Questions about swaping 6V6's/6L6's in guitar amp

I have a fender hot rod deluxe. I read an article about swaping 6V6's in place of 6L6's. I changed the screen resistors as recommended in the article, but the article makes the following statement:

"6V6s also have a greater plate resistance than 6L6GCs, so there will be an impedance mismatch. It won't be enough to cause damage, because 6V6s draw a lot less current than all 6L6s, but if you plan on permanently using 6V6s you ought to install an appropriate output transformer. A high pass filter is created between the plate resistance of the tube and the inductance of the output transformers primary. In other words, installing 6V6s is going to cut a fair amount of low end."

So my question is: Will continued operation without changing the OP TX cause any damage? I'm guessing not, but want to be sure, as I love the sound of the amp as-is.

Thanks,

Outside of the 6V6s themselves (which may not stand the higher plate voltage found in a circuit designed for 6L6s), you're not likely to hurt anything. But do double-check for stability, especially if there's negative feedback coming off the secondary of the OT. The phase shift through the transformer may be altered by a few degrees compared to running with 6L6s.

[quote author="NewYorkDave"]Outside of the 6V6s themselves (which may not stand the higher plate voltage found in a circuit designed for 6L6s), you're not likely to hurt anything. But do double-check for stability, especially if there's negative feedback coming off the secondary of the OT. The phase shift through the transformer may be altered by a few degrees compared to running with 6L6s.[/quote]

I re-adjusted the bias so that the Max plate dissapation is'nt exceeded, the higher plate voltage doesn't seem to be an issue with these tubes as long as you change the screen resistors.

There is negative feedback, so in theory, is there the potential for oscillation??

So what is the plate voltage you're seeing with the 6V6s in? I have a mid-70's SF Deluxe Reverb that had Si diodes soldered to the back of the rectifier socket when I bought it. It had something like 485V on the plates! I quickly undid that mod and got back to a more "sane" 425V or so IIRC. NOS 6V6 (GE, RCA, etc.) usually can take this beating. I would never put a Chinese flashbulb in any amp that exceeds 350V on the plate. JJs 6V6 are built like tanks and can easily take the higher voltages that Fender used.

A P

You might wear the tubes out prematurely due to impedance mosmatych.

Gereal Weber has tons of info on this in question and answer form.

His two amp books are pretty good.

What is the purpose of swapping? The same distortions on less power?

> the article makes the following statement:

What a bunch of half-bunk.

Just do it.

If the amp really USED the 6L6 for all it is worth, vintage 6V6 will die fast. But thousands of amps use good new 6V6 (notably JJ brand) in 6L6 conditions and work fine. It is 6V6 abuse. Few 6V6 will last 50 years at 6L6 conditions, as they did at 6V6 conditions. But at current JJ-6V6 prices, your 6V6 replacement costs are probably lower than your picks-and-strings costs.

Instability and "loss of bass" are non-issues. The amp won't be hurt, may live longer.

I've got a similar question... 6v6's and el84's appear very similar in terms of operation. Would it be difficult to modify an amp running EL84's to use 6v6's instead? Obviously the valve socket would be the first to go...

Why would you wanna do that?

EL84 blows smoke around 6V6.

But thats just opinion.
We need as many amp sounds as possible.
Lots of good music has came thru that 6V6.

Oh, what kind of bias?
You could drop in a 6V6 if there's a cathode resistor, but if it's fixed bias, you need to get on that.

If it's -50, my first guess would be try minus 30.

Or, lower the bias til the plate starts to barely turn red, then back it down out of the red zone.

Why not? :green:


I have a stereo Mesa poweramp with EL84's in both sides. Since I only ever use one side running in mono I figured why not try sticking 6v6's in the other for some tonal variety.

I'll have to pop the hood and take a looksee...

Or get weird and stick one EL84 in one socket, and 6V6 in opposite push-pull socket.
Asymetrical push-pull.
This is how they do the distortion trick on that new S S L. :razz:

Crazytown... I wonder if they do it by jamming an octal valve into a 9 pin socket too :green:

That raises an interesting point though. I have an older Mesa 50/50 6L6 power amp sitting in the cupboard. Perhaps I should just modify one side for 6v6's then stick THD EL84 yellowjackets in the other side... It would probably be a whole lot simpler.

Yelloe Jackets?
Russell Ferante and Roben Ford make tubes?

Cool!

:grin:

does robben ford still play with Yellowjackets?

less talking more doing please.

6v6s and 6l6s do sound different. EL84s have more gain than a 6v6 you need to be mindfull of the drive to the grids for tone.

If you build a few amps and adjust the gain in the stages and the HPs and LPs between stages you can make a nice sounding amp.

A friend that traced a lowpower matchless using two el84 measured 4k primary that in books is for four EL84s What does matchless know??...............

So much crap on the web.

Train.... built a amp that uses 6v6 or el34 with no rebias.

Mismatches can be fun sound good or sound like crap.

[quote author="Gus"]

A friend that traced a lowpower matchless using two el84 measured 4k primary that in books is for four EL84s What does matchless know??...............
[/quote]

Ha. THat's why I'm using a Hammond 125E on my Lightning copy because it is supposed be 8K for two EL84s I thought. I'll just try both and see what sounds best.

Kiira

[quote author="CJ"]This is how they do the distortion trick on that new S S L. :razz:[/quote]
:green:
but do we know this for sure yet ?
that was an early question asked
and is there any control to turn it off and on ... and vary the amount ?

[quote author="Gus"]less talking more doing please. [/quote]
:green: