18 watt Superlite TMB Reverb with 6V6 Tubes

[JMPGuitars]

Your B+ voltage is a little high, see the voltage dropping thread in my signature.

Your power tubes are biased too hot. Somewhere between 100% to 117% depending on which type of 6V6 and whether or not you stuck with the 250Ω bias resistor. I'd shoot for somewhere around 85%.

Thanks,
Josh

[fizzyone]

Hi Josh,

thanks for the fast reply OK, will look at the infos in your footer and drop the voltages.
Yes, biasing is at around 40 mA as it is now and needs to get down to max 30 mA for 6V6 (as far as I know), but I first wanted to check all other voltages before biasing, because changing these might also affect biasing.

I use 6V6 S Tubes and I used a 270 ohm Resistor.

Thanks, will work on that now

[fizzyone]

Hey,

built in the zener diodes and the voltages are lot better/closer now. Biasing is a little below 85%.

What makes me think are the voltages of the PI, they are very low compared to the other voltages, does this affect the sound in some manner?

Tried the amp with a cabinet and compared to another 6V6 amp (played through the same cabinet), it's missing some power and also dirt. Could the low voltages of the PI affect the sound this way or do I need to bias a little higher? The amp is also breaking at a very low level, could really use some more gain at the top end.

[JMPGuitars]

The PI voltages aren't expected to be the same since you changed the cathode and tail resistor values.

You can bias that differently if you want, but you should share a schematic of what you currently have.

Also play with the master volume and see how it sounds cranked. 6V6 tubes do not behave the same as EL84s, and this circuit (I'm assuming) is different than the other 6V6 amp you compared to. Circuit matters more than tubes, but tubes still matter.

[fizzyone]

Hi Josh,

thanks for your fast reply. I just wondered about the amount of voltage differences and if that could affect the sound of the amp. I cranked both, gain and vol fully and it barely broke. Yes I know, 6V6 behave different and are meant for a more cleaner sound, maybe tweaking some values might give him more crunch.

Here's the schematic I used for the build:

[JMPGuitars]

Did you use 22k or 27k for the tail resistor?

Did you change your 270Ω cathode bias resistor value?

Try 330k grid leak resistors (replace the 470k pair to ground connected to the 8.2k grid stopper resistors at the power tubes).

[fizzyone]

I used 22k on the tail, that's what most schematics use. If switchable from EL84 to 6V6, 47 K is common (whats originally use for the EL84)

Bias resistor is 270 ohm, biasing could be a little hotter here I think. Maybe 250 ohms? Rob Robinette writes on his website, that you could go up to 100% by using cathode biasing and still be in the safe zone for the tubes. Wouldn't that eat up the powertubes a lot faster?

Will change grid leaks and try what happens.

In some tweaking options you offered to lower the cathode resistor of the second stage of the oreamp V1b, is that an option for more crunch?


Thanks a lot

Ralf

[Bieworm]

You could go the 6G3 route and change the plate resistor of V1a to 220k and also raise its cathode resistor in value? Maybe a route you can try?

[JMPGuitars]

I used 22k on the tail, that's what most schematics use. If switchable from EL84 to 6V6, 47 K is common (whats originally use for the EL84)

Bias resistor is 270 ohm, biasing could be a little hotter here I think. Maybe 250 ohms? Rob Robinette writes on his website, that you could go up to 100% by using cathode biasing and still be in the safe zone for the tubes. Wouldn't that eat up the powertubes a lot faster?

Will change grid leaks and try what happens.

In some tweaking options you offered to lower the cathode resistor of the second stage of the oreamp V1b, is that an option for more crunch?

22k is probably what you want, so that's good.

Keep the bias resistor for now. Yes, you can go higher bias. No, you probably don't want to.

Try 470Ω to 620Ω on V1b cathode resistor.

Try the grid leaks first. Do one change at a time so you know what's happening while you tweak.

Thanks,
Josh

[fizzyone]

Hey guys,

thanks for your help So I will start with the grid resistors and work my way through, will test in between and come back with the results. I'm gone for the weekend so hopefully at the beginning of next week.

Whish you all all nice weekend and thanks again

Ralf