Power transformer spec question for recent build.

[tony321owen]

I am very happy with my recent build which is a cathode bias push-pull amp using some princeton reverb style transformers I had left over from another project. I used the low voltage tap on my pt secondaries which gives me 275-275 @ 100ma.
While experimenting I somewhat foolishly substituted a 5u4gb rectifier tube in place of the 5y3 that I initially was using unaware of the heater current requirements. I fell in love with what it did to the amps tone and feel! As expected it increased the b+ a bit and all though I usually prefer the softer compression and sag of a 5y3 in this case it tightened up the low end and headroom a bit while maintaining the compression that I love so much. It felt like a very well balanced amp feel that gave up the goods at a very usable headroom level for my  needs..
Then I read about 5u4s and that they require 3A heater current and I quickly saw my error..

Now I am on the hunt for a transformer to match the specs of what i'm using but that allows for 3amp heater current on the 5v rectifier tap so I can recreate the tone that I found to be so glorious. The trouble is I am having trouble finding a pt with the exact specs I need so my question is about if over spec'd PTs will affect the tone..

Here are the specs for the original one i'm using now, the ideal specs for the one i'm looking for and the closest one I can find that matches it. Anyone who can way in on considerations and options would be much appreciated to help me get back to my desired tone without overheating my PT or significantly altering the tone/feel of the amp..

Original:
275-0-275@100ma PT secondary
6.3v@2amp
5v@2amp

Ideal:
275-0-275@100ma PT secondary
6.3@2amp
5v@3amp

Closest I could find: Edcor XPWR038
275-0-275@125ma Pt secondary
6.3v@4amp
5v@4amp

Will using this PT significantly change things or would it be alright to use.. ? I guess I could just buy a small 5v transformer though my chassis space is a bit limited..
Thoughts?

Thanks!
 

[SILVERGUN]

Closest I could find: Edcor XPWR038
275-0-275@125ma Pt secondary
6.3v@4amp
5v@4amp

Thats close enough for me, 'specially if it physically fits. I went right to Hammonds page and 270EX is closest I saw. You did better.

I guess I could just buy a small 5v transformer though my chassis space is a bit limited..
Thoughts?

If you choose to go that route there is this
Project Style, Up to 50W Added Tube Rectifier Power Transformer, 120 / 240V, MADE IN USA (triodeelectronics.com)


What voltage did you wind up with the 5U4GB in there? Edit - not a clearly worded question
What voltage did the 5V supply sag down to with the 5U4GB in there?

[sluckey]

Try a 5AR4/GZ34 before replacing the PT.

[tony321owen]

thanks for the tips! I tried a gz34 in there and all though it sounds really good and the bass is tight it doesn't have the sag characteristics that I require so I went with ordering the classictone 5v transformer as silvergun suggested. I think I can fit it on my chassis in between the PT and OT. Im guessing that I will need to orient it so that it's 90 degrees off axis from the OT. Do you guys think a small transformer like this is a noise risk if its within a few inches from the OT?

[dude]

If the increased voltage of the 5AR4 didn’t satisfy you, maybe a 5V4GT. You won’t get the 5UG4 sag but over double what a 5AR4 gives. Just make sure your first filter is not much higher than 20uf

[pdf64]

Before buying another PT, I suggest trying a 5R4 rectifier.
They’re pretty close to a 5U4, feel wise.
However, they’re a big valve!

[DummyLoad]

Hammond 290HAX is exactly your specs.


--Pete

[Bieworm]

Try putting a 100R to 250R 10W resistor after the B+ at the rectifier..  it provides sag too..
I do this on my SS rectifier builds when I want some sag

[dwinstonwood]

Hammond 290HAX is exactly your specs.


--Pete

I've used both the 290HAX (in my 6G3 Deluxe) and the 290AX (in my Hoffman 6V6 Hot Plexi).

As you can see in the image, the differences are that the AX has two HT secondaries, while the HAX has a 50V bias tap. There's also a 1/4A difference in the 6.3 ratings.

[mresistor]

Before buying another PT, I suggest trying a 5R4 rectifier.
They’re pretty close to a 5U4, feel wise.
However, they’re a big valve!

The 5U4 can be bigger than some 5R4s .  left is 5U4GB  right 5R4GB

[DummyLoad]

> ....the differences are that the AX has two HT secondaries,

The 290AX has a single HT secondary with two taps, not two HT secondaries.

--Pete 

[tubeswell]

How hot does the PT get when running the 5U4? Some ‘underrated’ PTs can still cope, even though they’re working harder (thinking about the original PT for the 5U4 rectified Supro Tbolt). If you love the tone, but are buying another PT anyway, why not just keep running the 5U4 for as long as the current PT holds out? You might be surprised how long it lasts like that.