Anyone got Data sheet for New Sensor "Tung-Sol 6V6GT"?

[tubeswell]

I can't find one on Duncan's site (although there are older 6V6GT specs on there), and the link on the new sensor site to the 'tube specs' page doesn't seem to be working today ;-).

The only blurb I can find on the new sensor site (and in all the parroted advertising gook I can google on the web) is that these tubes are supposedly designed to handle 'higher voltages' on the plate and screen.

[soundmasterg]

Unless they have changed their policy, New Sensor doesn't provide datasheets for any of their tube products.

[tubeswell]

Okay cheers

Well that would explain why the 'tube 'specifications' part of their site loads up blank. Fancy making tubes and not bothering to tell anyone how they're spec'ed.

[soundmasterg]

Well I guess they just figure that you can look at an old datasheet and that is close enough. Obviously it isn't but they don't seem to care too much about it. JJ provides datasheets for their offerings.

Greg

[J Martin]

I asked for data sheets for some of the Russian tubes and New Sensor sent them within a few days. That was a few years ago. Maybe they have changed their policy? I have been buying from them since about '94 before they even had a web site. I also know you can't compare tubes by looking through the glass. You need to measure element spacing, grid winding and do a metalurgical analisys of plate and cathode material.

[tubeswell]

I also asked New Sensor at the time I first posted this link, but I haven't got any response and that was a couple of weeks ago.

[MWJB]

What particular perameter concerns you?

[tubeswell]

Hi MWJB

Just curious to know what I bought. It seems to be working fine in the (5F2A) amp I just built (Many thanks for your helpful advice BTW)

I was wondering what the voltage and dissipation ratings were for the Plate and Screen, as well as the typical operation parameters for single-ended operation. (I haven't measured the actual plate voltages with the tube plugged in yet). I got 439VDC at the plate node and 432VDC at the screen node when I did readings yesterday without the pre-amp and output tubes plugged in. Having passed the 'visual-smoke' test to my eyes after I plugged everything in, I presumed it was safe to take it for a test drive for a while. No probs so far (touch wood). Hardly even has any hum.

[MWJB]

Voltage ratings for plate & screen exceed those of most NOS tubes (and FAR exceed any published figures for NOS).

Dissipations - assume regular 6V6GT values...not that either are going to be an issue in your amp - that 439v at the plate will drop considerably under load, then you subtract the cathode voltage (tube only sees difference between plate & cathode, rather than ground), so (I think you said you had 318VAC at B+ secondaries?) you're probably only looking at 340-350vdc max on the plates, less 18-19v at the cathode = 330v. 14W/330 = 42mA ...but SE designs like this regularly dissipate over 20W with no problems, they're pretty tough.

B+ voltages should always be measured with tubes installed, without a current load they will always read high.

[tubeswell]

Thanks MWJB

Although I'm starting to wander of the topic of this thread, FWIW I took a reading of the voltages (w.r.t. ground) yesterday with all the tubes plugged in and got:

PT HT secondary at 5Y3GT rectifier (a NOS Toshiba) = 290VDC on each side
B+ = 360-361VDC
Plate of 6V6GT (New Sensor 'Tung-Sol') = 355VDC
Screen of the same = 297-298VDC
Preamp B+ supply = 255VDC
Preamp Plates (NOS Philips 12AX7) = 157VDC

Would I improve the tone any if I nudged the screen voltage up a wee bit? (not that it sounds bad at all - just wondering).

I guess the 12AX7 could take higher voltages on the plates too (for more chime, even though it sounds nice as it is), so I was wondering about just changing the 10k resistor I've got at the plate-to-screen B+ node (to say a 4k7?).

And if I did that, would I also need to put in a wee screen grid resistor (say 4k7) on the screen grid pin of the 6V6GT? And what difference between the plate and screen voltage is the 'safest' minimum I could go to.

[MWJB]

360-361vdc seems a lot for a 290-0-290VAC secondary with a 5Y3, that's the sort of voltage I'd expect from a GZ34/5AR4 (which would have been my first suggestion for more chime)? Are you using a 470ohm cathode resistor?

BF/SF Champs use 1K between main B+ and screen supply, though you might find that screen voltage creeps above plate voltage with this value? (If so, that would be the time to try a screen grid resistor). Perhaps 2.7K (with the stock arrangement) would keep the screens below the plates? At the voltages that you have you are very unlikely to incurr any damage whatsover to the 6V6.

To get a significant change to your preamp voltage (differences of less that 20v can be hard to hear) you will need to do more than halve your B+ to screen dropper. Reducing the B+ to screen dropping resistor will reduce distortion and reduce the "tweediness" of the amp's character in general. If you want to raise preamp plate voltages specifically, reduce the value of the screen supply to preamp supply dropping resistor (that feeds the 100K plate resistors). Be aware that current accross this resistor is very low, so you will need to make big changes in value to see a significant change in voltage, halving it may only just get you a perceptible change.

[tubeswell]

Originally Posted by MWJB

360-361vdc seems a lot for a 290-0-290VAC secondary with a 5Y3, that's the sort of voltage I'd expect from a GZ34/5AR4 (which would have been my first suggestion for more chime)? Are you using a 470ohm cathode resistor?.

Yes it is a wire-wound jobby - and I checked it with the meter before I put it in. (The pre-load voltage off each side of the PT was 318-319VDC). I was worried that a GZ34 would draw too much current off the PT, so I stuck with the 5Y3GT. As it happens, I think the PT was overdesigned in terms of its volts/amps rating, because the wires for the secondaries are all quite thick, teflon or kapton-coated, solid core wire, so maybe I could run a GZ34 off there after all.

Cheers