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New Goodies - Harman-Kardon A230 and A300 + Hickok 533A

David_NC

David_NC

Super Member
Like many, I'm always looking for a new project to add to my others! Over the weekend, I found a local guy liquidating his 'collection' due to downsizing his living space. I picked up a couple integrated amps - HK A230 and A300 (A30K, actually). Both are very good to excellent cosmetically and are complete. Both appear to have been updated somewhat - I see a few new caps in the A300, and the A230 looks to have had a couple of its multi caps replaced with separates under deck. I'm probably going to do the same with the rest of the caps. I've ordered some terminal strips to make this a bit easier and tidier vs just having them suspended by their leads.
Any suggestions as to what caps to use for this and any tips would be appreciated. As to these amps, I'm not finding out a lot about them. They look very simple and roomy underneath, for integrated units, compared to my Sherwood! My only tube recap experience is a Dynaco ST-70, which I found easy and straightforward, and much of that is due to that model being so well documented.
The A230 has an assortment of EL84's and an RCA rectifier. The small tubes are Mullard, Raytheon, and Westinghouse. The A300 has Magnavox 6v6GT's and GE and HK for the others. I'm curious as to opinions of these amps. I'd like to power them up before working on them. I have a DBT and a variac on hand as well as some load resistors, so suggestions for this are definitely appreciated!
Here they are. I haven't cleaned the chassis yet, but they look like they will clean up nicely. The A230 has some ugly wooden blocks attached to the sides, but they sure make it nice to work on!
IMG_1350.JPG IMG_1351.JPG IMG_1356.JPG IMG_1357.JPG IMG_1360.JPG IMG_1362.JPG

I also picked up a Hickok 533A in nice condition. It's in some sort of big metal case that is designed to sit up vertically, so I assume it was used as in a retail setting vs being used by a service tech. Once it's proven to work properly, I'll build a much smaller wooden case with a cover like most of this model have.
IMG_1355.JPG
 
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Dswankey said:
If you haven't already seen this

https://stevenjohnson.com/hickok/data/hickok-533a-600a-605a-data.pdf
Click to expand...
I think I found a similar link, but I'll def print that out for ease of use. Thanks for that.

I wonder if it's safe to plug in and turn it on. I pulled it from the case and found the power cord had lots of crumbling insulation. I just mounted an IEC fused socket and will hook it up with a new cord in a bit. It all looked good inside, otherwise. I should probably start a thread on safe startup of a tube tester! ;)
 
Dswankey said:
I doubt it would hurt it also you might want to consider calibrating it.
Click to expand...
Def a good idea. Before plugging it in, I opened it up, fortunately; the power cable's insulation had cracked and crumbled off the cable, and the wires inside were really close to touching, if not already touching. I took care of that and added a fused IEC socket on the side. It was late last night, so I didn't get a chance to plug it in. Perhaps I'll put in on a DBT just for fun and see if it appears fine. Then, I'll give it a shot!
 
Dswankey said:
Fingers crossed the unit works as for calibrating you might like this (See attached)
Click to expand...
It seems to power on fine at least. I thought I'd try to test something. I have a 6J1P, but I don't see a listing for that. How about a 6BQ5? Nope; the listing goes from 6BN6 to 6BQ7. My unit must have a really old ! I did find the settings for this tube online. I haven't found a good operation manual. I assume I set everything listed - line voltage, bias, English, the selectors, filament, etc. I've been told to test for shorts first, so I assume I test shorts 1-5. Next, I'd guess I'd move that switch to Tube Test and press P4.
 
Dswankey said:
I've tested many a 6BQ5's on it, as for testing progression I read and re-read the instructions until I figured it out.

View attachment 2026081


It took awhile but was worth the effort.

PM sent
Click to expand...
Well, it looks like I need to test my tester! It powers up, the 5BQ5's filament lit up... and then nothing when I press P4. I got no deflection of the meter's needle at all on a known good (or at least functional) tube. I sure hope it's not the meter itself.
 
Check & double check the instructions step by step, if one little thing is off it could cause it to not work correctly.
 
buickguy62 is the man you want if you need help restoring the amp. He knows everything related to HK tube amps, and is an awesome guy to boot.
 
Nice scroe, I have trouble with scroe, not score, but somehow, that's what we say. OK, fine. I think you will really like the A230 and the A300.
Both are 15 WPC HK integrated tube amps, the A230 is earlier, the A300 replaced it in about 1962. The A230 is EL84 based, the A300 is 6V6/7408. The A230 is tube rectified, the A300 ss. The A300 uses the phono stage filaments for cathode bias, gives DC to the filaments. Not uncommon for the era. The A230 has more bells and whistles, multiple (A&B) speaker selection, center channel for both A&B consequently a fair amount of wiring to incorporate the features. . The A300 cleaned that up significantly. I like them both, easy to work on, especially the A300.
If you go to AK forums, under Audio, find the Digital Docs. forum, follow the trail to open it, then under HK you can find the owners manual for the A230, pretty complete, includes schematic. Nothing there on the A300 but Google finds schematics, etc.
Let's look at the A230 first. Previous owner looks to have a good job on recapping the power supply. In addition I generally replace the two brown jelly bean coupling caps (I prefer Sprague/Vishay 716 series orange drops), also, often the power supply resistors (10K, 1K, 1K) and the four 470k resistors have drifted and I replace them out of habit. I keep the values as selected by the HK engineers on components.
I have stiff line voltage here, lucky me, I have a distribution transformer just outside my den window and I'm the only house connected to it. I've experienced as high as 126 VAC on occasion-yikes. Consumers Power tech said lucky me, normally they get calls for low voltage. Anyhow, I've started adding CL-90 thermisters to amps as I restore them.
On both the A230 and A300 I liberally use DeOxit D5 and F5 for the controls and pots, including the four balance pots under the chassis. Verify they are working, if open they can cause you grief. Also include the rear panel switches (phase and impedance). Not uncommon for the EL84 sockets to need to be retensioned. (As a matter of course I retension all the tube sockets).
More later on the A300.
Tom
 
I've read that one should repair audio equipment before doing recaps so as to not introduce more issues. With amps like these that appear to be in good shape (no obvious failed components, burned areas, etc) and that have had some maintenance performed in the past, what's the best way to test these? I have a variac and DBT here, but I'm not sure how to go about this. Do I run them at reduced voltage for a while and then fire them up on the DBT? I have load resistors as well as a pair of test speakers, so I'm good there, too. Any suggestions will be appreciated!
 
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