Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Misc Schematics and Layouts => Topic started by: Markbou on March 10, 2025, 02:50:20 pm

Title: 1968 Fender Silverface Bandmaster (Fender_bandmaster_aa763_layout.pdf)
Post by: Markbou on March 10, 2025, 02:50:20 pm

Hello~

I’m in a situation and was hoping to get some guidance with it.

I have my uncle’s ’68 Silverface Bandmaster (Fender_bandmaster_aa763_layout.pdf, https://el34world.com/charts/Schematics/files/Fender/Fender_bandmaster_aa763_layout.pdf).  I went through it replacing most of the electrolytic caps and some resistors.  When I finished, the amp sounded great.  I took it back to him and mentioned that the tremolo channel wasn’t working and asked if he wanted me to replace the optocoupler.  He said yes, even though he never uses that channel, so I ordered a replacement roach and installed it.  Didn’t work.  I reported my results to him and he said no problem, so I left it as is and gave it back.

A week later, he told me the sound was distorted and the amp sounded terrible.

I took it back and the mistake I made was to cut the entire optocoupler out.  Now the amp plays nice and clean now, but the volume is very, very low.  I suspect I took one or more of the gain stages out of the signal loop.

What I was hoping to find out was if I should have only cut one of the leads to the neon bulb to keep the signal flowing into the remaining gain stages. Or possibly, if someone knows another way to install another component or two, or manipulate the roach in some other way that would enable the overall circuit to run properly even though the tremolo channel won’t be used.

Thanks in advance!

Title: Re: 1968 Fender Silverface Bandmaster (Fender_bandmaster_aa763_layout.pdf)
Post by: mresistor on March 10, 2025, 06:19:32 pm

Well the replies just disappeared.  What the heck.


Is the normal channel working properly?


It's unclear is there a tremolo roach presently installed? And the vibrato channel is clear and clean  but low valume.  I believe if you don't have a shorting plug or a footswitch connected to the footwitch jack on the back the tremolo will be off.  The rest of the vibrato channel should then be working just fine.


If you disconnect the yellow wire from the right side terminal of the intensity pot does then vibrato channel work normally?