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Harman Kardon TA260 Restoration Begun

richiem46

richiem46

Retired and enjoying life and music!
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I have seen several Harman Kardon TA260 receivers for sale and it looked like an interesting receiver. I was tempted to obtain one but didn't want to overspend on one as all my experience is with Fisher amps and receivers.

I saw this one on the big auction site and the faceplate looked to be in good shape though the chassis will not win any beauty contests. It was also missing 4 12AX7 tubes which made me suspicious of the claim that the amp "made sound" but I got it at a good price so here I am! I am attaching a few pictures from the big auction site of the unit as advertised.
 

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I received the unit and did a once-over on it for any obvious issues. I tested all of the tubes in the unit and replaced several in the Radio section that were bad and ordered a 6AL5 that I did not have on hand, The 7355 output tubes all tested strong which made me happy as they are hard to come by. I have four 7591XYZ tubes I replaced in a KX-200 with EH 7591's a while back and kept on hand. They apparently are a plug-in replacement for the 7355's which is another reason I got the TA260. The outputs looked to be ok so I installed four used but ok 12AX7's in the TA260, attached a DAC/IPAD combination to the "spare" input, plugged the TA260 into a variac and slowly powered it up.

At about 75VAC the left channel began to play weakly and the right channel was silent. I used the "blend" control to put the unit in mono mode and both channels played but kind of weakly. the B+ and bias seemed to be within the realm of reason so I powered the unit off and first replaced two small electrolytic cathode caps as I had them on hand. I then cleaned the 12AX7 and 12AU7 sockets, de-oxed all of the switches and controls, the slide switches were so stiff that I could not move most of them without fear of breaking them and then powered the amp on again.

I was really pleasantly surprised that the TA260 now played extremely well, as good as many of the Fishers I have restored even in it's present state. It has plenty of punch and I will now continue to restore it.
 
Here are a few pics of the unit as it is presently. I cleaned up the front panel and knobs, replaced the power-on indicator light (cool Red light!). A few of he coupling caps have been replaced and I ordered replacements for all of them. Some of them are not "standard" values (.5, .05, etc) so I ordered the closest value available. Some of the diodes and filter caps have been replaced and I will try and determine which caps need a refresh, sever of them bet a bit warm.

PXL_20220312_181702107.jpg PXL_20220312_181712106.jpg PXL_20220312_181723478.jpg

I will have to think about bias mods I might make and also screen resistors.
 
I had one of those quite some years back, partially restored, nice beefy transformers. I thought it sounded good with 7355 OP tubes and wished they were more plentiful. It was a heavy beast too.
Good luck with the restoration.
 
Tinkerbelle said:
I had one of those quite some years back, partially restored, nice beefy transformers. I thought it sounded good with 7355 OP tubes and wished they were more plentiful. It was a heavy beast too.
Good luck with the restoration.
Click to expand...

Thanks!
Oh yeah, it is very heavy. I went through it more closely and the B+ voltages were a bit high at 120VAC input but nothing to be concerned about. The bias voltage was -29.2 vs. -32V called out in the schematic. The output tubes are a bit out of balance but I left the settings alone until I can verify the 50 ohm DC balance pots are ok.

I am in the process of identifying which filter caps need replacement. I suspect I should replace all of them but the amp has 5 can caps and the two in the high B+ supply I will probably replace under the chassis and the rest with can caps. Pretty interesting ground arrangement, all the can caps are insulated from the chassis and tied to a common ground buss that also runs across the chassis above all of the 12AUX7 tubes. It took me a while to figure it all out but am sure the effort will be worth it.
 
Voltages posted on the schematic may be in FM mode. My TA-5000x shows it this way. They will be higher in the AUX(Spare) mode as the selector switch cuts plate supply to tuner tubes. It may not be the same in your receiver, but since FM was used more than any other mode consistently, I bet the voltages are posted for FM operation. Curious to know...
 
I have received most of the filter capacitor replacements and will start working on them probably today. I also discovered that 7355 outputs have no connection internally to pin 4 while the 7591XYZ tubes do. In the TA260 they use pin 4 as a tie-point for the grid bias resistor and the bias voltage. In the 7591XYZ and all 7591's for that matter pin 4 is tied to the screen as is pin 8 and it is recommended they also be tied together externally. I will have to modify the TA260 to allow the use of the 7591XYZ's. Guess I could use regular 7591's also if I modified the bias circuitry to accommodate them.
 
Another issue is that I can't find a decent manual for the TA260. All the usual sites seem to have the same marked-up schematic which is difficult to read. I have the SAMS folder but their schematics are generally a bit suspect based on my experience with Fisher amplifiers.

Does anyone have a decent copy of the TA260 manual they can share?
 
An update on the ta260. I have either replaced or re-stuffed most of the power supply capacitors in the unit and it is working pretty well at this point. I was comparing it to my Fisher X-202-B playing through the "spare" port and while the TA260 isn't quite in the same league as the X-202-B it is still a very nice sounding amp. I also made the output socket modifications I mentioned previously to allow 7591XYZ tubes to be substituted for the 7355's. I tried the 7591XYZ's and they played quite well in the TA260. Good to have a spare set of output tubes on-hand.

The FM section was kind of working but only one or two stations came in. I checked and cleaned all the tube sockets in that section and the FM radio is now working quite well. I am going to try and follow the sketchy alignment procedure in the owner's manual to see if I can improve reception a bit.

I also sanded down the steel case and will re-paint it once the weather permits it here in Florida. The wind has been blowing briskly for the last several days, not good for spray painting!
 
I have one of these in storage along with several other models that use the 7355 (Guess I'm an HK fanatic). My TA260 is in good condition generally, but I'm planning to eventually strip the iron and build a power amplifier. I did this recently with a TA7000X, and it worked out well. Before you spend too much time on the receiver section, bear in mind that this one requires an external MPX adapter to decode stereo FM broadcasts. Also, I don't consider the 7591 to be a good sub for the 7355. The 6L6GC and 6P3S-E (Russian) are much closer to the specs of the 7355. The biggest difference is somewhat greater filament current. I'll check to see if I have a good schematic somewhere.

Jack

My "TA7000X":

TA7000X top sm.jpg
 
Jack:
Thanks for looking for the schematic, I even contacted Harmon Kardon and they emailed me the same marked-up copy that is on the internet.
I put the first coat of paint on the case yesterday and it is looking good and will put on the next coat today once the wind dies down a bit. It will look good in the case!

I was not able to better align the FM section as I seem to have a problem with my RF signal generator which I will have to investigate. It is playing decently but as you say it is mono so was just getting it in decent working condition. It sounds ok but the amp portion of the TA260 is really quite nice.
 
It turns out I have the SAMS Photofact folder just like you, so no go. You're right about occasional errors, but that's not always the case. Many of them are OK. I definitely don't trust their replacement lists for items like chokes and transformers though.

Yes, the power amp section of the TA260 is excellent. The output transformers are very large for this power rating, just like those in the TA5000X. I have one of those in storage too, and also an A500, A260 and TA3000X. The last two use different output tubes (6L6GC and 7408 respectively). I'm hoping to convert all of these to standalone power amps as time permits.

At the risk of repeating myself, it's pretty straightforward to replace the 7355s with 6L6 types. Ironically, I converted the TA7000X from 7591 to 6L6GC. That was tricky, and it required an entirely new driver design. Biasing and gain of the 6L6 is nearly identical to the 7355, so you would have a much easier task.

Good luck with the project. It's a beautiful piece of equipment!

Jack
 
I finished painting the case for the TA-260 and after touching up the balance controls on the 7355's one last time I put the unit in the case. I have to say it is not a bad looking piece of equipment.

PXL_20220429_130941031.jpg PXL_20220429_130951711.jpg
 
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