Rectifier/Power Tube questions for 12W Class AB amp

When rectifier tube is used without a Choke there should be current limiter resistors on anodes. They form first RC filter stage with first capacitor although there are diodes in between. They "flatten" sine wave peaks and then current flows longer time and peak current does not come too high and rectigier tube can last the time it is specified. Look datasheet to verify this. There usually are examples for RC and LC filtering. If your amp does not have a Choke after rectifier possibly you could install it if thee is room on chassis? Choke lowers operative voltage.

JJ is a 6V6 which is said to handle most Voltage but I think that high would need at least 10 000 ohm output transformer impedance.

 

If your amplifier uses 6V6 typical 8000 ohm impedance and has 460V plates using fixed 21mA bias its loadline looks lime this which makes it very powerful and hot. It won't produce 40W because 6C6 can't deliver 200mA but when loadline runs that much above 12W power curve tubes overload although they work push pull.

If amp power supply 6,3V filament could deliver 0.9A more current you could install 6L6 tubes.

 

Replacing the 5AR4 rectifier tube with a 5Y3 will drop voltage by around 40 volts.

 

5V4 will also drop a dozen-20 volts.

 

The tables where voltage drops are listed are when tubes rated max current is used and I believe they are also equipped with current limiter resistors and a capacitor what datasheets define. Still they are nowhere exact but rectifier tube which is rated for more current usually drops voltage less when same current is used than rectifier which is rated for lower current.

However datasheet often show U / I graphs for few rectified AC voltages. Current limiter resistors have minimum value and they could or perhaps they should be bigger when modern transformers are used which are machine wound over plastic bobbin which make windings tight which make voltage drop less when current increase. I use tube rectifier only when I want sag effect and I also use bigger current limiters and sag comes stronger but also because I use toroidal power transformers which voltages seem to stay stable better than EI core transformers.

 

Have no knowledge of this. Maybe wiser minds ........ You may soon find out through experience.
I thought the main component related to sag was the caps.

More 'sag' may improve this.

 

I use a pair of (new prod) Tung Sol 6V6 at ~350V plate voltage and about 10.5W plate dissipation in a Lite 2 (6V6) circuit with 5V4 rectifier. They've been good for 3 years so far, with one of those years seeing VERY regular gig play.

I've redplated JJ6V6 when biased at 95% in cathode bias at 375V.

EH 6V6GT seem to hold up to same conditions as the JJs, and I tend to use them interchangeably.

NOS tubes are ridiculously expensive, and not worth it IMHO. You really can't guarantees the "New" part of OS, and really inventories have been picked through by now, it stands to reason, in most cases. That said, I have a buttload of used 6V6, old stock. They are easy to source in pulls/old tube tech boxes etc. I just roll them, and if they sound good I use them until they don't (I've yet to get to the "don't" part with any pairs I've selected by ear).

IMHO, I wont use a 5AR4 in any amp. If I want that type of response, I use diodes. I use 5Y3, 5V4 and 5U4 primarily.

 

I would try a JJ 5Y3 and 6V6 tubes. What does the tube chart say?

 

This ^^^
For the 6V6s, I've gotten great sound and longevity with new production EH 6V6GT tubes, they're the ones I usually get. The modern Tung Sol tubes sound great too, but they don't last long in my 5E3. The JJs always sound stiffer and a little harsh in comparison to me, though they are very robust.