Vox lead escort 50 - integrating valve stage

[jbmdisco]

Hi, I have been given a VOX LE50 SS amp to have a 'play' about with. It was dead when brought in but after some work it is now working quite well but the customer/friend who it belongs to would like it to be 'different'. He seen one a number of years ago which had been modified by the introduction of a valve stage using a 12ax7 valve which he reckons gave a nice sound with some mild distortion and has basically given me the green light to try and replicate the effect using his amp as the guinea-pig.

Any ideas guys? I did think about creating a separate board with a basic valve circuit and grafting it in place of the op-amp. I have had a browse around schematics of some hybrid amps for some ideas but hoping that someone will have tackled a similar project. He's not got any great sentimental value with this amp so basically anything goes.

I have in the past replicated this amp as a handwired version which took me some weeks to complete but was quite successful and if I can find my jottings and the valve stage works I might do another.

[J M Fahey]

Start by posting the original schematic here.

As a general rule, if you replace an Op Amp clean gain stage (say, 20X gain) with an equivalent clean tube stage, same gain, you'll hear little or no difference.

Now on an overdriven stage, they are very different.

But to go any further, we need the schematic.

Worst case, you may build a tube distortion pedal, such as the Matchless ¿Hotbox? or one of the Soldano or Mesa Boogie versions, and insert it in the effects loop or between preamp and power amp.