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5AR4 verses 5V4

8/13/1999 3:53 AM
5AR4 verses 5V4
I just blackfaced a 73 DR and was going to put in a NOS gz34/5ar4 as a rectifier tube but found I didn't have any. My books cross to a 5V4. I put it in and found my plate voltages running at 420 with the bias around 22 to 23. I was wondering what the the difference is between the two tubes? I notice a cleaner sound almost a fender twin sound in this amp. Can this be attributed to the 5V4? Thanks in advance.  
8/13/1999 4:04 AM
John Stokes
They are similar. The 5AR4 can handle higher current. It will also typically have less voltage drop.  
8/13/1999 10:23 AM
If there would be less voltage drop I would assume that the 5ar4 would be cleaner than the 5v4. This isn't the case on this amp. I took a 5ar4 out of one of my other amps and the sound was more like a BFDR. Had more break up and edge. I thought that I read in here that the higher voltage and less voltage sag means cleaner sound. Do I have that backwards?  
8/13/1999 1:11 PM

I've always heard that the 5V4 was somewhere between  
the 5Y3 and 5AR4 in terms of "stiffness".  
Perhaps your old 5AR4 is going "south".  
8/14/1999 12:24 PM
When I put in the 5ar4 my voltage at the plated jumped to 440 with a bias of 18. I biased the amp to 22 and the voltage came down to 430. Thats in comparison to the 5v4 with 22@420. That would seem to support your claim for cleaner but the sound doesn't. I stuck in another 5ar4 out of one of my other amps and it sounds the same. I don't think they could be bad. They also test good in my conductance tester but I like to test them in a circuit to make sure. I have 2 DR's a 71 and a 73. Both have been blackfaced internally. I like the sound of both of them but they sound distinctly different and it seems that the only difference in the amps is the rectifier tube and the fact that the transformer was changed in the 73 to one from 1978. Could that make a difference?  
8/14/1999 12:27 PM
thats the power transformer that is from 78
8/14/1999 4:04 PM

For what it's worth, I find that it's kinda hard to get a good sweet sound out of 6V6 tubes when the plate voltage is much higher then 410-420.  
440v@18ma might be "safe", even 430@22ma when using NOS tubes might be OK but I'd try and physicaly get the plate voltage down.  
Not that you were implying this, but, I think it's a mistake trying to get plate voltages down by increasing idle current.  
If you are not using NOS 6V6s, then that is maybe is why the 5V4 sounds better anyhow.  
For fun go out an buy a Sovtek 5Y3.  
This are MUCH stiffer then a NOS 5Y3 and actually work pretty good in a DR. They won't last as long as your 5V4.  
IMO, most new 6V6s tube start sounding very poor at plate voltages in excess of 420vdc.  
The RUBY 6V6 is better but a good NOS 6V6 kicks it butt too.  
Just for fun, I ran a pair of RCA 6V6GTAs in a BF Super Reverb for a while. Hard to believe they could take it, but I did run them for a fair number of hours with no I'll effects, while a matched pair of Sovteks lasted as long as it took me to get the bias voltage set right and start putting a big signal into them... less then 5 mins.  
I've been using idle current that places the 6V6s in the +10 watt range for a pretty nice sound, but they still sound better to me when the plate voltage is 410v or less, and I really like them better at 390v-400v @ 26ma-32ma when using the OT shunt measuring method.  
As mentioned a number of times, the SF and newer DR amps used a 5U4 and the PT was slightly overwound to compensate for the additional voltage drop of the 5U4.  
So when using a 5AR4, or any other rectifier that is stiffer then a 5U4, rectified B+ is always a bit too high.  
When using a 5AR4 in these amps, I've been sticking a 24v zener diode in the center tap to drop the B+ down a little and then redo the bias supply to get the 6V6GTA tubes to idle around 10-12watt area. I know that's a bit hot.  
Don't forget to use a 1K 2w screen resistor on each tube socket's pin 4 too.  
I use NOS 5V4s in a 40 watt version of a Super Reverb I build with three 12AX7s, one 12AT7 and a pair of Svet 6L6s.  
The 5V4 is not stressed too much and I like it a lot.  
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