Enhanced SEX 2.0 Some more watt needed

[hirez69]

Hi,

there is any  way to obtain some more watt (like 4 watt) from S.E.X amp?
My Version is 2.0 with PM and CS4.
Thanks

hirez69

[BNAL]

hirez69,

You could use a 6EM7 in place of the 6DN7. I do not have the manual in front of me so not sure if the just need to change a resistor or make a change to the C4S board. I believe the 6EM7 will give you about 3 watts. Not the 4 watts you are looking for but something closer.

[VoltSecond]

Twice the power is only 3 dB.  That's not a lot when it comes to volume.  You need 8 - 10X power ( 10 dB) to sound twice as loud.  This didn't really strike home until I used a stepped attenuator in my system.  1dB steps are useful for tone and balance controls, but not as useful for volume.

Now that is just talking power.  A more powerful tube amp can have different a damping factor which can affect the tone of the speakers.

[Grainger49]

Contrary to VoltSecond's title under his moniker, he is no Newbie to audio or the Bottlehead forum.  You should seriously consider his advice.

Most of us would say to consider more sensitive speakers.  I had a pair of dearly loved 84dBW speakers when I started with Bottlehead and I ended up selling them and getting something more sensitive. 

[Paul Joppa]

What is "PM"?

There are tradeoffs between power, distortion, and damping factor, which could be exploited to get a bit more power at a sonic price. These involve changing the transformer wiring, or substituting a different transformer.

Basically though, it's like asking to double the horsepower in a car - it really makes best sense to get a different car (or amplifier) that is designed to produce the desired power.

You can in theory convert a SEX amp to parallel or to push-pull operation. Going with the car analogy, it's like strapping two motorcycles together to get a car. You can get double the power, and maybe more with push-pull, but it's complicated, untested, and you need another amp to get stereo.

[Paul Birkeland]

You can indeed substitute the 6EM7 with a few circuit changes, but one of them is changing the primary impedance of the output transformer (from ~8k to ~4k). 

Which output transformers do you have?  The Specos will not really be up to the task, but PJ might be able to comment on the suitability of the new iron. 

-PB

[Paul Joppa]

There is some confusion because of the many variations that have been thought up. But the basic SEX amp is designed for an 8K transformer primary, in both 6EM7 and 6DN7 versions. The 6EM7 is a bit more efficient, giving theoretically more power, but it is also less linear, giving in practice less power than the theoretical value.

Both versions can get more power, at the price of increased distortion, by reducing the load impedance. Personally I would not go below 5500 ohms but it's a tradeoff and listening tests might lead you elsewhere.

At one time we looked at doing a fully shunt regulated amp, using one side for the regulator and the other for the amp - making it monaural of course. This would reduce the available voltage and call for a different operating point, optimized at around 4000-5000 ohms load. The power would be reduced - I don't remember but maybe 1.25 watts? Anyhow, we never built one because it didn't seem reasonable to go to that much trouble for such small power and without the advantages of a DHT.

[keto]

I tried the 6EM7 variation, and it sounded nice -- a little more "detailed" and "bright" -- but in the end I preferred the 6DN7.

[Paul Birkeland]

Yeah, my observations with the 6EM7 tend to suggest it is better suited to driving speakers rather than headphones in the SEX circuit.