6L6 / 6V6 swapping?

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sepulchre
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6L6 / 6V6 swapping?

Post by sepulchre »

I just got an old silver face Pinceton Reverb on my bench. Looked in the back and lo and behold, it has 6L6s in it! I checked it out and there have been no changes to the circuit so it's got me scratching my head. Am I that much of a noob? Can you simply swap 6V6s for 6L6s? I tried a pair of Vs and it works fine, about the same with the Ls but I haven't tried cranking it yet (working late at night).

So if there is little difference in the wattage output I'll order some Vs for this guy, cheaper than Ls, eh? One of the Ls has a broken center post so it does need tubes. Everything else seems to work though it's pretty noisy. I could clean up the heater wiring - it's kinda sloppy.

So what is the effect, if any, of slapping 6L6s in the place of 6V6s with no change to the circuit?
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nworbetan
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Re: 6L6 / 6V6 swapping?

Post by nworbetan »

The short answer is that 6L6 are going to draw more current than 6V6 and cause both the power and output transformers to dissipate more heat. Proceed with caution.

However, there is a possibility that the power transformer is robust enough to handle the extra current, but not quite robust enough to supply enough current to cook the output transformer or anything in the path between them. Someone who has first hand experience with how much abuse silverface Princeton Reverb transformers are able to handle gracefully should show up before too long.

It sounds like you're experienced enough to have checked the amp against the schematic, and can recognize sloppy silverface wiring when you see it. So I suspect that you're not as big of a noob as you're letting on. ;) Are you interested in learning about the details of exactly which currents are going to be exactly how much higher with 6L6 compared to the correct tubes? Or is "Proceed with caution" a good enough answer for now?
Stevem
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Re: 6L6 / 6V6 swapping?

Post by Stevem »

As posted , your asking the PT to output a additional amount of heater current that it just does not have so in time it will burn up and or just start blowing fuses.
The 6Ls are going to want to be biased hotter and this added current will make for less peak wattage .
If you want more clean head room out of these 6V6 amps then running JJ 6V6s and stuffing in a bigger OT is the way to fly!
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martin manning
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Re: 6L6 / 6V6 swapping?

Post by martin manning »

Yes, they are close enough that 6L6's can be swapped into a 6V6 Princeton Reverb circuit. In that case you are just under-utilizing the 6L6 with 6V6 primary impedance. If you don't adjust the bias voltage, the idle current will be ~2x higher (and you could easily dial it down), but the power output will be about the same because the load is unchanged, and the high impedance probably means you won't get any more headroom. 6L6's will draw 2x the filament current of 6V6, and that is probably the biggest risk. If the PT can handle that, the OT would likely be ok. I'd definitely switch it back to 6V6, though, as there's really no advantage using 6L6.
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sepulchre
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Re: 6L6 / 6V6 swapping?

Post by sepulchre »

Thanks guys. I did check out the current draw of 6Ls vs 6Vs and saw exactly what you're telling me. I'm not going to change his PT and ordered him a pair of JJ 6Vs.

Thanks again guys!
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Re: 6L6 / 6V6 swapping?

Post by Stevem »

Unless the owner is only playing at home I find that biasing the outputs in on these amps at anything much more then .022 amp will make the low end too mushy for playing with the volume above 5 to 6 dependant on the guitars pickups.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!😊

Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
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