I'm fairly new to the hobby; I have a 50s Magnavox console and another Magnavox tube tabletop. I'm looking to aquire a nice pre-war table top set and I keep seeing the term push-pull in regards to the amp.

What's the audio difference between a push-pull amp vs a single ended amp? Was the P-P standard on radio models during the 30s, or only found on higher end models?

This should adequately explain it.

http://www.aikenamps.com/SingleEnded.htm

http://www.all-science-fair-projects.co ... _amplifier

In a regular circuit with one output tube, the tube amplifies the entire waveform. In push pull, one tube amplifies the top half of the waveform while another amplifies the bottom half. It's important that the tubes are biased equally and are a close match to each other. Push pull, because it uses an extra tube, wasn't used in bottom end sets but can be found in many others. Some record players with only three tubes had two as push pull outputs. Some table radios are also push pull output.

EDIT, Micheal beat me to it but I already had it typed out so I added it anyway.

Speaking of bottom-end sets with push-pull outputs, I recently acquired a small two band, three-knob, six tube Silvertone model 7144 (1936). The dial is the round "gold dial" variety that came just before the "green dial" sets. Controls are: band switch, on/off/volume, and station select. There is no tone control. Tube line-up is 6A7, 6D6, 75, 42, 42, 80. The SW band is 5.5-15 MHz. An odd but interesting set!

bottom end with Push-Pull:
http://www.radiomuseum.org/r/eca_132.html

Push-Pull 25L6s driven by a 6SL7 driver/inverter

AND--it has TWO 25Z6 rectifiers

I'd like to add that push-pull can be run in Class A as well, were both
tubes are in conduction over the full AC cycle. Philco and others used Class A push-pull
amps in their higher end table and console sets.

Pete

This is true for Class B Push-Pull output circuits, but most radios use Class A where both tubes handle the entire waveform. Class B (As well as the similar Class AB) is more efficient and allows more power handling for the same tubes than Class A

Either way, not only do you get greater power handling, the push pull circuits automatically cancel second harmonic distortion.

Another benefit, with a center tapped audio output transformer, the DC current going to each tube is equal and opposite, therefore the DC magnetic fields cancel.
This keeps the core from being saturated and gains better fidelity.

Single-ended output transformers have an air gap and usually have bigger cores to reduce this issue. Still, the core can saturate reducing its effectiveness on transferring the audio energy.

-Steve

People, please he said he was NEW to electronics. You are giving him explanations for someone with a very detailed knowledge of electronics theory. KISS.
Top/bottom half of the waveform, tubes are biased, the core can saturate, conduction over the full AC cycle, close matched, air gap, class A, class B, class A/B?????
Are these terms the best way to explain a paper clip to an alien ? Just explain it in simple terms rather, then try to impress the rest of the group. Really guys you are looking at the question through 20 to 30 years of practical experience. This poor guy is new and probably looking into a tube radio for the first time and doesn't even know what all the parts are yet.
Dan

Ok, Two tubes in the output stage instead of one?

Ok, that doesn't explain parallel...

More power?

That doesn't seem to describe much either.

Oh skip it... I get walked on anytime I try to answer technical questions so I'll stop doing so.

This is why I stay out of the Electrical/Mechanical Restoration forum...

-Steve

Explanations shoud be technically accurate.

But, if it helps... the two tubes work by opposing each other. While
one tube is going in one direction, the other tube is going in the other.
In effect, one tube is pulling more current, while the other is pullling
proportionally less current. Whether a tube is pushing or pulling
depends on the polarity of the input signal at that instant.
How much they are pushing or pulling depends on the signal level.

The tubes are sharing the work, but they are 180 degrees out of
step with each other.

So how does this relate to fidelity? I mean whats the benefit that makes it desirable? Louder music, or clearer music?

Two tubes doing twice the work means twice the power.
As Azenithut mentioned push-pull inherently cancels even order
harmonics when they are combined at the output. So, it should
sound cleaner.
Also, the requirements for the output transformer are lessened
in Class A as was mentioned by Azenithnut due to the cancellatiion
of the DC magnetic field in the primary winding.

Pete

Let me see how simple I can explain it.

Class A (Single Tube)...Single tube does all the work, low wattage output, power hog especially when the tube is sitting idle, cheap to build.

Class B (Two Complementary Tubes)...Each tube does half the work, high wattage output, power efficient especially when the tubes are at idle, more costly to build.

Hopefully I've got the facts right on this otherwise I'm sure someone will correct me.

No, that's not right. Class B *requires* push-pull using two tubes but most push-pull output circuits in home radios and phonographs use Class A or AB, as was posted previously. The advantage is much lower distortion, that is why all true high-fidelity amplifiers run push-pull outputs.

Class B is usually used when the maximum in efficiency is required, such as the modulator section of a high-power AM transmitter. Class B can result in *higher* distortion (crossover distortion) than even Class A single-ended outputs.

Class A is least efficient, Class B more efficient, Class AB in the middle. Class C is most efficient but it applicable only for RF circuits, not audio.

-David

Ugh....

You guys need to explain in layman's terms, not 'simpler' terms. I'll try to think of something.

This is very typical of seasoned hobbyists trying to help newbies. They have problem relating in lay terms.
Dan

I try not to talk down to people. Boiled down to essence, the comparison might be something like:

"Push-pull sounds better than the alternative "single-ended" amplifier output. It has both lower distortion for cleaner, more natural sound, as well as more power for loudness. But it costs more (uses more tubes or transistors), so it was used in higher-end models of radios and phonographs. Push-pull amplification is one of the foundations of hi-fi."

Better?

-David

No analogy is perfect...

"Push Pull" is pedaling a bicycle with both feet. You get pretty smooth forward motion and lots of power.

"Single Ended" is pedaling a bicycle with one foot. You still move forward, it can be an acceptable answer, but it's not as smooth and maybe half the power.

Curtis Eickerman

Analogy: Two guys on a crosscut saw. One's pushing while
the other's pulling. They'll get through a log twice as fast.
(Probably more class AB in practice... you can't really push
a crosscut very well.)

-well, I tried.
Nelson

Skip all that . It is something you do when trying to get a console radio into a small car .