question for experienced express builders

[phsyconoodler]

We built a 6V6 express and I have a couple of questions.
1)it has a hair-trigger volume control.It's either full blast or basically off.I know it may be just the taper on the pot,but I'm asking anyway.
2)does it have any clean tones in it or is all the cleans just when you roll off the guitar volume?

The amp sure has lots of gain and it's nice,but there are short comings that I guess I'm either going to live with or alter a bit.I followed the Ceriatone layout using old Garnet iron.I have 437v on the plates which makes the PI voltages a bit too high for comfort,but I'll drop that down before I get too far.
It's very loud for a pair of 6V6's that's for sure!

[selloutrr]

When you get the Volume issue sorted out you will have some what of a clean tone, until the amp is pushed.
The amp was intended to run hot set and forget the clean is dialed in by rolling your guitar volume pot back effectively lowing how hard you hit the input.

Did you over heat the pot soldering the bus wire to the back? you could have burned the trace.

[dartanion]

They are a hairtrigger volume control by nature. I would also say your voltages are quite high, so maybe use the reverse zener trick on the HV CT to knock it down to around 400V.

[phsyconoodler]

What Zener diode would one use to drop 30v?What I mean is what wattage Zener would be adequate?

[Allynmey]

Sounds like you have a linear taper on the volume instead of audio. I've fixed a few amps that have had this problem. Plate voltages should be between 380v and 400v.

[phsyconoodler]

Thanks guys,
I ended up dropping the voltage with a 1k/25 watt resistor between the center tap and ground,bypassed by a 22uf/450v cap with the positive end to ground.It brought the plate voltage down to 388v and it sounds fine now.I haven't changed the pot yet;don't know how a linear one got in there?

One more quick question: what wires besides the grids should use shielded wire?I shielded the input and volume grids but there is still some noise.It may be related to how much gain this little sucker puts out.
With a vintage 30 the voicing is not quite to my tastes.I'm thinking a slight slope resistor adjustment might do wonders.
I'm calling it the 'Little Gainiac'.
Cool design.Not for everybody thats for sure. Next build will be a rocket.
Thanks again for the help!

[dartanion]

You will have some noise as there is quite a bit of gain. This is why tube selection is very important. Find the lowest noise and lowest microphonic 12AX7 for V1 out of your stash and things should be better noise wise.

As far as tone is concerned, I would consider something other than a V30. TW can be quite bright and the V30 just accentuates the brightness.

[jelle]

The noise...what plate resistors did you use? The 1W Carbon films are a little more quiet.

Jelle

[phsyconoodler]

we used metal films.They shouldn't be noisy.
It's in small chassis which might be an issue.It's definitely an instant gain monster to be sure!
I do have the negative feedback wire running right through the middle of a sensitive area so I guess it wouldn't hurt to shield that too.

[ForcedFire]

I built a 6V6 version as well. I used a VVR to set my B+ to around 415V. This leaves the preamp voltage higher than a standard Express. I ran some simulations and found that raising the 18k resistor to 25k dropped my preamp voltages to the standard values.

[phsyconoodler]

I have good voltages now after reducing the B+.
V1 is definitely where the issues lie.I played it last night at a jam and V1 went down.I replaced it with an NOS TungSol and it not only worked better,it never sounded that good.What a great amp!
Thanks for all the tips!

[jaysg]

I think the guitar needs to be down to around 2 to 3 for clean, no matter what the output is. The preamp has so much gain in it.

[ForcedFire]

I had my guitar wired for independent volumes (pickup on volume lug 2, output on lug 3). This amp convinced me to go back to dependent volumes. Much better clean tones with the guitar turned down.

[M Fowler]

I agree my LP guitar is usually bridge pup at 3-4 volume range for clean.

Such an aggressive amp even with 6V6s.

Mark

[phsyconoodler]

Yes indeed it is aggressive! The noise from the excess gain is kind of a drag but live it's livable.
I liked the little bugger so much I converted my other amp as well.It has 6L6's and it's a much louder version to be sure!