5U4 --> 5Y3 in a Recto?

[Mr. SD-1]

Hi,

I have a 3 channel Mesa Dual Recto which runs 4x6L6 and 2x5U4 as stock.

I prefer to run the amp with 2x6L6 (observing push-pull operation) and 1x5U4. I use the 4 ohm tap with an 8 ohm speaker. I always use the 'spongy' AC power setting. All together, it sounds pretty cool.

Would it be safe to run 2x6L6 and 1x5Y3?
Why exactly does a 5Y3 'sag' more than a 5U4?

Thanks!

[jetlag]

The 5Y3 doesn't have the current handling capability for larger amps like yours. It'll work for a little while, then smoke. If you want more sag, try a 5R4G recto or a GZ37 (the former is much cheaper).

[Mr. SD-1]

The 5Y3 doesn't have the current handling capability for larger amps like yours.

What about 2x5Y3 and 2x6L6?

[Blue Strat]

What about 2x5Y3 and 2x6L6?

That would probably work. In the '50s, there were numerous cheap PA amps that used 2 6l6s with one 5Y3. With your amp, I'd feel safer with 2 5Y3s or maybe one 5V4.

[Mr. SD-1]

In certain amps with two rectifier sockets, would it be safe to mix types? For example, could I run 1x5U4 and 1x5Y3 together with 2x6L6 in my Mesa? Just curious at this point...

[Old Tele man]

...although you *can* use two different types of rectifier tubes in parallel, it's not really a good idea...because the one with lower voltage drop will tend to "hog" all the current so the other tube conducts much less than anticipated.

...this same situation actually happens when two of the same type rectifiers are operated in parallel--here, the "differences" between their "mismatched" voltage drops is much smaller so the current "hogging" becomes very small, but it's still there.

...short answer: try it, but it won't simply "halve" the current loads between the two different rectifiers.

[Leftee]

That would probably work. In the '50s, there were numerous cheap PA amps that used 2 6l6s with one 5Y3. With your amp, I'd feel safer with 2 5Y3s or maybe one 5V4.

Or 2 6L6's 2 5Y3's. :D

http://www.leftee.net/images/boggy_IV_chassis_front.jpg

[Mr. SD-1]

Thanks, that makes sense. I have a related question:

I've been using a Fender 5D8 Twin with 2x5Y3 and 2x6L6 cathode-biased. I guess the amp was meant for 110VAC operation, 'cause the amp runs hot. Every voltage is high, and so is the bias.

Could I use a different rectifier tube in place of the 2x5Y3 to lower the voltages? Maybe it would be better to use a variac...

[Leftee]

I'd run a variac with that one.

[Blue Strat]

Thanks, that makes sense. I have a related question:

I've been using a Fender 5D8 Twin with 2x5Y3 and 2x6L6 cathode-biased. I guess the amp was meant for 110VAC operation, 'cause the amp runs hot. Every voltage is high, and so is the bias.

Could I use a different rectifier tube in place of the 2x5Y3 to lower the voltages? Maybe it would be better to use a variac...

There's no rectifier that I know of with the same pinout that would lower the voltage more than a 5Y3.

I wouldn't worry about the voltages since they're probably already lower than spec with the 5Y3s. If the bias is to hot, increase the cathode resistor value about 30-50%. This is about a $1 mod.

[Mr. SD-1]

All of the internal voltages are higher than spec with the stock 5Y3s. Even the heater supply is higher than normal. What is your recommendation for a Variac? Built-in output voltage display would be a useful feature...