Fender rectifier tubes.

Haych

What’s the deal with rectifier tubes? Are all equal or do they vary in function (pin out - I.E. can one do harm to an amp by plugging in the wrong tube) and sound. 

Is one type of tube “better” than another, if so, how/why?

When changing rectifiers, either for the same type or an alternative type (assuming that’s possible) will the amp need rebiasing?

Lastly, the plug in solid state type, does using this type put more strain on internal amp components? I hear these are more efficient at rectifying the juice and give a tighter sound but can also affect tube bias and stress caps and valves more? Is this correct?

Thanks in advance. 

jpfamps

Different types of rectifier will have greater voltage drop across them, which does affect the sounds.

For example the GZ34 / 5ARA drops the least voltage, so you would anticipate greater headroom and less compression whne the amp is cranked.

In contrast a 5U4G will drop more voltage and compress the output more.

You should be a aware of this is you want to experiment with different recifier types, as for example the higher voltage you would get from using a GZ34 in an amp designed for a 5U4G could result in components in the power supply be run over their voltage tolerance (eg filter caps).

A simple SS replacement plug in would result in the highest voltages, although there are some SS plug in devices that replicate the voltage drop from a valve rectifier.

Anything that affects the HT voltage in the amp may also affect the biasing of the output valves, so this may need to be taken into consideration too.

There is no "better" recticifer valve; however if the amp is designed correctly then it should work best with the rectifier valve it was designed to have.

Haych

So an amp that’s designed around a 5AR4 should be fairly safe to experiment with different rectifiers? Or have I got that wrong?

RiftAmps

You'll need to check the specification of the Power Transformer to see what current rating the 5v winding is. Nearly all 5v rectifier valves need 2A heater current but a 5U4 needs 3A. Plug one of these into a PT that can't handle it and you'll risk damage.

The simple idiot-proof rule is:

"If you're not sure, don't try a 5U4"


Here's a simple comparison chart

ICBM

Haych said:

So an amp that’s designed around a 5AR4 should be fairly safe to experiment with different rectifiers?

Not necessarily.

Depending on the amp, some rectifiers (especially the 5Y3) may not have a high enough forward current rating for more powerful amps and could be damaged. You also need to be a bit careful with filament current draw - some types (especially the 5U4) draw more current and will put an additional load on the PT.

The higher the forward voltage drop of the rectifier, the lower the output power of the amp will be and the greater the 'sag' when driven hard. Lower forward voltage drop gives more power and punch.

Most modern amps will be fine with a solid-state (non-valve-emulating) plug-in which has no voltage drop and no filament current draw, but with older ones you may need to increase the filter cap voltage rating (usually 450V to 500V is enough). You should check the bias and adjust if necessary.

Some of the less common types are worth investigating - especially the 5R4 which has very similar characteristics to the GZ34/5AR4 (low filament current draw, high forward current and voltage rating) but with much more forward voltage drop so is suitable for reducing power and increasing compression in a typical 40-50W amp, and the 5V4 which has more voltage drop than the GZ34 but less than the 5Y3, and adequate forward current rating for 30W amps which the 5Y3 doesn't.

Haych

Thanks all, interesting stuff. I really wish I knew more about how amps work in this regard (and all others tbh). I am aware of the basics but just knowing this stuff by rote is something I doubt I’ll ever have. 

I dont suppose it happens overnight though, it’s very obvious you guys have years of hands on experience and knowledge. Much kudos to you.