Philips 3226 Oscilloscope VDR repair

[jpwolfe31]

I just finished a minor repair to a Philips PM3226.  I purchased this used about 25 years ago. 

However, it is not clear exactly how this repair worked and am looking for some advice.

Only 1/2 of the x axis on the scope was working.  I traced the problem down to a VDR in the x final amplifier.  This VDR and several others used in the scope were not specified beyond the word “VDR”.  All are brown with a black band, red top and a white dot on one side.

My preference would have been to replace the VDR with a new one.  However, I was not able to locate the same part.

I found this thread that addressed the VDR issue and it stated this VDR had the following specs:  asymmetric VDR with a reference of 1.35V at 1mA - Red top = 1.35V @1mA, Black = 10%, White spot is the cathode.  (http://www.tv-forums.com/forum/TV_Equipment_C4/TV_Repair_Forum_F3/VDR_Philips_4822_116_20063_P144808/)

The last poster in the thread stated he fixed a bad VDR in the y output amplifier of the same scope by leaving the VDR in place and adding two signal diodes in series across the VDR leads to keep the voltage across the VDR to less than 1.5 volts.

I tried this and it worked for my issue as well.  The scope appears to be working fine now!  See attached pdf showing the x final amplifier and the diode additions.  I also attached the amplifier description and the full schematic from the manual if this might be of interest. 

Two questions.

1.  I would have preferred to replace the bad VDR with one that had the same specs.  Is it possible to find a replacement with just the info above?  In my searches, I did not see any VDRs specified this way.

2.  What is the VDR intended to do in this circuit and how have I compromised the circuit’s function by adding the diodes? 

Appreciate any insights.  Thanks!

[jpwolfe31]

I was able to find this Philips color code chart for caps, VDRs and resistors.  The part at issue is the 1.35 volt asymmetric VDR varistor in the lower left.