Alamo 2570 tremolo too fast

[66merc]

Simple question--the tremolo on this Alamo amp is too fast.  Which caps do I change to slow it down?  Tons of info out there on how to do this on old Fender amps, but nothing on cheap amps from San Antonio.  I'm guessing it would be the .22 caps near the speed pot--but only a guess.

Really is a cool amp and, even with the solid state front end, sounds great.  I can post a pic of the amp soon, but it's snowing and the amp is in the backyard studio shed!



Appreciate any info.

[Raybob]

Not quite sure what this has to do with "Tube Amp Building", which you posted this in..   

[66merc]

Well, Raybob, I realize this is a hybrid tube amp and the question is about the solid state front end, but I've always found the members here to be informative and helpful.  I have no doubt that someone will be able to point me in the right direction.  The 6v6 power section through the two 10's really does sound good, but the speed of the tremolo, even at lowest setting, is quite rapid.

[sluckey]

Increase the size of one or both of these caps. I'd try .47µF for starters. See pic...

[66merc]

Thanks much, Sluckey.  I'll give it a try. 

Gosh, this may actually get me motivated to finish up all those half finished chassis that are gathering dust on the bench!

[eleventeen]

Unusual amp, that's for sure.

Around Q4, clearly the trem oscillator ("speed" control) you see the characteristic 3 caps in series, making a phase-shift oscillator. Your suspicion is correct, one or more of those .22 caps forming the feedback look from collector to base have to be fattened up. It doesn't especially matter which one or which ones. They probably want to be non-polarized caps. Fortunately, they don't need the big voltage rating. Probably 100 volt ones would be fine. Without voltage readings on the transistors it's not entirely clear but I can't imagine any kind of volts on that Q.

[PRR]

This is a C-R-C-R-C-R network, three caps.

Ideally all three caps (the 0.22, including the one squarshed against the collector).

For small changes it works to just bump one or two caps. If you want to go down a lot, it may stall unless you do all three.

[sluckey]

Without voltage readings on the transistors it's not entirely clear but I can't imagine any kind of volts on that Q.

The filter cap for that B+ node is 47µF @ 25V.

[66merc]

Thanks again, folks.  I'm lazy so I think I'll try the one-cap-at-a-time approach.

[sluckey]

I was gonna mention the third cap but I felt pretty sure changing one of the caps I circled would get you where you wanna be. Here's a very similar circuit I built for a Twin Reverb back in the early '70s. It goes from verrrrry slow to plenty fast. Notice the switch for two speed ranges...