Jcm800 Downscale

[J M Fahey]

I already considered 2 double triodes per side
The main problem is not that, but that triodes as power amps lack bite, simple as that.
For bedroom approved 50mW, a 12AU7 is enough.

[exclamationmark]

I vaguely remember posting a thread about using these triodes roughly a year ago, asking if I could run them off a 48v B+ supply. I didn't end up building it, but from my preliminary load lines the output was surely greater than 1 watt. Another thing you could do it direct couple it to a mosfet and squeeze a lot of extra power out of it. I scrapped some mains ac transformers that look to be a suitably low impedance (you can pull the load line practically vertical with these tubes) so it might just be my next science experiment. Another thing I found is that the drive requirements of these tubes generally out-voltage the B+ supply used to run them!

In the context of the OP, I wonder if they would allow them to use +40 AND -40 rails. I've seen some hi-fi amplifiers use a bipolar scheme though I don't know what the benefits would be...

[Austin]

So four triodes instead of just two?!? That changes everything. So if Juan is even fairly accurate in his considerations that would raise the meager 1/2 watt output to a whopping 1 watt!!! Better get some ear plugs.

Two tubes at 10 watts each in push pull ab1 is going to be alot more than one watt and Ab2 could be close to 20 watts or even more. Just sayin...

[J M Fahey]

Two tubes at 10 watts each in push pull ab1 is going to be alot more than one watt and Ab2 could be close to 20 watts or even more. Just sayin...

You are confusing *dissipation* with *power output*.
Very different things.

My calculations are accurate referred to a +40V B+ voltage.
You will probably bve able to extract more out of them at higher voltages, but that's not the point in this case. Sorry.

Dear exclamationmark. What you suggest is not allowed by University Rules.
No 2 points inside the chassis can be more than 40V apart.
So if you feed the tubes with +40V and need , say, -6V to bias them, that is not allowed either.

In fact the rules do not even consider tubes at all, it was a surprise for them when Florian suggested a JCM800 like project.

[Austin]

You are confusing *dissipation* with *power output*.
Very different things.

My calculations are accurate referred to a +40V B+ voltage.
You will probably bve able to extract more out of them at higher voltages, but that's not the point in this case. Sorry.

Dear exclamationmark. What you suggest is not allowed by University Rules.
No 2 points inside the chassis can be more than 40V apart.
So if you feed the tubes with +40V and need , say, -6V to bias them, that is not allowed either.

In fact the rules do not even consider tubes at all, it was a surprise for them when Florian suggested a JCM800 like project.

What you said is true about single ended amps but in push pull (as I am sure you know) you can get much closer to the actual max plate dissapation for power output.
Look here: http://www.mif.pg.gda.pl/homepages/frank/sheets/093/6/6BQ5.pdf

Look under "push-pull triode connection" it gets about 5 watts class ab1 from a tube with a 12 watt max plate dissapation. Ab2 could get even more...

[J M Fahey]

pure class B;

Clearly I was referring to a push pull amp; 1 double triode per side.

Can't find why you refer to that 6BQ5 amplifier, it states 300 Volts plate supply.
At least in this thread, please offer suggestions based on Florian's needs, I fail to see how we are helping him otherwise.
Thanks.

[Austin]

Clearly I was referring to a push pull amp; 1 double triode per side.

Can't find why you refer to that 6BQ5 amplifier, it states 300 Volts plate supply.
At least in this thread, please offer suggestions based on Florian's needs, I fail to see how we are helping him otherwise.
Thanks.

I was just looking for a triode class ab1 output in watts in relationship to max plate dissapation in watts and the 6bq5 came to mind since some people like them in triode mode they even listed an example. The plate voltage is different obviously but the internal resistance of the tube is also different so the actual power made is very similar. You are right though I could have probably found a more appropriate example.

Here is an even better tube: the awesome 6336! http://www.mif.pg.gda.pl/homepages/f...27/6/6336A.pdf It has 30 watts max power dissapation PER PLATE.. They can be had for about 20 bucks each on ebay. You would need a big toroidal transformer just for the heaters, 5 amps each tube... So you could probably just use a single tube for push pull but two might be even better. That might make for a pretty loud all tube amp that runs fine on 40 volts..

[Steve Conner]

At the risk of repeating myself, there is no relation between idle dissipation and power output in a push-pull amp. Look at those old Peavey CS800s that made 800W with no idle current whatsoever. Those were solid-state of course, but the theory is the same for tubes. You can still get 100W out of a 100W tube amp with the idle current turned right down to nothing, it just sounds dreadful.

In a single ended amp, or a pure Class-A PP one for that matter, power and idle dissipation are related by the mathematical properties of the sine wave.

[Steve Conner]

At the risk of repeating myself, there is no relation between idle dissipation and power output in a push-pull amp. Look at those old Peavey CS800s that made 800W with no idle current whatsoever. Those were solid-state of course, but the theory is the same for tubes. You can still get 100W out of a 100W tube amp with the idle current turned right down to nothing, it just sounds dreadful.

In a single ended amp, or a pure Class-A PP one for that matter, power and idle dissipation are related by the mathematical properties of the sine wave.

[Austin]

At the risk of repeating myself, there is no relation between idle dissipation and power output in a push-pull amp. Look at those old Peavey CS800s that made 800W with no idle current whatsoever. Those were solid-state of course, but the theory is the same for tubes. You can still get 100W out of a 100W tube amp with the idle current turned right down to nothing, it just sounds dreadful.

In a single ended amp, or a pure Class-A PP one for that matter, power and idle dissipation are related by the mathematical properties of the sine wave.

Given the low voltage and small bias amount any tube is going to be running into grid current to get any power, but class *2 increases efficiency so that is good at least. A mosfet driving the grid or even a LM3886 really pushing it would be really neat-o and easy to do. How much power could you get before it melted down? Lots I bet.

[Chuck H]

At the risk of repeating myself,

And then... Due to a dual post.

At the risk of repeating myself,

Lol! Good one.

[J M Fahey]

You would get less power than with the earlier dual triodes: less than 200 mW.
Current with 10V on plates is 20 mA, go figure.
And yes, I'm considering a push pull amp.

As of your second suggestion, I'd just skip the tubes and go straight for the LM3886.
Two of them bridged, with +40V rail (only one) can provide some 60/70W into 8 ohms.

PS: I refuse to consider these for class AB2 designs unless plate curves are supplied for grid voltages higher than "0". Sorry.

Before throwing datasheets on the table, please check yourself how much current they can handle between 40 and 10 V DC.
Remembering that *max* current must be achieved at *min* voltage, because the remainder must be transmitted to a load.

[Austin]

You would get less power than with the earlier dual triodes: less than 200 mW.
Current with 10V on plates is 20 mA, go figure.
And yes, I'm considering a push pull amp.

As of your second suggestion, I'd just skip the tubes and go straight for the LM3886.
Two of them bridged, with +40V rail (only one) can provide some 60/70W into 8 ohms.

PS: I refuse to consider these for class AB2 designs unless plate curves are supplied for grid voltages higher than "0". Sorry.

Before throwing datasheets on the table, please check yourself how much current they can handle between 40 and 10 V DC.
Remembering that *max* current must be achieved at *min* voltage, because the remainder must be transmitted to a load.

That makes sense kinda. But now I really want to really try this! Here already I have to use some dewault 18 volt rechargeable batteries in series for b+, and a largish 50 amp 12volt battery charger from an rv to use for the heaters and I already have the tubes and sockets. Do you guys think an LM386 would drive the grids? I already have some but no LM3886. The hangup is the impedance of my output transformer, I will have to run a 2 ohm load to get any power out as it was made for two 6L6 from a bogen p.a.

The tubes I have are 6080/6as7 not 6336 to be clear, I bought a couple these 6080 and one big 6as7g to experiment with a while back.

I think the 6as7g looks just fine.. With the large glass bottle and interesting looking internals..

[printer2]

Can we get 100's of mA through the tube at 35V?

[Steve Conner]

It's a triode, so you can work out the plate resistance and use that in the maximum power transfer theorem.