5V4GA in SF Pro Reverb?

[Drewline]

I was wondering if anyone has an opinion on using a 5V4GA in place of a 5AR4 in a Blackfaced 69 SF Pro Reverb. A 5U4 was the original rectifier. The amp has the exact same transformers as a 66 BF Pro Reverb I'm working on. The 66 with a 5AR4 has 460VDC on the plates, The 69 has 425 with a 5U4, 445 with the 5V4, & 460 with a 5AR4. I'm not looking to spend boatloads on a NOS 5AR4 & I do have a 5V4. I do not know much about 5V4s so thats why I'm asking.
Thanks in advance!

[mozz]

If you have used lower and higher voltage dropping tubes, why not then? If it's a current issue, it should be easy to look up and see what each handles. There is a website with a chart showing drop, current needed, and current handling.

[Drewline]

I was wondering about reliability. I've only used 5U4s in this amp. I don't trust the current production 5ar4s & don't want to spend the money for a NOS tube. I was hoping someone on the forum had experience with 5v4s.

[g1]

I'd be concerned about the max voltage and current specs.
The attached charts shows basic specs and voltage drops for most common rectifier tubes.

[robrob]

The 5V4-GA pulls the same 5v current as the 5AR4/GZ34 but it does supply less B+ current. It's adequate to run the amp but you may get a little more dynamic voltage sag--which can be a good thing.

Chart from 300Guitars.com

[g1]

The 69 sf pro PT is rated at 375V out to the rectifier plates. The 5V4 is rated 375V max.
With modern line voltages being hotter, the PT may put out more than 375V so reliability of a 5V4 may be compromised.
I know tubes are constantly being used beyond their max. ratings, but the poster did mention that reliability was the concern.

[Drewline]

Thanks guys for the replies. I'm not comfortable with the 375V max rating so I've decided to abandon this idea & just go with a modern 5AR4 after installing diodes between the transformer & pins 4 & 6. I'll save the 5V4GA for another day.

[Gingertube]

I used 5V4 on an HiFi Amp I built for Niece Jessica. 2 channels of 6V6 push pull.
Fot your possible interest:
Cheers,
Ian

[Drewline]

All's well that ends well. 465V on the plates with a Sovtek 5AR4. The 66 Pro Reverb measures 462V. Sounds good, the 5V4 will most likely go into my old Gretsch 6156 Playboy instead of the 5Y3. But that's for another day. It's too nice to stay indoors. Cannondale time!

[robrob]

Thanks guys for the replies. I'm not comfortable with the 375V max rating so I've decided to abandon this idea & just go with a modern 5AR4 after installing diodes between the transformer & pins 4 & 6. I'll save the 5V4GA for another day.

Using rectifier socket mounted "backup diodes" will pre-rectifiy the high voltage AC and feed your tube rectifier plates DC pulses so the tube doesn't have to deal with 750+ volts AC RMS plate-to-plate. The diodes also almost double the tube's peak inverse plate voltage rating, in other words backup diodes make life much easier for the tube rectifier and they protect the amp including the power transformer from a tube rectifier short failure. You still get the tube's dynamic voltage sag so the amp's tone isn't affected. The 375v rated 5V4-GA would more than likely live a long happy life in your Super Reverb when paired with a set of 10 cent backup diodes.

[Drewline]

Hi Rob,
Thanks, I never thought about the diodes as raising the peak inverse plate voltage, just as a means of making current 5AR4's last longer. At this point I'm leaving the Sovtek 5AR4 in since the amp sounds great.