Best DX-100 mods advice

[W9RAN]

I popped a fuse in my DX-100 doing some audio testing on dummy load last night.  Haven't determined the cause yet, but as long as I've got it on the bench I decided I'd finish the audio mods, having only replaced a few caps when I first got it years ago.  I've got the WA1HLR book around here somewhere, plus his internet mod page and others from ER, etc.   'll do all the no-brainer stuff like increasing the coupling caps and audio bypasses in the speech amp,  but I'm wondering what the consensus is on other mods, such as:

 - adding negative feedback (to speech amp and/or driver or both)
 - 1625 bias changes
 - "turbo mod" ala Timtron (turning mod tranny into auto-tranny)
 - beefing-up power supply filters  (I am not inclined to solid-state 'em without good reason - but will if it's really recommended and won't exceed component ratings)
 - adding a PTC thermistor in series with the HV transformer primary to limit inrush current when switch to transmit mode
 - Others?
 
I've always thought the DX-100 was pretty well designed and works OK as-is so I'd rather not fix what ain't broken, but would appreciate suggestions as to what's been proven to be best practice.

Lastly - that .02uf 1600V ceramic cap across the mod transformer secondary?  It shorted soon after I got the transmitter so I removed it as per Timtron as part of my original "lite" modifications.   How important is this cap anyhow (other than as a fuse-tester?)   It's shown in most of the ARRL handbook modulators with the note that it's supposed to limit high frequency harmonics.   Essential or no?

Thanks and 73,

Bob W9RAN

[Jim KF2SY]

Bob,
The "best" mods for a DX100 can be very subjective.  There is tons of DX100 & similar rigs advice on this board.  Do a search.  But my 2 cents is the following.  Don't do all of the mods at once.  It could be a real dog troubleshooting if "something goes awry".
Continue with the coupling caps, grid resistor, and defintely change the plate caps as well.  Also do Tim's mod for 1625 bias with the zener on the driver transformer.  That mod is a must to clean up lots of distortion when you lean in to it.  After that I would use it for a while and get to know the care and feeding of that little beast operationally to establish a baseline. 

Furthermore... down the road:
I would only bother to use PTC thermistors if solid stating the power supplies.
I would not worry too much about removing that cap across the secondary, I think everyone does that one.
The turbo-mod is one I've never tried yet because it is written rather vaguley and Tim has told me on many occasions if done wrong you can instantly zorch your mod transformer. 
Negative feedback is another area to play around with later on as well, but some folks think it's not necessary and you will find  lots of opinions on that as well, especially from the audiophile crowd. 

Have fun.

[W9RAN]

Thanks Jim - you must have said all there is to say about this!   I made an attempt to compare the various articles, then did what seemed prudent along the lines you suggested - coupling and bias caps and bias stabilization.   Got good reports on  it tonight.

73, Bob W9RAN

[Jim, W5JO]

That .02 cap across the modulation transformer is a build out filter.  There is mention of why in the manual.  I would read that part.

[flintstone mop]

I performed the auto-transformer mods and it was a dramatic change in modulation and freq response, along with the audio caps. mods
Go with the phase inverter and get rid of the driver transformer. Or buy the expensive driver xfrmr from Antique Electronic Supply

In Tim's info somewhere in the AM Window, he explains clearly how to check for the proper wiring of the mod transformer to "auto-transformer mode, in "using a TV power transfomer as a modulation transformer". A little time consuming, but educational and rewarding. Huge pos peaks and no strain on the pubes.
Fred