dlucy's guide to Harman Kardon Twin Powered series 430, 630, 730 and 930 ... and Montgomery Ward 450

[dlucy]

The fourth era of Harman Kardon's solid state stereo receivers were the Twin Powered series:




This thread is a guide to those models, their specs, and pointers to schematics and restoration threads for each. Note: If you have additional information on any of these models or have a great thread on one elsewhere on AK, send me a private message and I'll get your info inserted into the right spot in the top posts.

The looks of these were very similar to the prior 330abc minimalist series, but they used one power supply for each channel, hence the "twin powered" moniker, these power supplies were dual rail instead of single, and the Twin Powered series stopped using the cap-coupled design of the 330AB models and continued the direct-coupled design of the 330C.

• “Twin Powered” trademark for their dual monoblock design.
• Switched from cap-coupled to direct-coupled output

The models in this era came out in two waves:

• Series 1 (1973-75) built by Roland
  • Harman Kardon 630
  • Harman Kardon 930
• Series 2 (1976-78) built by Roland
  • Harman Kardon 430
  • Harman Kardon 730
• And the HK 730 was rebadged as the Montgomery Ward 450

Other Harman Kardon solid state receiver guides:

• Stratophonic (SR-300, SR-300B, SR-400, SR-400B, SR-600, SR-600B, SR-900, SR-900B)
• Nocturne (Seven Twenty 720, Two Ten 210, Two Hundred 200, Five Twenty 520, Five Thirty 530, Two Thirty 230, Three Thirty 330, Eight Twenty 820)
• 330 minimalist (330, 330A, 330B, 330C)
• Twin Powered (430, 530, 630, 730, 930)

 

[dlucy]

Harman Kardon 630 Twin Powered stereo receiver





First in the twin-powered line (?)

Produced for HK by Roland
30 watts per channel RMS into 8Ω (stereo)
Frequency response: 4 Hz to 70 kHz
Total harmonic distortion: less than 0.5% at full RMS power across 20 Hz to 20 KHz
Series 1: 1973-75
Price: $350

• AM-FM stereo tuner-amplifier.
• RMS power 30 watts per channel into 8 ohms(both channels driven) with 0.5% harmonic distortion at any frequency 20-20k Hz.
• Overall frequency response 4-70k Hz +/-0.5dB(aux input), IHF power bandwidth 10-40k Hz.
• Hum and noise -85dB(aux input).
• IM distortion 0.15%.
• FM sensitivity 1.9uV(IHF), S/N ratio 68dB.
• Stereo separation 32dB@ 1k Hz with 0.7% harmonic distortion. IHF capture ratio 2.5dB.
• Independent power supplies for each channel.
• Defeatable interstation muting and loudness circuit.
• High frequency filter.
• Illuminated function indicators.
• Has rear panel connectors for external Dolby FM processor.
• Has rear panel connectors for PRE-OUT and MAIN-IN
• Remote speaker outputs.
• Front headphone jack.
• Phones/main/remote/both speaker switches.

Useful links:

• Service manual for Harman Kardon 630 stereo receiver
• Service bulletin for Harman Kardon 630 stereo receiver
• Flyer for Harman Kardon 630 stereo receiver
• Comments about the 630 and its preamp section https://www.audiokarma.org/forums/i...twin-power-receivers.4694/page-5#post-7868381
• Very detailed HK twin powered 630 restoration with many schematic errors noted and corrected by @hopjohn
• HK 630 Receiver - FM Issues and Amp Adjustments by @David_NC

 

[dlucy]

Harman Kardon 930 Twin Powered stereo receiver



Produced for HK by Roland
Series 1: 1973-75
Price: $475

• AM-FM stereo tuner-amplifier.
• RMS power 45 watts per channel into 8 ohms(both channels driven) with 0.5% harmonic distortion at any frequency 20-20k Hz.
• Overall frequency response 4-70k Hz +/-0.5dB(aux input)
• IHF power bandwidth 10-40k Hz.
• Hum and noise -65dB(phono input), -80dB(aux input).
• IM distortion 0.15%.
• FM section has FET front-end.
• FM sensitivity 1.8uV(IHF), S/N ratio 70dB.
• Stereo separation 38dB@1k Hz, 30dB@10k Hz, with 0.6% harmonic distortion.
• Alternate channel selectivity 50dB, IHF capture ratio 2dB. Defeatable interstation muting and loudness circuit.
• Independent power supplies for each channel.
• Remote speaker outputs.
• Front panel headphones jack.
• Illuminated function indicators.
• Has rear panel connectors for PRE-OUT and MAIN-IN
• Has two PHONO inputs
• High and low frequency filters.
• FM noise cancel switch.
• Phones/main/both speaker switches.

Comments by Todd Krieger in Vintage Asylum on June 22, 2002 at 23:50:18:

"Strengths: Pre/amp like the H/K 560 except more-musical. But with much better bass drive than the 730. Maybe the most-musical '70's integrated receiver made. The tuner section is not only the best I've heard in an integrated receiver, but also the best amongst tuners period."​

"Weaknesses: More solid-state character than a good 730, but only slightly so. (But unlike the 730, the two units I have sound almost identical.)"​

Useful links:

• HiFi Engine page with manuals and ads for Harman Kardon 930 (new access limited now, so see the flooring links)
• service manual for Harman Kardon twin power 930 stereo receiver or HK930
• instruction manual or user's manual for Harman Kardon 930 stereo receiver
• Tracking down a short, blown fuses and bad outputs in HK 930 https://www.audiokarma.org/forums/i...930-short-out-need-help.805341/#post-11218290
• Intermittent tuning dial lights on HK 930 https://www.audiokarma.org/forums/i...n-kardon-930-dial-wont-light-bulbs-ok.797386/
• Adjusting idle (by replacing transistors) and some caps in HK 930 https://www.audiokarma.org/forums/index.php?threads/hk-930-tech-advice.757415/#post-10302111
• Adjusting DC offset ion HK 930 https://www.audiokarma.org/forums/index.php?threads/hk-930-dc-offset-voltage-problem.183587/
• Adjusting bias in HK 930 https://www.audiokarma.org/forums/index.php?threads/hk-930-bias-adjustment.284799/
• Which replacement lamps for meter and tuning dial on HK 930 https://www.audiokarma.org/forums/index.php?threads/harman-kardon-930-receiver.308483/#post-3914338
• No sound from one channel on HK 930 https://www.audiokarma.org/forums/index.php?threads/harmon-kardon-930-left-channel-no-sound.369482/
• Some diagnosis and repair on HK 930 https://www.audiokarma.org/forums/index.php?threads/fixing-non-working-hk-930-need-advice.828081/

 

[dlucy]

Harman Kardon 430 Twin Powered stereo receiver

The hk 430 is nearly identical to the Harman Kardon 330C except the 430 has two separate power supplies where the 330C one has one.



produced for HK by Roland
Series 2: 1976-78
Price: $325

• Stereo tuner-amplifier.
• Power output 25 watts rms per channel into 8 ohms with 0.5% harmonic distortion, 20-20k Hz, both channels driven.
• Frequency response 4-40k Hz, power bandwidth 10-40k Hz, IM distortion 0.12%, hum and noise -65dB.
• AM/FM-stereo tuner with 1.9uV FM sensitivity, S/N ratio 77dB. Selectivity 50dB, capture ratio 1.7dB channel separation 39dB with 0.7% harmonic distortion(stereo).
• Signal strength meter, defeatable interstation muting, loudness switch(contour), high and low frequency filters, tape monitor circuit.
• Front-panel headphone jack.
• Does NOT have rear panel connectors for PRE-OUT and MAIN-IN
• Outputs and switches for two sets of stereo speakers.

Useful links:

• Harman Kardon 430 twin power stereo receiver owner's manual
• Harman Kardon 430 twin power stereo receiver service manual
• Adjusting the idle on Harman Kardon 430 twin power stereo receiver
• Harman Kardon 430 Restoration (with great photos) by mrhandshake
• Harman Kardon 430 Recap (also with great photos) by @Spenser
• Harman Kardon 430 recap and upgrades by @Sir.Byrd
• Undocumented “slow start” circuit that protects speakers from the “thump” at power-on. https://audiokarma.org/forums/index...-startup-question.890138/page-2#post-13201154

 

[dlucy]

Harman Kardon 730 Twin Powered stereo receiver

The hk 730 is considered by many to be the "sweet spot" of the Twin powered series: plenty of power, great tuner, very good power amp section.

The power amp section of the hk 730 is nearly identical to the power amp section of the Harman Kardon A-402 integrated amplifier. The A-402's power amp board appears to be a slightly later and, in a few ways, better design... but 98% identical to the 730.

produced for HK by Roland
Series 2 (1976-78)
Price: $400

• Stereo tuner-amplifier.
• Power output 40 watts rms per channel into 8 ohms with 0.2% harmonic distortion from 20-20k Hz, both channels driven. Frequency response 4-40K Hz, IM distortion 0.12%, hum and noise -65dB.
• AM/FM stereo tuner with 2.0uV IHF FM sensitivity, S/N ratio 70dB, selectivity 80dB, capture ratio 2dB, harmonic distortion 0.3%(stereo), separation 40dB.
• Quieting meter, defeatable interstaion muting, loudness switch, high and low frequency filters, two tape monitor circuits.
• Front panel headphone jack.
• Has rear panel connectors for PRE-OUT and MAIN-IN
• Has two PHONO inputs
• Outputs and switches for two sets of stereo speakers.

Comments by Todd Krieger in Vintage Asylum on June 22, 2002 at 23:50:18:

"Strengths: A good one is 90 percent of a H/K 930. Musical, almost tube-like in character. Honest 45 WPC rating. Excellent tuner section."​

"Weaknesses- Has severe sample variation. Bad ones sound "dry." A little "anemic" in the bass. Needs a benign speaker load."​

Useful links:

• HiFi Engine page with manuals and ads for Harman Kardon 730
• Recapping and repairing a Harman Kardon 730 twin power series stereo receiver
• Undocumented “slow start” circuit that protects speakers from the “thump” at power-on. Harman Kardon 430 - startup question
• The power amp board in the 730 is the heart of (nearly identical to) the A-402 integrated amp.
  • Excellent HK A-402 restoration thread by @jheu02 (which has plenty of info useful to anyone working on a HK 730)
• Comments on 730 Harman Kardon A-402 opinions? (and some info and photos from the Montgomery Ward 450)
• Updated BOM for hk730 HK730 Rebuild - Observations

 

[dlucy]

Montgomery Ward 450 stereo receiver (a rebadged Harman Kardon 730 Twin Powered)

Montgomery Ward produced a stereo receiver that was mostly the same as the HK 730.

Like the HK 730, the power amp section of the Montgomery Ward 450 is nearly identical to the power amp section of the Harman Kardon A-402 integrated amplifier.

• Stereo tuner-amplifier.
• Power output 40 watts rms per channel into 8 ohms
• AM/FM stereo tuner
• Quieting meter, defeatable interstation muting, loudness switch, high and low frequency filters, two tape monitor circuits.
• Front panel headphone jack.
• Has rear panel connectors for PRE-OUT and MAIN-IN
• Has two PHONO inputs
• Outputs and switches for two sets of stereo speakers.

Useful links:

• Excellent photos and insight on the Montgomery Ward 450
• FM meter issues in the Montgomery Ward 450
• downloadable for-fee SAMS repair manual including Montgomery Ward 450
• HiFi Engine page with manuals and ads for Harman Kardon 730
• Recapping and repairing a Harman Kardon 730 twin power series stereo receiver
• Undocumented “slow start” circuit that protects speakers from the “thump” at power-on. https://audiokarma.org/forums/index...-startup-question.890138/page-2#post-13201154
• The power amp board in the 730 is the heart of (nearly identical to) the A-402 integrated amp.
  • Excellent HK A-402 restoration thread by @jheu02 (which has plenty of info useful to anyone working on a HK 730)
• Comments on 730 https://audiokarma.org/forums/index.php?threads/harman-kardon-a-402-opinions.641011/#post-13577992

 

[milo63]

You sir, are an AK treasure.

 

[jpreza]

Harman Kardon 930 Twin Powered stereo receiver

View attachment 2229764

Produced for HK by Roland
Series 1: 1973-75
Price: $475

• AM-FM stereo tuner-amplifier.
• RMS power 45 watts per channel into 8 ohms(both channels driven) with 0.5% harmonic distortion at any frequency 20-20k Hz.
• Overall frequency response 4-70k Hz +/-0.5dB(aux input)
• IHF power bandwidth 10-40k Hz.
• Hum and noise -65dB(phono input), -80dB(aux input).
• IM distortion 0.15%.
• FM section has FET front-end.
• FM sensitivity 1.8uV(IHF), S/N ratio 70dB.
• Stereo separation 38dB@1k Hz, 30dB@10k Hz, with 0.6% harmonic distortion.
• Alternate channel selectivity 50dB, IHF capture ratio 2dB. Defeatable interstation muting and loudness circuit.
• Independent power supplies for each channel.
• Remote speaker outputs.
• Front panel headphones jack.
• Illuminated function indicators.
• Has rear panel connectors for PRE-OUT and MAIN-IN
• Has two PHONO inputs
• High and low frequency filters.
• FM noise cancel switch.
• Phones/main/both speaker switches.

Comments by Todd Krieger in Vintage Asylum on June 22, 2002 at 23:50:18:

"Strengths: Pre/amp like the H/K 560 except more-musical. But with much better bass drive than the 730. Maybe the most-musical '70's integrated receiver made. The tuner section is not only the best I've heard in an integrated receiver, but also the best amongst tuners period."
"Weaknesses: More solid-state character than a good 730, but only slightly so. (But unlike the 730, the two units I have sound almost identical.)"​

View attachment 2233529


View attachment 2229765

View attachment 2229766

View attachment 2229767

Useful links:

• HiFi Engine page with manuals and ads for Harman Kardon 930

Do you have a list of all the capacitors that should be replaced in the power supply, amp, preamp, FM, AM, and tone boards for the HK 930/430/330C/330B receivers? I know you did an awesome list for the 730. It would be nice to have such a list for the others!

As always, thank you for the wealth of information you provide!

JP

 

[dlucy]

Do you have a list of all the capacitors that should be replaced in the power supply, amp, preamp, FM, AM, and tone boards for the HK 930/430/330C/330B receivers? I know you did an awesome list for the 730. It would be nice to have such a list for the others!

Thanks, JP. I'm happy to gather useful info into one place for the general benefit of AK.

I've searched the Solid State thread archive... and no one has assembled and published a BOM parts list, a Bill Of Materials, for recapping (and sometimes more) a Harman Kardon 930 receiver yet.

I have gathered some of the threads I searched through and listed the ones with good amounts of useful info. The list at the bottom of my HK 930 guide posting has been updated with links to those threads. https://www.audiokarma.org/forums/i...ies-430-630-730-and-930.960074/#post-14792829

 

[Byron Boldt]

Hope I am not hijacking this thread, but I stumbled across a 730 with a couple odd enhancements. First of all, someone installed a small protection circuit PCB underneath it and a relay attached to a transformer with silicone. It seems to work. The relay kicks in after about 10 seconds. Second, there were some .01uF 400V caps connected across the speaker 1 jacks. I took them off and it seems to work fine without them. Can anyone explain why they might have been there and were they possibly related to the protection circuit?

Thanks

 

[dlucy]

Hope I am not hijacking this thread, but I stumbled across a 730 with a couple odd enhancements. First of all, someone installed a small protection circuit PCB underneath it and a relay attached to a transformer with silicone. It seems to work. The relay kicks in after about 10 seconds. Second, there were some .01uF 400V caps connected across the speaker 1 jacks. I took them off and it seems to work fine without them. Can anyone explain why they might have been there and were they possibly related to the protection circuit?

Thanks

You’ll need to start your own thread… and AK will be happy to help you there.

 

[3MY]

This is a very nice discussion. I purchased my Harman Kardon 730 in 1975, along with a pair of JBL L100s (dark brown foam). I loved both as they played symphony orchestra flawlessly. When I had children, all three of them played the stereo. Somehow the stereo survived. The 730 is in my bedroom, along with a pair of JBL L100 Classic 75s. In my opinion, there is no other receiver which provides stable, and linear performance than this 730. I continue to love the dynamics in which this receiver provides. Yes, this is a true mono-block in one unit.

 

[Kingpin5]

@dlucy, Thank you for assembling this information. You are a King!

 

[ignoramustot]

This is an excellent condensed resource - thankyou @dlucy !

From the specification information provided above, it appears that the "Contour" function on the 730 boosts the bass only, and not the treble as well, unlike the Loudness function on most other amplifiers and receivers of this era - have I understood that correctly? Is that true also of the 930 and the others in this series? The 930 brochure and owners manual seem to not provide this info.

 

[tarior]

If you find yourself working on a 75+, pay extra close attention to the pass throughs on the double sided preamp board. If they aren't pinned and soldered perfectly, you will get unwanted operation that sounds and acts like shot noise from a failing small signal transistor.

 

[gslikker]

If you find yourself working on a 75+, pay extra close attention to the pass throughs on the double sided preamp board. If they aren't pinned and soldered perfectly, you will get unwanted operation that sounds and acts like shot noise from a failing small signal transistor.

thanks, I have one on the pile to ever restore!

 

[Yused Towork]

Harman Kardon 930 Twin Powered stereo receiver

View attachment 2229764

Produced for HK by Roland
Series 1: 1973-75
Price: $475

• AM-FM stereo tuner-amplifier.
• RMS power 45 watts per channel into 8 ohms(both channels driven) with 0.5% harmonic distortion at any frequency 20-20k Hz.
• Overall frequency response 4-70k Hz +/-0.5dB(aux input)
• IHF power bandwidth 10-40k Hz.
• Hum and noise -65dB(phono input), -80dB(aux input).
• IM distortion 0.15%.
• FM section has FET front-end.
• FM sensitivity 1.8uV(IHF), S/N ratio 70dB.
• Stereo separation 38dB@1k Hz, 30dB@10k Hz, with 0.6% harmonic distortion.
• Alternate channel selectivity 50dB, IHF capture ratio 2dB. Defeatable interstation muting and loudness circuit.
• Independent power supplies for each channel.
• Remote speaker outputs.
• Front panel headphones jack.
• Illuminated function indicators.
• Has rear panel connectors for PRE-OUT and MAIN-IN
• Has two PHONO inputs
• High and low frequency filters.
• FM noise cancel switch.
• Phones/main/both speaker switches.

Comments by Todd Krieger in Vintage Asylum on June 22, 2002 at 23:50:18:

"Strengths: Pre/amp like the H/K 560 except more-musical. But with much better bass drive than the 730. Maybe the most-musical '70's integrated receiver made. The tuner section is not only the best I've heard in an integrated receiver, but also the best amongst tuners period."​

"Weaknesses: More solid-state character than a good 730, but only slightly so. (But unlike the 730, the two units I have sound almost identical.)"​

View attachment 2233529


View attachment 2229765

View attachment 2229766

View attachment 2229767

Useful links:

• HiFi Engine page with manuals and ads for Harman Kardon 930 (new access limited now, so see the flooring links)
• service manual for Harman Kardon twin power 930 stereo receiver or HK930
• instruction manual or user's manual for Harman Kardon 930 stereo receiver
• Tracking down a short, blown fuses and bad outputs in HK 930 https://www.audiokarma.org/forums/i...930-short-out-need-help.805341/#post-11218290
• Intermittent tuning dial lights on HK 930 https://www.audiokarma.org/forums/i...n-kardon-930-dial-wont-light-bulbs-ok.797386/
• Adjusting idle (by replacing transistors) and some caps in HK 930 https://www.audiokarma.org/forums/index.php?threads/hk-930-tech-advice.757415/#post-10302111
• Adjusting DC offset ion HK 930 https://www.audiokarma.org/forums/index.php?threads/hk-930-dc-offset-voltage-problem.183587/
• Adjusting bias in HK 930 https://www.audiokarma.org/forums/index.php?threads/hk-930-bias-adjustment.284799/
• Which replacement lamps for meter and tuning dial on HK 930 https://www.audiokarma.org/forums/index.php?threads/harman-kardon-930-receiver.308483/#post-3914338
• No sound from one channel on HK 930 https://www.audiokarma.org/forums/index.php?threads/harmon-kardon-930-left-channel-no-sound.369482/
• Some diagnosis and repair on HK 930 https://www.audiokarma.org/forums/index.php?threads/fixing-non-working-hk-930-need-advice.828081/

Hey Dlucy,
What was the service bulletin in the HIFI engine page for this amp? I am not an old user and I can't download it. Are you a member, or do you know anyone, as I am trying to fix the one on my bench.

 

[painttoad]

Hey Dlucy,
What was the service bulletin in the HIFI engine page for this amp? I am not an old user and I can't download it. Are you a member, or do you know anyone, as I am trying to fix the one on my bench.

 

[Yused Towork]

PAINTOAD-STOOL! Thank you for the bulletin! Unfortunate, it is not connected with my power supply butcher shop.... but thanks, again!

 

[2270 in play]

The fourth era of Harman Kardon's solid state stereo receivers were the Twin Powered series:

View attachment 2227868


This thread is a guide to those models, their specs, and pointers to schematics and restoration threads for each. Note: If you have additional information on any of these models or have a great thread on one elsewhere on AK, send me a private message and I'll get your info inserted into the right spot in the top posts.

The looks of these were very similar to the prior 330abc minimalist series, but they used one power supply for each channel, hence the "twin powered" moniker, these power supplies were dual rail instead of single, and the Twin Powered series stopped using the cap-coupled design of the 330AB models and continued the direct-coupled design of the 330C.

• “Twin Powered” trademark for their dual monoblock design.
• Switched from cap-coupled to direct-coupled output

The models in this era came out in two waves:

• Series 1 (1973-75) built by Roland
  • Harman Kardon 630
  • Harman Kardon 930
• Series 2 (1976-78) built by Roland
  • Harman Kardon 430
  • Harman Kardon 730
• And the HK 730 was rebadged as the Montgomery Ward 450

Other Harman Kardon solid state receiver guides:

• Stratophonic (SR-300, SR-300B, SR-400, SR-400B, SR-600, SR-600B, SR-900, SR-900B)
• Nocturne (Seven Twenty 720, Two Ten 210, Two Hundred 200, Five Twenty 520, Five Thirty 530, Two Thirty 230, Three Thirty 330, Eight Twenty 820)
• 330 minimalist (330, 330A, 330B, 330C)
• Twin Powered (430, 530, 630, 730, 930)

@vendo81