AMPEX AVR-2 Low Band Monochrome board set

Model Details

Ampex AVR2 can't play low band, usually.


As a note, they are alternative demod and equalizer boards on the internet. We found this:

Great information on how to build this board yourself by www.cameratim.com
Currently there is an issue on his website, so you may use this link:
http://www.cameratim.com/electronics/ampex-quad/avr2-lowband-modification.

Additional Detailed Information:

The Ampex AVR2 can't play lowband, usually.  There are alternative demod and equaliser boards that can be swapped in, but we didn't have any.  We did find a website selling custom modified boards that could be switched between lowband and highband playback, but the cost was rather incredible, and couldn't see that being cost effective, for us.

extract from www.cameratim.com:

Since we do have the manuals that detail both the highband and lowband boards, we went down the route of modifying some spare highband boards, and would live with swapping boards over, for the few lowband tapes we have to deal with.  There's very little difference between the highband and lowband boards, namely:

• Capacitors and coils in the equaliser RF output low-pass filter.  The highband filter turnover frequency is 14 MHz, and the lowband filter turnover frequency is 10 MHz.
• Capacitors and coils in the demod input low-pass filter.  The highband turnover frequence is 6 MHz, and the lowband filter turnover frequency is 4.5 MHz.
• Some gain and DC bias resistors for the FM demodulator.
• Various resistors and capacitors that form the demod de-emphasis filters.

Whilst the low-pass filters can be left in their original highband configuration, they won't attenuate noise that may appear in the picture as much as they probably should do.  And probably don't equalise the video signal as effectively, either.

We couldn't find core formers that would fit on the board, and faced with special ordering something to do the job, disassembling the original cores and rewinding the coils, or finding something else to wind the inductors on, we took the latter route.  We used plastic sewing-machine cotton bobbins to wind new coils on.  While they're not easily tuneable, we don't have access to a reference playback tape to align them with, nor a spectrum analyser, to do a proper alignment, anyway, but they do the job respectably well.