JJ 6V6's and output transformer.

[Gingertube]

The 6GW8 (ECL86) was a Tiny Terror Clone (without the half power switch) and is stunning.
The 6V6 power section is a Fender 5E3 copy. I did'nt want massive overdrive capability otherwise I would have gone for something with a differential phase splitter rather than the 5E3's cathodyne.
Cheers,
Ian

[Gingertube]

Finally looked at the JJ 6V6S datasheet. Check out the anode curves. At 0V on the grid at at the 14W dissipation there is 170V at the anode.
Compare that with a 6V6GT datasheet. At 0V on the grid and the same power dissipation there is 100V at the anode.
That difference in Vsat accounts for why guys are getting less power out with the JJ 6V6S. This was my guess in a post above, but a squizz at the datsheets confirms it.
Cheers,
Ian

[loudthud]

Are both data sheets at the same screen Voltage? Published curves usually use a conservative screen supply.

[pdf64]

'Finally looked at the JJ 6V6S datasheet. Check out the anode curves. At 0V on the grid at at the 14W dissipation there is 170V at the anode.
Compare that with a 6V6GT datasheet. At 0V on the grid and the same power dissipation there is 100V at the anode.'

I think that the JJ chart is for a triode connected tube.

Ginger, I can see where the 170V figure for the JJ comes from, but I can't find a chart for other 6V6 that show 100V?
Using say http://www.mif.pg.gda.pl/homepages/f...5/6/6V6GTA.pdf could you point me to it?

[Gingertube]

pdf,
Try this one:
http://www.mif.pg.gda.pl/homepages/f...84/6/6V6GT.pdf
Cheers,
Ian

[Mickey]

pdf,
Try this one:
http://www.mif.pg.gda.pl/homepages/f...84/6/6V6GT.pdf
Cheers,
Ian

What is with you guys? Running 6V6s at max output and high output voltages will ensure they have a short life. If output power is the main criterion go with higher wattage output valves eg 6L6, 5881, EL34/6CA7s etc. There are also many different ways to achieve that "brown" sound that is so desired by guitarists, but using max output power is in my opinion not the way to go.

[Gingertube]

Mickey,
I agree, in my own 6V6 amps (either quad or pair) I run the 6V6s at an absolute max of 350V. I get 28W from a quad and 14W from a pair. Was not advocating pushing tubes to the limit, was simply trying to explain why the JJ give less power than the older "real" 6V6s.
I find this (not voltage stressing the output tubes) a general "rule of thumb". EL34 (for example) sound so much better at 380V than they do at 450V.
Cheers,
Ian

[pdf64]

Ian, thanks for that.
Regarding that 100V Vsat thing, are you looking at the tetrode chart (g2 at 285V) on p3 of the pdf, or the triode chart on p8?
I can see it on the tetrode chart, but the JJ info seems to be for a triode arrangement, and so would be more comparable to the triode p8 chart on the Radiotron info?
The Radiotron triode chart seems close to the JJ one.
Thanks for bearing with me!

[Dave H]

I measured my 4 x 6V6 30W cathode biassed amp. It looks like the Vsat is 80V (see below). It has 2 x EH 6V6s and 2 x JJ 6V6s in pairs each pair with a 300R common cathode resistor. It will run 2 x EL34 for about 30W output or 2 x 6L6 for 25W but it's no contest. It sounds much better with 4 x 6V6.

[wozt]

I measured my 4 x 6V6 30W cathode biassed amp. It looks like the Vsat is 80V (see below). It has 2 x EH 6V6s and 2 x JJ 6V6s in pairs each pair with a 300R common cathode resistor. It will run 2 x EL34 for about 30W output or 2 x 6L6 for 25W but it's no contest. It sounds much better with 4 x 6V6.

[ATTACH=CONFIG]33283[/ATTACH]

Dave H what HT have you got on the 6v6's .

[Mickey]

Hi Guys, if you're trying to achieve that "brown" sound have you ever placed another driver between the phase splitter and the output valves. Years ago I wired in a 6CG7 with variable gain (by a combination of various anode load resistors,variable cathode resistors and a variable HT supply to this valve) and the owner of the amplifier was more than pleased with the result as he could alter the sound (distortion) to his liking.
From memory the output valves/tubes were running with a HT of just under 300V.
There are numerous ways to skin that cat!
Mike

[Dave H]

Dave H what HT have you got on the 6v6's .

Vp 370V, Vs 357V, Vk 23V so the 'real' plate voltage is 347V. It's 30W at < 2% THD. I don't like too much distortion. It has a very rich 'clean' sound when you crank it up a bit.

[wozt]

Vp 370V, Vs 357V, Vk 23V so the 'real' plate voltage is 347V. It's 30W at < 2% THD. I don't like too much distortion. It has a very rich 'clean' sound when you crank it up a bit.

Dave calculating the JJ's as 14watt, 14/347 = 0.040mA (x2), your bias 27/300 = 0.09. so you are biased at around 100%, was this chosen by ear a designed to be 100%.
When plotting this on the JJ 6v6's plate curves graph -27v for a 347HT shows 45ma but the bias point is well into the 14watt max area. These graphs always seem at odds with my calculations, do you ignore the graph and just use calculations?

[wozt]

Dave have you a schematic of your amp you can point me too or share. A clean 6v6 is what I'm hoping for.

[Dave H]

Dave have you a schematic of your amp you can point me too or share. A clean 6v6 is what I'm hoping for.

I measured the bias current at 70mA (35mA per 6V6) so the Pd is (370-23)*0.035 which is just over 12W but I also have a little fan running at low speed (so it's not too noisy). The schematic is below. It's a very simple amp but it works for me. I really like that one knob tone control because it is not affected by the volume control unlike most one knob tone controls (5E3 etc.)

J30.pdf



I've just been observing the solar eclipse. I projected it onto a card through a colander. You could see lots of little crescent suns and it went eerily dark, great fun!