RE: Ask your "someone" if they thought of this.

Posted by Jim McShane (D) on January 26, 2015 at 06:04:52

In Reply to: RE: Ask your "someone" if they thought of this. posted by finewatchrepair on January 25, 2015 at 18:22:20:

There are a number of misconceptions in your post and they are leading you astray:

1. The signal is not split in half in a push-pull amp. We lazily (myself included!) tend to call the phase inverter the "phase splitter". There is no splitting of the signal occurring - what is happening is analogous to one of those two person saws that are used to cut down trees - one person pulls the saw while at the same time the other pushes. The phase inverter sets up the push-pull output to do the same to the signal by creating a 180 degree out of phase image of the signal. So while one tube is "pushing" the other side is "pulling". In the VAST majority of audio amps each tube sees the entire waveform or quite close to it.

2. Just because the tubes were measured for matching purposes at one current level does not mean that is where they always have to operate. Those figures (25.9 and 25.5 ma.) are the current measured under an arbitrary set of conditions in the matching process. Those tubes can be biased at any current you wish as long as you don't exceed the tubes' maximum ratings for current and/or dissipation.

If the Heath amp was operating the tubes in a way that exceeded the ratings for those parameters then a circuit modification needed to be done so the tubes could operate within their capabilities. Changing the value of the cathode resistor is one way to change the current and dissipation.

I think you would be wise to invest in Bruce Rozenblit's book - "Beginner's Guide To Tube Audio Design". It will clarify a lot of things for you, and it's not over the top in theory and math. You'll be much more comfortable with all this with a bit more study!

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Follow Ups Full Thread

Topic - HELP adjusting my EL84 modified cathode amp - finewatchrepair 16:39:15 01/24/15 (10)

RE. Have you tried the Weber bias calculator? - DAK 16:28:02 01/27/15 (0)

Ask your "someone" if they thought of this. - Chip647 07:59:16 01/25/15 (8)

RE: Ask your "someone" if they thought of this. - finewatchrepair 11:25:17 01/25/15 (7)

RE: Ask your "someone" if they thought of this. - Chip647 13:27:12 01/25/15 (6)

RE: Ask your "someone" if they thought of this. - finewatchrepair 18:22:20 01/25/15 (4)

RE: Ask your "someone" if they thought of this. - Jim McShane 06:04:52 01/26/15 (2)

RE: Ask your "someone" if they thought of this. - finewatchrepair 06:58:52 01/26/15 (1)

RE: Ask your "someone" if they thought of this. - Jim McShane 10:09:27 01/26/15 (0)

RE: Ask your "someone" if they thought of this. - Chip647 05:04:58 01/26/15 (0)

RE: Ask your "someone" if they thought of this. - finewatchrepair 16:43:26 01/25/15 (0)

Follow Ups

RE: Ask your "someone" if they thought of this. - Jim McShane 06:04:52 01/26/15 (2)

RE: Ask your "someone" if they thought of this. - finewatchrepair 06:58:52 01/26/15 (1)

RE: Ask your "someone" if they thought of this. - Jim McShane 10:09:27 01/26/15 (0)

RE: Ask your "someone" if they thought of this.

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