Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: gfj on April 13, 2021, 02:42:49 am

Title: Hot Rod Deluxe switch issue
Post by: gfj on April 13, 2021, 02:42:49 am

Hi , first time poster and first time repairer of a HRD rev A

First thing done was to replace 3 resistors and 2 zeners , then hard wire the connections to restore some integrity to a heat damaged board.
This is a 2007 build with a 1970's single sided 1 oz copper pcb---WTF.

What i did notice was:

In  normal mode (off) : yellow light on
In  drive    mode        : yellow light on
In  more drive mode   : red light on

Here are the test point readings :  Readings in brackets are from schematic for a rev A Jan 2001

TP31  normal       : + 1.04v (+1.39v)
         drive          : + 1.04v (+1.08v)
         more drive  : + 1.04v (+1.08v)

TP32  chn sel out     : + 0.56v (+0.536v)
         chn sel in        :+ 9.60v (+9.69v)

TP33  normal           : - 13.6v (+16.0v)
         drive              : - 13.6v (- 13.0v)
         more drive      : - 14.0v (- 13.5v)

TP34  normal           : - 4.8v   (- 12.5v)
         drive              : - 4.8v   (- 4.9v  )
         more drive      : - 4.36v (- 4.14v)

TP35  more drive out : - 0.54v (- 0.52v)
         more drive in   : - 9.35v (- 9.92v)

TP36  normal            : - 15.8v (- 15.5v)
         drive               : - 15.8v (- 15.4v)
         more drive       : +17.4v (+16.0v)

Can anyone shed some light on this issue.

Thanks