Harman/Kardon A500 Tube Amp

tube-a-lou

Addicted Member
Hi all,

Went shopping today and someone had a Harman/Kardon A500
Tube amp, needs to be redone and the gentlemen said he'll sell it me
for $250.00, good deal, I always redo these tube's amps anyway so
what do you think??:scratch2:

Tube
 
Well I have one, and will be using it as my bench amp. I have the matching tuner too. My A500 has the HK tubes still. I have not done anything with it yet, They say they are nice amps. Like 25w per ch.

Pics?

WO
 
Hi,
No pics yet, haven't brought it home, looks to be in good shape, look underneath
it has those huge Sprague black beauty caps on it. the guy told me when he put it
on, one of the can caps started to smoke, so I guess that needs to be replaced and
all the rest!

Tube
 
They're really good, once they've been recapped.

I replaced every coupling cap, and every electrolytic cap (including the cans) on the last one I had on the bench. Total of 24 caps. Be sure and don't forget the little electrolytics in the preamp/phono stage!

It sounded magnificent afterward.

Regards,
Gordon.
 
These really are sweet amps once they have been recapped. Here is mine I used for years before giving it to Kamakiri.

HK_A500.jpg



Cap job
b4nafter.jpg


More pics and the matching tuner here:
http://wardsweb.org/misc/HK_A500.jpg
 
I've restored a number of these with input from Jim McShane. I replace at a minimum all the electrolytic and coupling caps, the balance pots and the diodes, and liberal use of De-Oxit. I have an Excel spreadsheet that lists the components and sources I use --it's a good place to start--you might have your own preference on component selection. PM me for the spreadsheet if interested, I also have the schematic if you need one. One trick I've found is to use two of the dual 50/50 ufd. 500V JJ can caps from tubesandmore (to replace C29 A&B, and C30 A&B). They are under $10 each (plus the clamps), they fit in the existing holes and allow plenty of room underneath for the additional caps-see pics--that area gets crowded if you put all of the replacement caps under the chassis. See pics.
Tom
 

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Hi all,
Thanks for all the info, I'm really thinking of getting it maybe I'll try to get
him down a little, how about the power tubes 7355 is there replacements,
would 6V6's be good or 7591, I've read that with a little mod you can use
6L6's??

Tube
 
7591XYZ are known to be a good (and cheap) replacement. Some mods have to be done however to allow it.
 
Hi,
Decided not to buy it, I'm going to stick with the Fisher. besides he would not
go down in price, it's odd the knobs are off, the front panel is off, the bottom panel
is off and the light button the the switch is missing, so that's it thanks for all the help
and I'll wait for a better one to appear.

Tube

Tube
 
7591XYZ are known to be a good (and cheap) replacement. Some mods have to be done however to allow it.

Actually, the only mod that is needed, is to snip off the one pin (from the base of the tube itself) that the 7591 (and 7591XYZ) uses, that the 7355 does not. IIRC, that's pin 4. Check with a good tube manual... it'll be the pin that's also connected to the screen grid, in parallel with the "normal" pin that's used for screen in the 7355. You only need one screen grid connection... so that one that's in the unused position on the 7355, can go away safely.

Regards,
Gordon.
 
Thank you!! I plan on running my electrovoice ev sixs with it and also bozak concert grands. Any input would be appreciated!
 
Class AB. Not too far into the "B" realm, but definitely AB.

Regards,
Gordon.
Am I correct to assume that it stays mainly in Class A at low volumes and goes to AB when pushed hard? Like most of Hi-Fi tube amps...?

Anyway, listening now to my own A500 and Dynaco FM-3, bliss!
 
Am I correct to assume that it stays mainly in Class A at low volumes and goes to AB when pushed hard? Like most of Hi-Fi tube amps...?

Anyway, listening now to my own A500 and Dynaco FM-3, bliss!

Technically, it doesn't drive the output tubes into cutoff each cycle, until probably over 65% of its max power output. But, it's still a bit different from "Class A" even at low volume, primarily due to lower bias than what a true "Class A" amp would be at that power rating. The differences are mostly academic, but they do exist...

Regards,
Gordon.
 
Technically, it doesn't drive the output tubes into cutoff each cycle, until probably over 65% of its max power output. But, it's still a bit different from "Class A" even at low volume, primarily due to lower bias than what a true "Class A" amp would be at that power rating. The differences are mostly academic, but they do exist...

Regards,
Gordon.
Thanks, better to verify with an expert (you) than self believing false things...:)
 
BTW, as I posted here, better to explain a little problem I have with mine since it's out of storage (since last fall): loudness pot misbehaving, scratchy and sometimes losing volume on the right channel.

This amp was recapped back 8 or 9 years ago and almost all resistors replaced. I did the job myself. To resume, new lytics, new caps and resistors... but left the original ones in the front panel (around the volume pot and tone controls). Once I rotate the pot a couple of times, it's back to normal. Deoxited the pot carefully before Christmas but the problem is still there.

Should I replace the caps? Clean again the pot? Something else?

Thanks,

Patrice
 
see if there is any DC voltage leaking into the pot. That tends to make pots really scratchy and it comes back frequently.
 
see if there is any DC voltage leaking into the pot. That tends to make pots really scratchy and it comes back frequently.
Just to be sure: I check for DC on the lugs of the pots, correct?

Edit: obviously not on the grounded lug :)
 
Last edited:
right. I'd expect it on the "top" of the pot not so much the moving wiper. If a cap between the volume pot and whatever feeds it had gone leaky, thats where you'd get voltage. Doesn't take very much either to make a pot noisy.
 
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