How would frequency response be altered by using 1 mF coupling capacitors from plates to grids instead of the usual .05, .1 or .47 ....etc.? Would this totally ruin the high frequencies or only slightly? I really like room shaking bass but would this make the sound all muffled?Thanks for any info.

You won't loose the highs the caps will pass em
MRO

:How would frequency response be altered by using 1 mF coupling capacitors from plates to grids instead of the usual .05, .1 or .47 ....etc.? Would this totally ruin the high frequencies or only slightly? I really like room shaking bass but would this make the sound all muffled?Thanks for any info.
:

:You won't loose the highs the caps will pass em
:MRO
:
::How would frequency response be altered by using 1 mF coupling capacitors from plates to grids instead of the usual .05, .1 or .47 ....etc.? Would this totally ruin the high frequencies or only slightly? I really like room shaking bass but would this make the sound all muffled?Thanks for any info.
::Thanks Mark!
:

A capacitor of any size passes less as you go down in frequency, and an inductor passes less as you go up in frequency. The size of the capacitor or inductor determines where the slope will fall. Only capacitors block DC, so don't get any ideas to replace the capacitors with inductors, though if you could, this would chop off the highs. ...But to elaborate on what was said, increasing the capacitor's size won't affect the highest frequencies, but will increase the lower ones.

Depending on the radio, you may have bad luck with increasing the capacitor size. There are some frequencies that the speaker might not reproduce that would still overload the amplifier, and so instead of increasing the bass you wind up with a radio amplifier that bogs down and distorts at high volumes. If you make the capacitances large enough, the mere shifting of the AVC voltage might drive the amplifier into saturation. Increase the capacitances in small amounts. Increase a .02 MFD cap to perhaps a .05 or .1 MFD cap. Depending on the circuit, you can also increase the grid or plate resistances, which will increase the bass, and this still might increase the bass into the super low and unusable region, but not necessarily as much. Don't get carried away with increasing resistances, as there are definite limits.

You will have better luck with big powerful radios than with small ones, though be careful, too, to not overload a big and powerful amplifier.

With my portable Zeniths they use small value bypass capacitors and high resistances, and then put a tone mellowing capacitor across the output's plate circuit. This makes for a very high gain amplifier, and gives the illusion of a warm and mellow sound, even though the amplifier can't actually handle large amounts of bass. In my first attempt in repairing one of these radios I increased the values of the bypass caps, and converted the radio from strong and capable of loud volumes even with the weakest signals to a distorted mess that'd block out everytime the volume was turned up.

T.

:A capacitor of any size passes less as you go down in frequency, and an inductor passes less as you go up in frequency. The size of the capacitor or inductor determines where the slope will fall. Only capacitors block DC, so don't get any ideas to replace the capacitors with inductors, though if you could, this would chop off the highs. ...But to elaborate on what was said, increasing the capacitor's size won't affect the highest frequencies, but will increase the lower ones.
:
:Depending on the radio, you may have bad luck with increasing the capacitor size. There are some frequencies that the speaker might not reproduce that would still overload the amplifier, and so instead of increasing the bass you wind up with a radio amplifier that bogs down and distorts at high volumes. If you make the capacitances large enough, the mere shifting of the AVC voltage might drive the amplifier into saturation. Increase the capacitances in small amounts. Increase a .02 MFD cap to perhaps a .05 or .1 MFD cap. Depending on the circuit, you can also increase the grid or plate resistances, which will increase the bass, and this still might increase the bass into the super low and unusable region, but not necessarily as much. Don't get carried away with increasing resistances, as there are definite limits.
:
:You will have better luck with big powerful radios than with small ones, though be careful, too, to not overload a big and powerful amplifier.
:
:With my portable Zeniths they use small value bypass capacitors and high resistances, and then put a tone mellowing capacitor across the output's plate circuit. This makes for a very high gain amplifier, and gives the illusion of a warm and mellow sound, even though the amplifier can't actually handle large amounts of bass. In my first attempt in repairing one of these radios I increased the values of the bypass caps, and converted the radio from strong and capable of loud volumes even with the weakest signals to a distorted mess that'd block out everytime the volume was turned up.
:
:T.
:Why does increasing the plate or grid resistors increase the bass response?Is it because it allows more signal to the capacitor?If you increase the plate resistor would this not decrease the plate voltage making the amp have less gain.I don't understand this.

::Why does increasing the plate or grid resistors increase the bass response?Is it because it allows more signal to the capacitor?If you increase the plate resistor would this not decrease the plate voltage making the amp have less gain.I don't understand this.
:
The coupling capacitor is feeding the grid of the next stage. The grid has a resistor to ground to reference it for cathode bias.

That resistor in combination with the coupling capacitor form a high pass filter.
the formula for which is 1/2pi F R
( 1/ 6.28 x F x R

"High-pass filters have a rated cutoff frequency, above which the output voltage increases above 70.7% of the input voltage. Just as in the case of the capacitive low-pass filter circuit, the capacitive high-pass filter's cutoff frequency can be found with the same formula:

In the example circuit, there is no resistance other than the load resistor, so that is the value for R in the formula. "

More info:
http://www.play-hookey.com/ac_theory/hi_pass_filters.html

Here's a typical example:
If as an example you have a .1uf cap in series with a 4.7k resistor feeding into a grid that has a 220k resistor to ground:

The 0.1 uf cap feeding the grids is a high pass filter (and as long as the grids don't draw current) the effective resistance is 220k + 4.7k so the cutoff freq is 1/(2*PI*(0.1uf*224.7k)) or 7 Hz.

In a typical AA5 radio you will see a .01uf coupling cap from the plate of the 12sq7 feeding into a 470k resistor on the grid of the 50L6 output amplifier.

Now ...using the formula 1 / (2pi * F * R) will show a cutoff freq of 33hz.

Increasing that coupling cap from .01uf to .1uf will lower the cutoff freq from 33hz down to 3.3hz

The difference will hardly be noticeable unless the speaker and your ears can both detect frequencies down there between 3hz and 30hz.

Here's cool on-line calculator to experiment with. Makes the math headaches go away.
http://www.muzique.com/schem/filter.htm

I like that!

...Actually we learned that formula in class, but I forgot it.

T.

Regarding bass response and gain, if you increase the value of the plate resistor of the 1st AF tube, the gain will go up to a degree. The tube and resistor are in series. The larger the resistance in series with the tube, the more effect the tube has on voltage changes across the resistor. These voltage changes are sent through the capacitor to the next stage. There is a degree at which the resistance is so great that the tube can no longer function normally, which is why increasing the resistance won't always increase the gain.

Increasing the grid leak resistance of the next stage will also increase gain because you are reducing the load imposed upon the capacitor that's feeding the grid.

Increasing either plate or grid resistance will increase bass response because you are changing the time factor of the circuit. A lower resistance will discharge the capacitor more quickly. A higher resistance will do so less quickly. If the capacitor discharges too quickly when a very slow voltage change is imposed upon it, the capacitor will have discharged in a direction opposite the change's polarity before the signal has even completed its cycle. The two will null eachother and nothing will result--little or no bass. In the other extreme, if the capacitor isn't discharged fast enough, voltage will build up on it and block the amplifier from functioning. This is done purposely in grid leak detectors. The positive portion of a wave is cancelled out since if the grid goes positive it becomes a plate, and current flows between it and the cathode. However, when the negative half of the wave hits the grid, it can't flow, and instead builds up in the capacitor. The grid leak is of such a value that enough of the negative charge remains in the capacitor so that when the next positive wave hits, the negative charge isn't completely absorbed. This repeats itself with each cycle until a significant negative charge builds up to a predetermined level (set by the resistor's value). This negative charge causes the grid to rectify and 'detect' the signal--cutting off one half so that the audio information riding in its amplitude can be utilized. This situation is undesirable in audio amplifiers, because you don't want to rectify the audio signal. You will wind up with a distorted mess, or if the grid becomes negative enough, you'll wind up with nothing. 1st audio tubes often utilize the grid leak circuit, but the leak is set to such a value that the signal ordinarily cannot drive the tube's grid positive or so negative that the tube cuts out. The range is maintained in the linear region.

Regarding a plate resistor's affect on bass, it, too, affects the rate at which the capacitor returns to a 'neutral' state, when the tube isn't manipulating the circuit, and so if the resistor is too small, the capacitor will be discharged too quickly, and won't be able to build up a charge from a slow, long wave (bass).

T.

:Regarding bass response and gain, if you increase the value of the plate resistor of the 1st AF tube, the gain will go up to a degree. The tube and resistor are in series. The larger the resistance in series with the tube, the more effect the tube has on voltage changes across the resistor. These voltage changes are sent through the capacitor to the next stage. There is a degree at which the resistance is so great that the tube can no longer function normally, which is why increasing the resistance won't always increase the gain.
:
:Increasing the grid leak resistance of the next stage will also increase gain because you are reducing the load imposed upon the capacitor that's feeding the grid.
:
:Increasing either plate or grid resistance will increase bass response because you are changing the time factor of the circuit. A lower resistance will discharge the capacitor more quickly. A higher resistance will do so less quickly. If the capacitor discharges too quickly when a very slow voltage change is imposed upon it, the capacitor will have discharged in a direction opposite the change's polarity before the signal has even completed its cycle. The two will null eachother and nothing will result--little or no bass. In the other extreme, if the capacitor isn't discharged fast enough, voltage will build up on it and block the amplifier from functioning. This is done purposely in grid leak detectors. The positive portion of a wave is cancelled out since if the grid goes positive it becomes a plate, and current flows between it and the cathode. However, when the negative half of the wave hits the grid, it can't flow, and instead builds up in the capacitor. The grid leak is of such a value that enough of the negative charge remains in the capacitor so that when the next positive wave hits, the negative charge isn't completely absorbed. This repeats itself with each cycle until a significant negative charge builds up to a predetermined level (set by the resistor's value). This negative charge causes the grid to rectify and 'detect' the signal--cutting off one half so that the audio information riding in its amplitude can be utilized. This situation is undesirable in audio amplifiers, because you don't want to rectify the audio signal. You will wind up with a distorted mess, or if the grid becomes negative enough, you'll wind up with nothing. 1st audio tubes often utilize the grid leak circuit, but the leak is set to such a value that the signal ordinarily cannot drive the tube's grid positive or so negative that the tube cuts out. The range is maintained in the linear region.
:
:Regarding a plate resistor's affect on bass, it, too, affects the rate at which the capacitor returns to a 'neutral' state, when the tube isn't manipulating the circuit, and so if the resistor is too small, the capacitor will be discharged too quickly, and won't be able to build up a charge from a slow, long wave (bass).
:
:T.
:Thankyou Peter and Thomas for that info!!This is really quite interesting and exciting.