Earth Sound Research/Fender Twin Trem/Verb questions

[shiner555]

Hey Everyone,

New to this forum! Hope I can get some info.

I have been completely rebuilding an Earth G-1000, which is an EXACT copy of a blackface twin(no wonder why Earth got shut down). I have gone through and replaced and rebuilt the powersupply, and also replaced every cap in the entire amp. I've also checked out all of the tubes, and they are all good. Awesome for me since they are all NOS Mullard!! I've also tried to check out the resistors, etc.

Here is the schematic if your curious:
http://www.schematicheaven.com/barga...uperguitar.pdf

So far the amp sounds really nice, but the Tremolo is totally dead and the reverb is really quiet. Since I've re-capped and checked out the resistors in the trem circuit, I'm figuring that the LDR is dead. Any good way to check it out to make sure before I order a new one?

For the Verb, I checked the tank and one of the wires on the input of the tank on the inside was broken...fixed it, but now I only get some verb, but it's so quite, I think it's just the tank making noise when the amp is cranked up. Any ideas??

Thanks in advance!
-Jason

[Don Moose]

Set the trem rate really low and measure the voltage hitting the bug - it should swing up & down at a rate controlled by the speed knob.

... wait - is this the trem circuit where you have to ground the control switch to get it to work?

If not:

If you have some heatshrink tubing of appropriate size, you could split the bug open and see if the lamp flashes, and if exposing the photocell to light sucks the volume down.

If all is well, reassemble.

Otherwise, replace the affected part, check again and rewrap.

Or, replace the bug with one from www.tedweber.com ($7 USD) or any of the other guys who sell replacements.

Hope this helps!

[ken]

Yer bug is dead... the LDR in the bug went bad. Replace it. If that doesn't work, replace the caps from the plate of the vibrato tube to the grid. Works 99% of the time...

Ken

[shiner555]

Yer bug is dead... the LDR in the bug went bad. Replace it. If that doesn't work, replace the caps from the plate of the vibrato tube to the grid. Works 99% of the time...

Ken

Hey Guys,

Thanks for the comments. I'll check out the LDR/Bug when I get home tonight. Sounds like it's bad, since all of the caps around it are brand new. However, dosen't mean I didn't mess up installing em...I'll take a look.

Any ideas on the Reverb issues?

Thanks!!
-Jason

[52 Bill]

Check to see if the bulb is flashing, if it isn't check the foot switch first. I don't remember if the foot switch jack on these amps were normally shorted to ground, but the oscillator will not run if it isn't grounded.

If the ft.sw. is grounded and the oscillator still won't run, then do as Ken sez and check the tube and the three phase shift caps and all the related resistors.

If the bulb is flashing and the effect is weak, then replace the photocell.

As for your reverb, if the tank itself checks out ok, be sure that the cables are plugged in correctly, drive signal to tank input and return line to tank output. Reversing these will cause little or no reverb symptom.

You already know that the return signal is getting to the amp, so next check the drive signal. Take the signal from the drive cable and feed it to small 8 ohm speaker. Is there signal there?

Hope this helps.