5AR4 to 5U4 Rectifier

[Tenderfoot]

Fender has said I could use a 5U4 in my Fender Custom 64 Deluxe Handwired to reduce the plate voltage on my NOS 6V6GT power tubes. They said it would not affect my warranty but cautioned that I would have increased SAG and less power output.

I currently do not have a 5U4 to experiment with.

[So] My question is, will the increased SAG present a tone change? If yes, will it be to the better or worse?

Anyone who has went from a 5AR4 to a 5AU4 in there DRRI (or similar amp) i would appreciate your input.

Thanks Tenderfoot

 

[Viejo]

You may like the sag or you may not. A 5U4 will run the Power tubes at a lower voltage than a 5AR4 and should increase their lifespan. My only worry with 5U4s is the increased filament(heater) draw. A 5U4 will draw more heater current than a 5AR4. A DRRI like the Blackface Deluxe Reverbs that are copied from have a lot of tubes so the current draw is already pretty high. I have no idea how robust the Heater winding is on a DRRI. There is a NOS tube, the 5R4 that has the lower voltage of a 5U4 and draws nearly the same current as a 5AR4. I have run them as replacements for 5AR4s they are relatively inexpensive and have lasted for years in my amps.

 

[telemnemonics]

I have amps that can handle a variety of rectifier tubes as well as amps that don't have the current capacity to support for example a 5u4, or that require more current than a 5u4 or greater sag rectifier can deliver.
Sag is slang, but current draw of power section requires current capacity of the rectifier tube, and you'll hear not only sag going to a 5u4 in that amp but also lower voltages in the power section.
Lower B+ voltage generally results in the power tubes producing less bass & treble, which changes the tone.

A given amp might respond differently than this generalization though.

And in old production there have been same model Fender amops that called for 5ar4 in one era and 5u4 in another era.
In many cases you can't swap because the PT doesn't supply enough current to run a 5u4 which draws more current while supplying less current. A 5u4 also has more startup voltage spike than a 5ar4, which may stress components in certain amps.

 

[AndyPanda]

5U4 tubes can be had very inexpensively for NOS made in USA tubes. Well worth buying one and trying it to see if you like it. I bought a pair of "used test like new" Tung-Sol USA for less than $20 (for the pair) after shipping. I've got several brands of 5U4 and they all give a different B+ voltage. I have one old 5U4 that is 30-40v lower than my strongest 5U4 and that old/weak one is my favorite for how the amp behaves when pushed.

Like others have said already, make sure your amp can handle the increased current draw.

 

[Vibrolux59]

I have a few '60s blackface Fender amps including a Deluxe Reverb. Over the years I've experimented with other rectifier tubes and always come back to (Mullard so far) GZ34/5AR4 tubes because anything else I've tried changed the sound and feel for the worse to my ears.

 

[scooteraz]

Some folks love sag, some don't. Since FMIC says you can experiment, it appears your power transformer can handle the additional current draw of the 5U4. So, buy a tube and let us know how it works for you.

 

[schmee]

I doubt you will hear sag just going to a 5U4GB, it's a ton more amp draw on the power transformer though. I often go to a 5V4 instead if I'm concerned about draw on the PT.

 

[muchxs]

Voltage drop or "sag" depends on load. If you were swapping from 5U4G to a 5AR4 in a '70s Super Reverb you might hear the difference. I can't speak for the '64 Custom but if its' anything like the DRRI... that transformer is a horse. It won't even fit the knockout in an original Deluxe Reverb chassis.

Lemme look up the specs near as I can tell...

It's 325v-0-325v @ around 150ma on the high voltage. It has 5v / 3a available and 6.3v @ 4.5a.


In other words Fender anticipated musicians swapping to 6L6s or alternative rectifiers.


I'd be interested in how much a 5U4G rectifier moves the needle. I'm guessing not much. Bear in mind that if you adjust the plate voltage you need to re- bias as well.

 

[Tenderfoot]

I have a few '60s blackface Fender amps including a Deluxe Reverb. Over the years I've experimented with other rectifier tubes and always come back to (Mullard so far) GZ34/5AR4 tubes because anything else I've tried changed the sound and feel for the worse to my ears.

Thanks, Vibrolux59. I read about the Mullard 5AR4 but understand it is (somewhat) rare and very costly. Ones for sale that appear to have been tested on reliable testes and rated near NOS run anywhere from $100 - $200.

 

[Tenderfoot]

Some folks love sag, some don't. Since FMIC says you can experiment, it appears your power transformer can handle the additional current draw of the 5U4. So, buy a tube and let us know how it works for you.

Thanks, scooteraz. The schematic for the 64 DRHW lists the 5AR4 but right beneath, in parenthesis, the 5U4 is also listed. That's why I contacted Fender as I felt that the OT would handle the 3 ma vs 1.8 ma of the 5AR4.

 

[Tenderfoot]

Voltage drop or "sag" depends on load. If you were swapping from 5U4G to a 5AR4 in a '70s Super Reverb you might hear the difference. I can't speak for the '64 Custom but if its' anything like the DRRI... that transformer is a horse. It won't even fit the knockout in an original Deluxe Reverb chassis.

Lemme look up the specs near as I can tell...

It's 325v-0-325v @ around 150ma on the high voltage. It has 5v / 3a available and 6.3v @ 4.5a.


In other words Fender anticipated musicians swapping to 6L6s or alternative rectifiers.


I'd be interested in how much a 5U4G rectifier moves the needle. I'm guessing not much. Bear in mind that if you adjust the plate voltage you need to re- bias as well.

Thanks, muchxs. I was aware of having to rebias (have a bias probe and technical knowhow) but appreciate the reminder - sometimes when we get older we forget some of the required details

 

[Vibrolux59]

Thanks, Vibrolux59. I read about the Mullard 5AR4 but understand it is (somewhat) rare and very costly. Ones for sale that appear to have been tested on reliable testes and rated near NOS run anywhere from $100 - $200.

Yeah, I've seen that and that's why I said so far. I stashed a couple of exras sometime when you could still find NOS for under $100 and they are a well-made tube that tends to have a long life. These are my life long amps so if it takes a few bucks to keep them right I'm still in cheap for what they are and 50 years of service. As someone mentioned above I've used 5V4s in some amps and my Clark Piedmont has a Russian 5AR4 and performs well.

 

[Axis29]

I run Weber Copper Caps in two of my tweed amps (one a vintage amp) to lower B+ to align properly wit the original schematics. They are solid state rectifiers that approximate tube rectifiers. I use the equivalent of a 5R4, which is an even bigger voltage drop than the 5U4. I really like what it does.

I wouldn't' say it changes the tone, exactly. But, it does create a little more feel to the amp. It makes the gain a little softer, maybe? Nice thing is, good vintage 5u4 and 5r4 tubes are rather inexpensive. Easy, inexpensive experiment. One of my amps originally came with a solid state rectifier installed ('59 Bassman Ri). It was the equivalent of a GZ34 and it was rather stuff, a little less dynamic. I much prefer the lower B+ (and this lower almost everything else) and how my amps behave.

I use Weber Copper Caps because I cannot guaranty that my transformers can handle a different draw and are affordable. The CC's have no filament draw, so no load, no worry. But, it sounds like Fender has insured that the new amp can handle the draw. That's excellent.


Besides, the price of good vintage GZ34/5AR4 tubes is retarded! I can't justify it... But, I've had two modern GZ34/5AR4 rectifier tubes leave me silent at gigs.

 

[markos]

I've been using a 5R4-GYB for years in my Deluxe, and it works great, bringing my plate voltages down to around 390-395, and introducing a lot of sag. The GYB version can handle up to 20uF input capacitance, but I've seen a few other versions that handle far less, so I recommend checking the tube specs carefully.

A 5U4 is no problem in that regard, but the 3A current draw is cutting it somewhat close. Even here, I doubt if it'll present any problems, esp. considering the above statements. Even if you can't here any extra sag, the lower B+ can have other benefits.

 

[muchxs]

I run Weber Copper Caps in two of my tweed amps (one a vintage amp) to lower B+ to align properly wit the original schematics. They are solid state rectifiers that approximate tube rectifiers. I use the equivalent of a 5R4, which is an even bigger voltage drop than the 5U4. I really like what it does.

A couple SS diodes and a big resistor doesn't exactly emulate the performance of a tube.

Years ago it only took me a couple minutes to measure supply voltage under load to prove to my satisfaction that SS and tube don't act the same under load.

A substantial voltage drop will get your amp down towards "Brown Sound". That's what EVH did with his Variac. He'd drop the supply voltage 20%.

A 5U4 is no problem in that regard, but the 3A current draw is cutting it somewhat close. Even here, I doubt if it'll present any problems, esp. considering the above statements. Even if you can't hear any extra sag, the lower B+ can have other benefits.

Near as I can tell the '64 Handwired has 5v / 3a available. If Fender said it's o.k. it's o.k.. They're picky about such things. Their usual answer is, "Don't do that. You'll void your warrantee."

 

[Axis29]

A couple SS diodes and a big resistor doesn't exactly emulate the performance of a tube.

Years ago it only took me a couple minutes to measure supply voltage under load to prove to my satisfaction that SS and tube don't act the same under load.

A substantial voltage drop will get you ramp down towards "Brown Sound". That's what EVH sis with his Variac. He'd drop the supply voltage 20%.



Near as I can tell the '64 Handwired has 5v / 3a available. If Fender said it's o.k. it's o.k.. They're picky about such things. Their usual answer is, "Don't do that. You'll void your warrantee."

Muchxs, I know it's not exact. But, I feel more comfortable with the SS rectifier because of the lack of filament draw. But, i just looked at the rectifier voltage drop chart on 300 guitars, and I see that a 5r4 only pulls 2 amps. So, now I am questioning it all! LOL

 

[zombiwoof]

A couple SS diodes and a big resistor doesn't exactly emulate the performance of a tube.

Years ago it only took me a couple minutes to measure supply voltage under load to prove to my satisfaction that SS and tube don't act the same under load.

A substantial voltage drop will get you ramp down towards "Brown Sound". That's what EVH sis with his Variac. He'd drop the supply voltage 20%.



Near as I can tell the '64 Handwired has 5v / 3a available. If Fender said it's o.k. it's o.k.. They're picky about such things. Their usual answer is, "Don't do that. You'll void your warrantee."

The Weber Copper Caps are not plain old SS rectifiers, they are designed to mimic the voltage drop/sag of tube recs.
Al

 

[Dacious]

Voltage drop or "sag" depends on load. If you were swapping from 5U4G to a 5AR4 in a '70s Super Reverb you might hear the difference. I can't speak for the '64 Custom but if its' anything like the DRRI... that transformer is a horse. It won't even fit the knockout in an original Deluxe Reverb chassis.

Lemme look up the specs near as I can tell...

It's 325v-0-325v @ around 150ma on the high voltage. It has 5v / 3a available and 6.3v @ 4.5a.


In other words Fender anticipated musicians swapping to 6L6s or alternative rectifiers.


I'd be interested in how much a 5U4G rectifier moves the needle. I'm guessing not much. Bear in mind that if you adjust the plate voltage you need to re- bias as well.

I swapped between 5U4 and 5AR4 in my 78 VR. B+ barely moved but the sag altered - IIRC the 5U4 had a lot more internal plate impedance.

A 5V4 dropped it a fair bit, like 20-30 volts but I didn't like the effect on tone.