Fender Deluxe Reverb 1976 Using 6L6 instead of 6V6, and No Vibrato

[misterc57]

I am working on a FDR and was surprised to find it using a pair of 6L6 on the output. The owner was surprised by this but he likes the way the amp sounds.

All voltages look good for a FDR at the outputs.

After replacing V4 (had a bad triode) the amp is working again and sounding good but now needs the vibrato fixed.

Thoughts on using 6L6 in this amp?

I have not dig into the vibrato issue yet.

Thank you, MC

[Tom Phillips]

It's not something I would recommend. Firstly, the 6L6 has nearly double the filament current of the 6V6. You could cause a PT failure. Having the substituted tubes installed could also be the cause of your vibrato not working since it's a bias wiggle type.

Agree about over stressing the PT but you are thinking of another amp regarding the bias wiggle tremolo.

[The Dude]

Oops. Yes, wrong amp. Thanks, Tom. Post edited.

Edit: Well hell, I accidentally deleted the entire post. You copied it in yours anyway, so that's that.

[Jon Snell]

If you keep the 6L6s in there, I would price up new transformers as you may need them due to excess current drawn from the output stage through the output transformer windings, not to mention the power transformers added strain.

[pdf64]

The concern is that the 6L6 heaters will draw more current than the amp’s mains transformer can cope with.
I suppose that if it’s been running with 6L6 for a while though, then the ‘proof of the pudding has been in the eating’, and so such concerns might be allayed somewhat.

The other thing is that 6L6 will need a greater magnitude of (negative) bias voltage than a Deluxe Reverb was set up for. It’s not a big deal to tweak things into range, and as it hasn’t caused a problem yet it’s probably already been done, but whatever, the idle current that the output valves are drawing should be checked anyway.

[Helmholtz]

6L6s don't even significantly increase output.
Using a loadline calculator (https://www.vtadiy.com/loadline-calc...ge-calculator/) shows a power difference of only 1.5W.

All in all not a good idea.

[misterc57]

It has the original PT. I am ordering a new matched set of 6V6.

The vibrato is fixed (wiring issue).

Thank you all.

[Chuck H]

It has the original PT. I am ordering a new matched set of 6V6.

The vibrato is fixed (wiring issue).

Thank you all.

It's possible the 6L6 tubes and the "wiring issue" were intentional mods. Was the vibrato disabled in such a way that the 50k load from the vibrato pot was lifted from the output of the channel mix stage? This was a popular mod in the mid 90's. As was running 6l6 tubes in those amps.Both a little goofy as mods go but no one ever reported a problem. My point is just that if the owner likes the way the amp sounded when he brought it in you may be "fixing" it unfavorably.

[pdf64]

6L6s don't even significantly increase output.
Using a loadline calculator (https://www.vtadiy.com/loadline-calc...ge-calculator/) shows a power difference of only 1.5W.

All in all not a good idea.

Maybe with current production valves, their poor Vsat characteristics would result in a greater difference?
Whatever, even with vintage production valves, I prefer 6L6 to 6V6 in my DR based build.
It does have a beefier, Vibrolux / Tremolux style mains transformer though. Which makes the darn thing somewhat heavier to lug around.

[Helmholtz]

Maybe with current production valves, their poor Vsat characteristics would result in a greater difference?

The power output of a PP class B amp is given by Pout = 2 (Vsat - B+)²/ Raa.
The only influence of tube type used is via its Vsat.
In other words, under identical operating conditions tubes having the same Vsat will produce the same sine power independent of tube type.
Vsat varies with the plate load and the screen voltage.

A good 6L6 should have a somewhat lower Vsat than a good 6V6, so slightly more output in the same amp.

When using a loadline calculator it is essential to insert plate and screen voltages measured at full output.