Fender Deville 212 Speaker Change

ICBM

Octafish said:

Yes, the little plastic block connector has become detatched.

The worse problem is that the weight of the plastic block vibrating about on the pins is often enough to break the very fine coil wires where they pass over the edge of the bobbin. This is very hard to fix, although it can usually be done. (I have a success rate of about 2 out of 3.)

It's just a poor design - Accutronics introduced it about 20 years ago. The real shame is that when Accutronics were bought out by Belton a few years ago, Belton chose to adopt the Accutronics design and not their own directly-wired (like the original Accutronics method) construction - TAD/Ruby tanks use the direct wiring. Losing Fender as a customer must have hurt.

crunchman

Octafish said:

ICBM said:

Octafish said:

I've just checked the bias and it was at 57mV, so a bit under. I last biased it about a year and half or so ago when I did a valve change and set it to 69-70mV. Can it wander out that much?

Yes, as the valves wear.

With the relatively high plate voltage in the Deville - it should be around 485V even with the mains voltage reset to 240 - you ideally need about 31mA per valve, or 62mA for the pair. (15W dissipation per valve.) Even at the lower voltage and accounting for screen current, 70mA is too high really.

Ah, ok! I was going off info from the old Hot Rod Deville/Deluxe site that suggested that the bias Fender set in the factories (about 60mV) was too low/cold and to aim for around 67-68mV. I will knock it back a bit.

The 67-68mV might be about right for a Hot Rod Deluxe as the plate voltage on that is lower (nominally about 430V), although I measured 456V on the plates of my old one when the wall voltage was 246V.  I didn't realise there was another tap on the mains transformer though. That would have put it closer to the nominal voltage.