I live in an area devoid of any quality electronics repair. And before I send the unit off to AR, is there any simple visual things I can check or should be aware of?
I bought the unit from Upscale Audio. I’ve purchased an AR PH3se from them and it’s been great. I know used equipped like this is a bit of the throw of the dice, but they “say” it’s been bench tested and looked over and comes with a 90 day warranty, but I will call them to verify what was exactly done. |
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@djohn
I was considering trying to change the caps myself. I've done very little soldering in all actuality, but I am pretty hand and have good dexterity in small spaces. To that end I've been watching all manner of youtube vids on the subject and I was going to go find some old broken gear and start practicing on it in hopes of trying to do this myself, but I might be kidding myself.
I will call to get a price on having this done for me.
This is going in my secondary system so it's not a rush job for me.
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I called Mr Scott Frankland, nice fellow, and spoke with him about work that could be done on the Classic 60. He indicated that the 4 caps aren’t soldered in, but screw in. So, in preparation of getting the amp I have purchased 4 Kemet capacitors that are a direct fit for the Classic 60. But with a bit more overhead.
On Scott’s recommendation I purchased a variable voltage transformer to slowly bring the voltage up once the new caps are plugged in to make sure the electrolytics disperse evenly. He highly suggested I do this, so I am.
my question is after the new caps are in and the amp has been brought up to power do I need to rebias the tubes, or is that only necessary if the tubes are replaced? |
I got the original manual, and even the original sales brochure, but the manual only says how to do it, no pictures, and the description is only basic.
but if the device above eliminates the need to stick probes in dangerous places and all I have to do is turn a screw that would help immensely. |
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The 8 power tubes are new. Thing sounds amazing for a 30 year old amp. Can’t imagine what a modern AR amp would sound like today. Can’t afford new, that’s for sure. |
Got the amp! Damn thing is HEAVY.
So I plugged it in and went to listen to each tweeter to see if there was audible hum - ear right up to it - NOTHING - ZERO NOISE!! No hiss or hum at all. I thought hmmm , maybe it’s broke, nope it’s just that quite. Music sounds wonderful. I can’t tell if the caps have been changed. What color are the stock caps color? Mine are blue.
As far as being able to connect to the screw type speaker connectors on the back of the amp, I ended up cutting one of the legs off my speaker cables spade termination. This narrowed the spade width just enough to just fit between the fins of the amps speaker connectors Snug too. Don’t worry about the speaker cables too much, there just old Blue Jeans cable, so no house mortgage was harmed. |
I’m only focused in so far as making sure it initially runs without any hiccups and is set correctly, I will then focus on fixing other things down stream say in the next year or so.
After speaking with Scott, he was of the opinion that I shouldn’t rush to do anything just yet, but make sure it’s adjusted right and listen to it for a while. He says in many cases these units can sometimes check out in good health Ians don’t really need anything done to them in the immediate time. |
@djohn
thanks for your thoughts.
The tubes are Sovtek 6550’s. So there should be no issue with those.
As as for the tester I mention above, if I understand it right, it basically replaces the probe leads you would otherwise need to use. So the danger of sticking probes into unwanted places is greatly reduced. It would seem the only thing I need to “adjust” is the bias screw with a non metallic screwdriver.
I emailed AR the tester probe and asked them if it would work for bias adjustment but I haven’t heard back from them yet. I also asked they send me any info for biasing the unit.
As for the mod you did for the bias adjustment, according to what he remembered it was over the $1000 dollar mark. An while it appears to be a great mod, I only paid $1500 for the whole unit.
The unit does sound amazing- no doubt about that - and I’m amazed at how quite it is. |
If I wanted to discharge the current caps, is it simply done by leaving the music on, turning off the amp, and waiting for the music to fade out until there is zero sound? Then unplug the system. Or is there still residual voltage in the caps? |
No biggie. I found many videos and write ups explaining safe ways to do it. It’s not too complicated.
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So I purchased the correct probes to set the bias, the kind that extend out from a long insulated sleeve and can lock into the small capacitor legs.
I had AR email me the instructions.
One thing I’d like some input on is there appears to be only one adjustment screw for both the right and left side tubes. So how does adjusting for one side not upset the other and vice versa when adjusting for bias. |
Ok. I finished the mini refresh.
I biased the tubes and changed out the main caps. One side was 4 mVDC lower, not really out of spec. But I figured I could do better, I flip flopped a tube set from the left side to the right side. This got me 65mVDC on the right and 63mVDC on the left, then I turned my attention to the servo adjustment. I had to adjust one channel a quarter turn and that was it. Then I switched out the 4 large caps. That was simple, just discharge them, pull them out and reconnect the new 4. Then over the course of two hours I slowly brought the voltage up to operating spec. Once that was done I threw a record on and enjoyed the music!
Everybody says how dangerous this bias stuff is on this unit. I agree if your a total nimrod and don’t do a bit of reading and pay attention to basic safety. Not to toot my own horn too much, but I‘ve never done any of this stuff before today. I just made sure I had the right tools, took some simple safety precautions and researched a bit. Saved my $’s and too. I am lucky, the unit was basically in great shape to begin with, so I have that going for me! |
