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by Old Tele man
Replies
27
Views
802

### The REASON for eqaul-sized "balancing resistors"...

The REASON for eqaul-sized "balancing resistors" is to "EQUALLY" divide the voltage across the two caps at FULL/peak voltage and NOT during the initial "charge/pump" up when the voltages are smaller...
2. ## Thread: Amp Wattage Measurement - Approximations

by Old Tele man
Replies
64
Views
1,930

### SINE-squared: 54093 COS-squared: 54094

SINE-squared:
54093

COS-squared:
54094
3. ## Thread: Amp Wattage Measurement - Approximations

by Old Tele man
Replies
64
Views
1,930

### Actually, you are correct -- I mis-typed -- the...

Actually, you are correct -- I mis-typed -- the Vg "value" should be 35Vg, derived from one-half of Vgg; ie: Vg = (70Vpp/2). Hopefully, I haven't made other such errors in my previous posts, for...
4. ## Thread: Amp Wattage Measurement - Approximations

by Old Tele man
Replies
64
Views
1,930

### 0.637 is AVG of fullwave rectified signal. ...

0.637 is AVG of fullwave rectified signal.

Because both ELECTRONICS engineers and ELECTRICAL engineers use the same physics principles and terminologies, people like National Semiconductor's Bob...
5. ## Thread: Amp Wattage Measurement - Approximations

by Old Tele man
Replies
64
Views
1,930

### Regarding amplifiers, I repeat "...there is NO...

Regarding amplifiers, I repeat "...there is NO such thing as RMS power...it's AVERAGE power."

The Root-Mean-Square (RMS) mathematics simply converts the peak VOLT or AMP value of a sinusoid to...
6. ## Thread: Amp Wattage Measurement - Approximations

by Old Tele man
Replies
64
Views
1,930

### That value is directly quoted from the GE/RCA...

That value is directly quoted from the GE/RCA 6L6GC datasheets...worked great from them back in the hey-day of vacuum tubes.

For example:

Po ≈ (%)*(Zoo/4)*(gm*|-Vg|)^2

Where GE/RCA Class-AB1...
7. ## Thread: Amp Wattage Measurement - Approximations

by Old Tele man
Replies
64
Views
1,930

### Your assertion *IS* valid when Vg(rms) exactly...

Your assertion *IS* valid when Vg(rms) exactly equals Vg(bias.dc), which rarely happens; typically Vgg/2 is "less than" Vg(dc) by a couple volts, just for "good measure," For example, see GE/RCA data...
8. ## Thread: Amp Wattage Measurement - Approximations

by Old Tele man
Replies
64
Views
1,930

### ...and he (me) also later explains that the DC...

...and he (me) also later explains that the DC bias voltage is assumed to equal the AC(rms) driving signal for estimating Po from the schematic values of Zoo (OT), gm (power tube), and applied BIAS...
9. ## Thread: Amp Wattage Measurement - Approximations

by Old Tele man
Replies
64
Views
1,930

### See this brief paper: ...

See this brief paper: http://thermionic.info/mccaul/McCaul_PhaseInverterDriveVoltage_2008.pdf
10. ## Thread: Everything is better with a tube in it! Lol!

by Old Tele man
Replies
18
Views
631

### Good use for "past-useful-life" tubes...except...

Good use for "past-useful-life" tubes...except those with "open" filaments (ha,ha)!
11. ## Thread: Amp Wattage Measurement - Approximations

by Old Tele man
Replies
64
Views
1,930

### Class-AB1 PP amps do not conduct 360-degrees,...

Class-AB1 PP amps do not conduct 360-degrees, only about 190-205-degrees, or more generally 'slightly more' than 50% of a FULL sinusoid, so referencing a 'pure' sinewave is only valid prior to the PI...
12. ## Thread: Amp Wattage Measurement - Approximations

by Old Tele man
Replies
64
Views
1,930

### First, there is no such thing as WATT(RMS)! ...

First, there is no such thing as WATT(RMS)!

Why? Because RMS is just the mathematical-equivalency operation (0.707*pk) that's applied to the peak value of sinusoidal VOLTS and/or AMPS to convert...
13. ## Thread: Amp Wattage Measurement - Approximations

by Old Tele man
Replies
64
Views
1,930

### No, as Vg is BIAS (DC voltage), not Vgg which is...

No, as Vg is BIAS (DC voltage), not Vgg which is AC peak-to-peak, which I believe you are thinking about.
14. ## Thread: Amp Wattage Measurement - Approximations

by Old Tele man
Replies
64
Views
1,930

### *IF* you're wanting to 'guess-ti-mate' an...

*IF* you're wanting to 'guess-ti-mate' an approximate output power for a Class-AB push-pull amp by simply looking at its schematic, here's an equation:

Po ≈ (%)*(Zoo/4)*(gm*Vg)^2

where:
Po =...
15. ## Thread: Amp Wattage Measurement - Approximations

by Old Tele man
Replies
64
Views
1,930

### Just to add some more mud to the waters: AMPS and...

Just to add some more mud to the waters: AMPS and SPKRS are (unfortunately) spec'd differently, for example, on many Fender schematics, it's 400Hz for bass amps and 1kHz for guitar.
16. ## Thread: Amp Wattage Measurement - Approximations

by Old Tele man
Replies
64
Views
1,930

### Just remember, it's AVERAGE power in Watts, not...

Just remember, it's AVERAGE power in Watts, not RMS power!

Root-Mean-Square (RMS) is merely the mathematical conversion technique that's applied to sinusoidal VOLTAGE and CURRENT to derive their...
17. ## Thread: How to determine fuse rating

by Old Tele man
Replies
16
Views
656

### ..or, we could just slap on some TEMP-IT shipping...

..or, we could just slap on some TEMP-IT shipping stickies, which change colour when their temperature threshold is exceeded.
18. ## Thread: How to determine fuse rating

by Old Tele man
Replies
16
Views
656

### Also, always *inspect* the blown fuse link (clear...

Also, always *inspect* the blown fuse link (clear glass body assumed): if it's *splattered* that indicates a sudden high current load, but if the link is just *sagged* and pulled-apart in the middle...
19. ## Thread: How to determine fuse rating

by Old Tele man
Replies
16
Views
656

### Nice article!

Nice article!
20. ## Thread: Screen Grid Connected to Plate ? Caused Big Hum.

by Old Tele man
Replies
13
Views
616

### ...or, parallel another output tube with the...

...or, parallel another output tube with the original SE tube, but remember input drive (due to lower Z.in) will change.
21. ## Thread: Screen Grid Connected to Plate ? Caused Big Hum.

by Old Tele man
Replies
13
Views
616

### 2W is fine...plate should be catching 90-95% of...

2W is fine...plate should be catching 90-95% of total (ie: cathode) current flow, so unless something else is wrong, screen current should be roughly 5-10% or less than plate current.
22. ## Thread: Screen Grid Connected to Plate ? Caused Big Hum.

by Old Tele man
Replies
13
Views
616

### Try inserting a 100 ohm resistor between the...

Try inserting a 100 ohm resistor between the screen and plate and verify the hum isn't coming through a bad/weak filter capacitor.
23. ## Thread: question about capacitance and gate drive in power mosfets at high frequencies

by Old Tele man
Replies
8
Views
561

### Analog analogy: think about "slew-rate" of...

Analog analogy: think about "slew-rate" of signals through capacitors.
24. ## Thread: Output Transformer driven hard, What does I sound Like ?

by Old Tele man
Replies
23
Views
995

### Pushed" OT's do not handle squarewaves (grossly...

Pushed" OT's do not handle squarewaves (grossly over-driven sinewaves) anywhere as they do for true sinusoidal waves, which is what they're designed to handle. Note that a true squarewave/pulse...
25. ## Thread: Gretsch (Valco) 6156 - Phase Invertor, What is it ?

by Old Tele man
Replies
12
Views
705

### On that Gretsch_G6156 schematic, did you notice...

On that Gretsch_G6156 schematic, did you notice that the right-half triode of the 6SC7 has NO cathode connection -- nothing connecting the two cathodes together. Obviously a drawing error, or the amp...
26. ## Thread: Pentode Reverb Driver Part II: subminiaturization of the stand-alone reverb and preamp

by Old Tele man
Replies
9
Views
719

### Interesting, but I wonder about lack of EMI...

Interesting, but I wonder about lack of EMI shielding with that plastic case since the old (original) models had metal case which served as shield against EMI.
27. ## Thread: New production Brimar tubes (valves?)

by Old Tele man
Replies
14
Views
1,604

### I'll guess the packaging co\$ts more than the...

I'll guess the packaging co\$ts more than the actual tube/valve does.
28. ## Thread: EL34 cathode biased question

by Old Tele man
Replies
9
Views
848

### A single, common, cathode resistor "smooths-out"...

A single, common, cathode resistor "smooths-out" possible conduction differences between the banked tubes (think "mean" value here), while separate cathode resistors can be individually...
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