5F1 amp - can I substitute a 5U4 for the 5Y3?

[leevc5]

I read on the SDUF that using a 5U4 gives a better tone than the 5Y3.  I would like to try and see for myself but I wanted to find out if using the 5U4 instead of the 5Y3 could possibly damage my amp particularly the PT or OT.

[Paul1453]

Maybe you could compare the data sheets and tell us what you think then.   

[Paul1453]

Or do you just want someone to tell you what they think?

What if someone told you wrong and you plugged in a tube and wrecked your amp?

I could just tell you what I think, could be right / could be wrong.

But you really wouldn't learn anything by that, right?   

[leevc5]

You are right and I've been looking and trying to make sense out of what I'm finding.  The only thing I have found that gives me cause for concern is that it looks like the 5U4 is 5 Amp FIL and the 5Y3 is 2 Amp.  Next step I guess is to look at my PT specs...blundering through the darkness.

[Paul1453]

Close the 5U4 is 3A 5VAC vs 2A for the 5Y3.

If your PT can't handle 3A on it's 5V winding you could burn up your PT.

What else would be a big red flag, that you would usually find on the 1st page of the DS?

[leevc5]

Max ACV 5U4 = 450 , 5V3 = 350?

[leevc5]

My 22772 PT will handle 3A on the 5V winding according to the spec sheet.

[Paul1453]

Whenever comparing tubes one of the 1st things you should check would be the pin assignments on page 1.

If they were different, RED FLAG!

There are a few other things to consider with rectifiers, but I have a few questions for you 1st.

How many mA of current does your 5F1 use?

How many mA of current can your 5Y3 supply?

How many mA of current can the 5U4 supply?

How many volts do each of these tubes drop during rectification?

If the 5Y3 can supply more than 2x the current needed, and the 5U4 4x the current, each with about the same voltage drop.

Do you really think there will be much difference if you swapped them?   

[Willabe]

If your PT has a 3A 5v heater wind then put in a 5U4 and see if you hear/feel a difference you like when playing.

   

[Paul1453]

So you could just plug in the 5U4 as Willabe suggested, and see if you notice any difference.

It is my opinion that you would benefit from comparing the DS some more before you did that, but.

There are a few more things that you could consider, before putting your gear at risk.

I have not tried this swap before, so this is only my guess at what you would find.

With the 5U4 pulling 3A of heater current, the listed limit of your PT, I expect your PT will get hotter.
Probably not enough to damage or burn it up, but hotter just the same.

Since the 5F1 is just a 12AX7 and a 6V6 you are not pulling much B+ current.
You could get a good estimate by looking at their Data Sheets.

The 5Y3 is also used by many PP 6V6 amps with more pre-amp tubes too.
In these cases the 5Y3 is running much closer, but still below, it's current supplying capacity.
This is where I would expect you could notice a difference if you put in a 5U4.
The 5U4 would probably not sag near as much as a 5Y3 in one of these amps.

In your amp, I'm not sure I would notice the difference in sag because your 5Y3 shouldn't sag all that much when supplying less than 1/2 it's current capacity.

Now I could be completely wrong, or maybe just unable to hear any slight difference in these 2 rectifiers.

I personally don't think there should be a huge difference in tone with the 5U4, unless your 5Y3 was almost dead or of poor quality manufacturing.   

Best regards,

[tubeswell]

Provided your PT 5V winding is rated for 3A, you will be fine using a 5U4G in your 5F1. Will you like it? -  only you can tell.

[HotBluePlates]

I read on the SDUF that using a 5U4 gives a better tone than the 5Y3. ...

Everyone tip-toed saying "yes" or "no" because "better tone" is subjective.

A 5U4 is a bigger tube (physically and electrically) than the 5Y3. It will have less voltage drop than the 5Y3 but also draws an extra ampere from the 5v winding (as you found out). If there was a lot of variation in the current drawn from the power supply, the 5U4 would have less age than the 5Y3.

But a class A amp (the 5F1, as a single-ended amp, is class A) has little change in current drawn from idle to full-roar. As a result, the rectifier doesn't really contribute to sag (though other things might). You could expect voltages throughout the amp to rise somewhat.

[leevc5]

Thanks Paul (aka Socrates) and all you all for your help.
Lee