harman/kardon hk775 amplifier restoration

[z-adamson]

If you can get a nice picture of how the trimmers are oriented it will help in selection. It's hard to tell from the SM whether you'll need side adjust or top adjust, hence the photos. I'm not having much luck finding 150ohm...you may need to go to 200, again, depends on orientation. VR402 for setting Bias would be better served by a single turn or it will take forever. DC Offset will benefit from multiturn. Haven't yet lookd for the dual resistors. Do you know if they're bad? Most times they're fine.

Top adjust on both, I will get pics

Havent diagnosed the dual resistors as bad, just want to have them in case. They are quick and easy to change so I figured why not, as long as good replacements are available. I seem to recall from those who use HK citation 16 that multiturn VRs for bias are a must so I figured they would serve well in this amp too.

 

[jheu02]

When you say Top Adjust, the boards are horizontally mounted in the case and you look down on the top of the trimmers? I ask because it looked like the amp board plugged into something and was oriented vertically, with the trimmer sticking out of the side. So, even though from overhead it looks "top adjust", the trimmer would ACTUALLY be a side adjust part.

 

[z-adamson]

The boards that the VRs install to are perpendicular to the ground and the adjustment is made from the top of the amplifier chassis which would be the side of the VRs.

 

[jheu02]

That's what I thought. So they're side adjust. Is the middle pin above the other two or below? SM makes it look like they're above on both VRs.

 

[z-adamson]

That's what I thought. So they're side adjust. Is the middle pin above the other two or below? SM makes it look like they're above on both VRs.

As viewed from a birds-eye-view with the amp right side up?

 

[jheu02]

If the amp is sitting on a horizontal surface...say a table...and you have the top cover off and are looking down into the amp...you can see the adjustment slots in the trimmers, but the circuit boards themselves look like thin slices with the components sitting horizontally to you looking down on it, yes?

Here's a pic looking down into a Pioneer SA-8500II I rebuilt. The amp boards are mounted vertically on the heatsinks (as referencing the ground plane) but you can see the tops of the trimmers circled in yellow. These are "side adjust" trimmers, because the mounting pins go sideways into the board as referenced from above.

 

[z-adamson]

If the amp is sitting on a horizontal surface...say a table...and you have the top cover off and are looking down into the amp...you can see the adjustment slots in the trimmers, but the circuit boards themselves look like thin slices with the components sitting horizontally to you looking down on it, yes?

Yes, I follow 100%, we are on the same page. Thats what I meant with birds-eye-view, right side up. I will check that when I get home.

 

[jheu02]

I edited my post to include a pic. please refer to it so we make sure you order the correct trimmers. There's MANY variations and you have to order the correct part number.

 

[z-adamson]

Middle pin is up as per the point of view we discussed.

 

[z-adamson]

Viewed this way they would be considered side adjust.

 

[jheu02]

OK. One other question: are you comfortable with using breadboard to turn a "top adjust" into a "side adjust"?

This would be a perfect replacement for VR402, but it's top adjust. If you place it in breadboard and run jumpers sideways it will work.

Otherwise, you'll need to go to 200ohms to get side adjust.

Here is a single turn that should work well. 200ohm

And a multiturn if you insist. 200ohm

For VR401 1K ohm

These are on order.

Also on order some Bourns

Finally, some that are in stock

 

[jheu02]

Some other items I am trying to replace but not sure what to use.

-Cement resistor...R446,447,448,449,450,451,452,453...part# 5723 R33672.....0.33ohms, 3watt x 2 special dual (2 leads on one end, 1 on the other).

I haven't found any double resistors yet, but you can use two singles if necessary. Just make sure you give them some space from each other for heat dissipation. You'll twist one leg of each together to make a "V" out of the resistors. Solder the double leg in the one hole (may need to enlarge it a tad with an X-acto blade) and the single leads in their respective holes.

These would work.

 

[z-adamson]

Finally, some that are in stock

Thanks for the list


This last one says 6 weeks lead time. Any other alternatives?

 

[jheu02]

Numerous fuse resistors:

100 ohm 1/4W - R24
1.5K ohm 1/4W - R403, 404, 409, 410
56 ohm 1/4W - R431, 432
39 ohm 1/4W - R473, 474

47 ohm 1/2W - R438, 439
27 ohm 1/2W - R443

I like the following:

Vishay/Dale RN60C or RN60D (don't let the 1/8W rating scare you off...it's underrated for Mil-Spec, the same resistor for industrial use is CMF and it has a 1/2W rating) VERY low noise resistors
KOA Speer MF 1% tollerance (500V rating vs MFS 250V rating)

Others are fine also, but just stick with 1% vs looking for 2%...better resistor.

 

[jheu02]

Thanks for the list


This last one says 6 weeks lead time. Any other alternatives?

Do you need more than the 725 that can ship immediately???

 

[z-adamson]

Do you need more than the 725 that can ship immediately???

Oops, the on order, 6 week lead time threw me off.

 

[z-adamson]

Numerous fuse resistors:

100 ohm 1/4W - R24
1.5K ohm 1/4W - R403, 404, 409, 410
56 ohm 1/4W - R431, 432
39 ohm 1/4W - R473, 474

47 ohm 1/2W - R438, 439
27 ohm 1/2W - R443

I like the following:

Vishay/Dale RN60C or RN60D (don't let the 1/8W rating scare you off...it's underrated for Mil-Spec, the same resistor for industrial use is CMF and it has a 1/2W rating) VERY low noise resistors
KOA Speer MF 1% tollerance (500V rating vs MFS 250V rating)

Others are fine also, but just stick with 1% vs looking for 2%...better resistor.

Thanks, I did plan on replacing every fuse resister considering both of them in the hk725 were way out of spec.

 

[deltalight]

Filter cap pics...

52mm diameter, 80mm length, 22mm center to center in the terminals

15,000uF 100v 51mm x 80mm x 22mm(screw): 647-LNR2A153MSE

 

[z-adamson]

15,000uF 100v 51mm x 80mm x 22mm(screw): 647-LNR2A153MSE

Thanks!

 

[z-adamson]

One thing that the manual says is...

Replacement for output and driver transistors, if necessary, must be made from the same beta group as the original type.

....what exactly does this mean and how do I make sure that the replacements, if I decide to replace, are appropriate??