Fender SR2035 Vibrolux Reverb Solid State Service Info

[cjlectronics]

A friend is selling some of his collection of amps and tubes and this amplifier is one of them. It is dead with no power and I can't find any service info on it. The speakers are dated 1969. It has a 2 prong power cord (which I will replace with a 3 prong) and the fuse is blown. Does anyone have a service manual for this? There is very little info on the WWW, hopefully someone will breakout their stash of info.

TIA!!

CJ

[loudthud]

A 5A fuse has got to be just inline with the speaker. First thing to check is the circuit breaker. Then replace fuse and see if the amp powers up with a light bulb limiter (no speaker connected). Internally the power rail is probably less than 50V.

[52 Bill]

There is a second fuse just out of frame to the left that is the ac power fuse. The 5 amp one on the right is as LT mentioned is a speaker fuse.

These amps are similar to the Thomas Organ Vox and very early Kustoms, with a transformer phase inverter output stage. Blown fuses are typically caused by shorted rectifiers or output devices.

There are some schematics out there, but not all that many. I'll dig through some of my old files and see if I have anything.

[loudthud]

Virtually nothing comes up on Google.

Check this thread: https://music-electronics-forum.com/...matics?t=34647

Here's one thing I found in that thread that might be close:

Fender SS Vibrolux Reverb Power Amp Schematic.pdf

[Jon Snell]

How quaint and old fashioned.
If it were mine, I would look for obvious semiconductor failures and smoothing capacitor issues before even powering it up, fit a 3 prong lead and mains plug throwing away C10, the death cap, in an attempt to make it safe.
A very simple amplifier and if the issues are in the output stage, I would seriously consider removing CR3 & CR4, for peace of ming in the future, however R9 & R11 do limit the Base current and that might mitigate a total disaster.

[J M Fahey]

CR3 and CR4 are needed, emitter resistors are full 2 ohm, not 0.2 ohm as you might assume.

Removing bypass diodes will require reducing ballast resistors to 0.33 or 0.47 ohm, worsening thermal stability.

[cjlectronics]

UPDATE: The schematics for this amplifier are attached. TY to loudthud for the link to the power amp and in the same thread is the PREAMP schematic for this amplifier. The PREAMP and PWR AMP schematics are 99% correct. The problem with the blown fuse was unknown. I replaced it, the power cord, and the unit powered up. However, the dual 500uf cap was very leaky. Replaced it and this cleaned up the power rail. The next problem was the output was very farty and distorted. Traced the problem to a leaky 5uf capacitor at the input to the power amp. After this, the amp works and surprisingly is VERY loud and sounds really cool. I will continue to replace many bad electrolytic caps, especially in the VIBRATO circuit. The Light is on but not oscillating and I'll start with replacing capacitors (see the Preamp schematic). Hope this helps someone else and TY to all that replied!

Fender SS Preamp Schematic.pdf
Fender SS Vibrolux Reverb Power Amp Schematic.pdf

CJ

[loudthud]

vintagekiki deserves all the credit. His Fender schematic thread is where I found those schematics. Link: https://music-electronics-forum.com/...der-schematics

I just had to go through several pages to find them. It's a long thread.

I wish there was more info available on the Solid State Fender amps of that era, collected in one place. What amps were available, any significant variations or tweeks ? Do any of them have the usual FMV tone stack ? I remember there were some Rhodes pianos with solid state power amps built-in to those "suitcase" speaker cabinets. Were they the same or completely different ?

[vintagekiki]

https://music-electronics-forum.com/forum/schematic-requests/35547-more-older-fender-amp-schematics-guitar-wiring-diagrams-etc
More Older Fender Amp Schematics, Guitar Wiring Diagrams, etc.

https://music-electronics-forum.com/forum/schematic-requests/35546-fender-early-70-s-solid-state-amp-schematics
Fender Early 70's Solid-State Amp Schematics

https://www.tdpri.com/threads/fender-zodiac-amps.170408/
Fender Zodiac Amps

https://www.offsetguitars.com/forums/viewtopic.php?t=65513
Amp Repair Issues (But mostly just a Fender Libra pic-bomb)