Cathode biased Express?

[nickt]

Has anyone tried cathode biasing their express?

What is the downside (or upside) ?

Just askin'

[jjman]

I used cathode Biased 6v6s for mine. I wanted lower volume, more compression, earlier breakup, and output bias tremolo from the extra triode. Of course these all nullify any "clone" status. Took some time but it's all come together nicely.

[nickt]

How did it sound? I'm also thinking of 6v6's - don't know where I'd ever crank up EL34's

[dave g]

Personally, I much prefer the sound of fixed bias amps. A lot of cathode biased (and I'm talking non-global negative feedback here) amps sound fizzy and flabby to my ears when the power tubes are clipping. I think it has a lot to do with the negative feedback and presence circuit acting as a limiter on the bass and preventing the tube from clipping too hard on the low frequencies. Cutting the lows in the preamp helps, but always makes the amp sound weaker. Fixed bias just seems to keep those bass frequencies exactly in the right place. For lower gain stuff cathode bias might suit you just fine, though.

Alternatively, you could probably just go ahead and do cathode biased with global negative feedback a la the Liverpool - might be worth a try with 6V6s!

[jjman]

How did it sound? I'm also thinking of 6v6's - don't know where I'd ever crank up EL34's

So far it's sounding fantastic. The real test will be Saturday at an outdoor gig. I'm gonna run my '71 Deluxe Reverb along with it by splitting with my signal with my Boss analog delay. Not sure if I'll leave the pedal switched off, for basic splitting, or “on” to send the dry to the TW and the echoes to the DR. Both setups sounded good when I did some testing. If I set the pedal and the amps right, I should be able to use both modes depending on if I want dirt + cleaner or dirt + clean echoes for a given song. (Turning down the guitar for cleans only.) And my fuzz pedal could complicate matters more.

Actually the real reason I'm running it this way is just in case the new build dies. This way the proven reliable DR is ready to take over. I'm hoping it's a large field and we can turn way up!

[rfgordon]

I did an Express with cathode bias EL34s, and it was still "instant on" and definitely blow-your-hair-back loud! But, man, did it sing! The current owner is very happy.

[Zippy]

Rich,

Did you bypass the cathode bias resistor? How hot did you bias?

Thanks,

george

[RJ Guitars]

This is some good sounding info... I've recently been considering a 6V6 Express, or even using 2 6V6's as ouput for a Rocket. I've got the chassis ready to go but I'd sure like to see a schematic, layouts, or sound clips to sort out the final build specs...

I really like that idea of a cathode biased 6V6 output, and it's also really great to hear that it worked well with the EL34's. Do you think you can swap EL34's and the 6V6's without a reconfigure?

Give us a report on the outdoor gig if you don't mind.

rj

[jjman]

Just got back from the outdoor thing. It was a car show in Wall NJ. Sounded nice but I couldn’t walk away from the amp to get a real good feel for it’s sound in the overall mix. I was surprise that I found myself turning the treble up more that at home probably since the cab was so close to my feet. I used my 4x10 Marshall for the TW. The trem sounded very good. We were playing on top of a flat bed truck and, even though I’m wireless, I couldn’t jump down to check the overall sound. I couldn’t use the guitar’s volume control as a means to clean the tone since that would have lowered the volume in the SFDR too. Although I played thru both amps, my SFDR was on the other side of the “stage” behind the other guitarist. I used pedals for more grind and it’s good that I have my MXR Dist+ on the board since my homebrew fuzz started acting up again. We play a wide variety from mellow Elvis to Ramones so the pedals helped keep the tone horizon broad.

Each guitarist played thru 2 amps and each had control of one of their own and one of the other guy’s amps. This was an excellent way to go since we each could balance both guitars on each side. Of course this only works with non-competitive type guitarists. He used his Line 6 and an old tube Ampeg, which is also cathode biased 6v6s. The Ampeg itself doesn’t distort unless dimed. He split with a nice old rack preamp multi-sounds thing that sounds much better than most. No Line 6 digital stuff this time. I highly recommend this 2 + 2 approach for anyone who has the room and the supply of amps on hand.

We video taped so I’ll eventually get to check out the mix.

[rfgordon]

Zippy,
I made mine for EL34s, and each tube had a 300 ohm/10watt resistor and a 100 mF bypass cap. The B+ was about 400 or so, and the OT was a beautiful piece from an early 60's mono tube amp.

The guy I made it for tried to give it back after a week or so, but I told him, "Learn to use the guitar knobs." Not long after that all the overdrive pedals mysteriously disappeared from his pedalboard. Imagine that.

[Ampsterdoom]

Does anybody have info on what the right resistor and capacitor values are to use with 6V6 tubes?

Dr. Doom

[nickt]

Hi Dr Doom

the 5E3 value is 250 ohms however that's with a low plate voltage due to the 70V drop across the 5Y3 rectifier.

When I used a GZ34 in my 5E3 I had to raise the cathode resistor to about 390 ohms to calm down the 6V6 dissipation. I've heard of others going to 470 ohms.

In the end I think you want to keep your plate disipation under 12W from memory.

The cap should just be as big as possible - but 220 uF should be ok.

[jjman]

I'm using the lower voltage HT taps on the Toneslut PT and have 351-357 volts on the plates. A 280 ohm shared resistor resulted in ~12.5 plate watts each. A 360 yielded ~10watts plate each. I also have a 100ohm pot on each side to fine tune down about one watt if wanted. Probably should put a 300 ohmer.