Thread: A Friends DIY For Me

This description and pictures will take me a while so I apologize for it dragging on for the whole story.

I have owned a pair of Audio Research 610t amps for 7 years. They were 10 years old when I purchased them from a dealer and were shipped directly from ARC after tube change and through testing.

They use 8 matched pairs of 6550 power tubes, 1 6550 regulator, 16H30 regulator amplifier, 2 6L6GC driver, 1 6N1P input and 1 6H30 follower. I shake my head every time I look at it written out.

During their manufacture life ARC offered an upgrade to KT120 tubes that were more stable as they ran at lower a voltage and increased the watts per amp to 840, not that I possibly need that. The upgrade for that is actually rather simple, assuming you know what you are doing.
In this case my EE friend Phil that worked in Bell Labs for years.

He has built and rebuilt every piece of equipment he has ever owned. Built numerous crossovers for speakers he has created. He is extremely particular about the quality of parts he will use and tests and discards parts that don't match with in very small tolerances.

This description is from notes I have made and I claim no knowledge of electronics. I will do my best to describe it properly.

Last summer I talked to him about doing the upgrade to KT120 tubes as 6550 are less stable in this amp and are getting harder to find. ARC could no longer provide enough matching pair that would meet their standards last time I wanted to re-tube one amp.
We have traded woodwork for electrical work and he said he would do it.

He had a speaker build project last summer and fall and I had spine surgery so that postponed moving the 2 180lbs beasts from my second floor listening room to his home. They have now been there for a couple weeks and he is making great progress.
The upgrade has been pushed to the end of the line as one repair and the decision to replace many old out of spec resistors, capacitors and relays along with some parts I will describe as I describe the process.

Originally Posted by brad225

This description and pictures will take me a while so I apologize for it dragging on for the whole story.

I have owned a pair of Audio Research 610t amps for 7 years. They were 10 years old when I purchased them from a dealer and were shipped directly from ARC after tube change and through testing.

They use 8 matched pairs of 6550 power tubes, 1 6550 regulator, 16H30 regulator amplifier, 2 6L6GC driver, 1 6N1P input and 1 6H30 follower. I shake my head every time I look at it written out.

During their manufacture life ARC offered an upgrade to KT120 tubes that were more stable as they ran at lower a voltage and increased the watts per amp to 840, not that I possibly need that. The upgrade for that is actually rather simple, assuming you know what you are doing.
In this case my EE friend Phil that worked in Bell Labs for years.

He has built and rebuilt every piece of equipment he has ever owned. Built numerous crossovers for speakers he has created. He is extremely particular about the quality of parts he will use and tests and discards parts that don't match with in very small tolerances.

This description is from notes I have made and I claim no knowledge of electronics. I will do my best to describe it properly.

Last summer I talked to him about doing the upgrade to KT120 tubes as 6550 are less stable in this amp and are getting harder to find. ARC could no longer provide enough matching pair that would meet their standards last time I wanted to re-tube one amp.
We have traded woodwork for electrical work and he said he would do it.

He had a speaker build project last summer and fall and I had spine surgery so that postponed moving the 2 180lbs beasts from my second floor listening room to his home. They have now been there for a couple weeks and he is making great progress.
The upgrade has been pushed to the end of the line as one repair and the decision to replace many old out of spec resistors, capacitors and relays along with some parts I will describe as I describe the process.

Sounds like a great project!

Phil rebuilt a pair of Clayton amps for me some years back.
He is a great guy and does class "A" work.
I'm sure you will be very pleased when they are completed.

Brad, it's good to have friends like that !! I wonder if he knows my friend Mark Obrien (Rogue Audio) ? For Mark worked at Bell Labs years ago.

Originally Posted by Mikado463

Brad, it's good to have friends like that !! I wonder if he knows my friend Mark Obrien (Rogue Audio) ? For Mark worked at Bell Labs years ago.

Phil said he did know a Mark that was a programer. He looked at his picture and said he was sure Mark O was to young to be the same one.

So, the next thing was while waiting to move the amps I turned them on to warm up and more than likely went to the kitchen for a beverage to enjoy with the music.
When I returned to the room it smelled really hot. It is obvious as the room is well air conditioned when all the tubes are on.
I walked up to the amps and I could see that the power regulator tube on the middle shelf was runaway and extremely bright. I immediately turned the amp off and when I did the tube made the huge pop sound they make when they go bad. I shut off the other amp and shook my head thinking I guess Phil will have something else to look at.

A few weeks went by and I was off restriction from surgery and the amps were moved to his home for diagnosis and hopeful move forward with repairs and upgrades.

This is what the amps look like with the sides and top removed. There are parts on the bottom of both boards but I don't have pics of them at this time.

With the Power regulator tube going down the first thing he needed to do was find out why and did it do damage to anything else. He checked parts in the path the power followed and everything except the resistor directly at the tube was fine. It appeared the resistor went bad and allowed the tube to runaway at full power. He temporarily replaced that resistor and checked the value of EVERY resistor, diode and capacitor in the amp.

Phil had been able to acquire a complete set of schematics and parts list. originally used by ARC along with the upgrade schematics and parts list.

After determining that the other parts in the amp were fine to operate he put it in standby for 25 minutes then in operate position for 15. Everything was operating properly so he moved to the second amp and tested all parts as in the first.

This pic is really only exciting to Phil and myself when the repaired amp glowed happily.

That is it for know. 2 and 3 year old grand niece and nephew are coming to spend the night.

Once it was determined that the amp was functioning properly it was time to move ahead. After a few conversations about the amps I said that any parts he thought should be replaced and he was willing to undertake I was in favor of. I had know idea how much work I had created for Phil when I said that. There had to be moments he thought, what have I gotten myself into.

The first thing to strip all of the parts to be replaced on the top board relating to the power tubes and driver tube resistors. The top pic.

Middle pic shows parts removed and all holes cleaned to receive new resistors and relays.

Bottom pic shows all the new parts installed on the top board. All of the resistors he uses are noninductive type.

For the proper resistor pairing Phil first checks the value of each one of the 220 resistors being replaced. For some to achieve the proper .2 ohm value
2-.1 ohm resistors are soldered together and value checked again. He is able to match the values for each tube pairing for purposes of biasing the banks of tubes.
Virtually all of the pairings are exactly the same with the farthest difference being .001 ohm.

First pic shows testing of 64 of 220 single resistors and their value.

Second shows pairing and again the value so pairing can be completed as perfect as possible.

Wow Brad, looks like a 10, 000 mile service on a Ferrari !

Next is changing out the low voltage power supply capacitors. That is all the blue ones and then the soft start relays.

The first set of power supply capacitors on the lower level next to transformers. When he pulled the board to replace them he found a huge ground loop on the bottom of the board. He cut through the trace to eliminate it then put on the new capacitors.

It was interesting and surprising when Phil told me that the capacitors in the amps had a life span of only 3,000 hours before the begin to degrade. He said this is true for most equipment make as longer life are expensive. We tried to get 18,000 hour caps but I would have had to purchase 3,000 of them and so we ended up with an 8,000 hour capacitors for the 48 power supply capacitors needed for the 2 amps.

This was the board and the 8 power capacitors were replaced. These look to dusty to be the new ones.

The main power supply board that holds the other 16 capacitors had no ground loop.
Here is the board with old ones removed awaiting new capacitors.

That is where it stands right now. As the week goes on there will be more progress. Still waiting on some parts that hopefully will come early this week.

Originally Posted by jadedavid

Phil rebuilt a pair of Clayton amps for me some years back.
He is a great guy and does class "A" work.
I'm sure you will be very pleased when they are completed.

I'm sure I will. We have done a few projects together. I'm doing 2 bass speaker towers for him after the first of the year. They will go with the panel speakers and subwoofer we did together.

Originally Posted by Mikado463

Wow Brad, looks like a 10, 000 mile service on a Ferrari !

I can't imaging what that bill would be Dave. I guess if you can afford the Ferrari you don't have to ask.

Brad-

One heck of an interesting project.
I was not a double E major but what I find of particular interest is the discovered ground loop. Of late, a lot of aftermarket audiophile dingleberries are appearing for grounding purposes.

Was this ground loop a manufacturing defect or design flaw? Or something that developed over time?

John

Hi JohnJ
It was clearly a design and manufactured situation. Phil said cutting through the metal was a substantial endeavor.
He could not come up with any reason that it would have been put there.

Today was not real exciting but very satisfying. I went up to Phil's with numerous cleaning items to attack the interior while everything is discharged.

I set about first cleaning all 276 pin sockets in 46 tube sockets and 2 IEC connections with abrasive pipe cleaners and isopropyl alcohol. Though tedious it was clearly noticeable.

Once I was finished with that I used pieces of cloth with limited alcohol on them to wipe off 17 years of dust and crud. Long forceps made it possible to reach tight areas.

Around the tiny diodes and resistors on the mid shelf compressed air will be used to gently remove the dust that has accumulated.

Brad, you are clearly demonstrating to me why I went back to SS amplification !

Trust me I gave it some thought Dave, but, for what the upgrades cost, I don't think a SS exists that would sound as good. Though I have not heard it yet I'm confident it is going to be stunning. I can't wait.

Both amps are back working with 200 new parts in each one.
The upgrade to KT120 tubes should not take long at all.

Front screen lit and tubes happily glowing.

I had planed on replacing both front screens as they were getting hard to see in places. Phil said they were covered with dirt, finger prints and gunk. Who would have thought they only needed to be cleaned.

Great Stuff , interesting to hear the SQ difference on your ESL’s when you do make the switch to KT 120’s ..


Regards

Partial group of old parts that were replaced.

Upgrade parts are in and we installed the new tubes. One amp is fine and bias is great. The other won't bias correctly on one bank of tubes. One of the variable resistor is not allowing adjustment to the correct specs. Phil thinks the V18 bias control tube is bad.

Waiting for a response from Greg at ARC before putting a new tube in the socket.

They are so close to being finished and coming home. I can't wait to have music again.

Originally Posted by brad225

Upgrade parts are in and we installed the new tubes. One amp is fine and bias is great. The other won't bias correctly on one bank of tubes. One of the variable resistor is not allowing adjustment to the correct specs. Phil thinks the V18 bias control tube is bad.

Waiting for a response from Greg at ARC before putting a new tube in the socket.

They are so close to being finished and coming home. I can't wait to have music again.

Woo Hoo!!!!

Just think Brad, your wait will be like a second coming of Santa !

That looked like fun ! how long did it take ya ?

It didn't take me long at all. Then again I didn't do the technical work.

I moved them to Phil's home the second week of November. He was working on other things for a while and started taking measurements on existing parts on the 17th.

Then waiting for parts and more parts and then more parts.

Should have parts for one of the two bias circuits in one amp by mid week and both amps should be complete. One amp is finished and passed every test on ARC's checkout procedure.

What is loud, that you can't hear, is the sound of Phil and I tapping our respective feet. ARC didn't ship the parts order until a week after they were ordered.
They are scheduled to arrive on Tuesday the 10th.

I am so ready to have them finished and me back in my listening room. Tap-tap-tap.

Wow! What an undertaking! Looking forward to hearing your amps/setup as well as Phil's latest speaker project sometime down the road.

Originally Posted by brad225

They are scheduled to arrive on Tuesday the 8th.

Holly Molly Brad, not until August ??? That's the first month I could find where the 8th fell on a Tuesday !

I am so ready to have them finished and me back in my listening room. Tap-tap-tap.

patience my young Jedi warrior !

OK mister technical. Tuesday the 10th.

Originally Posted by brad225

OK mister technical. Tuesday the 10th.

well I'll be.......... that's today !!

all kidding aside Brad, looking forward to your comments once everything is back together and playing music !

THEIR ALIVE.

Last delay was replacing the adjacent parts for the "adjustable offset resistor" in the left amp this time. This controls the bias voltage to the tube controlling the bias of half the KT120's.

It is hard to tell the difference A to B as the amps are still at Phil's. Considering all new tubes and hundreds of new parts they sounded amazing. Unlike his rebuilt McIntosh amp has sounded.

I won't be able to bring them home until next weekend it looks like. Strong nephews have work commitments.

They put out about less than 1/2 the heat with the KT120 upgrade.

More to come.

Originally Posted by brad225

their alive.

Last delay was replacing the adjacent parts for the "adjustable offset resistor" in the left amp this time. This controls the bias voltage to the tube controlling the bias of half the kt120's.

It is hard to tell the difference a to b as the amps are still at phil's. Considering all new tubes and hundreds of new parts they sounded amazing. Unlike his rebuilt mcintosh amp has sounded.

I won't be able to bring them home until next weekend it looks like. Strong nephews have work commitments.

They put out about less than 1/2 the heat with the kt120 upgrade.

More to come.

wooo hoooo!!!

Good looking portable space heaters Brad !

Originally Posted by Mikado463

Good looking portable space heaters Brad !

You can actually hold your hand an 1" over the tubes and not need to bandage your hand afterwards.

Originally Posted by brad225

THEIR ALIVE.

Last delay was replacing the adjacent parts for the "adjustable offset resistor" in the left amp this time. This controls the bias voltage to the tube controlling the bias of half the KT120's.

It is hard to tell the difference A to B as the amps are still at Phil's. Considering all new tubes and hundreds of new parts they sounded amazing. Unlike his rebuilt McIntosh amp has sounded.

I won't be able to bring them home until next weekend it looks like. Strong nephews have work commitments.

They put out about less than 1/2 the heat with the KT120 upgrade.

More to come.

Brad , could you give more details regarding your McIntosh comments..


Regards

His Mac was purchased new in 1972 I don't remember the model. He has rebuilt it numerous of times and by his admission the limitations are the age and designs of the amp.

In comparison the ARC that is 33 years newer with mostly new parts has a much larger and way more defined image and staging. The upper mids and highs are so much more apparent and precise in ARC.

The Mac in and of itself didn't sound bad. It is just in comparison the 610t's sound so much better in his system.
He is currently watching the internet for a Ref 150SE to replace the Mac.

I went to Phil's on Wednesday to so the final disassembly of tube removal and put sides and top back on in order for moving them home on Thursday.
We needed to put the final pair of 6n1p tubes in each amp that control the biasing. We had been using a mix of tubes, as some from each set I purchased had issues.

Those tubes need to be adjusted to 0 volts on the + and - side by way of a zero Offset Variable Resistor.
When tubes, that a few days before would 0 out now would not, Phil decided it was something else other than the tubes.

He looked at the schematic and determined it was the field effect transistor "FET" in the path of the circuit to the variable resistor. We shut the amp down and after finding the value that should be attributed to the FET he tested it and it was the issue. He tested all of the resistors again the that part of the bias circuit and they all tested to within .001 of each other at the proper rating.

He ordered 4 new FETs from ARC that afternoon and they will arrive on Saturday. I will be there on Sunday for the install and final (I HOPE) check the 0 voltage is working properly again. We are replacing it in both amps even though the other amp has not had issues with the "0" adjustment.

They, will be ready to come home after that.

I asked him to tell me honestly the other day. Has there been many times you are sorry you agreed to do the rebuild. Without hesitation, he said, nope I find the whole process so satisfying. I thanked him again, for probably the 100th time.

Originally Posted by brad225

I went to Phil's on Wednesday to so the final disassembly of tube removal and put sides and top back on in order for moving them home on Thursday.
We needed to put the final pair of 6n1p tubes in each amp that control the biasing. We had been using a mix of tubes, as some from each set I purchased had issues.

Those tubes need to be adjusted to 0 volts on the + and - side by way of a zero Offset Variable Resistor.
When tubes, that a few days before would 0 out now would not, Phil decided it was something else other than the tubes.

He looked at the schematic and determined it was the field effect transistor "FET" in the path of the circuit to the variable resistor. We shut the amp down and after finding the value that should be attributed to the FET he tested it and it was the issue. He tested all of the resistors again the that part of the bias circuit and they all tested to within .001 of each other at the proper rating.

He ordered 4 new FETs from ARC that afternoon and they will arrive on Saturday. I will be there on Sunday for the install and final (I HOPE) check the 0 voltage is working properly again. We are replacing it in both amps even though the other amp has not had issues with the "0" adjustment.

They, will be ready to come home after that.

I asked him to tell me honestly the other day. Has there been many times you are sorry you agreed to do the rebuild. Without hesitation, he said, nope I find the whole process so satisfying. I thanked him again, for probably the 100th time.

The look heavy but so cool. Thanks for sharing

Are you using dedicated 20- or 30-amp lines to feed each of them. I read each can draw as much as 2300 watts from your wall outlets

They are CPP 180 lbs of dead weight. It's a good thing they have 2 sets of handles but, they are still a pain to move.

Yes, each amp is on a 30 amp circuit of its own.

It will be about a week short of 3 months when they return next week. I am so ready to listen to music again.

Originally Posted by brad225

They are CPP 180 lbs of dead weight. It's a good thing they have 2 sets of handles but, they are still a pain to move.

Yes, each amp is on a 30 amp circuit of its own.

It will be about a week short of 3 months when they return next week. I am so ready to listen to music again.

Unreal how heavy those are. YA need good friends for sure.

Dual 30 amps circuits. Now will these do double duty when it gets chilly

Seriously can't wait to hear your reaction when they get hooked up and playing tunes.

I was told with the circuit changes and the KT120 tubes there would be less heat. In the 3 hours we sat and listened to them at Phil's there was probably 1/4 the heat as when the 6550 tubes were in there.

As I joked with Dave in a previous post. You can hold your hands an inch above the tubes and not get burned. That was not the case previously.
Woofer and Tweet has done cartoons about them, showing someone roasting hotdogs on a stick over them.

Nephews in their 20's, that work out, is once again a blessing.

Pic of removing them in November with one of my nephews.

We took them one at a time on a hand truck down ramps I put on an exterior set of stairs I was rebuilding. Between my oversized body, small space to step backwards between the ramps and no handrails. The first one was a bit uncomfortable. The second was much easier.

The advantage is my listening room is at the top of the stairs across the hall. Down side is one long set of stairs rather than 2 short sets inside.

Opportunity to do reps before delivery was lost ..

Well, today was progress but not quite there yet.

Phil installed the FET's and 3 of the 4, Zero Offset Variable Resistors immediately allowed the + and - side of the current flowing through them to "0" out on the meter. One of them was still unstable and not responding as it should.

Soooooooo, He is ordering 4 new ZOVR's from his supplier in Canada today and changing them to a higher voltage for safety sake. If one has issues it is only a matter of time for the others.

My beloved wife of 49 years is beginning to lose her any sense of humor and understanding of this project. She is a CPA working with 1-9 +0 and mechanical things don't compute well in her mind.

I tried the explanation of, taking your car in the shop because the engine is running a bit rough.

A best calculation of the issue is thought out and something replaced or cleaned. If that doesn't work the mechanic moves to the next part that could be it.
You don't just replace the engine.

She clearly understood but wasn't swayed much in thinking, this could still be 2 very fancy rabbit holes I have at Phil's.

She did though, after kissing me good night say she was sorry about my parts. I then laid there for a moment, wondering if she meant the 17 year old amps or my 69 year old parts. I'm going with the amps.

Hopefully by the end of the week, parts should be here, again.

Brad, that finish line is inching ever closer !

Variable Resistors are set to arrive on Wednesday. So, Thursday morning I'm ready for 6 or 7 or..... whatever, of.

This time, they will be ready to pull the tubes, close the sides and top and prep them for coming home.

I know, I probably jinx myself each time I make the prediction but one of these times it will happen.