AB-763 w/ EL-84's?

[duke of earl]

Anyone ever build a  rig like this with a tube rectifier? I like the AB-763 a lot but would like to lower the wattage.

[HotBluePlates]

Power output would be the same as if you used 6V6's.

In fact, you could use the schematic of the AA1164 Princeton Reverb, though you should expect to have to tinker the bias circuit for less negative voltage to happily idle the EL84's.

[tubenit]

I have not built a AB763 with EL84's.  I think it would be pretty close to the same wattage as a Deluxe Reverb and more than a Princeton Reverb.

If you're wanting a lower wattage AB763, one way of approaching  would be to build a cathode biased Deluxe Reverb and use a VVR to get the voltage lower on some 6K6 tubes?  Just a thought?  The amp would have about 8 watts of power (way less than 18watts using EL84's)

Using 330R/10W resistors, I am able to switch between 6L6 & 6V6 using a GZ34 or 5V4.  Then using a 5Y3GT, I can use 6K6's.  This is in my
D'Mars ODS.

So, with a VVR and three different rectifier tubes & cathode biasing ...................   you could easily use 6L6, 6V6 or 6K6 tubes in this amp.

The VVR would allow 275v on the 6K6 plates while still allowing the higher voltages on the preamp and LTPI tubes.

The schematic was drawn quickly and is only a DRAFT for illustration purposes.  Check for errors!  

With respect, Tubenit

[Geezer]

For lower wattage, I would use something like a 6BM8 or similar.

G

[duke of earl]

I am currently building a BFDR style amp w/ 6v6's. What size cathode resistors would be a good starting point for this application?

[sluckey]

The BFDR is fixed bias and uses no resistors under the 6V6s. But if you intend to convert to cathode bias, then a shared 250Ω or separate 500Ω cathode resistors would be typical.

If you're talking about the little tubes, just use what's on the schematic.

[tubenit]

Got to thinking about it ...............

IF you used a PT that had 275-0-275 & then used a rectifier tube socket, you could use a 5Y3GT, or 5V4, or GZ34 or the solid state plug in rectifier that Hoffman sells.

That would give you around 300, 325, 350 or 375v and allow you to use the 6K6 or 6V6 or 6L6/5881.  IF you used cathode bias, then swapping tubes would work instead of using a VVR.  OR if you set up the fixed bias with enough sweep, you might still be able to use a fixed bias approach?

I thought about mentioning the 6BM8 tubes, but I think the 6K6 will preserve more of a Fenderish tone. I have used both & feel like the 6BM8 tube does more of a Marshallish type tone.  I also have learned that I prefer to use a 12A_7 for the LTPI with 6BM8 so I can use different 12A_7 tubes.

With respect, Tubenit