Anyone know about...Harman Kardon A700 integrated tube amplifier
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mhardy6647
Lunatic Member
hk has much (most!) of their legacy manual information on-line at:
http://www.harmankardon.com/estore/hk/us/support/supportProductSupport.jsp
I don't see an A700 offhand... nor do I know this amp offhand.
Best bet, peruse 1950s-1960s catalogs at www.radioshackcatalogs.com and www.alliedcatalogs.com
EDIT: d'oh! That was easy; sorry! see page 148 of http://www.alliedcatalogs.com/catalogs/1964-230/
Yes, that's a nice amplifier; I am not sure what output tubes it used; maybe 'odd' ones (7355s?)
http://www.harmankardon.com/estore/hk/us/support/supportProductSupport.jsp
I don't see an A700 offhand... nor do I know this amp offhand.
Best bet, peruse 1950s-1960s catalogs at www.radioshackcatalogs.com and www.alliedcatalogs.com
EDIT: d'oh! That was easy; sorry! see page 148 of http://www.alliedcatalogs.com/catalogs/1964-230/
Yes, that's a nice amplifier; I am not sure what output tubes it used; maybe 'odd' ones (7355s?)
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secret4mula
Active Member
Found some basic info from the web in my notes.
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HK Award Series Integrated Amplifier
-----------------------------------
Model .................... W/ch .... Output .... Bias ......... VA/PI
-----------------------------------------------------------------
A700 .................... 35w/ch ... pp7591 ... Fixed ....... 7199
A500 (A50K - kit) ... 25w/ch ... pp7355 ... Cathode ... 12ax7/12au7
A300 (A30K - kit) ... 15w/ch ... pp7408 ... Cathode ... 12ax7/12au7
-----------------------------------------------------------------
-----------------------------------
HK Award Series Integrated Amplifier
-----------------------------------
Model .................... W/ch .... Output .... Bias ......... VA/PI
-----------------------------------------------------------------
A700 .................... 35w/ch ... pp7591 ... Fixed ....... 7199
A500 (A50K - kit) ... 25w/ch ... pp7355 ... Cathode ... 12ax7/12au7
A300 (A30K - kit) ... 15w/ch ... pp7408 ... Cathode ... 12ax7/12au7
-----------------------------------------------------------------
buickguy62
Active Member
A700
Richard Sherman has info on the HK's including the A700.
http://shermanr.web.prw.net/Page_02.htm
The A700 is about halfway down the page.
Richard Sherman has info on the HK's including the A700.
http://shermanr.web.prw.net/Page_02.htm
The A700 is about halfway down the page.
maestro826
New Member
Greetings! I know this is a REALLY old post, but I own now the Amp that Richard Sherman featured on his page, I had helped him work on it further until we got it finally set up beautifully about.. 2 years ago?
Feel free to reach out if you have any questions on it!
bluesolrac
New Member
I have a working A700 it could use an overhaul but is it worth the cost or should I sell it?
The audio portion of the A700 is the same as the TA7000X receiver. My last scratch-built amp used the transformers from the latter to build a 6L6-based amplifier. Performance is very good.
Jack
Jack
Dr Morbius
Well-Known Member
I’ve heard the A700 with Klipsch Cornwalls - sounded really nice to me!
WopOnTour
Hoarder Extraordinaire
The last of the HK Award Series amps. I restored one many moons ago. Great iron. I also liked the fairly powerful headphone jack
About the only thing negative I would say about it is the use of 7591s.
I know 7591s sound fine but hard to find and as such, far too expensive and annoying. I dunno maybe they are easier to find these days? Any new production?
Anyways on the A700 I ended up re-pinning the output sockets to accept 6L6GCs and only having to re-work the negative bias to make them individually adjustable to suit. (it already utilizes fixed bias)
In the end was happy with the result and so was the owner
WOT
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The factory cathodyne driver has insufficient headroom to drive 6L6 output tubes properly. It needs to swing about ±17V maximum for the 7591, but the lower gain 6L6 types need roughly twice that. Based on the quiescent DC voltages on the anode and cathode of the inverter, it will be operating in less linear portions of the curves as it approaches maximum drive. In addition, the driver as a whole needs to provide about twice the gain in order to maintain similar operating settings with 6L6s. HK amplifiers using the 7355 output tube (gain similar to 6L6) utilized positive feedback in the driver to accomplish this. Driver gain is greater than 300. The A700 is simply a straight pentode driver design with gain only a little above 100. I'm not saying you did a bad thing here given the situation with tube availability, but the A700 will perform better if it's fitted with 7591.
Jack
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WopOnTour
Hoarder Extraordinaire
In the finished product gain seemed sufficient IMO, although truthfully I never had the chance to hear it operate on 7591 as I had none. But like I said I changed the negative bias generator completely using a different transformer that delivered over -40V to start with and added individual bias pots. It biased the 6L6GCs just fine with something just over 400v on the plates. Never had to touch the driver stage itself, although it might have been better optimized after the change. I did mess around a bit with the feedback to the driver stage IIRC trying to improve the square wave. This tube change was essentially the only solution I had at the time, but it was over 20 years ago so will have to refer to my old scribbler to confirm what else I did. Would sure like to hear another A700 with new production 7591 since they seem to be a bit more available these days. Maybe I add it once again to my list of "looking fors" lol
WOT
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