5R4-GY Rectifier Tube in Deluxe Reverb?

[waspclothes]

Hey guys,
I have a SF Deluxe Reverb with a very high B+ of 456V. Currently it uses a 5U4-GB rectifier tube and I impulsively picked up a 5R4-GY tube, expecting that the B+ would drop about 16 additional volts based on the charts I've seen.

Before I stick this into the amp, is there anything I should be worried about? Can the 5R4-GY handle 40uF before the choke for example?

Mike

[The Dude]

I see no reason it wouldn't work.

[nashvillebill]

Did you try modeling it on Duncan's Power Supply Designer PSUD2 (free download if you don't have it already)

[Jammin'John]

Yes

That will be no problem.
I use 5R4's for the same reason.

JJ

[waspclothes]

Hi guys, I installed the 5R4-GY in the DR. B+ Dropped about 15V from 456 to 441V, and I rebiased the amp accordingly. Truth be told, I don't hear any differences.

Does the 5R4-GY have different sag characteristics compared to the 5U4-GB, or is sag just related to how much filtering there is?

[pdf64]

Don't get too hung up on a few V this way or that on the B+; it's just a multiple of the line supply, which can vary a fair bit, according to anticipated cf actual load on the distribution system etc.
My experience is that a 5R4 will give about the same VB+ as a 5U4, but will reduce the load on the PT, as its heater is 2A cf 3A.
And there will be bit less heat build up in/around the amp cab.
What really matters with VB+ is what happens at full load, with the amp screaming; it will likely drop way below 400V, nearer to 350V even. That's the real effect of sag.
Whereas with a GZ34, it will stay maybe >50V higher at full load.

[mhuss]

Does the 5R4-GY have different sag characteristics compared to the 5U4-GB, or is sag just related to how much filtering there is?

The sag depends on the rectifier effective series resistance as well as the filter capacitance. The 5U4 is about 200 ohms and the 5R4 is about 270 ohms, so the latter will drop more voltage and also cause a *bit* more sag, but as you've observed, probably not enough to notice.

Edit: Actually the older Deluxes used a 5Y3 and the newer ones use a GZ34/5AR4; the 5U4 uses a lot more heater current, and is probably stressing the PT. A 5Y3 will give you more sag if you want to try it.

[waspclothes]

Don't get too hung up on a few V this way or that on the B+; it's just a multiple of the line supply, which can vary a fair bit, according to anticipated cf actual load on the distribution system etc.
My experience is that a 5R4 will give about the same VB+ as a 5U4, but will reduce the load on the PT, as its heater is 2A cf 3A.
And there will be bit less heat build up in/around the amp cab.
What really matters with VB+ is what happens at full load, with the amp screaming; it will likely drop way below 400V, nearer to 350V even. That's the real effect of sag.
Whereas with a GZ34, it will stay maybe >50V higher at full load.

Thanks for the reply pdf64. I'm actually looking for LESS sag in this amp as well. I run it full out screaming as you said, and I find the excessive sag sort of kills the dynamics at that volume.. just too much compression. I tried the 5R4-GY rectifier tube instead of the original 5U4-GB because I was hoping the lower B+ would give me a bit more distortion at lower volume, but that isn't something I noticed.

Interesting that GZ34 has less sag. It's too bad that this SF amp would have a -very- high B+ with a GZ34, otherwise I'd try it.

[pdf64]

Maybe consider a small bucker transformer Vintage Voltage Adapter to reduce the PT primary voltage, if the heater voltage is high too (which it tends to be)?
Then the B+ may be low enough to use a GZ34, which have way less sag.

Bear in mind that bias shift / blocking distortion at the power tube grids may be causing some of the compression under overdrive.
I like to lower the power tube grid leaks to 100k to reduce that effect.

[km6xz]

Less sag means moving to rectifiers with less forward drop, lower IR drop but that means higher but stiffer B+. A GZ-34 is more efficient and due to the lower drop handles more current, a very good tube from Ruby is the only one that acts like a Mullard GZ34 of old. There are a number ways to drop B+ including power zeners, and then with low enough PT secondary voltage getting to the rectifier tube, the even stiffer solution is solid state rectifiers which drops load on the transformer which lowers heat and increased supply stiffness even more.Another way is a bucking transformer in the primary but make sure the heater voltage is not dropped too much. It is even possible to use the unused 5 volt heater winding as a bucking coil, putting it in series with the primary lead, and reverse the phase which would drop B+ about 20-30 volts. The insulation of the 5 volt winding is easily high enough for 120 volts.

[waspclothes]

Hey guys,
I have a SF Deluxe Reverb with a very high B+ of 456V. Currently it uses a 5U4-GB rectifier tube and I impulsively picked up a 5R4-GY tube, expecting that the B+ would drop about 16 additional volts based on the charts I've seen.

Before I stick this into the amp, is there anything I should be worried about? Can the 5R4-GY handle 40uF before the choke for example?

Mike

Update:

So I've been using the 5R4-GY for a while, it did drop the B+ about 15V but I found the sound to be worse. I play the amp volume at around 9 most times, and I noticed that the sag was a bit more with this rectifier and not worth the pretty insignificant attempt at getting the 6V6's operating voltages closer to spec.

So I've gone back to the old rectifier.

Does anyone want the 5R4-GY? I believe I paid $15 for it, but will sell it for $10 plus shipping (from Canada).