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In Reply to: RE: 6N1P posted by Brad225 on January 21, 2023 at 12:59:10
I'm now happy to say that I have working 6n1p tubes in the amps.
After bringing all of the good and bad tubes back home arranging them to go to a vintage repair company on Tuesday that tests tubes.
I was surprised to make a discovery with the tubes that were in the amps.
The 6n1p tubes that we removed from the amps were installed by Audio Research when they went back to get a clean bill of health by Echo Audio in 2015 prior to my purchasing them. The amps were shipped directly to me from ARC.
When I looked closely with a magnifying glass to make out what was left of the original cables all 4 had rockets on them signifying they came from the Voshkod factory. Only one of the of the tubes was marked Sovtek. Two of the tubes had identical markings from the Voshkod factory and the fourth had the rocket and markings from another company the labeled Voshkod tubes with their name. The latter 3 tubes have the exact markings as some of the tubes I ordered from different sellers.
The 4 6n1p Sovtek tubes I purchased from a known dealer, that were no good had the rocket and the same markings as the current tubes I have been receiving. I was surprised Sovtek used their tubes for many years or someone is putting Sovtek on old tubes.
The only difference is they charged almost 3 times as much. That's my fault for not knowing enough about the tubes currently available.
I explained the rebuild of the amps and missing the warranty time and I accept I did. I even offered to pay to ship them back and if they found they were in perfect condition I would be happy with some credit toward other tubes or I would pay to ship them back to me and I would attempt to sell them. They suggested it my EE fault and had no interest in anything I offered.
I understand being in business I was self employed for all but 2 years of my working life but there is a thing called customer service.
Just interesting ARC has no tubes that fit their specs but there are obviously 1000's of 6n1p EV-EB tubes that they have used. I realize they have high standards but surprised none are their standards. We will see in time.
The EV-EB tubes are said by other ARC owners to have the factory rating of 5000 hours in their amps.
Oh well that is part of owning older tube equipment. At least my wife hasn't taken away my credit and debit cards.
Can't wait to get them home. Hopefully by the weeks end.
Follow Ups:
I finally got a chance to dig around and found a quintet of 6N1P I had purchased as part of a complete retube set for an ARC VS110. I actually bought it for the SED Winged C 6550 output tubes I like to use in my ARC D70. So the 6N1P's have just been sitting in their boxes.
When I looked at the actual tubes they are a bit of a scramble deciphering the apparent relabelling. Looks like these are actually 6H1N EB. Note that EB military designation is by design more rugged but with that comes a difference in their data sheets.
Again, similar to my earlier posted reply regarding apparent equivalent tubes that have medium or high gain, it's possible you are not running across defective tubes but tubes that are not ideal to your unit's needs.
It's kind of like some output tubes that aren't recommended for auto biasing amps but ok for amps that have manual biasing.
These are my observations anyways and wish I knew more on the subject.
In any event, to make a long story short, I did find a company that sells the 6H1N EB, for consideration while you continue to research the situation. And they appear to have a lot in stock. I have never dealt with them though.
Jonesy
"I know just enough to get into trouble. But not enough to get out of it."
Thanks Jonesy. Well as any normal rebuild of, well, virtually anything goes more issues discovered and being dealt with.
When the 3 group of 6n1p tubes still had some problems, my EE friend decided to investigate a bit closer. He found that the 2 Field Effect Transistors in the bias circuit would test fine one moment and then test wrong moments later.
He changed the 2 of them in both amps. Tubes were reinstalled and 3 of the Variable Resistors would allow him zero out the voltage in the + & - side of the bias current worked perfectly but one was still very unstable. 4 new VR's should arrive tomorrow or Thursday and we will attempt to be finished with the amps.
Our new assumption is that the tubes I have are more than likely fine and it was the inconsistent parts that made us think they were bad.
The odd thing is that with the old tubes that had 3000+ hours on them were always stable. Who knows.
On another note. I purchased the amps used from a known seller in the US. The amps had gone back to ARC for a checkup and new tubes throughout before being shipped directly to me from ARC. I was given copies of the bill showing what was done and new parts installed in the amps.
I had never looked closely at the 6n1p tubes ARC had installed until the perceived problem with the new tubes.
I took a magnifying glass to clearly see the markings. All 4 tubes had the Voskhod Factory rocket on them. 1 of them was labeled Sovtek and said 6n1p-EB. 2 of the tubes had different markings but labeled as 6n1p-EB and the last one had a different company logo with the 6n1p-EB markings.
It was surprising that ARC used those tubes to re-tube the amps in 2015 but not now.
They were obviously good quality as they had many hours on them.
One interesting thing, on the day we listened to them for 3+ hours in his system. With the KT120 tubes the heat output had dropped by almost 3/4 from what the 6550 produced. You could hold your hand 1" above them and it was nothing like the 6550. If you tried that previously, you would be bandaging up your burns.
Ah, always seems to be something. But at least the trouble shooting is going in the right direction.
I replaced all trim pots in my amp some years ago and it really helped stabilize any measurement readings.
The octet of power tubes in the set I purchased consisted of 7 6550 Winged C and 1 6550WE. They are all matched extremely close and I believe originally came from ARC. Due to availability I suspect they chose the best options available to make up the sets. That may explain the different tube brands you likewise have come across.
Glad you are able to use the KT120 instead of the 6550's. That is a lot of tubes and I can only imagine the heat. I only have 5 6550's total and it is indeed very hot. Unfortunately ARC says I cannot run the KT120's in my amp. It would have been nice to have that option as tube supplies diminish.
While doing some research on your amp I came across your rebuild on another forum. I don't usually spend much time anywhere other than Audio Asylum but looks like you've been at it for some time. I admire your passion and especially your patience. Quite the journey. Thank you for sharing some of it here.
Jonesy
"I know just enough to get into trouble. But not enough to get out of it."
Repair comes to a standstill... again.
The variable resistors were to be shipped out last Monday. The company in Texas had computers down and nothing could go out.
Then the ice storm pretty much handcuffed everyone in the state.
Oh well nothing to do but dream of music.
Variable resistors always work better when there's an ice storm delay! Hope they arrive safe and get you back into music soon.
Jonesy
"I know just enough to get into trouble. But not enough to get out of it."
Maybe, it will help them stay cooler in the midst of all of those tubes, Jones.
Phil found unused holes in the traces when he removed the resistors.
He said its not good for current flow when they heat up and cool down over and over again.
He solder filled them all.
I learn something new each time he replaces a part.
Filling unused holes is new to me as well. Makes sense though as you say. I suppose it's possible especially narrow traces may even crack at thise points. Barely visible and enough to drive a tech crazy.
Thanks for sharing this.
Jonesy
"I know just enough to get into trouble. But not enough to get out of it."
Funny you mentioned that as I forgot to include it.
He did spicily say after many heating and coolings the chances of cracking the sides of the trace are very good.
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.
Edits: 02/10/23
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.
I am ecstatic to say the amps are home and functioning properly. I can't say I was excited at 69 years to be moving them to my second floor listening room but I guess you have to pay to play. Nothing that ibuprofen and wine couldn't fix.
I will try and make this short. The last 2 months Phil spent trying to figure out why one amps, 2 adjustable resistors would not zero out, turns out to be surprising and frustrating at the same time.
Apparently during the production of the 610t amps ARC received more orders than they ever expected for the time. They ran out of some resistors and chose to make a design change to the board and not include it on the schematic. The change was only used until more of the original parts arrived.
We found this out because one of the engineers that Greg at ARC spoke with, as Phil encountered more dead ends with the amp remembered they changed it.
ARC offered to send us the proper parts at no cost, which was great. The problem is when Phil put the new resistors in, the amps + and - voltage at the 2 zero out resistors was still too far off to adjust properly.
Phil next decided he had to eliminate the chance of a problem tube socked or something under them that was unseen. We ordered 6 sockets, as he wanted to keep both amps the same for base line readings. Under the sockets he found some ugly soldering but nothing he thought would be the problem. He did though find more ground loops under sockets 19 & 20 and he eliminated them on both amps.
He installed the new sockets and the amp that had been problem free was still just that. The amp with the issue still had that.
He decided that the new replacement parts ARC sent to fix the issue had to be the problem.
On the side of the amp that the voltage was to low he, through best guess measuring and trial and error added different value resistors in series until it was at a value that was within specs to be able to zero out.
On the side that was to high he did the same thing but in reverse and lowered it to be within spec. That side also zeroed out.
We were both ecstatic and frustrated that was a long 2 months trouble shooting the problem that was an unpublished design change.
So, the end result was they sent 2 different design 610t amps to the original owner.
From the 1 1/2 hours Phil and I listened to them yesterday evening they are going to be amazing in more than one way once broken in some.
I was stunned that even after 1 1/2 hours I could actually put my hand on 4 or 5 tubes and they were hot but you could have never gotten close to the 6550 tubes with your hand. We found that the room was much to cold to be comfortable listening to music at the same thermostat setting when the 6550 tubes were in and running.
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