Thread: A Friends DIY For Me

Ice storm in Texas. Shipping date unknown at this time.

Originally Posted by brad225

Ice storm in Texas. Shipping date unknown at this time.

It is literally SOLID ICE out my window. Everything - including fast food restaurants and such are shut down.

I actually had to go without getting my morning iced coffee today. <gasp>

No ice coffee out? The inhumanity of it all.

I'm doing my part from Florida Michael. I just put ice in my tequila.

Originally Posted by brad225

No ice coffee out? The inhumanity of it all.

I'm doing my part from Florida Michael. I just put ice in my tequila.

Oh yes, its another day of shorts and tee shirts

Originally Posted by CPP

Oh yes, its another day of shorts and tee shirts

Well I just tried the roads and they aren't that bad for the first time. But EVERYTHING is still shut down.

I read in the news yesterday the police were delivering medicines to those in need so people wouldn't have to try and drive. I was wondering if Iced Coffee withdrawals qualified for that....

Good news is we'll be back in the 60's Sunday.

So, the parts came in and the install commenced. They are a major improvement in their ability to adjust + & - current to "0" without fluctuating up and down a few tenths or hundredths.
One of them still doesn't want to "0" out so Phil is going to start tracing back through some parts he didn't test. He believes that that are going to be a couple of weak resistors to replace.

I again, told him I was sorry for the problems the amp was giving him. His response, again was.
No, its fine. I love figuring these things out.

Says the guy that woke up at 2:24AM Thursday and was thinking about the amps. He got up and installed all of the new parts he had prepped for, went back to bed at 5:45 and fell asleep till 10AM.


*Another learning session for me. I asked him "Is it detrimental to the amps if that one doesn't "0" out?" He said no, but.

Think of the wave the electricity as it makes sweep from + to - up and down.
If it is not able to zero out then it will cut off the top or bottom of the wave depending whether it is the + or - that is not zeroed out.
As the wave is cut off so are the dynamics of current, hence, the dynamics of the sound you hear.

I have learned a lot. I just don't have the ability to apply it. That is what the professionals are for.

Good news is we'll be back in the 60's Sunday.[/QUOTE MichaelsMinute]

Good news is. Maybe you will be in Florida next week for an Audio Show?

Originally Posted by brad225

Good news is we'll be back in the 60's Sunday.[/QUOTE MichaelsMinute]

Good news is. Maybe you will be in Florida next week for an Audio Show?

I would LOVE to be but unfortunately it did not work out with my "real-life" schedule this year.

Swing and a miss, yet again. Phil has cleaned all of the boards and cleaned all connections that are detachable for that one side of the amp. ARC suggested it may be something in the main control board on the front panel of the amp.

After a thorough check, he removed the front of the good amp and installed it on the non zeroing amp and the problem still exists.

I spoke with him last evening and he is going to remove all of the parts related to the KT120 upgrade path for that side of the amp. Possibly one of the parts has issues.

More to follow in the story of.... Phil & Brad verses the 610t.

It looks like the problem has an answer.

Yesterday Phil did a diagram of the entire bias circuit with values large enough to make notes on it.

This morning he started unsoldering some parts to test values and found 5 resistors on the "non zeroing" side of the amp that were nothing like the schematic or the resistors on the other side of the amp. Their values or markings were not there on any of them. Phil mentioned other parts that they had removed any identifying marks in the past, probably for proprietary design reasons.

He texted today me and said the believes he found the problem being, the 5 resistors.



An hour later he called to tell me that he had received an email from Greg at ARC. Greg said that he found an engineer that had been there long enough that he remembered an issue they encountered with the bias circuitry.

Apparently during production they ran out of the parts that were originally designed to be used and changed the 5 resistors in different places (with no markings) and never put it on the original schematics. So, the only people that ever knew were the engineers and the person installing the parts.

The weeks Phil has been trying to figure this out is a design change with no public record. Pardon my language but, that is F-ed up. I guess, the only good news is that they owned up to the unrecorded change and gave us the correct information.

They do have the original correct parts and will sell them to us so Phil is ordering them today.

As one of my pair of amps has both configurations I asked Phil to find out what year my amp was assembled. It would seem, it was possibly the first one, hence, the different design on each side of the same amp.


I am so thankful for Phil. I don’t think I could find anyone else that would have the patience and curiosity to make this happen. To say nothing of the labor bill if I didn’t trade my furniture making skills for his EE skills.

Hopefully my next post will be confirmation of the problem being corrected.

again Brad, fingers crossed !!!

So, here we are a couple of weeks later and the issue is even more of a conundrum than ever.

Plus, I completely spaced out on my updates.

The zero out resistors got replaced and thought they worked much more accurately and quickly it didn't resolve the zero out problem with one side of the bias circuit.

After 2 weeks we heard back from ARC and found out that in the time frame that my amps were being built they had a shortage of resistors. The remedy was to change the way the circuitry worked with different parts but not show that on the schematics that were connected with the amps.

On the positive side one of the engineers that still works there remembered and they sent us free of charge the proper original parts that would have been in my amp. That change was only in the one amp of mine that is the problem not both.

We received the parts and Phil installed them and to our surprise or not ...... nothing changed. One side of the bias circuit still won't zero out.

Phil reached out with the latest information request but the person we are working with is out with Covid. So, we are having another delay. In the last 2 days I helped phil turn the amps upside down so he could re-solder all connections in the bias circuit. He has tested EVERY part in the problem bias circuit and it is an exact match to the amp that works perfectly.

While waiting, the only thing he can think of is, something under one of the 3, bias circuit tube sockets is an issue. There are traces in the board that have nothing to do with the bias circuit that run under the sockets. I ordered new ceramic sockets today and he will destroy and remove the old ones and see if there is something under one that might be a problem.
He actually asked me to order 6, and he would change them in the other amp so both amps will be exactly the same.

I am so fortunate to have a friend that is this smart and challenged by trying to solve a problem. He has admitted a couple of times that this, is the most complicated issue he has ever faced. I have told him more than once, if you get to the point you have had enough, I totally understand.

I suggested to Phil that he asked the intermediary he works through at ARC, if we paid his hourly rate could Phil speak directly with the engineer to work through this. He liked the idea, but, we will see if they will allow this to happen.

So that is where it stands today.

On my side, in the repayment column. I have started working on the bass speaker towers for Phils system to go with the panels I previously built for his line array speakers. They will also match the subwoofer box I built a few years ago.

After I ordered the new ceramic tube sockets, Phil proceeded with the prep for the installation.

I received the sockets on Tuesday and took them up to him. He lives about 45 minutes away. He had removed the 3 sockets from each amp. Cleaned up and re-soldered any place that looked questionable on the traces where the sockets mount.

He also found ground loops under 2 sockets on each amp. He eliminated the ground loops was ready for the install. He asked if I was going to stay as he was going to do it immediately. I could not stay so, I left and he commenced.

By the time I was arriving home he called to say they made no difference in the problem amp and the amp that was problem free was, still exactly that, working perfectly.

He said, he was going to remove all of the parts from the bias circuit and retest them. He would also check all of the traces to be sure there were no issues. He said he was going to sleep on it and start in the morning.

We spoke in the morning and he said he thought through the process he had preformed with the parts ARC had sent to correct the non-published circuit change they had told us about.

He said he was convinced that the problem still had to do with the change ARC had made and the parts were still not correct.

He started with the part of the circuit that controlled the positive + voltage going to the zero adjust resistor we had replaced. It was always to high. He removed one of the resistors and lowered the value. The result was it lowered the starting point voltage closer to where it should be to start the adjustment with the adjustable resistor.
He pulled that resistor he put in and added a different value resistor and this time the starting value was correct and the zero adjust resistor was able to do it's job and "0" out the voltage on the positive + side.

From there he moved to the negative - side and changed the resistors until he got to the proper starting value. With that the negative - zero adjust resistor was able to zero out and it appears the amps are complete and ready to come home.

That was a lot of time, work, and frustration due to a non published schematic change and then sending the wrong parts for the repair.

When Phil finished it, and the amp worked properly this afternoon he called and was so excited he could hardly contain himself. I told him that, I was happier for him than I am for myself to be getting my amps back.

I am praying this saga is truly over for both of us.

I jokingly said to him. What if the changes that were made makes me not like the sound of the amps anymore?
I assured him that would not be an issue and he agreed.

Hopefully the only addition to the thread will be to confirm that the amps sound amazing and they are better than new.

IMG_2802.JPG


Their home for the foreseeable future.

A nephew helped me move the amps to my second floor listening room yesterday.
With company for the last 2 days I started re-assembling the system this afternoon.

The worst part was getting the NAS, Sonictransporter, Ultrarendu, Playback Designs I-stream and Mps5 to talk properly after being shut down for 4 months. The problem is always me remembering how to get them to see each other not them.

Anyway it just so happened Phil was at an audio club meeting this afternoon and our house is on his way home.

By the time company left, I cleaned up my mess, got everything organized in the music room and connected, Phil was at the door.

Sorry these thought and comments aren't necessarily in the best order.

We went upstairs and could only smile at seeing the amps finished and back in place. We turned on the pre and power amps and sat down for a new tubes new parts break-in listen session.
After only 5-10 minutes listening the sound had different characteristics than I was use to hearing. Even at that time there was a quietness that was different. More spacious with specific details of sounds I wouldn't think possible at that early stage.

With that in mind, I have previously experienced a difference between single ended and balanced cables.
I had used an amp from my HT at the beginning of not having my 610t's but didn't like the sound. At the 10 minute mark, I looked at the preamp and noticed that I had not changed it to BAL from SE. When I did the sound was almost 20% louder and the image was very noticeably wider and deeper.

I know the sound will make many changes in the hours ahead.
At the 50-60 hour point Phil will need to re-adjust the zero out resistors as the other new parts will change as they break in.

As the 1 1/2 hours I had ended you could hear more breath and detail in horns being blown. You could tell the difference that the tubes and new parts were starting to warm.

I had not expected was after 1 1/2 hours you could actually put your hand on the KT120 tubes and though they were very hot you would not burn yourself. Related to that is my normal AC setting in the room I used with the 6550 tubes was way to cold.

I'll hopefully post more coherent information as they break in further and the sound improves.

Brad, take a deep breath, listen and enjoy !!