vintage H/K 730

canadianicon25

there is an old H/K 730 amp available in my area for 60 bucks. Is it worth buying and re-capping? Does anyone know anything about it or worked on one before?

mhardy6647

Well - I don't know if it's worth it to you, but I think it's an excellent receiver; it's the big brother of the popular hk430. The hk730 (like the 430) has completely separate power supplies for each channel (two power transformers, too). Rated at 45 wpc; the tuner section will win no awards for its RF performance, but it is a very good sounding tuner - and the amplifier section is very, very good. The weak spot in these is said to be the preamp section, but there are jumpers - I think - on the back panel so that can be rectified if need be :-)

Also - and my tastes may not align with yours, of course! - the design aesthetics of the hk330c, 430, and 730 are among my very favorite - ever. Extremely elegant and timeless looking receiver IMO.

I'd jump all over one in working condition for sixty smackers.

You can download the owners manual from hk:
http://www.harmankardon.com/images/media/HK730_OM_EN.pdf

I don't think I have a handy scan on the hk730, but coametically it is virtually identical to its 25 wpc little brother (the aforementioned hk430) with the addition of one little pushbutton switch on the front panel (display lighting dimmer), if memory serves.

These things sound great powering vintage Polk Audio "Monitor Series" loudspeakers... just sayin'...



(the keen-eyed will notice that the photo shows a different Philips tt than the GA-312 advertised with this particular system)

EDIT: FWIW, here's a not-too-good photo of my rather beat-up hk430 en rack :-)



The amplifier just above and to its right is the hk A402, which is essentially the amplifier section of the hk730 (again, FWIW).

canadianicon25

hmmmm..


The weak spot in these is said to be the preamp section, but there are jumpers - I think - on the back panel so that can be rectified if need be :-)


i'm not sure what you mean by this. i found a picture of it and can see the jumpers. are you saying that it makes for a lousy sounding pre-amp?

any idea how many caps would have to be replaced? i've never worked on a ampflier/rx before.

mhardy6647

Some folks think its preamp's not so hot - I think it's perfectly OK.

cnh

I have to agree with mhardy above. I own both the 430 and the 730. The 730 does have jumpers so you can bypass the pre as mentioned. But I also, do not find the pre to be problematic and for 40+ watts per channel the HK pounds well above that wattage, well above! Has really weighty bass and does the rest well too.

DEFINITELY worth 60! A steal at that price. Can't help you with the recapping, not my thing. I have a guy who does such work--been in the business over two decades and does not charge an arm and a leg. Actually my 730, I believe, is still original and sounds pretty good.

Have fun!

cnh

stubby

I was very impressed by the 730. Very robust sound, full if you will. I never had any reservations about it's sound quality.

stubby

mhardy6647

Recapping a piece of ss equipment with PC boards is tedious but easy - it sounds like the OP knows the drill.

FWIW, my three tips (offered strictly 'as-is', YMMV, and all that rot) - don't overheat the solder joints when desoldering (the hk PC traces seem, in my somewhat limited experience, to be more sensitive than average to lifting when over-cooked!), make sure electrolytics are installed with proper polarity (duh!) and don't mess with the tuner section unless it's not working. IMO one will likely do more harm than good futzing with tuned circuitry (i.e., I am chicken to do too much, and I have a half-a-clue as to what's going on in an FM radio).

As a gratuitious aside :-) I've always been sort of amused (and bemused) by my observation that a vacuum-tube, push-pull stereo integrated amplifier might have, say, eight capacitors in it (not counting tone and EQ networks), and an equivalent, solid state amp probably has about seventy-three of 'em! :-P

canadianicon25

so i got e hk 730 for nothing. the preamp section is toast but the power amplifier section works as i have my audioengine d1 connected directly to the amp in section and it is working. does anyone know how to star tshooting the preamp section of this amp?

canadianicon25

okay. the amp works. all of it. feeling guilty. just really dirty. and most of the fuse lamps are burnt out too.

the big question i have now is not how to a ts hoot the pre-amp section ( thankfully) but how clean pots without removing them. waaayy too much work if not necessary.

mhardy6647

CAIG DeOxit is very fluid (low viscosity and good wetting properties, too); IMO, virtually all controls will "take" some DeOxit if it is gently squirted into some gap in the control housing. E.g., there's usually a gap on a pot between the metal shield and the phenolic insulator that sticks out and holds the contacts to which the pot's wires are soldered. A gentle flow (just barely depress the can's sprayer, so the product just kind of "oozes") will wick down through that gap and at least a bit of it will wick down to the pot itself. I prefer several rounds of treatment with small-ish portions of cleaner, rather than flooding the pot and/or its surroundings. Work each pot and switch liberally and repeat the cleaning as needed.

HTH.

The 730 is a very, very nice piece of hardware by vintage or (yes) even modern standards.
Well worth a little sweat equity; especially for a freebie. If you dig around teh webs a bit, you should be able to find the service manual for it - which might come in handy if a more substantial tear-down ends up being necessary.

canadianicon25

thanks. so far it sounds nice with headphones. after some more work i can't wait to connect them to some decent sounding speakers. looking forward to the project.

canadianicon25

i don't suppose there is a good cleaner for this case of this old h/k. looks like something was spilled on the side and it sort of hardened on there.

its metal covered with some kind of plastic stick on stuff.

mhardy6647

I like windex. If you go to stronger things, you might attack that weird laminated stuff on the hk case... you could try GooGone... but start somewhere inconspicuous :-)

canadianicon25

so i've been listening to it mostly through headphones with pre-amp bypassed and...not bad. full sounding is right! bassy but not overdone. good clarity and that is with stock components! i don't think i would have spent more than 60 bucks due to how much money and time re-capping this sucker will take. maybe tomorrow i'll start doing an inventory of how many caps i need to buy.