I love how tastefully you always do the display lights. Some techs do the bright LED retrofit and I can’t help but think that in a dimly lit living room it would look like a lighthouse beacon.
I like to retain the original look and lighting is a big part of that. I find LEDs too bright & harsh for my liking. Another problem with LEDs is they have a very specific colour which to me looks artificial, Incandescents have a broader light spectrum and seems more natural
Thanks for posting this one! As always, great, methodical troubleshooting. Older HK receivers always seem to have ample room to maneuver and sort out problems. This one looked like it hasn't seen a caring human in quite some time; you definitely got this one sorted out and ready to continue a good life.
I was working for a temp agency while in college in the early 90’s, cleaning a rental. I was instructed to remove everything and deposit in the dumpster. On the top shelf of a closet was a Pioneer pl-50 turn table and a Harmon Kardon 230 B receiver. Well, needless to say, those units came home with me. All those years since I have enjoyed them both. Last summer I was browsing Craigslist and found a 730 for $350.00, dear lord this 730 punches way above its weight and sounds AMAZING! It will never be sold, I love how it looks, and I would put it up against any of the Popular Marantz, Sansui, Pioneer gear that is so popular.
IMO the power amp stage of this receiver would outperform a very good ratio of new amplifiers and performs among the top 10-20% of all amps I have heard. It is eminently musical and satisfying, having among the best attributes of very good SS and tube amps. It sounds shockingly good. IIRC my 730 had dual trafos, it was true dual mono.
I agree. All the HKs from this era were good performers. I especially love the sound of my A-402 amp which is very similar in design to the 730. I've also heard several 330c receivers that sound awesome despite their low power. When you look at the circuitry inside it all looks very basic. I guess simplicity = less coloration of sound. Thanks for watching James
@@TrevorsBench I have 330c and sounds quite nice. I am using it with some old Rogers LS2 speakers, Rega P3 TT running through a Dynaco Pas tube pre-amp into the HK. The overall system is a nice sounding vintage combo.
This receiver makes hip hop sound excellent the way it should. The key is to run a powered subwoofer to speakers 2. One free channel concentrating only on lows with its own power supply. Dam that's big Pimpin!
Nicely done. One of these units just fell into my lap that a coworker buddy had been sitting on for 15 yrs or so from a fellow who gave up on repairing it. One channel is out, fuses are blown. It seems to be a very service-friendly unit, most parts look very accessible. The dual transformers are a nice touch, not sure if they're necessary but why not. Beefy.
HK's philosophy on the dual power supplies was that when you're really pushing one channel, the power for the other channel doesn't drop. In "the old days," I think some companies would measure output for advertising purposes with one channel driven, which would then give an exaggerated reading compared to both channels driven. I know that in the advertising for the 930 (which I own) they did it with both channels driven. I used to read "Stereo Reports" back in the day, and their engineer who tested equipment for reviews said that the 930, rated at 45 watts per channel, would be rated by other companies at 65 watts per channel or more. Which, if you're listening, is not a significant increase in volume level anyway. Twice as loud = 10x power because of the logarithmic nature of the ear's sensitivity.
It's always nice to see a vintage receiver that's well designed, inside and outside. No nonsense and very stylish in a clean, non frilly way. And seeing it come back to life is even better. BTW, I saw You were using Wuerth capacitors for power related things; did You know that they also make "audio grade" capacitors? They're labeled ATLI, are 105°C labeled and have a very low ESR. the 150µF at 50V cap has 0,055 at 100kHz with a lifetime expectancy of 5000 hrs. Oh, and could You please post Your list of "Bad transistors" somewhere? That would be really useful so those who might need such a thing, like me, heh, could look up suspicious transistors and spot them easier. That would be great! Keep on rocking! :D
Thanks for the info on caps. I will look for them when I run low. I'm well stocked right now, lol. The transistor naughty list I stole from the AudioKarma forums. I will look for a link when I get time
Great video, I enjoyed watching you do all of that work. I've got a 930 (also twin powered, 45w/channel rating); one difficulty with it from the get-go was that the FM tuner drifted as the unit heated up, would have to re-center the channel. Other than that, no problems other than panel lights going out, in almost 50 years owning it. I did get some interesting speakers (Polk SDA-1A) that put more load on it, I think they are rated at 4 ohms rather than 8, and when the volume is turned up, the panel lights dim to reflect the power output; it's not steady dimming, but reflects the dynamics of the music.
really enjoy your channel. have you ever used "electronics cleaner" to detail the interiors? upgraded filter caps will eliminate the DC ripple. I restore turntable lids regularly. each grit up spend 2x as long sanding. the best finishing step......mothers scratch x2.0 wool buff pad followed by spray wax (i use lemon scent no name) on a flannel cloth buffed by hand with firm pressure, finish with a dry flannel cloth . better than new.
Nice piece! Mind revealing an estimate of hours into the unit? I’m guessing somewhere in your humble abode, there is one hell of a music room. If you ever care to share it, love to see it. Take care Trevor
Hi Mike, I don't keep track of hours as I will come & go and I sometimes work on more than 1 unit. I don't have a dedicated music room but I do have systems set up in different rooms for my enjoyment. Nothing fancy or flashy, just the basics so I can hear music when i want
You Rock Trevor, no defective unit will stand in your way 😁 I’m also interested in the bad transistor list. Would you please mention what device you replace the 2SC1400’s with, and the switches you replaced. I thought they would be a ‘no longer avail item’. Cheers
You made me laugh. I'm not that good. I have gave up on a few items in the past. You can replace the 2SC1400 with KSC1845, should work ok. The KSC1845 is getting hard to find. Parts shortages and out of stock on DigiKey and LCSC dot com The switches can be found at Digikey, search for F4UEE and F2UEE. You can get gold contacts for line level signals
100 Watts into an 8Ω load. Is that combined? Just curious, as it's rated @ 40W/ch. I use a 330c as my daily workshop driver, which I restored 8 years ago. And now I have a customers' 730 in for a restore, so I appreciate this video, as I picked up some good pointers from you. Thanks!
I just picked one up for 30 bucks! Guy said it didn't work. Some de-oxit, and it came to life. Lights are mostly out, only the stereo and power light works. I ordered a kit. I was able to set the bias for the right channel, but the left channel the bias is unstable, i can only set the bias to a 16mv then it starts to jump around. . Audiokarma seems to think that it may be a bad diode and or a bad transistor near the trim pot, possibly the trimpot it's self. I plan on doing a partial re-cap: driver board, filter caps, the underneath power supply board. How hard was it to get to the tone control board? I don't have a wire wrap tool, and I'd rather not solder it back. I also want to avoid un-tying the tuner knob cord. Is there enough slack on the phono board to just leave the wires connected and flip it around and re-cap it?
Great score. Tidy that 730 up and it will reward you with great sound & looks. I don't remember accessing the boards for recap being that difficult. The service manual identifies were all the coloured wires go so board removal shouldn't be hard. If you have enough wire to leave the board attached then go for it but remember some wires might break off with flexing. The guys at AK are probably right about the bias upset, I would replace the trim pot first as the originals are of low quality and are now 40 years old
Peerless attention to detail, Trevor. Kudos! I wish you were local to restore my h/k. I have an A-402 (bought from The Audio Place in Kitchener, ON for $500CAD in Feb/1979) and an A-401. My metal cases are in similar condition. How did you clean the top/sides?
Great Video man! 👍…… just wondering why you went with higher capacitance from 4700 to 10 k on the main filter Caps???? Isn’t it good to keep it as per factory spec and original design??? Thanks
@@TrevorsBench Hello Trevor! Lemme say at the get go, I wasn’t expecting a reply but it’s fantastic that you did Sir! Yes I was thinking on the lines of your reply but wasn’t quite sure. Always thought that one doesn’t meddle with the original design since it’s built that way for a specific reason but I get what your saying. Once again I really do appreciate the quick response. Actually I’m getting this very same model next week off the second hand market here in India. I’m writing to you from Bombay! You have a wonderful channel and a new subscriber now! Peace brother. Keep up the great work that you put in. 🍺 BTW I’m getting it for 350 USD which is on the high side of cheap for the 730 I’m guessing, but it’s 8/10 cosmetically inside and out. So fingers crossed 🤞
My HK 730 has major hum from phono input.Don't think it's ever had any work done on it and with the nonexistence of techs anywhere near me looks like I'm gonna have to learn the art of repair myself.Really don't want to give up on this beauty. Thankyou for the video.Don't see much in the ways of comprehensive repair work on the 730's on you tube.
If both channels are not working it suggests a power failure or open ground Check for power to the phono board on pins LP703 (+15v) and LP702 (-15v) If the voltages are there and correct I would say there is a problem with the phono amp (maybe bad transistors or open resistor, or a open ground wire) If the voltages are not there, check the wiring back to the tone board (LP703 to LP511 and LP702 to LP509) Look on the tone board at the voltage reg circuit (zener diodes D501 and D502) Check resistors R559 to R562. Although, if the voltage regulator on the tone board is faulty, the tone amp will not work. The other possibility is the phono amp is fine and the signal isn't making it's way through the input selector to the tone board
so ballpark, how much did all the parts you replaced cost? My 730 Twin has been working wonderfully for years, I did a thorough cleaning and lubing of the switches but aside from that I haven't done anything else but thinking since it is nearly as old as I am I should consider doing some deeper work on it.
My HK 730 doesn’t have a fuse unit in the back of amp there a factory dot for one or some thing there, but inside a lot of fuses…is this compensation for this? I am the original owner I got it post graduation 1975. Is there a way I can date this? I am going to clean the pots with Deoxit 5 Gold, but maybe cleaner first after >I blow the dust out first of each pot< I have dusted the unit with my air compressor, it powers on all lights come on…yeah ! But not so fast…
These were sold world wide, maybe they are not all wired the same depending on the market it was intended for. That's only a guess. Good luck on your cleanup. these are easy units to repair and work on
Have you ever had any issues with the Wurth electrolytic caps? I've used them successfully in the past, but some forums say they are rebranded Taiwanese caps.
Hey Trevor fantastic video. I have a 730 that’s operational including all lights but it needs some restoration. Would you consider doing it for me? I can send a video and pics with more info. Let me know and thanks again. Rick
Hello Trevor, would you please add me to your list of potential HK 730 repairs? Might be nice to know where you live to determine the cost of sending the weighty amp. Thank you, Brian
Hello I have the same in working conditions however some hum occurs. Would you be willing to help changing some of the components with a restoration kit I have?
I have both the A402 integrated amp and the 730 receiver. They're cousins and both sound wonderful. Have you A/B tested your A402 and 730 just to see if you could hear a difference between the two? Would be interesting to find out. I know that the 730 had a different equalization curve in the phono board and there is a mod to make it match the RIAA equalization curve, and thus, sound much better. I wonder if the same mod needs to happen with the A402? I compared the schematics for the board between the two units and they looked a little different, but I'm not experienced in this hobby to know if I was seeing a difference in board layout design or a real electronics difference.
I find the 730 sounds a little softer but still really good. The A-402 is just pure music machine, crisp and powerful. Haven't used the phono stage in the 730 yet so I wouldn't know. I'm very fond of the A-402 phono stage and think it's near perfect. I'm interested in what mods are done, I'm always looking for ways to improve the sound and enjoyment we get from these units
@@TrevorsBench Yeah, just search on Modding the Harman Kardon 730 phono stage over at AudioKarma and look for the thread that is started by a user named dyche01. It's a long thread, but packed full of knowledge. I would link to it, but for some reason, the post gets deleted.
And as far as the A402 is concerned, look for a thread named Harman Kardon A-402 Restoration started by a user named jheu02. That thread is mainly about restoring an A402, but they also get into modding the phono stage on that one as well, but it's a bit opaque to me. That's because my knowledge level isn't up to your or their level.
@@almograve Yes, I did manage to change the lamp for the power switch. As I remember the biggest issue was removing the original factory applied glue that held it in place. But it's doable. Unfortunately I lost the stereo indicator lamp in the process. Haven't resolved that one yet. I put it on the back burner.
Hey man I have this amp and was always wondering if it was worth getting repaired, and about how much it would cost? not sure if there's much wrong with it but the lamps are for sure burnt out
I can't quote costs because I have no idea what state your 730 is in. I think they're worth repairing because they hold their resale values very well. If yours is in good cosmetic condition then it's a keeper
I don’t understand why you didn’t replace the capacitors in the power supply!!!! If you removed why not to replace it with new ones, for my understanding, the power supply is the brain of the receiver.
I have a 730 that I purchased New in about 1977. Use it every day. No Issues. Hard to find better when you may have the Best.
I love how tastefully you always do the display lights. Some techs do the bright LED retrofit and I can’t help but think that in a dimly lit living room it would look like a lighthouse beacon.
I like to retain the original look and lighting is a big part of that. I find LEDs too bright & harsh for my liking. Another problem with LEDs is they have a very specific colour which to me looks artificial, Incandescents have a broader light spectrum and seems more natural
Always liked this particular model of Harmon kardon
Its a classic. Thanks for watching
Thanks for posting this one! As always, great, methodical troubleshooting. Older HK receivers always seem to have ample room to maneuver and sort out problems. This one looked like it hasn't seen a caring human in quite some time; you definitely got this one sorted out and ready to continue a good life.
Thanks Craig. I'm listening to the 730 right now and love the sound & looks
I was working for a temp agency while in college in the early 90’s, cleaning a rental. I was instructed to remove everything and deposit in the dumpster. On the top shelf of a closet was a Pioneer pl-50 turn table and a Harmon Kardon 230 B receiver. Well, needless to say, those units came home with me. All those years since I have enjoyed them both. Last summer I was browsing Craigslist and found a 730 for $350.00, dear lord this 730 punches way above its weight and sounds AMAZING! It will never be sold, I love how it looks, and I would put it up against any of the Popular Marantz, Sansui, Pioneer gear that is so popular.
I love my Marantz and Sansui Solid state Vintage receivers, but my Harman kardon HK730 is going nowhere, what a fantastic sounding receiver it is!
Well done Trevor. I always glean knowledge from your videos.
Thanks, stay tuned lots more to come every week
IMO the power amp stage of this receiver would outperform a very good ratio of new amplifiers and performs among the top 10-20% of all amps I have heard. It is eminently musical and satisfying, having among the best attributes of very good SS and tube amps. It sounds shockingly good. IIRC my 730 had dual trafos, it was true dual mono.
I agree. All the HKs from this era were good performers. I especially love the sound of my A-402 amp which is very similar in design to the 730.
I've also heard several 330c receivers that sound awesome despite their low power. When you look at the circuitry inside it all looks very basic. I guess simplicity = less coloration of sound.
Thanks for watching James
@@TrevorsBench I have 330c and sounds quite nice. I am using it with some old Rogers LS2 speakers, Rega P3 TT running through a Dynaco Pas tube pre-amp into the HK. The overall system is a nice sounding vintage combo.
I have a 430 Twin Power: with 25 W per channel, my 70 W speakers can not keep up with it.
How would the big HK dual mono amps sound w a transparent tube class A Pre Amp??
This receiver makes hip hop sound excellent the way it should. The key is to run a powered subwoofer to speakers 2. One free channel concentrating only on lows with its own power supply.
Dam that's big Pimpin!
Nicely done. One of these units just fell into my lap that a coworker buddy had been sitting on for 15 yrs or so from a fellow who gave up on repairing it. One channel is out, fuses are blown. It seems to be a very service-friendly unit, most parts look very accessible. The dual transformers are a nice touch, not sure if they're necessary but why not. Beefy.
Nice, time to rescue and repair. These gems are worth the effort
HK's philosophy on the dual power supplies was that when you're really pushing one channel, the power for the other channel doesn't drop. In "the old days," I think some companies would measure output for advertising purposes with one channel driven, which would then give an exaggerated reading compared to both channels driven. I know that in the advertising for the 930 (which I own) they did it with both channels driven. I used to read "Stereo Reports" back in the day, and their engineer who tested equipment for reviews said that the 930, rated at 45 watts per channel, would be rated by other companies at 65 watts per channel or more. Which, if you're listening, is not a significant increase in volume level anyway. Twice as loud = 10x power because of the logarithmic nature of the ear's sensitivity.
@@j.patrickmoore9137 Yes I enjoyed Julian Hirsch's objective reviews in Stero Review back in the day, any ratings were put to the test.
It's always nice to see a vintage receiver that's well designed, inside and outside. No nonsense and very stylish in a clean, non frilly way. And seeing it come back to life is even better. BTW, I saw You were using Wuerth capacitors for power related things; did You know that they also make "audio grade" capacitors? They're labeled ATLI, are 105°C labeled and have a very low ESR. the 150µF at 50V cap has 0,055 at 100kHz with a lifetime expectancy of 5000 hrs.
Oh, and could You please post Your list of "Bad transistors" somewhere? That would be really useful so those who might need such a thing, like me, heh, could look up suspicious transistors and spot them easier. That would be great! Keep on rocking! :D
Thanks for the tip on the Weurth audio grade caps!
Thanks for the info on caps. I will look for them when I run low. I'm well stocked right now, lol. The transistor naughty list I stole from the AudioKarma forums. I will look for a link when I get time
Great video, I enjoyed watching you do all of that work. I've got a 930 (also twin powered, 45w/channel rating); one difficulty with it from the get-go was that the FM tuner drifted as the unit heated up, would have to re-center the channel. Other than that, no problems other than panel lights going out, in almost 50 years owning it. I did get some interesting speakers (Polk SDA-1A) that put more load on it, I think they are rated at 4 ohms rather than 8, and when the volume is turned up, the panel lights dim to reflect the power output; it's not steady dimming, but reflects the dynamics of the music.
love the hk730!
So do I!
Great work, mid 70’s receivers for me were the HK twin power and the luxman.
really enjoy your channel. have you ever used "electronics cleaner" to detail the interiors? upgraded filter caps will eliminate the DC ripple. I restore turntable lids regularly. each grit up spend 2x as long sanding. the best finishing step......mothers scratch x2.0 wool buff pad followed by spray wax (i use lemon scent no name) on a flannel cloth buffed by hand with firm pressure, finish with a dry flannel cloth . better than new.
At what grit do you start? And then how many subsequent grit ratings do you use? thx
I've never heard of electronics cleaner but I'm interested in knowing more. Is it made for purpose specifically?
Hi Trevor thank you for another great video. On your future projects if you need to repair a board can you show how to repair solder pads? Thank you.
Thanks Alexis, I'll keep that in mind next time I come across one
wow you do great work! Have you thought about moving to Raleigh NC !!
Yes I have! Maybe farther south. Time to escape the tyranny
Raleigh is nice - growing like crazy!
@@chadsteinacker7948 There really are no techs around here that fix vintage SS and Tube equipment that I know of....
What a sexy machine
Glad you liked it
Nice piece! Mind revealing an estimate of hours into the unit? I’m guessing somewhere in your humble abode, there is one hell of a music room. If you ever care to share it, love to see it. Take care Trevor
Hi Mike, I don't keep track of hours as I will come & go and I sometimes work on more than 1 unit. I don't have a dedicated music room but I do have systems set up in different rooms for my enjoyment. Nothing fancy or flashy, just the basics so I can hear music when i want
@@TrevorsBench who needs flashy when you have the real deal?
You Rock Trevor, no defective unit will stand in your way 😁
I’m also interested in the bad transistor list.
Would you please mention what device you replace the 2SC1400’s with, and the switches you replaced.
I thought they would be a ‘no longer avail item’.
Cheers
You made me laugh. I'm not that good. I have gave up on a few items in the past. You can replace the 2SC1400 with KSC1845, should work ok. The KSC1845 is getting hard to find. Parts shortages and out of stock on DigiKey and LCSC dot com
The switches can be found at Digikey, search for F4UEE and F2UEE. You can get gold contacts for line level signals
@@TrevorsBench KSC1845 is out everywhere. is there a alternative?
@@anthonypopovic7626 LCSC says they have 1600 in stock
100 Watts into an 8Ω load. Is that combined? Just curious, as it's rated @ 40W/ch. I use a 330c as my daily workshop driver, which I restored 8 years ago. And now I have a customers' 730 in for a restore, so I appreciate this video, as I picked up some good pointers from you. Thanks!
Love this video!!!! Is there a link to show you took off the faceplate?
I heard HKs do not have relays and could blow speakers if they become unhealthy. Can a relay or protection be added?
I just picked one up for 30 bucks! Guy said it didn't work. Some de-oxit, and it came to life.
Lights are mostly out, only the stereo and power light works. I ordered a kit.
I was able to set the bias for the right channel, but the left channel the bias is unstable, i can only set the bias to a 16mv then it starts to jump around. . Audiokarma seems to think that it may be a bad diode and or a bad transistor near the trim pot, possibly the trimpot it's self.
I plan on doing a partial re-cap: driver board, filter caps, the underneath power supply board.
How hard was it to get to the tone control board? I don't have a wire wrap tool, and I'd rather not solder it back. I also want to avoid un-tying the tuner knob cord.
Is there enough slack on the phono board to just leave the wires connected and flip it around and re-cap it?
Great score. Tidy that 730 up and it will reward you with great sound & looks.
I don't remember accessing the boards for recap being that difficult. The service manual identifies were all the coloured wires go so board removal shouldn't be hard. If you have enough wire to leave the board attached then go for it but remember some wires might break off with flexing.
The guys at AK are probably right about the bias upset, I would replace the trim pot first as the originals are of low quality and are now 40 years old
Peerless attention to detail, Trevor. Kudos! I wish you were local to restore my h/k.
I have an A-402 (bought from The Audio Place in Kitchener, ON for $500CAD in Feb/1979) and an A-401. My metal cases are in similar condition. How did you clean the top/sides?
Great Video man! 👍…… just wondering why you went with higher capacitance from 4700 to 10 k on the main filter Caps???? Isn’t it good to keep it as per factory spec and original design???
Thanks
Hi Shane, It's ok to upsize the power supply filter capacitors from stock. Gives it a higher power reserve for when the music is most demanding.
@@TrevorsBench Hello Trevor! Lemme say at the get go, I wasn’t expecting a reply but it’s fantastic that you did Sir! Yes I was thinking on the lines of your reply but wasn’t quite sure. Always thought that one doesn’t meddle with the original design since it’s built that way for a specific reason but I get what your saying. Once again I really do appreciate the quick response. Actually I’m getting this very same model next week off the second hand market here in India. I’m writing to you from Bombay! You have a wonderful channel and a new subscriber now! Peace brother. Keep up the great work that you put in. 🍺
BTW I’m getting it for 350 USD which is on the high side of cheap for the 730 I’m guessing, but it’s 8/10 cosmetically inside and out. So fingers crossed 🤞
My HK 730 has major hum from phono input.Don't think it's ever had any work done on it and with the nonexistence of techs anywhere near me looks like I'm gonna have to learn the art of repair myself.Really don't want to give up on this beauty.
Thankyou for the video.Don't see much in the ways of comprehensive repair work on the 730's on you tube.
Ola amigo tengo uno igual prende pero no se escucha que podrá ser la falla
If you hear no sound, check all the fuses first
Can you refurbish mine? My local tech said it will take 6+ months to fix it.
I have a HK 730 and there is no sound on phono 1 or 2. The fuses in the amp are ok, where should I start to check?
If both channels are not working it suggests a power failure or open ground
Check for power to the phono board on pins LP703 (+15v) and LP702 (-15v)
If the voltages are there and correct I would say there is a problem with the phono amp (maybe bad transistors or open resistor, or a open ground wire)
If the voltages are not there, check the wiring back to the tone board (LP703 to LP511 and LP702 to LP509) Look on the tone board at the voltage reg circuit (zener diodes D501 and D502) Check resistors R559 to R562. Although, if the voltage regulator on the tone board is faulty, the tone amp will not work.
The other possibility is the phono amp is fine and the signal isn't making it's way through the input selector to the tone board
Why 10,000 uf instead of the original 4,700 uf value for the filter caps?
I was curious too.
so ballpark, how much did all the parts you replaced cost? My 730 Twin has been working wonderfully for years, I did a thorough cleaning and lubing of the switches but aside from that I haven't done anything else but thinking since it is nearly as old as I am I should consider doing some deeper work on it.
My HK 730 doesn’t have a fuse unit in the back of amp there a factory dot for one or some thing there, but inside a lot of fuses…is this compensation for this? I am the original owner I got it post graduation 1975. Is there a way I can date this? I am going to clean the pots with Deoxit 5 Gold, but maybe cleaner first after >I blow the dust out first of each pot< I have dusted the unit with my air compressor, it powers on all lights come on…yeah ! But not so fast…
These were sold world wide, maybe they are not all wired the same depending on the market it was intended for. That's only a guess.
Good luck on your cleanup. these are easy units to repair and work on
at 29:00, when you're testing the amp idle, doesn't the manual require you to connect 8 ohm resistors between the speaker terminals?
Have you ever had any issues with the Wurth electrolytic caps? I've used them successfully in the past, but some forums say they are rebranded Taiwanese caps.
No troubles with Wurth.
Hey Trevor fantastic video. I have a 730 that’s operational including all lights but it needs some restoration. Would you consider doing it for me? I can send a video and pics with more info. Let me know and thanks again. Rick
Hello Trevor, would you please add me to your list of potential HK 730 repairs? Might be nice to know where you live to determine the cost of sending the weighty amp. Thank you, Brian
Hello
I have the same in working conditions however some hum occurs. Would you be willing to help changing some of the components with a restoration kit I have?
What brand 10 turn trimpot and what value to replace
I have both the A402 integrated amp and the 730 receiver. They're cousins and both sound wonderful. Have you A/B tested your A402 and 730 just to see if you could hear a difference between the two? Would be interesting to find out. I know that the 730 had a different equalization curve in the phono board and there is a mod to make it match the RIAA equalization curve, and thus, sound much better. I wonder if the same mod needs to happen with the A402? I compared the schematics for the board between the two units and they looked a little different, but I'm not experienced in this hobby to know if I was seeing a difference in board layout design or a real electronics difference.
Just to follow up on this, someone on the AK forum did suggest that HK A402 owners should perform the phono board upgraded like HK 730 owners do.
I find the 730 sounds a little softer but still really good. The A-402 is just pure music machine, crisp and powerful.
Haven't used the phono stage in the 730 yet so I wouldn't know. I'm very fond of the A-402 phono stage and think it's near perfect.
I'm interested in what mods are done, I'm always looking for ways to improve the sound and enjoyment we get from these units
@@JerryPemberton Thanks I'll look there
@@TrevorsBench Yeah, just search on Modding the Harman Kardon 730 phono stage over at AudioKarma and look for the thread that is started by a user named dyche01. It's a long thread, but packed full of knowledge. I would link to it, but for some reason, the post gets deleted.
And as far as the A402 is concerned, look for a thread named Harman Kardon A-402 Restoration started by a user named jheu02. That thread is mainly about restoring an A402, but they also get into modding the phono stage on that one as well, but it's a bit opaque to me. That's because my knowledge level isn't up to your or their level.
Tengo un amplificador de estos y que bueno el video, el problema es el idioma
do a demo of the sound
Struggling to remove the lamp assembly in order to change the stereo indicator lamp. Is there a trick to removing this light strip?
did you manage this? any ref you used?
@@almograve Yes, I did manage to change the lamp for the power switch. As I remember the biggest issue was removing the original factory applied glue that held it in place. But it's doable. Unfortunately I lost the stereo indicator lamp in the process. Haven't resolved that one yet. I put it on the back burner.
Hey man I have this amp and was always wondering if it was worth getting repaired, and about how much it would cost? not sure if there's much wrong with it but the lamps are for sure burnt out
I can't quote costs because I have no idea what state your 730 is in. I think they're worth repairing because they hold their resale values very well. If yours is in good cosmetic condition then it's a keeper
Just as an example about how much did you put into yours? Just so I have a round about number to expect from it
730 haman kandon no radio ic ba402
Ebay?
No
I have trying to find one of these for about 20 years. They have not been manufactured since about 1980.
One of my Channels died!
I don’t understand why you didn’t replace the capacitors in the power supply!!!! If you removed why not to replace it with new ones, for my understanding, the power supply is the brain of the receiver.
What capacitors are you referring to? I did replace the main filter capacitors in this 730
All the capacitors in the power supply board, I think I think should be removed by now after all, they are 50 years old,
Telephone
Hi can I ask what type of transient capacitor did you add to the power line to reduce the noise thanks for response