New build 5G9 Tremolux

[Moid]

This is my first post here, but I've been lurking around awhile. I just finished my latest creation. I used a Weber chassis that was re-silk screened and MM iron. The cab is finger-jointed pine with lacquered tweed. The dimensions are almost the same as stock except I angled the front slightly, like a Deluxe. The amp sounds fantastic. Big, tight bottom end that is not mushy. Lots of headroom. It starts to break up around 6 and the breakup is really sweet. Tubes are reissue Tung-Sols, with a mix of TAD and EH preamp tubes. The speaker is a Hellatone 30 which really gives it a nice full, rounded tone. Although I've never heard a real 5G9 this sounds as good as any amp I've ever heard. Really pleased with the result. Here's some pics:

[tubeswell]

At last! another 5G9 builder on this forum!
Wow that looks real pretty! (It actually looks like a real one)

Aren't they the coolest? super-wow trem - don't know why more people don't build them. (Maybe after this they will).

I use my build all the time now, for jams, gigs and everything I am sooooo in love with it, I'm making a stand alone reverb to go with it (when I get some help with working out the reverb tranny/driver tube configuration).

I'm not sure what speaker I've got - think its an old Jensen or something.

I also use an EH12AY7 in the front, and 'Tung Sol re-issue' 6V6GTs at the back. What have you got yours biased at BTW? (Mine are about 28.5-29mA and touch wood, they seem to be handling it ~3 months and counting)

[Moid]

Weber makes a kit for the stand-alone reverb. I'm sure he sells the trannys separately as well. I thought about making one as well. I haven't checked my bias yet. Mine is non-adjustable like the original but I'll check it when I get it open again. I've only had it up and running now for a couple of days now, so I'm still playing around with the different inputs and jumpering the channels, etc. So far so good. No red-plating tubes. I'm loving it.

[tubeswell]

I built mine with an adjustable bias and set it to be the same at the 56k resistor to ground that is in the bias voltage divider. It ran my tubes at about 31.5mA (including screens) from memory (I was only getting -22V at the grids) - sounded nice, but I chickened out and lowered it to 28.5. After a couple of months of running the tubes, I had found that it had crept back up to 31.5 (along with the plate voltage which had crept up to 376), so I lowered it again yesterday. I think this is a result of the tubes having run for a little while. Still sounds swell.

[Moid]

I checked mine this weekend and its around 41mA with about 390 volts on the plates. Is that too much? It sounds great as is. How hot can you bias the re-issue Tung Sols?

Moid

[tubeswell]

What method did you use to measure the current? And did you measure this with the tremolo switched off?

If you are measuring tube current, and you take off about 5mA for screen current, that gets you to about 36mA plate current (which is 14W dissipation - basically 100% dissipation for those tubes), which is too high for Class AB1 - I wouldn't go higher than 85% - some people wouldn't go higher than 70%). On the other hand, JJ6V6s 'Might' run okay at 36mA plate current (but I've never tried this - I have a pair which I could pop in and see)

But 41mA of plate current sounds too high for those 'reissue' tung-sol6V6GTs (would be running at 16W). You could keep them running there as an experiment to see how long they last. Personally I wouldn't run them that high. I'd try changing the 56k resistor in the bias circuit to something like 60k (or maybe 68k), if you have measured plate current at 41mA. You could install an adjustable fixed bias (in place of the 56k resistor, wire a 50k pot as a variable resistor and put it in series with a 38k resistor. With mine I wired the unused tag of the 50k pot to the wiper so that if the wiper contact point ever fails, I've got some resistance to stop my tubes running away)

[Moid]

I used a Weber Bias rite, so I'm not sure exactly how that works. I belive there's a one ohm resistor inside so that it converts mA to read out in voltage. I did have the tremolo off, but I'll recheck to make sure.

[tubeswell]

okay I don't have one of those, and I think you can get them in configurations that measure either plate current or tube current. (Tube current will include screen current and plate current)

[Moid]

I finally got around to adding a 50 K bias pot. I first tried a 33K resistor in place of the 56K but could not get the bias cold enough. I ended up putting the 56 K back in which brought the bias down. I ended up with 420 volts on the plates with about 23 mA. Still sounds great.