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I've had my SEP16CS in line for a few days now. The other day I cranked it up for a while to enjoy a few tunes at high volume. (Love to FEEL the bass!)At idle, the amp puts out very little heat even though it's single ended. After playing at around 15 watts continuous for a few songs, the tubes heated up to about double what they were at idle. This is the way it should be when an amp is DC biased. If it feels like you could roast a turkey over it even idling, that's not a good setup. The plate inside a tube has a heat dissipation rating. If that tube is already using 70% of that rating doing nothing, it will lead to poor performance. That's not an opinion, it's just physics. You can't get blood out of a stone as they say. Watch your amp's heat output. If it's blowing tubes frequently, this is another sign there are issues somewhere and they can be related to too much constant heat dissipation. NOTE: It is possible to make cathode biased amps run efficiently, although I rarely see it done. The capacitor bypass I see in some circuits never turned me on. In fact, it often increases distortion. Ditch the cathode capacitor and find other ways to obtain more power while reducing heat output. Tinker with the screen supply and various other things.
Hello Guy, Cathode biasing is great for smaller amps. It works well with amps up to about 25 watts per channel in push-pull. As the wattage demand increases, it becomes less practical due to inefficiency. DC biasing does not have to involve monthly checkups and meters. In fact, Fisher's 500C use a fixed DC biasing approach that worked quite well- although it was set to allow the tubes to run too hot. (Easy fix!)I use something called tunable biasing which makes it possible to calibrate the bias via heat output and sound properties. Best results occur with matched tubes. Easy instructions: Tune the tubes for best sound with the least amount of heat. Meters are not necessary and the adjustment can be made quickly.
The NS-40 uses tunable biasing. As long as the tubes are a matched quad, there is nothing to worry about. It has been my experience that it is best to use this system over any other DC biasing method. The frustration associated with the meter & multiple adjustment approach is not worth it. There has not been a single performance issue related to tunable biasing. Precision is not an issue because you tune for best sound at the lowest heat output possible. What if it sounds better cranked up? That would most likely indicate a faulty tube(s). Any amp designed with this feature is made to operate best with low tube temperatures. An NS-40 will not feel like an oven, nor will any other model using this system.
Hi Blair and all Audio Circle members.Which is better?Auto bias (Always adjusted - no maintenance) or manual bais with a meter and potentiometer (Precise as per the amplifier manufacturer) or completely manual bias (Simple, just look and smell and touch if the tube is too hot) method. ? ? ?I prefer the auto bias (Maintenance free and always within the right adjustment) or manual bias wih a meter, however might be more precise but I don't like the idea of adjusting the bias once a month...Any comments on my thinking?Guy 13
Dear Guy13,I love to adjust manual Bias every week, feel free to send me any manual Bias amp you reject.(joking) IF a fixed Bias amp had a tube in short it will burn until the end of the short-circuit. So fixed Bias and unreliable tubes are not safe in the same amp.My two cents, Gustavo>Never go to a psychiatrist, adopt a cat or dog from the street. On the streets pets live only two years average.
A little practice, not too much. There's no going back to the old system once this one is used. Tube amps should not be thought of as a burden. If they were thought of as fun and not loaded with maintenance issues, I know more people would be enjoying them. If there are any questions regarding heat output- I will be happy to help and others can jump in too.
Hi Brian and all Audio Circle members.Yes, why am I almost the only one posting here my opinions?All Audio Circle members don't be shy, take a step forward, jump in, share with us what you think, even if you disagree with Brian...Guy 13
Single ended amps can be made to operate cool. The SEP30 does not run hot- it's about the same as a NS-40. It's a balancing act between three voltages: plate, bias and screen. The right combination is necessary. I do not like ultra-linear amplifiers because it upsets the balance. Older single ended amps from the 60's do run fairly hot. Most of the ones I have used have either 6V6's or EL84's in them. BTW: I hooked up an old Admiral stereo receiver made in 1960. It uses a SE El84 amp section. It sounds excellent! However, the EL84's are run hotter than I'd like them to be. That will change soon.
