The Fisher Spacexpander

I got this thing plugged in to my Fisher 400 but there is not much reverb. I can barley hear a difference in the normal mode.
Anyone have any idea where I might look?
It does not have a remote. It has a pot attached to the chassis.
Thank you
Ed
 

Attachments

  • k10.gif
    k10.gif
    31.8 KB · Views: 70
Without a potentiometer connected to the "remote" jack (wired as per the schematic) you won't get any reverb signal, this is normal. The remote pot is for adjusting the reverb signal level mixed with the "dry" signal. Also check the wiring to the reverb unit (spring tank), a reversed (crossed) connection will result in no (or very faint) reverb signal.
The pot attached to the chassis is the "hum adjust" for cancellation of any residual hum.
 
Thank you for the reply.
It does have a 250K ohm potentiometer installed where the plug socket for the remote should be.
There is some reverb effect and the pot does control it but there is just not much.
Ed
 

Attachments

  • IMAG0534.jpg
    IMAG0534.jpg
    136.5 KB · Views: 55
Provided that the 250K pot is correctly wired there's not much who can wrong but the reverb tank or the driver amp. You may try reversing the IN/OUT patch cables to the tank and see what happens. Is the reverb tank the original one ? A picture would be helpful. You can test the reverb driver amp by connecting a headphone to the yellow and green wires coming from the small transformer (remove the tank and turn the pot fully CW), you should have plenty of volume. Allways replace the 25µF transformer coupling cap (C3 on your schematic), if this capacitor open up or has lost his capacitance your reverb level will be considerably reduced. This cap goes to the red wire of the driver transformer. You may use a 33µF/25VDC elcap in this position.
Please note that even when working properly, the SPACEXPANDER reverb effect is not very pronounced, though it must be clearly audible.
 
Last edited:
I believe that it is the right tank. It does say Spacexpander k10 on it. As far as I can tell the pot is wired correctly.
I may be expecting too much. I am going by the reverb that I had in my car in the 60s. It had lots of reverb and when you hit a bump in the road it made all kinds of noise. The good old days.

Thanks again
Ed
 

Attachments

  • IMAG0535.jpg
    IMAG0535.jpg
    54.5 KB · Views: 51
  • IMAG0536.jpg
    IMAG0536.jpg
    51.5 KB · Views: 45
Yes, it's the right tank. Replace C3 (see my previous post), chances are good it will be the culprit.
 
If the wires to the tank are reversed, there will be no reverb at all. The spring driver in the tank has an impedance of 8 ohms, while the receiver in the tank has an output impedance of several thousand ohms. Therefore, reversal will cause a complete no reverb condition.

Drive is surely important, but just as important is the preamp circuit that amplifies the spring signal. Just as with your 60's driving experience, the same is true of this unit as well. A good rap on the spring tank should produce a noticeable racket from the speakers. If not, the preamp circuit should be investigated for proper operation as well.

Dave
 
If the wires to the tank are reversed, there will be no reverb at all. The spring driver in the tank has an impedance of 8 ohms, while the receiver in the tank has an output impedance of several thousand ohms. Therefore, reversal will cause a complete no reverb condition.

That was my first thought and the reason why I suggested swapping the two leads going to the tank. It's too easy to make a mistake here and if the connections were inadvertently reversed there will be no reverb at all. (or a very faint one)

Drive is surely important, but just as important is the preamp circuit that amplifies the spring signal. Just as with your 60's driving experience, the same is true of this unit as well. A good rap on the spring tank should produce a noticeable racket from the speakers. If not, the preamp circuit should be investigated for proper operation as well.


Right, and this is an easy check. (aka the "Boooingg-Boooingg Test") But like in guitar amps,a dead reverb is most often due to a defective tank (open coils or broken wires) or a problem in the driver amp (mostly driver transformer open primary), or wrong connections (see above). In the Fisher circuit the driver primary is (partially) capacitively coupled to the tube cathode and a defective capacitor will result in a reduced driving signal to the tank. As the symptom described is reduced level reverb and not a complete lack of it, this would be the most probable cause. Bridging the cap for a test will only take a couple of seconds (be careful to observe correct polarity !).
Of course this is only a (educated) guess and there might be other reasons which requires more advanced troubleshooting techniques...
 
Last edited:
Agreed. If drive to the tank is the problem, the most likely problem in the drive circuit is C3.

This unit also likely uses one of Fisher's classic selenium bridge rectifiers. While all selenium units will sag with time, the small low current ones are rather famous for it, and for sagging in a big way when they do. If this has happened, it would certainly reduce drive as well. If none of the above efforts resolve the issue, then a check of the power supply voltages would be the next step in your troubleshooting efforts.

Dave
 
I replaced the c3 cap, that may have made a little improvement. I switch it to reverb only and it is definitely working. In the normal mode the pot is turned all the way clockwise and you can hear a slight reverb. When I rap on the tank there is a noticeable racket from the speakers
I will check the power supply next.
I have never heard one working so I do not know what to expect.
Thank you
Ed
 
Last edited:
If anyone is interested in purchasing THE FISHER "DYNAMIC SPACEXPANDER"
complete kit. It is is usually available online at the typical websites for around $50
to $75 bucks on a good day.

EZ install for FISHER enabled systems. The complete sytem sounds & works just fine.
 

Attachments

  • Fischer Space Expander-1.jpg
    Fischer Space Expander-1.jpg
    30.9 KB · Views: 61
  • Fisher Space Expandr-2.jpg
    Fisher Space Expandr-2.jpg
    46.3 KB · Views: 54
  • Fisher Space Expander-3.jpg
    Fisher Space Expander-3.jpg
    47.1 KB · Views: 62
Back
Top Bottom