Blues Deluxe channel Limbo

[Mars Amp Repair]

Hello,
with respect to the brute force cheapo zener regulator ciruits, I have found in some of the Crate amps, that the amount of current that is needed from the +- 16v circuit is much much less that the current feeding the zeners.

Years ago I think the standard in a standard voltage divider was to have the resistor to ground (or zeners in this case) drawing 4 times the current the circuit would require.

I've been able to increase the dropping resistors without any affect on the zenered voltages even under the most taxing switching or whatever is drawn through those dropping resistors. I've even dropped the a/c input with Variac & have not had issues with the voltage at the zeners even close to causing the zenered voltage to drop. When you're dropping 40volts down to 16, there's a lot of headroom to keep those zeners conducting.

In one Crate amp I was able to raise the value of the dropping resistors enough to replace the 10 watters with 5watters.

I don't usually believe in redesigning things but I have to think someone blew it with these zenered supplies. It's just way too much wattage being dissipated for the current needed on the +-16v lines.

Now I don't know about this particular Fender...you'd have to experiement. glen

[Enzo]

OK, but I'd make the case that a zener is not the same as a voltage divider.

VOltage dividers need rules like that so the divider resistance doesn't interfere with the circuit. Zeners don't work by resistance.

These are 5 watt zeners in the Crates The more current through the zener with respect to the load from the circuitry, the smoother will be the regulation. ANd that is the point. If you just want some nice voltage, replace them with plain old 1 watt zeners and raise the resistor appropriately.

[Mars Amp Repair]

I hear ya enzo. I believe the resistances of a voltage divider supply really have little to do with what circuits they are supplying...the supply should draw enough current so the circuit won't cause it to draw more current than the divider is. In the zener model, basically the same applies but agreed with different parameters.

if the load is only drawing max of say 1watt, then the zener supply doesn't need to be drawing 4watts. It just needs to be drawing enough so the load current never get close to it's current...thereby dipping below the zeners regulation voltage. Just intuititive on my part.

Perhaps someone who actually deals with design...conner I think does...could enlighten us from a design perspective.

glen

[Jay D]

Blues Deluxe Tweed Amp

Hello:
I also seem to have the same problem. I have a Fender Blues Deluxe amp, and was intermittently switching the normal and high gain channels, and the 2nd channel light was dim, and no sound came out of the amp.
In reviewing the Forum, I too have had to re-solder the two 470 ohm, 5 watt resistors, but with silver bearing solder that has a higher melting point than the standard 60/40 rosin core solder. PLEASE care in soldering to Printed circuit boards, as you will be lifting pads, traces, etc. due to the excess heat.
The higher temperature solder has done the trick a couple of times, but the problem sometimes returns.
I finished the Repair, and after about 6 months, another problem occurred. the Input jack became intermittent.
Any suggestions?

[52 Bill]

Yes, replace the input jack.

[eeijcon]

Hi Jay D,

All I can say is I re-soldered the 2 470 ohm resistors and I haven't had the silence/channel switching problem since. Sorry I can't be of more help.

Brs,
John.

[Ron Burati]

Hi Jay D,

All I can say is I re-soldered the 2 470 ohm resistors and I haven't had the silence/channel switching problem since. Sorry I can't be of more help.

Brs,
John.

Those Fenders have a zener diode in the ch switch ckt that can not be very far off or the ch switch circuit fails to operate.