fender 75 lead channel remove help

[MatGir]

Hi
Yesterday i've got a fender 75 for free without the pedal. Amp is working-ishh but master level is either on or off and reverb is always at the same setting no matter where the pot is. part of this trouble is due to the pedal not connected since i don't have it. Anyway, i just  want the lead channel completely gone. If i remove what ive highlighted and/or circled on the schematic, i should be fine. anything i've ben missing ?
- Is the 0.01 cap next to the lead master must stay ?
- The two 1.5M resistor next to V2B stay too ?
- Once removed, can i use the V3B to copy the AB763 reverb circuit ( i want to add dwell and tone control on the reverb by replacing the two pot for the lead channel) ?

regards
Mat
I'm fairly new to tube amp modding/building and want to learn, that's why i'll not refuse any input on this. thanks.

[Latole]

In my opinion, and for all Fenders, no pedal is required to operate the reverb or master volume.
Would this one be different?

It's a very difficult amplifier to repair, even for pros.

One forum's member modify one ; https://el34world.com/Forum/index.php?topic=17906.0

[pdf64]

...
I'm fairly new to tube amp modding/building and want to learn ...

This isn't a suitable amp for a noob to attempt extensive mods on.

The missing pedal isn't why the reverb isn't working, so why not get that fixed first?

Then make a pedal or just a couple of jack plugs with the necessary lugs shorted, so that you can get the amp into the mode you want?

It's a complex design and an absolute rats nest of white wires in there, it'll be very easy to go in beyond your depth and mess things up.

As it stands, your plan will mess up the 15W setting.

[MatGir]

since i got it for free, i tought i'll learn trought it...
i've found that for the foot switch: https://www.stratopastor.org.uk/strato/amps/prii/footswitch/footswitch.html.

Here the principal problem i have: master volume pot goes from no sound to full blast on 2
reverb is weak and always on with pot non working. even on lead "channel".

As far as i know the lead "channel" is just a boost.

is it a better idea to strip everything an rebuild a AB763 super reverb circuit out of it ? On the link posted by Latole, Blues man seam to have done exactly that....

[pdf64]

since i got it for free, i tought i'll learn trought it...
i've found that for the foot switch: https://www.stratopastor.org.uk/strato/amps/prii/footswitch/footswitch.html.

Here the principal problem i have: master volume pot goes from no sound to full blast on 2
reverb is weak and always on with pot non working. even on lead "channel".

Without the pedal, the amp isnt in normal or lead mode.
That's probably why you're finding at least some of these issues. Hence my suggestions.

As far as i know the lead "channel" is just a boost.

Yes, but that's not usual.

is it a better idea to strip everything an rebuild a AB763 super reverb circuit out of it ? On the link posted by Latole, Blues man seam to have done exactly that....

There's a few differences that make it non trivial to do that.

The key skills you need is to learn how valve circuits work, and how to fault find and fix them when they're wonky.

It's kinda unlikely that if you rebuild it into something else, it'll work perfectly first time. So I suggest you build your skills base first, before considering attempting a big project.

[Ronquest]

is it a better idea to strip everything an rebuild a AB763 super reverb circuit out of it ?

The best way to learn is fix what is wrong with this amp.  Like pdf64 said, fix the reverb, jacks, and sort out the amp as it sits first.  Then if you feel the need to mod....

If ALL you want is a AB763 build then you may be better off selling this amp, but you're missing out on a great amp. 

The desire to remove the lead channel parts is IMO not getting you anything other than no way of having a lead channel in the future for you or the next owner.  The lead channel gets some crap on the net, but it's another flavor that can be fantastic on it's own.  Less gain on the lead knob = more better.

[Ronquest]

since i got it for free, i tought i'll learn trought it...
i've found that for the foot switch: https://www.stratopastor.org.uk/strato/amps/prii/footswitch/footswitch.html.

Here the principal problem i have: master volume pot goes from no sound to full blast on 2
reverb is weak and always on with pot non working. even on lead "channel".

Without the pedal, the amp isnt in normal or lead mode.
That's probably why you're finding at least some of these issues. Hence my suggestions.

This!!  Circuit is wonky without pedal.

[Latole]

 " Here the principal problem i have: master volume pot goes from no sound to full blast on 2 "

Did you disconnect pot and read resistors with wiper from 0 to 10 ?

[Latole]

The footswitch;  from slukey. ; https://el34world.com/Forum/index.php?topic=17980.0


http://www.stratopastor.org.uk/strato/amps/prii/footswitch/footswitch.html

Amps using this footswitch
Princeton Reverb II*
Super Champ * (see Super Champ page for amp schematics and much more)
Concert (112, 210, 410, and Top (Top = separate amp head)) **
Twin Reverb II **
  Deluxe Reverb II **
Fender 75

[pdf64]

" Here the principal problem i have: master volume pot goes from no sound to full blast on 2 "

Did you disconnect pot and read resistors with wiper from 0 to 10 ?

Without the pedal attached, the lead gain control will be engaged but the lead master won't.
So anything above 1 on the lead control will have a boosted gain over the expected normal level.

[MatGir]

" Here the principal problem i have: master volume pot goes from no sound to full blast on 2 "

Did you disconnect pot and read resistors with wiper from 0 to 10 ?

Not yet. I'll do this on the reverb pot too before making a pedal for this amp to works as it should

[MatGir]

The footswitch;  from slukey. ; https://el34world.com/Forum/index.php?topic=17980.0


http://www.stratopastor.org.uk/strato/amps/prii/footswitch/footswitch.html

Amps using this footswitch
Princeton Reverb II*
Super Champ * (see Super Champ page for amp schematics and much more)
Concert (112, 210, 410, and Top (Top = separate amp head)) **
Twin Reverb II **
  Deluxe Reverb II **
Fender 75

That's exactly what i was looking for. Thanks a lot.

[MatGir]

Part are ordered for the pedal. maybe all my problem reside in the fact that i didn't have the pedal for the amp....
i've take a few minute to design and a few hour to print a custom enclosure for the pedal. Now is the long waiting for parts....


regards
Mat

[Latole]

Before making a pedal, you should simulate it with jacks ( or pieces of wire ) as mentioned by pdf64.
This will confirm what works and what doesn't.

Because in the event of several irreparable problems, you won't be stuck with a useless pedal.

[MatGir]

Hi to all,
I must emphasis on the fact that those amp must have the proper footswitch to work as intended. I've built the pedal according to the shematic you provided me and the amp work now perfectly. So without the footswitch, reverb, lead volume, lead master and master volume pot are all non fonctional and/or jerky. For posterity, be sure to have the footswitch with the amp. The previous owner didnt have the footswitch and tought the amp was broken. i've got it for free and build the footswitch for it and TADAM.... the amp is back to life.

For the tone, i must say that i'm very impressed by the amp. Cleans are stellar, reverb add brightness  and the tone stack pots interract with each other. Dial everything at 5 and goes from there. For the lead channel, it was designed as a boost so use it that way. Low gain and low lead master is the key. i must say that i prefer my dirtbox for overdrive sound than the one on the amp.

It's a great clean platform for pedal use, with a LOT of headroom and one of the best reverb fender has ever made.  The reverb is usefull from 1 to 10 without being overly surfy. I just love it. Tone pot are very sensitive but good tone are defenitly there. For the push-pull pot boost thing, it's not great at all. it's just too much... don't bother trying to used them...

I'will not modified this amp further for the moment so consider this thread as closed. i'will just enjoy the great fender clean tones from that amp that cost me 23$ CDN for the footswitch part. Thanks you so much guys for your help ! I had login issues so i could'nt post last week so i played the amp thoughoutly and Doug help me with the login issues...

regards
Mat

[Latole]

Congratulations on your work.

I had never seen or heard of an amp that required the F.S. to work like this Fender. You learn something new every day.