GDS 18 watt amp build + Need some help!

[Twistingcrow]

Hi!
After building almsot ten Metros (tried all of them except the JTM45/100) I delved into the 18 watter and it's also a great piece! Great sound really!
Here are some pics, don't worry about the OT secondary wires, they're not connected to a switch yet, I'm still waiting on that piece, so far it's only hardwired with the right impedance to the output switch:
















Yet I have one single problem, that has to do with the tremolo on the amp. Since it's a head I have A DPDT switch that is connected to a footswitch jack and a LED for the status. The tremolo channel works perfectly except that I don't have any tremolo. The DPDT switch lets you choose between "Footswitch" and "Manual". When it's on "Footswitch" the tremolo is OFF since I have no footswitch to plug in there. But when I set it on "Manual" the oscillation is audible but the effect doesn't come through. I know it must be a simple mistake on my part but I've re-read the instructions and I don't see what I could have done wrong. All my solder joints look good and everything is where the manual says it should be.

If you could help me that would be greatly appreciated since the 18 watt forum is down and since Graydon Stuckey, the boss of GDS amps and father of the 18 watt resurrection is on vacation... I'm alone on this one, so please chime in!!!
Thanks!

[VTM Mike]

Looks really nice! My Ceriatone 100 Plexi turned out great, and I'm now building a 2550 for my son per his request. An 18 watter is on my short list as well. Very nice work!

[Twistingcrow]

Thank you VTM! I'm still puzzled by that tremolo thing...

[Twistingcrow]

No one has a clue about that tremolo effect not working?

[Twistingcrow]

Hi!
Found the answer: it was a faulty tube at V3, nothing more than that! I spent a few hours checking the layout, voltages and solders and forgot to think about the first thing to check: tubes! The strange thing is that the same tube works perfectly well at V1 or V2. The Tremolo effect must be hard on tubes and since it's a NOS Baldwin it may be too old or used to stand the voltage variations there...

It sounds gorgeous, great little amp!

[Twistingcrow]

Update here: my Baldwin was not faulty, it's just that it is too gainy. High gain tubes at V3 will cause problems in the tremolo circuit. Simple as that. So if your tremolo isn't working, just put a low gain 12AX7 there and problem solved!

[neikeel]

Update here: my Baldwin was not faulty, it's just that it is too gainy. High gain tubes at V3 will cause problems in the tremolo circuit. Simple as that. So if your tremolo isn't working, just put a low gain 12AX7 there and problem solved!

I have just built an 18watt trem but when you posted your problem I had not tested it. When I did I had a trem pulsing effect constantly unless I chopsticked the blue plate wires with my hand in a certain position over the board so I used the Richie improvements (shielded wire on the plates) of V3 (trem) as it worked perfectly on normal channel with the trem tube removed (I had already used shielded wires on V1).

Apparently if you use too high a gain tube in one of these they can oscillate even with everything turned down (as mine did with a NOS Brimar ECC83) but when I replaced it with a Mullard M8137 (sl lower gain factor) it worked perfectly well. I understand that using an ECC81 may not trem and aN ECC82 will almost certainly not trem as it does not have enough gain (that is by searching on the 18watt tech forum - probably as you have ).

I used an RS EL84 OT and Heavy Duty PT as well as NOS Mustards and Pihers throughout, pres are Brimars (except for trem) and some Russian EL84s tt sent me and tesla EZ81. Great little amp, lots of balls and grit at reasonable volumes, not a lot of clean headroom as I have it in a 2x12 with a pair of pre-rola T1220s in series so might be a bit dark for my gigging needs at the volumes I need. Trem channel is best IMO as it has a bit more bite but I am going to dop the cathode bypass cap on V1 from 47uF to 4.7uF or lower to see where that gets me.

Glad you got yours sorted, I will post pics of mine in another thread once I get them off my camera!

[Twistingcrow]

Cool!
Are you happy with the RS OT you used? I'm pretty happy with the GDS trannies. Yet it's my first 18 w so I can't compare it to other 18 watters...

Tubetramp has just advised me to use a NOS 5751 in V3 to tame the tremolo effect. In fact even with the current Chinese 12AX7 I have there I can't turn the tremolo above 3/10 or it's just too much. Graydon Stuckey had forewarned me that tremolo circuits were a bit tricky and that it's not always easy to find the right tube to use in V3. Too gainy causes havoc, not enough gain and you don't hear a thing.

Anyway, I can't access the 18 watt forum as the frontpage still says that it is being updated, and since I don't have any acount there yet, I can't create one...

I think it's the perfect amp for me. I don't need my Alex attenuator anymore. All I have is a guitar, a tuner, a wha, a clean boost and that's it! It can go from great cleans to great bark. What a dynamic amp!

By the way, have you tried the Reverb pedal thing? It's like the amp had a stock FX Loop. It's amazingly good!

I'm looking forward to reading your 18w topic!

[Metal Handles]

I'm going to BUMP this thread back to the top. So I can find it easier.
I have an 18 watt that has (what appears to be) the same V3
tube issue.

I'm going to research all my details and get back to this thread.
Glad I may be able to get this thing where I want it without having
to send it off somewhere!

In the immortal words of Arnold.......... I'll be back!

[neikeel]

I'm going to BUMP this thread back to the top. So I can find it easier.
I have an 18 watt that has (what appears to be) the same V3
tube issue.

I'm going to research all my details and get back to this thread.
Glad I may be able to get this thing where I want it without having
to send it off somewhere!

In the immortal words of Arnold.......... I'll be back!

For me the shielded wire, good grounds and a M8137/cv4004/5751 worked perfectly, I use this amp for rehearals for 2 1/2 hours. I use the trem channel only and at rehearsal volume it has a nice clean sound with a hint of beak up (volume < 2) and takes pedals pretty well.
I have taken it to small gigs but have taken a 50w head too which I have ended up using to get headroom to match the drum and bass levels. If we were out and out rock it would probably be suffcient - just crank to 10 and dila the guitar back.