Has any one tried the Van Alstine st-70 input mod

This won't address bandwidth limiting but IMO the VanAlstine input board will be a huge improvement over the stock ST70. But there are some other things that you may want to do. For instance the Full VanAlstine mod. The power transformer should be replaced with a more modern unit that handles higher voltages. The bias supply should be rebuilt. The B+ supply should be rebuilt. There are alot of kits offered on this forum and others that don't offer these newer choices. Some just rebuild the ST70 and use the same old tube input (7199). The 7199 is a good tube but the circuits like Van Alstine, Sound Valves, Curico, Mapletree audio design ( which is one I really want to hear) that really make the ST 70 sound wonderful. Also, don't forget the Triode input board is a very good board indeed. There were companies like GSI from back during the 80's that made a wonderful ST 70 input mod. You really have to address all the other areas that need improvement to make the ST 70 kick some serious butt.

Mine has a Sound Valves input board but it was tweaked by Tom Tutay and all the other mods I mentioned were done over a 6 year period. I have had mine for over 10 years and I haven't found a better amp yet for small floorstanders and bookshelf speakers. I have even used it on Magnepan MG12's. Wonderful! After over 50 years this sweet sounding amp if done right will make you proud with the right tweaking.

I've done a direct comparison of the Van Alstine bandwidth limiting input vs stock Dynaco ST-70 input with two identically re-built Dynaco amplifiers.

The Van Alstine circuit cleans the ST-70 up alot. The amplifier is more neutral and transparent, while at the same time being more dynamic and quick paced. Much more interesting to listen to at lower volume levels as well. Soundstage with the Van Alstine input does not appear as big or forward, but I would say that is only due to the increase in transparency.

Although I am not familiar with the Van Alstine mod I am familiar with the ST-70. The front end tube of the stereo 70 is the 7199, 6AN8 on the MK lll. That tube really needs to go. It's a medium mu triode/ sharp cut off pentode that's prone to hum and premature clipping of half the waveform and high distortion. There are a few mods out there that actually replace the circuit board and use 2 front end tubes insted of one. It also improves the coupling caps and resistors from the stock unit. There are also replacement boards for the multi-stage filter capacitor. The stock cap is a twist lock lytic and were of poor quality. Look at some of the mods offered by Joe Curcio and you will see what I mean. Hope that helps. Have fun. G