Ab763 weak tremolo issue

[Meddon]

I reently built a ab763Deluxe Reverb, and while the amp sounds sweet, the tremolo is a bit weak, bordering on being useless. Even with the Intensity pot on max the tremolo is very shallow and barely noticable in a band setting.

I took some reading of the voltages on V5: pin #1 295 volt, pin #3 1.6 volt, pin #6 257 volt, pin #8 17 volt.

Any suggestions on what to do?


Thanks!

[Enzo]

Did you replace the trem bug?

[Meddon]

Yes, at first the trem didn't work at all, so I rebuilt the tremcircuit with a new bug.

[Enzo]

How much drive is coming from the oscillator?

[Meddon]

I'm not sure, how do I determine that?

[überfuzz]

Since it’s a home brew. You probably need to triple check your wiring. Actually, you should probably consider yourself lucky. Minor issues in new builds are somewhat a standard, I think. When you’re 102% sure that the wiring is dandy, start replacing stuff. I always start with the disk-caps if I have a bad tremolo circuit. With the info you gave I’d check resistors to see if there’s a faulty value somewhere in the trem-circuit.

[Meddon]

Checked the resistors, caps and wiring, and swapped the vibrato tube, but no luck. Still a weak and shallow tremolo. So I replaced the vibratobug (with the third bug), and hey presto, it's wobbling deep and sweet. Are the vibratobugs usually that un-trustworthy? The next amp I build are gonna have a trem circuit without bugs (pardon the pun).

[überfuzz]

So I replaced the vibratobug (with the third bug), and hey presto, it's wobbling deep and sweet. Are the vibratobugs usually that un-trustworthy?

Third times the charm. ;-) I don't really know, I don't think I've ever had any issues with the bug. Looking at posts here it seems to be quite common though. Some even claim that the bug tremolo is un-musical. I don't know about that, my experience is that this circuit gets the job done as long as the tremolo tube is good.

Hälsningar från Sverige!

[Tom Phillips]

I've has issues with aftermarket trem bugs too. IMO the suppliers selling them competitively can't afford to test each one and don't do much quality control. If they get a bad batch of LDRs then they get used until the returns start coming back. If they test select the parts and verify each bug then the sell price goes up to ~$30 and few people want to pay that. Been thinking of making my own bugs.

[1ampman]

Over the yrs I've replaced 6 or more trem bugs with no problem in volume dropping down. I get them from Antique Electronics. I've also use them to replace the Traynor trem module. Traynor's had the worst trem module quality ever. But I see Weber has several kits to build your own opt coupler. I need a Gibson trem coupler and was looking at these? Gibson uses an incandesent bulb and Fender a neon bulb. I not sure what voltage bulb to get. ???

[Tom Phillips]

I need a Gibson trem coupler and was looking at these? Gibson uses an incandesent bulb and Fender a neon bulb. I not sure what voltage bulb to get. ???

I dissected a Gibson tremolo LDR assembly (Gibson part number was LDR-500) in 2002 and here is some information from my notes that may be helpful.

Amp was a GA77RVT

I can offer the following information.

The bulb was original and the wires had corroded off close to the base. I was just able to salvage enough of the stubs to allow attachment of the lead wires. The bulb had the number “24” printed on it. I assumed that it was a 24 Volt rated incandescent bulb. With 24V applied to the bulb it drew 18mA and the filament glowed bright orange rather than white hot.

HTH,
Tom

[1ampman]

Oh my, I appreciate the info! It's a Gibson GA-20 RVT. and also has the LDR-500. I tried to get it apart but ended up in pieces. Now if you made a batch of those you could charge what you want. I don't know the LDR resistants etc. This has been sitting on the bench waiting. I need a working unit to measure the specs in and out of the circuit... These repairs slow me to a crawl..... ouch!