Tube rectifiers...

[FunkyE9th]

My experience playing through amps with tube rectifiers is very limited so I was wondering....How does it affect the amp? Is it more a change in the feel or a change in the sound of the amp?

Thanks,

-FunkyE9th

[Firestorm]

It depends a lot on the rectifier tube in question. They all will reduce B+ (in varying degrees), so you'll have all the sonic benefits/consequences of that. They also (in varying degrees) will tend to sag under load, so the amp will have more compression when playing hard; this can be beneficial in some blues or rock styles, but can also be problematic if you play a lot of fast runs -- you may find that the amp can't keep up with you.
Generally speaking, the "fastest" rectifier tubes are those with indirectly heated cathodes, in particular the 5AR4 which is closest to solid-state of all tube rectifiers (in terms of voltage drop -- the 5U4 delivers more current, but is sluggish by comparison).
It also matters greatly what brand rectifier tube you use (though on paper, it shouldn't). I once rebuilt a Bluesbreaker reissue amp to make it more JTM45-like, and finally swapped the Sovtek 5AR4 for a Blackburn Mullard. It was one of those I-can't-believe-what-I'm-hearing epiphanies.

[Phil_S]

You should also consider the tube rectifier in the context of the amp. If the amp is a low power amp you may not get any noticeable sag. For example, the 6CA4/EZ81 in a 18-watter supplies plenty of power. Irect=150, which is plenty of juice for that amp.

[jelle]

Firestorm,

After testing my Sovtek 5AR4 I have to say it works great as a bottleneck/slide:lol: ...I keep it away from my amp as far a possible.

It is amazing how much difference a rectifier tube makes. I used to bring a bunch of different rectifiers with me whenever I would gig my Vibroverb. A 5U4 for small clubs and a 5AR4/GZ34 for bigger ones. Worked great to get a breakup going on at the right volume levels!

Jelle

[FunkyE9th]

Thanks all. I'm looking at using a 5Y3 on my 1st build, which will be a SE amp.

[Andy Le Blanc]

playing style deos matter....and sag will show at high volumes
theres a bit-o-compression... some times blurr......or a softer edge
the 5y3 will get you a full load current of 125 ma. at 360 v
with a capacitor input filter....
the other rateing to look at is the plate supply impedance
the 5u4 has a lower impedance... 21.... half the 5y3.....50
and is sometimes described as more musical

[Ears]

Power supply sag effects are a feature of class AB and class B push pull operation much more than in SE operation, if they contribute anything much to SE at all. SE OTrannies run cooler at full power than idle (that's not the reason but illustrates some of the point of difference).
Perhaps someone else will correct me on this and/or inform you better as to why.

[Andy Le Blanc]

one of the factors used to define operation class in a push pull arrange ment is its conduction angle.
the math divides the zero signal plate current
by the max signal plate current..... CA =2*ACOS[-Ipq(dc)/^Ip(rms)]
IE: 2*ACOS[-116ma/210ma]=247.1deg

notice 2*ACOS[0] =180 and 2*ACOS[-1]= 360

a class A the CA = 360 and class B CA= 18O

so in a class A amp theres little or no difference between max and zero
the power has to go somewhere when its not being used and the
tranny looks like a resistor to pure DC

the math gives a good way to determine an operating point too
divide tube draw bias figure by full draw at clip
and the figure between 1.000 and 0.0000 tells you where you really are as far as class....
RCA recomends Ipq/^Ip ratios of 1/5 to 1/10

[FunkyE9th]

The way I understand it...on the positive the cycle of a SE amp, the OT will run hotter but on the negative cycle it will run cooler and the net effect on average is <= the idle dissipation. Are you guys saying that because of this the amp will not work the tube rectifier hard enough to make it sag?

As for the conduction angle where did the numbers 116ma and 210ma come from? Were you just giving an arbitrary sample? I guess I look at those as... 360 means the tube is conducting on both the positive an negative cycle. And 180 just on half the cycle.

[Andy Le Blanc]

the sample came from a GE sheet 6L6
the 360 and 180 are the idealized conditions for class A and B
AB falls between
yes some times an amp wont draw enough to really
push the limits of a rectifier one of the other characteristics of older amps
was to have smaller sized ( low value uf) filter caps..... not a lot of power reserve
youll have to add up what total draw is going to be (pre amp too)
and compare with the rectifier data

[Ears]

The way I understand it...on the positive the cycle of a SE amp, the OT will run hotter but on the negative cycle it will run cooler and the net effect on average is <= the idle dissipation. Are you guys saying that because of this the amp will not work the tube rectifier hard enough to make it sag?

That's what I think I've read in more than one source (sorry but I can't recall exactly where). I haven't personaly verified it and power supply is the area of tube design I'm weakest. It's probably not the rectifier but the reservoire cap that imposes any limitation. I'd also appreciate any confirmation from other readers.

Edit: To me, even from a purely intuitive viewpoint it stands to reason. Supply sag occurs when demand on the supply exceeds its ability to provide it over time. It's the average power demand being talked about, not just that on +ve peaks.

[rfgordon]

As an alternative to the 5Y3, you can run 5V4 or a 5AR4, since they all draw similar filament currents. Don't run a 5U4 on small PTs that might ordinarily take a 5Y3. The 5U4 draws 3 amps, so it'll stress the PT, if not damage it.

Vintage/NOS recto tubes are definitely better made than today's stock. I've had two brand new JJ 5AR4s go "fireworks in a bottle" on first power up in perfectly healthy amps. I think the technical term is "they suck."

I cried the other week when my OT problems burned my lovely German 5AR4!