FBT 500R Reverb and Tremolo on Both Channels?

[dankinzelman]

Hi,

Can I modify this circuit to connect reverb and tremolo to both channels?

Is there some kind of modification I can make so that activating the tremolo while playing does not cause a huge THUMP?

Also, how do you suggest I regulate the trim pots 'INTENSITY VOLUME' and 'INTENSITY REVERBERATION'? My understanding is that they set the input impedance of the following stages and so essentially allow me to trim how hard I am driving respective grids, right? So should I just use my taste in terms of how much gain and distortion I want, or is there a safe/proper way to set them?

[Willabe]

I just saw that the verb schematic is there if you scroll down to it.

Also, how do you suggest I regulate the trim pots 'INTENSITY VOLUME' and 'INTENSITY REVERBERATION'? My understanding is that they set the input impedance of the following stages and so essentially allow me to trim how hard I am driving respective grids, right? So should I just use my taste in terms of how much gain and distortion I want, or is there a safe/proper way to set them?

Those are there to balance the dry signal with the verb signal and to not over drive the effects channel. Int. verb is how hard you drive the verb tank and int. vol. is how loud the dry signal.

If you think the effects channel is too hot, distorts to early, try turning the int. vol. down. You can probably turn the int. verb up pretty high to drive the tank, it's a dwell control. Then you control the amount of verb by just using the verb pot. 

Just play with them a little until you get a good balance and good sound. 

Can I modify this circuit to connect reverb and tremolo to both channels?

Why? What do you need verb on both channels for.

Is there some kind of modification I can make so that activating the tremolo while playing does not cause a huge THUMP?

You might be able to kill it with a pull down R. and/or a series input cap? 

I'd change the e-caps 1st, K bypass caps in the trem.

[dankinzelman]

Ok.

Re tremolo and reverb on both channels, my client prefers the sound of channel 1, but wants tremolo and reverb on it, and says he would ideally prefer to have them on both channels.

Is there some kind of modification I can make so that activating the tremolo while playing does not cause a huge THUMP?

You might be able to kill it with a pull down R. and/or a series input cap? 

I'd change the e-caps 1st, K bypass caps in the trem.

Sorry I know to little to really understand what you are suggesting. Where and what value would I put the pull down R? Same questions for the series input cap. I've already changed all e-caps in the amp, not sure what K bypass caps means.

[SEL49]

The attached schematic mods should put trem on both channels and fix the trem thump when activating with footswitch. Both mods could easily be tested with a gator clip test lead.

It would be easy to move the reverb to channel 1. Not so easy to have reverb on both channels.

[Latole]

I'll try this wiring for reverb ;

[Willabe]

Sorry I know to little to really understand what you are suggesting. Where and what value would I put the pull down R? Same questions for the series input cap. I've already changed all e-caps in the amp, not sure what K bypass caps means.

K = cathode. The preamp tubes K has a small e-cap going to ground, it's called a K bypass cap. Your bypass cap is 20uF/20v.

Try what the guys have suggested for the verb and trem.   

[dankinzelman]

The attached schematic mods should put trem on both channels and fix the trem thump when activating with footswitch. Both mods could easily be tested with a gator clip test lead.

It would be easy to move the reverb to channel 1. Not so easy to have reverb on both channels.

Ok thanks, I'm away for a few days but will try these when I get home. Just to be clear, the tremolo thump happens when I use the tremolo frequency knob to turn on the tremolo (which also functions as a tremolo activation switch when set to its lowest setting, all the way left). I don't have a foot switch. Does this matter for your suggested modification?

[SEL49]

I don't know how you can activate the trem while playing if you don't have a footswitch. And turning the frequency knob is a terrible way to activate the trem. If you must activate by turning a knob, leave the frequency knob alone and just turn the Intensity knob.

Your schematic shows a footswitch jack. Just plug in a footswitch for hands free operation. There should be no thumps if the footswitch jack is wired to the intensity pot as I suggested.

[Latole]

Tremolo F.S is a must for tremolo. Or any short between the 2 contacts

[dankinzelman]

I'll try this wiring for reverb ;

I tried that, sort of, but didn't have time to desolder so I didn't put the reverb in series with Ch1, just clipped a lead from ch1 grid to the reverb input and used Ch2 volume to control reverb, and it worked. But boy was Ch1 noisy with the lead clipped in. I presume using properly grounded shielded wire would resolve this?

[dankinzelman]

The attached schematic mods should put trem on both channels and fix the trem thump when activating with footswitch. Both mods could easily be tested with a gator clip test lead.

Thank you. I tried clipping the Ch1 into the tremolo, that works, although it lowers tremolo intensity. If I want to stick with this mod, can I simply remove one cathode resistor to maintain tremolo intensity?

Haven't tried your fix for the thump yet, requires a little more fiddling around due to the layout of my amp.

[SEL49]

Thank you. I tried clipping the Ch1 into the tremolo, that works, although it lowers tremolo intensity. If I want to stick with this mod, can I simply remove one cathode resistor to maintain tremolo intensity?

Worth a try.

There are several ways to increase intensity in that circuit. You could change that 2.2M to a 1M. And/or put a 22µF cap across the 1K cathode resistor on the oscillator tube. But the best way to really boost the intensity is to replace that 1K cathode resistor with a red LED. The LED cathode would be connected to ground.

[dankinzelman]

I did some testing with the owner yesterday. We tried connecting Ch1 and 2 cathodes and lifting one cathode resistor and it made Ch1 dirty, even with tremolo off, which we didn't like, so we took it out. Is there anything else I can try here?

What about tremolo strength, is there any specific red LED I should use? Normal forward bias, right?

[SEL49]

What about tremolo strength, is there any specific red LED I should use? Normal forward bias, right?

I use the very common 5mm size red LED. Different colors have different voltage drops. Red works best. LED cathode connects to ground. Connect it wrong and it will not work. The LED will probably be damaged and not work even when connected correctly, so get it right the first time. They are cheap. Buy more than one just in case. When connected correctly the LED will flash at the tremolo frequency.