Seeking 6AQ5's Curve Chart

[Kenneth Zhu]

Audio Asylum is a good place to visit. But the speed of server is slower than here and it is difficult to post image there, perhaps due to the limited capacity of the rented storage. I always lose patience and can't help jumping to other sites when refreshing the webpage of Audio Asylum. That's why I was extremely excited when I found this place.

[Kenneth Zhu]

I studied the GE characteristic curve chart but found something comfusing. Coventionally, the plate load resistace for 6V6 or 6AQ5 will fall within the 5K to 7K range, which is manifested in many classical designs. However, according to the chart as following, I have to draw a conlusion that the optimal plate load resistance shall be around the 6K point rather than the widely used 5K benchmark. I've got completely confused 'cause my schematic, a classical design, chooses 5k as the primary resistance of OPT, and according to above conclusion, such choice may not be optimal. Can anybody help me to show an explanation?

[fdegrove]

Hi,

Some guy called Tim's going to love me for this but the EL95/6DQ5 is a formidable little penthode as well...

Some of these are DHT beaters, they really are...

Cheers,

[Kenneth Zhu]

According to manual, when operating in standard status, 6AQ5 will exert moderate power output 4.5w, while the THD will remain at a satisfying level:8%, lower than a group of beam tubes. So I believe THD won't be a big trouble maker.

[Kenneth Zhu]

And what truly confuses me and is still lingering for reasonable explaination is the choice of optimum load resistance of 6AQ5. I've browsed all the schematics available at my hands and regretfully found that if 6AQ5 is working as a beam tetrode, the OPT will choose 5K as its primary resistance without exception. I really wonder why the designers have not chosen 6K, as the above chart shows. Yes, it is true that the characteristic curve of tubes manufactured by various manufactures may differ from each other, but how come that the designers unanimously choose 5K as the best choice? Still waiting for an answer.

[fdegrove]

Hi,

Why worry?

Any OPT fit to take a 6V6, 6BQ5 will be fine.

I've seen circuits using anything from 5K to 10K using this kind of tube...
It's a matter of design choices...

Cheers,

[fragman56]

Just a wild guess here but perhaps the tube sounds best at something other than "lowest total distortion" point given on the curve? That is, perhaps the odd harmonics are too high at 6k and is better at 5k? Maybe the 3rd and 5th are lower at 5k with 2nd higher proportionately?

Rick

[Kenneth Zhu]

That's a talented suggestion. Thank you, fraqman56. It is very likely you've hit the point. I will keep the original design.