Click to enlargeCHECK IT OUT! SEE IF YOU HAVE
THIS PROBLEM
ALSO EZ TUBE AND PHASE INVERTER TEST!

WOW, MANUFACTURING ERROR on  the Fender HotRod Deluxe.

We found this error this week on a stock, untouched HotRod deluxe - a pretty severe error as the amps were obviously shipped with this error built in.

Since we know the circuit boards are loaded from "ammo pak" type parts batches this could appear in a LOT OF AMPS.

We noticed the amp sounded really ugly and weak. It obviously had crossover distortion, even with new tubes and bias set correctly.

As we have learned from experience the plate load resistors for the phase inverter burn out - they are often 1/4 watt resistors, not up to the voltages present on that circuit.

these resistors are on the tube circuit board,  R57 (82K) and R58 (100K) -

In checking these parts in place I found that R57 was 82 ohms, not 82,000 ohms. - this had NO GAIN and caused half of the phase inverter to not work at all -

this makes only one power tube work giving terrible terrible crossover distortion. Both both tubes should be working all the time.

This is why the amp sounded lousy.

BUT, the real worry is that this was a stock factory installation - machine inserted and wave soldered in place.

This amp left the factory, and later on left the store in this condition.

Why anyone would buy an amp that sounded this bad is beyond me, couldn't they hear?

EZ TEST FOR A BAD PHASE INVERTER - ALSO FOR A BAD POWER TUBE

To test your amp for this problem, take out one of the power tubes - if it doesn't sound any different, you have the bad phase inverter OR a bad power tube.

If you get no sound, you obviously have the bad phase inverter and/or a bad power tube.

the tube affected by the resistor error is the right hand one, the one next to the preamp tubes.

Check your amp to be sure R57 is really 82k ohm (Gray/red/orange is 82k - 82 ohms is Grey/red/black), and R58 is really 100k ohms (brown/black/yellow).

 If not,  carefully change them to the correct values so you have your whole amp working right. If this is too difficult for you - and it is pretty hard to get that board out of there, desolder from a printed circuit board, and refit parts without destroying traces, then get a pro shop like ours to fix if your you.

this also points out a really horrid "internet trick" that is totally wrong. You CAN NOT remove one power tube of a two power tube amp to get half power.

both tubes are needed in the Push Pull circuit. they "trade off" amplifying the signal milli-second to milli-second. Half the wave form on one tube, the other half on the other - taking one tube out clips off half the wave form creating a horrible sounding crossover distortion, and leaves half the output transformer  running its signal into no load - this will burn the output transformer up in short order, the bias supply, the phase inverter and  WILL NOT give half the power, more like 1/10th the power until eventual failure of many parts.

Of course we offer diagnosis and repair of this problem in our shop every day and can fix if for you.
Torres Engineering
Tech Dept.



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