Well, in my experience parallel is generally used to describe single ended amps, as these are. Push pull often uses several pairs of tubes, but I have not seen it described as parallel.

The question is, if SET's are better mid-range sounding but are necessarily flea-powered devices requiring high-sensitive speakers, why isn't the market for PSE (parallel single-ended) more popular? SET's are by far more common than PSE's. There must be a reason people decline to use multiple-way (theoretically better sounding) low sensitivity speakers to be able to enjoy SET's. Wouldn't it be easier for everybody to just increase the number of tubes in parallel and keep the advantages of SET's but with significant more power? It would be the ideal scenario.

It is obvious there are serious tradeoffs involved in PSE vs SET I just don't know which these are. Can someone shed some light in this? Thanks!

Having to use quads of tubes...but no big deal if you need the power. There are many speakers that would be better matched with one of these.

Google parallel single ended amplifier.

I believe that's an economical consideration, not a technical tradeoff. I'm pretty sure there's a sonic cost to more power in single-ended using more than one tube per channel, otherwise why would anyone bother with sets?l

I asked Dennis about parallel single ended design, and he was kind enough to send me a lengthy response detailing his thoughts. So now you know....

Here are just a few of my thoughts from experience with single-ended parallel tubes in class A amplifier circuits. First and foremost keep in mind the additional output power derived is not the key factor. As you and I both know very well 5 watts or so is an excellent usable power level for home audio providing the amplifier is of a single-ended class A tube design. Moving up the power level scale does not truly gain a lot of realized SPL level until you increase that 5 or so wattage level to 50 watts which will gain a 10dB addition SPL output level. In my opinion if one truly needs this higher 50- 100 watt level they might as well go with a 200 watt solid state ear bleeder. The extraordinary level of musical emotion presented by a single-ended class A tube amplifier in my opinion is saved for the music lover and not a head-banger, show-off! My audio, in the business experience, reveals very clearly that after a few weeks with a high power, hi-fi spectacular, impress your buddies system is in most cases turned off and ends up collecting dust. Just check out Audiogon and Ebay … the high power in your face noise making gear is up for sale by the boat loads.




Sorry for the soap box ….. after all these years I still have a passion for the musical presentation in a memorable, emotional manner. I only know how to present this musical experience in a home audio environment with single-ended tube audio. Since I was a kid starting with my first single-ended 6V6 class A audio amplifier. I simply do not know any better!!!!!!!!!!




Anyway … the advantages of multiple tubes in parallel SE a numerous. First the transformation ratio of the high impedance plate resistance of the vacuum tubes is lowered by additional tubes combining as one load to the primary output transformer winding. This ratio between the vacuum tube and the driving loudspeaker is lower. This lower ratio equates to great control of the system loudspeaker. The available dynamic peak envelope power is considerable greater with the load being shared by additional tubes in the output stage along with additional plate voltage because of the lower primary impedance. One of the absolute key factors … and once again in my opinion ….. is a lower distortion level at that actual user level of power. If one needs all of the 17 watts for instance in the new parallel KT88 PSE amp they might as well get a high power solid state amp. What I am saying … at the level of 5 or 8 watts that is usually more than adequate for the home environment … the distortion curve is mush lower with the 17 watt amplifier than using all the available power in the 5 or 8 watt total single tube amp. So your are gaining control and lower distortion in the usable power range. As far as bias is concerned in my designs I use individual cathode auto bias on each tube. The tube itself reaches the proper bias level no matter the brand or even the condition of the tube. Now the output transformer becomes even more critical as additional tubes are run in parallel. The current thru the transformer increase by each additional tube added and the impedance of the primary lowers as well. With grain oriental impregnated silicon steel luminance and high temperate wire insulation some very nice single-ended, air gap output transformers can be designed and wound. The transformers I have wound for these amps contain wire insulation with rating temps of 220 C and silver soldered Teflon lead outs. Run this new amp at the 5 to 10 watt level and I gotta tell ya the dynamic range and speaker control is exciting.

Analog Addict,

Thanks for elevating my question to the Man. I understand the differences now. I love my 5-10 Watt SET and would not replace it with anything. The key here is not to max out the SET's power to keep distortions at bay, and that is what I normally do. The use of the LP-27a preamp helps with this tangibly for those selections where you need the extra "oomph". I wonder if the Triode-strapping configuration is preserved in PSE's and given all these advantages, how come PSE's are not at least as common as SET's.

Thanks AA. Dennis is the man. My understanding of PSE is that it is difficult to pull off. More difficult than PP for the additional usable power. I think we all agree here that Musica is right about SE being superior for accurate presentation. Now SET/SEP/PSE? I have to let my ears decide. I cannot base this opinion on theory or internet opinions. If anyone can do it DH can and I want to hear one of these amps. I'm seriously contemplating trading some non-Inspire gear for one. I also have empathy for FB and not wanting to double my cost for a bit of rolling by having to buy 4 tubes at a time.

Quite simply, the parallel amp will better control many speakers. Especially, speakers with less than flat impedance and/or complex crossovers. :thumbsup:

Personally, I don't need that advantage but a lot of others may.

I agree. The bottom line seems to be few people can pull this up right, including a specially designed and more sophisticated output transformer. No wonder most go with P-P for enhanced power ratings but at the classical tradeoff with midrange sound quality.

This is why SET's are much more popular, as it is simpler to achieve but at the cost of limited power.

Finally, I've read that coloration is a cost to pay when using light, highly sensitive full-range drivers or horns to couple with SET's. Evidently, a good three-way speaker design ought to sound better than a simple full-range or horn-based speaker provided cross-over design is efficient. The tradeoff here is power requirements.

So, maybe the ideal combination is a well-designed PSE coupled to three-way low impedance curve loudspeakers (whichever those may be).

Here's an article that get's into the SE/PP difference if anyone is really motivated to read this much!

https://app.box.com/s/3j4joieng7zkgvz3ofuve51z53l5p6cr