PA135

[joesatch]

turn this into a 4 channel head? each channel with it's own tonestack, gain & master? Should i do it?

[Willabe]

I've seen posts where guys have done that. They said they ended up sounding very good. The iron set should be very heavy duty.

As you know, it's gonna be very heavy. 

[shooter]

ok, i'm missing something obvious, isn't it already a 4 channel head?

[joesatch]

ok, i'm missing something obvious, isn't it already a 4 channel head?

ya but it's a PA. so each channel has a separate input. I want to make a guitar head with 4 channels, Ex. Fender Clean,Vox Dirt,Marshall Plexi, Slo high gain

[shooter]

then my "suggestion" leave the inputs as they are for now, mod CH1 to "your tone", once you smile, move to next channel...Then worry about mux'ing them through your "channel selector" after each is where you want it.


the dave logic;
most PA's i've worked on have good "channel" isolation/separation already there, if you mux them 1st then try and mod each, you may be  unleashing gremlins into adjacent channels

[joesatch]

then my "suggestion" leave the inputs as they are for now, mod CH1 to "your tone", once you smile, move to next channel...Then worry about mux'ing them through your "channel selector" after each is where you want it.


the dave logic;
most PA's i've worked on have good "channel" isolation/separation already there, if you mux them 1st then try and mod each, you may be  unleashing gremlins into adjacent channels

nah. the front panel channels each  have 5 holes so pre,master, treble, middle ,bass for each channel. I'll switch channels internally with relays. two pots on the face at the far right will be master presence and depth or master volume and depth.  we'll see

[AlNewman]

That's a tall order.

You do have an extra triode by the looks of it.

https://el34world.com/charts/Schematics/files/Fender/Fender_pa135.pdf

[mresistor]

I don't see a non-used triode section. 

[shooter]

didn't either but it's brain-frying hot n humid so there's that.




have you modeled the current/as built TS vs your "new" version

[Carlsoti]

These CAN sound good, but I think the "4 different voicing" thing will be a bit of a challenge. Basically, each channel will only have 2 independent gain stages. As they are configured stock, all the controls are in between those gain stages, which might be fine for one voice, but fall apart for another. Also, that power amp is going to be LOUD and likely pretty clean, which may make it difficult to coax the PI/ power amp OD/distortions that contribute to the different FMV tones.

[mresistor]

Maybe gut it and make a new board.  Make it three channels.  On channel with two triodes and two channels with three triodes. 

[shooter]

one of the lessons I've learned here, re-inventing a wheel leads you to the original design of the wheel 

[tdvt]

one of the lessons I've learned here, re-inventing a wheel leads you to the original design of the wheel 

So true

[joesatch]

It's definitely a gut out situation. Gain stages can be shared and switched in/out for the various channels. I've done this before on a smaller scale with a 2 channel preamp ch1 Friedman BE and channel 2 SLO. This is not as difficult as it sounds. Will require probably a dozen relays to mute sections,switch component values and route the signal path. totally dooable

[AlNewman]

I don't see a non-used triode section.

You're right, for some reason i missed one half of v4 when I was looking at it.

[joesatch]

The PT has the HV secondary with a center tap which is grounded but also uses a FWB which is grounded. I thought that was a no no? unless it's just for the bias wind?

[pdf64]

Look again.
The CT isn't grounded.

[mresistor]

Joe look at the winding above the HV winding  it's labeled BN  what is that for?

[sluckey]

Joe look at the winding above the HV winding  it's labeled BN  what is that for?

bias

[mresistor]

Joe look at the winding above the HV winding  it's labeled BN  what is that for?

bias

yup  but you're not Joe

[sluckey]

sorry

[fossilshark]

Needs a switch that cascades all 4 channels for a "Jose" modded fender 

[jeff]

The PT has the HV secondary with a center tap which is grounded but also uses a FWB which is grounded. I thought that was a no no? unless it's just for the bias wind?

That is a no no, but the C.T. isn't grounded, it's sitting in the middle of the caps/100K resistors.
You can use this configuration to get a +/- voltage buy grounding the C.T.
OR
What Fender's doing, ground the - for twice the voltage.


C.T. is at 1/2 B+

[DummyLoad]

Leave it as is? They are a great vocal and pedal steel amp as is. Give it a try as such, of course refresh the electrolytic caps first.

--Pete