[WDC]

40W Parallel-Single-Ended, Triode, Pure class"A" Amplifier

Would someone please help clarify some of the terminology in this description? I am trying to sort out for myself the meaning of various terminologies to best help understand the principal of varying and circuitry ie single ended vs push pull, etc.

As I understand a principal of this description and a single ended circuit meaning that the high and low audio wave is processed in one tube unlike a push pull where one tube processes upper half of the signal and a second tube processes the half lower. I also understand that this circuit describes the single ended circuit being split and processed by two tubes in parallel doubling the amplification. Is this process described by a descriptive word “parallel” or “triode”?

Thanks in advance,
WDC

 

[WDC]

Can anyone explain what the term “triode” means?

 

[antonik]

Quote:

Originally Posted by WDC Can anyone explain what the term “triode” means?

You always can do a search before asking very basic questions on the forum

. In short - a triode is a type of electron valve with 3 electrodes, there are also diodes with 2 electrodes, tetrodes with 4 , pentodes with 5. There were in the past made valves with more than 5 electrodes but these are not really used now.

There is a lot of information available on this matter on the web.

Here is a good classic introduction:

http://www.oldradioz.com/manuals/rdh4/CHAPTR01.PDF

pages 6 to 8

Alex

 

[Len]

In short:

The differences between a diode, triode, tetrodes, pentode, etc. is the number of elements (heater element, plates, and grids) in the tube design. As the name suggests, a diode has two, triode has three, tetrodes has four pentode has five, and so on. Examples of triodes commonly used for output devices include 45, 2A3, 300B, 211, 805, and 845 tubes. Examples of pentodes include EL34, EL84. Tetrodes include 6550, KT66, KT88 and 6L6 .... but i keep hearing people referring to these as pentodes as well, so I'm really admittedly confused. edit: okay, I believe these are tetrodes per their specifications.

SET (single ended triode) and Push Pull are two different circuits. In a SET, the signal remains intact, amplified by a single output device (in the case of SETs, a single triode tube per channel). This is the simpliest circuit and is often sought-after because of the rich/expressive reproduction that you get from its simplicity.But because only one output deviced is used, SETs are hampered by power limitations (whatever the output tube and its transformer is rated for).

On the other hand, push pull takes the signal and splits them in half (phase and anti-phase) so that two output devices (e.g. tubes) are used to amplify the signal. This yields a lot more powerful output since you now have two devices working to amplify the output. However, it is argued that the signal isn't as "pure" as single ended (again, whose signal is kept complete from input to output). When done right, PP amps can be excellent, but they do sound different from SETs in general.

A parallel SET uses two (or more) output devices per channel, but unlike a Push Pull, it does not split the signal into phase and anti-phase (it's better to consider the signal "shared" by two output devices). The two signals are whole, but routed through two output devices. The easiest way to think about it is having two SETs in the same amp, thus increasing (usually doubling) the power output. It has been argued PSE amps aren't as pure as SET because the output device characteristics may differ and effect the sound. But you certainly get more power, and unlike PP amps, the signal is kept whole from start to finish.

There are, of course, several other differences, but this is the fundamental difference. There are also parallel Push Pulls and Output Transformer Less (OTL) amps

Hope that helps.

 

[WDC]

Quote:

Originally Posted by antonik You always can do a search before asking very basic questions on the forum .

Alex,
I appreciate your response and clarification it is helpful. Regarding your search first comment, I invite you to search both "Parallel-Single-Ended, Triode, Pure class"A" Amplifier" and/or the word "Tiiode". I think you'll agree nothing meaningful is to be gotten from a search in this forum using those two descriptions. Nevertheless thanks your description and link has been helpful.

WDC

 

[WDC]

In short:

The differences between a diode, triode, tetrodes, pentode, etc. is the number of elements QUOTE]

Len
Thanks for taking the time, that is an excellent clarification and solidifies what I understood about push pull splitting the two half’s of the signal and the open ended taking the signal half’s impact and multiplying the output strength by running multiple parallel tubes. It was the word “Triode” that was throwing me off and is now very clear as I now understand describes the elements within the tube. The circuit I was analyzing was using 300B tubes which explains the use of the term Triode and term parallel being the multiple 300B required to multiply the output wattage
Thanks again it's clear as mud now…

WDC

 

[Len]

Triodes have a heater element, a single grid, and a plate. The difference is pentodes have three grids. Just an FYI that you may find pertinent: A pentode can be wired for triode or tetrode operation (by "defeating" some of the grids), so sometimes you find amps that allow you to switch between "ultralinear" and triode operation.

 

[WDC]

Quote:

Originally Posted by Len A pentode can be wired for triode or tetrode operation (by "defeating" some of the grids), so sometimes you find amps that allow you to switch between "ultralinear" and triode operation.

Interesting, to clarify when you say "defeating" some of the grids" does this mean disabling two of the three grids? And if so what is the primary advantage of doing is, improved audio signal or the ability to use a different group of tubes? I understand that they 300B tube is commonly considered an excellent audio tube although I have also been reading some good reviews on the 845 group now understanding that they are part of the pentode group unlike the 300B tetrode.

 

[Len]

Defeating isn't really a good word for it (hence the quotation marks), but I can't find one that is appropriate. Usually when a pentode is wired in triode, grid #2 is tied to the plate and grid #3 is tied to the cathode or filament (five elements now acting as three). The way the resulting signal is reproduced is different depending on how you wire up the pentode tube. It's hard to say which way is better as there are too many variables, but suffice it to say sonic differences (and power delivery) is why its done. edit: Note, don't get confused with triode and SET. A push pull amp using a pentode tube wired in triode is not a SET.

A tube amp that allows user-switchability of operation still has to use the type of tubes its specified for. The amp is specifically designed to run this particular tube type in its specific operation(s); So no, you can't go sub'bing in other tube types.

The 845 is a big true triode. And the 300B is a true triode too, not a tetrode.

 

[kevin gilmore]

There are also 2 kinds of triodes. Directly heated triodes like the
300B have no cathode and can only work in very specific kinds
of circuits, and 6sn7's which have a filament isolated from the
cathode.

I'm sure there are a few directly heated tetrodes out there, can't
think of one at the moment.