Maintenance on Hafler DH200 & DH101

Peter S - your service person could wellhave been right about not needing to do anything - the achiles heel of all older electronics is the electrolytic capacitors. Counter intutivly - electrolyic's will last considerably longer in steady day to day use than they will in storage. In other words really old NOS lytics are not a deal!
The problem is that a lot of us have at least some closet queens - stuff we haven't fired up in quite a while - but either have fond memories of how good they sounded in the back way and when or alternativly can't bear to take the brutal hit finacially that some less than wise purchase faces us with in today's world.
Electronics that have sat - un-used for years - should have electrolytics replaced - this can be a bit of a challenge with some older tube units or cosmetically un-usual chasis designs ( big ,nearly empty rectangular boxes are the easiest.)
Frankly - I've never owned a piece of Hafler gear that didn't sound good - maybe not the ultimate best - but damm good for the $$ invested.

The DH200 really didn't need any maintenance. The DH101 has two weak points. The volume comtrol can get noisy - use contact cleaner if the pot has an access hole (the noisy ones usually did). The switches would stick in the white (on) position - electronically OK but cosmetically annoying). Use a little super glue to glue the catch back in position.

I found the Pooge booklet. See below. It costs about 17 bucks mail order.

http://www.audioxpress.com/bksprods/books/bkaa25.htm

On the DH 200 thak off the cover and find the MOSFET outputs. Take out the 2 screws and slip the MOSFET out of the socket. Clean all connections and slip the MOSFET back in ,put in the two screws and move on to the net output device. These have probably oxidized over the years and will benefit greatly.

Another simple thing you should do is bypass the input cap. Follow the input wires to the circuit board and you will see a 10mfd electrolytic cap there. Either bypass it completely or if you are not comfortable with the amp being direct coupled, replace the cap with a good film cap.

Both of these things are easy and will make the amp sound even better.

If you are thinking of DIY mods,I would get a copy of the POOGE article done by Marsh and Jung. You can do easy tweaks, not so easy tweaks, and highly-experienced-tech tweaks. I use a 12au7 based triode pre-amp and I believe that a tube pre with a ss power amp makes the music MUCH better. I had the Hafler DH101 preamp (for a very short time) and it sounded way too harsh. I have had my DH200 for 23 years and never any problems. Even some of the easy mods (different input/output terminals) do make a difference. Also, carefully clean the pins on the mosfets, the difference after twenty years of crud removed is something to hear. Good luck.

I had a DH200 for over 20 years in my main system. It's pretty good unit. I never did a thing to it as far as maintenance goes. It worked flawlessly for the entire time I had it. It produces a lot of clean power to your speakers. I never thought it was harsh, grainy or bloated. It also bettered a newer, highly regarded high wattage/high current amp, in my system. So I sold that unit. The Hafler got a second life in my brother's system. This thing has been going for 24 years! Not bad.

You can check out www.avahifi.com and www.musicalconcepts.com. Both of these sites do Hafler upgrades and mods, so they'll have some good info regarding that. Frank at avahifi told me he has never heard of a transformer from the DH200 burning out. Good to know. I wouldn't do anything until you install the units into your system and see if you like them. Then decide for yourself.

Enjoy 'em.