzinggggg! touch anything on or near it...zzzzzzinggggg... it's a marvel of sensitivity

I'd say at least 5x worse than any other tube I have here.

Anyway, in the great spirit of DIY I headed off to the local craft shop and bought a 2-part easymold silicon putty mix to make my own tube dampers with. 20 min set time after mixing and good for 400 deg F. Supposedly strong and flexible

I hope they don't SQUEEEEEZE the life out of your tubes! Please post pics in the DIY build thread!

Pah!

the silicon putty makes nice dampers but that 6h30 is beyond fixing. even totally damped it's insides still ring like a bugger. I put it on the 6n6p and when flicked, it went from ting to tonk.

I molded the stuff around a Starving student tube 19j8?!? whatever, nice sung fit on the bigger tubes

I have had limited success with tube dampers and microphonic tubes, they seem to lessen the ringing but not take it away. Have tried the thick silicone o'ring type as well as a couple of different types of Herbies tube dampers, Herbies do work better than the o'rings but only marginally.

They do look cool though.

Yeah, I never expected miracles seeing as most of what causes the ringing is internal where the damper can't reach. The best you can really expect is secondary damping.

A bit like damping a bell that's full of wind chimes

Hey all
My first post in the CTH threads.
I finally got around to stuffing my CTH board and I went through this tweak thread to get the latest & greatest BOM updates before wiring it up. My C3h and R18's are updated. I'm considering doing the multiple heater voltage tweak with a twist. I "upgraded" to a chinese stepped attenuator for my volume, so I have my kit's 50k alps RK097 left over. Any good reason to not parallel the stereo sides together (25K impedance) and tie one side to the wiper (creating a variable 25k log taper resistor) and then use it as a continuously variable heater control ? Looking at the chart it appears the voltage response to resistance is close to logarithmic so the heater voltage response should be close to linear? I thought I'd measure the heater voltage over the pot's range and mark the knob's position on the faceplate for various tube families. I'm thinking of putting a ~7k resistor in series with the pot (in R3H position) to limit the minimum heater voltage to ~6 volts. It seems it will still need a switch to break the R3H leg for 12.6 volts ~ or is there a combination of R1H + R3H (with the variable resistance in series with R3H) that would make a switch unnecessary? Like increasing R1H a bit (say 10.5K) to allow the adjustment range to exceed 12.6volts by a bit with no switch.



The potential advantages I'm wondering about -besides using tubes with oddball heater voltage requirements - would be the ability to tweak the heater voltage up or down on the fly and listen to the sound differences. It would be another step in making the CTH a truly universal test bed for tubes. It would be easy to add on a heater voltage display that would allow auditioning tubes with a range of heater voltages. It might add another interesting dimension to tube rolling. If the circuit can be made to behave quietly and be upgraded to greater current capacity, it could be an interesting addition to other tube amps. I'd love to see a ultra quiet, Bijou capable version of the circuit.

There is the risk of being overly aggressive with this heater knob and smoking heater filaments. Besides this risk, is anything horribly wrong with the plan, will it overstress or destabilize the heater switcher somehow? I don't understand the finer points of the switching regulator circuit, so there could easily be something stupid with the idea. If it will fly, can someone familiar with the details of the circuit do the calq's for R1h, R2h, R3h & 25K log variable resistor that will give a smooth, fairly linear adjustment from say 5.5 to 13.5 volts ?

???