Loss of memory - Do you remember the Split Load Plate Resistor Mod ??

[kagliostro]

I'm sure some (many) time ago here we were discussing about a particular mod that uses a Split Load Resistor as plate resistor

The signal for the next stage was taken from the node between the two resistors

Someone remember how acts this thing and which results it gives ?

Do you remember the old tread ? Have you a link for it ?

Thanks

K

[TIMBO]

Hi K, Is this what you are refiring to  http://www.valvewizard.co.uk/dccf.html bottom of page

[kagliostro]

Ciao TIMBO

and ...... no, isn't that

however the link is interesting ()

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As far as I can remember the mod consisted only in a split load plate resistor feeding the next stage

what I don't remember is how this acts on the tone and response of the amp

K

EDIT: I've just find this file in my archive

http://www.el34world.com/Forum/index.php?action=dlattach;topic=16354.0;attach=40088

However I would like to know your opinion about and if possible re read the old tread

[sluckey]

I can almost remember that thread. I want to say the guy was even thinking about using a switch to select signal directly from the plate or from the junction of the split load.

The Fender 6G15 Reverb uses a split load...  http://www.el34world.com/charts/Schematics/files/fender/REVERB_6G15.pdf

I used a pot (variable split load) in my warbler... http://home.comcast.net/~seluckey/amps/warbler/warbler_rev2.pdf

I've seen a few other amps that used a split load but I can't quickly recall which ones. The goal always seemed to be about reducing the signal that feeds the next stage. A simple volume control does the same.

[kagliostro]

A simple volume control does the same

that is the question

reading the pdf I posted seems that the use of a split load plate resistor

has some advantages respect the use of a voltage divider or pot

K

[sluckey]

A split load plate resistor is a voltage divider or pot.

I just noticed that all of the Fender 6Gxx amps with the harmonic vibrator circuit use a split load plate resistor.

[kagliostro]

I just noticed that all of the Fender 6Gxx amps with the harmonic vibrator circuit use a split load plate resistor.

It will be interesting to know why they did this choice

K

[sluckey]

Look at this schematic for reference... http://www.el34world.com/charts/Schematics/files/fender/concert_6g12a_schem.pdf

Look first at the NORMAL channel preamp. You'll see a typical Fender two stage preamp. The output of that preamp connects directly to the input to the PI.

Now look at the VIBRATO channel preamp. You'll see an identical two stage preamp. But the output of that preamp does not go directly to the input of the PI. Instead, it goes to another 7025 tube whose purpose is to modulate the guitar signal with the tremolo effect. That tube also has gain. The output of this 'modulator' tube is then sent to the input of the PI. This signal would be much hotter than the signal from the NORMAL channel due to the extra gain from the modulator tube. So, a split load plate resistor is used on the second preamp stage to knock down the signal level. The net result is that the signal from the VIBRATO channel will be about equal to the signal from the NORMAL channel when the two channels are mixed together and applied to the input of the PI.

[12AX7]

I find it a lot different than a volume pot. For one thing it doesn't cut high end like a pot does, requiring a treble bleed cap to retain highs. It doesn't seem to change tone at all aside from the fact theres less gain which of course makes it hard to tell if it does because turning up a gain pot to the same level to compare put's the pot's tonal change into the equasion ever with a treble bleed. (because no TB will perfectly keep tone exactly the same)

In any case, i find it the best way to reduce gain with no side effects.

[jjasilli]

Checkout:  http://www.blueguitar.org/new/articles/blue_gtr/amps/bp010629.pdf   http://www.ax84.com/bbs/dm.php?thread=297726

I suspect the older Fender amps used the split load to keep the signal clean. Overdrive has since become a "feature" rather than a "bug".  You can set your operating point to get a distorted waveform, basically the result of "too much" gain causing clipping and/or saturation; then divide away excess signal voltage with the split plate load circuit.  Another arrow in the quiver, instead of a voltage divider downstream.  Also, the split load uses one less resistor (than does a downstream voltage divider) and is a simpler circuit with less reactance in the overall LC network which couples preamp stages.

[DummyLoad]

early vibroverb 6G16 ckt. used a split load. interesting to note that the gain stage with split load also shared cathode source with another gain stage for the other "clean" channel.

http://www.el34world.com/charts/Schematics/files/fender/vibroverb_6g16_schem.pdf

--pete

[jojokeo]

I find it a lot different than a volume pot. For one thing it doesn't cut high end like a pot does, requiring a treble bleed cap to retain highs. It doesn't seem to change tone at all aside from the fact theres less gain which of course makes it hard to tell if it does because turning up a gain pot to the same level to compare put's the pot's tonal change into the equasion ever with a treble bleed. (because no TB will perfectly keep tone exactly the same)

In any case, i find it the best way to reduce gain with no side effects.

Another benefit is that it also lowers the output impedance of that stage