Dynaco Mark III 6AN8 Testing
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- Опубликовано: 5 фев 2025
- I had to test all eighteen of the 6AN8's that I have to make sure I did indeed have the best one in the amplifier and I am pleased to post that better than 50% were of them were very good.
I just did a conversion of a Packard Bell to guitar. I loved the sound! Thank you!
Good stuff. Like all your videos...good job and keep them coming.
I just got a NOS 6an8 from a electronics distributer. when I opened the box the entire area of the pins was covered in green corrosion. I was really dissapointed but after a little work with a wire brush on a dremel tool I found I had a real jewel. it worked perfectly.
Hi Harold - I understand. I recently went to an estate sale and found some very nice performing 12AX7's with the pins caked in dried mud/sand from being stored in an old leaking metal shed which cleaned up nicely and work great. Thanks for the comment.
Hi David, it's interesting to see that 3 NOS 6AN8's are duds! I always try to explain to many of my clients that just because a tube is NOS, doesn't mean that it's going to be good. As I clearly recall, back in the day, I had gotten many new RCA & GE tubes (along with other brands) that were duds...low emission, h2c shorts, and gassy! Many get the wrong impression when it comes to new tubes, vs old one's or old stock. There are many newly manufactured Chinese tubes that are royal crapolla, but there are also one's that are very good. As far back as I can remember, tubes were always a dice roll. I had taken notice that once 1971/72 rolled in, the quality control at RCA had taken a nose-dive. I was getting many defects and was returning them to my old supplier at a concerning rate. Also, RCA started to cheapen things at the same time by switching to the extremely shallow Octal bases which were cracking, or coming off the bottom of the tube because of heat and improper cement methods. It was then, that I had switched to Sylvania which became ECG in the 80's and found that I had less problems. I'm also uneasy about buying tubes from sellers on e-bay because of two things...one is, dishonesty of many sellers, or the sellers either lie about testing them, or have inadequate testers (not to mention the lack of proper knowledge of using them). A lot of my NOS tubes were obtained through garage sales, and Ham Fests Keep up the great videos as always! :)
Hi, Frank - you have touched on something that I have thought about so many times. I can only guess at how many tubes were made from, say, starting in 1960 that were bad right out of the box and what percentage have survived to this day. There is no way I can imagine how to prove what the actual percentage of tubes were top-notch when they were sold back in those days and are still around. As best I can remember, they were no more reliable back then than they are now. I am beginning to think that as the new production tubes go through stages of testing, they get up-branded and sold for more as they test better and better. There was a discussion not too long ago about how many thousands upon thousands of tubes are made - and sold - and how many are really good and how many not so good - but... none are going to be put in the trash can at the factory unless they are completely DOA. You know what I am talking about. Those Telefunken KT88's that I just received are as good as any I have ever seen. I am impressed with them. You know that tubes are such an ethereal thing on the Internet and for anyone to try and disprove some old standing superstition/belief just goes to prove that you are part of a conspiracy. Kind of like not believing that aliens landed in Roswell, NM back in 1947. Actually, I was pretty surprised at how many good 6AN8's I have. The three I mentioned that I recently bought, not sure why when I already had fifteen of them, turned out to have two bad ones and one good one. Not good odds. I guess I actually believed they were new and they did indeed look new. As for dishonest sellers, I can say that I have only run across one that was a real dirt-bag. After lots of communications with him, I told him he was either dishonest or did not know what he was talking about (or both) to sell me a 3-400Z that was so fried - but the Eimac box looked "new".. I have known all my hobby and professional career, which now is better than 52 years, that, as you mentioned, buying used tubes is buying a pig-in-the-poke at ham fests or where ever. You never know what you are going to get. Overall, nowadays, I prefer to buy new Russian or Chinese tubes from reputable dealers like tubedepot so that I can return them if they are bad - and I have returned a number of them.
Here's the data from the ones I could find with the data labels on them. This is percent THD at 50 watts at 1 KHz.
I think the one labeled CBS and the ?brand is made by GE but I can't be sure.
Motorola GE RCA Sylvania CBS ? brand
0.15% 0.075% 0.053% 0.047% 0.097% 0.062%
0.057% 0.096% 0.066% 0.105%
0.9% 0.081% 0.065%
dead 0.088% 0.058%
1.56%
6.9%
Dave,many people selling tubes on ebay have a misconception of what NOS means..Many actually thinks it means factory original and not New Old Stock as it should.
Thanks Mike - always good to hear from you. I am really glad that so many turned out to be good and I wanted to share that with the YT community.. I was afraid I would not get more than one or two that would actually meet specs. I think often times people sell on Ebay as NOS if the tube "looks new", in their opinion, i.e. the numbers, logo, etc are intact when as, no one can simply look at a tube and tell much about these small signal level tubes by just looking at them. Thanks for your comments. Hope to talk soon.
What Distortion Analyzer are you using? Thank you for your great videos! Keep up the good work! Never mind.....I see on the screen that you are using an HP 8903. Nice.
For this testing I was only testing at one power level (50 watts) and one frequency (1 KHz) so I used the Tektronix AA501. I was driving the amplifier with a Tektronix SG505 oscillator.
Did any particular tube brand have a higher percentage of quality performing tubes of the ones you tested. I think I saw mostly GE and RCA tubes. Also can a 6AN8A be used in place of the 6AN8. Thanks, great info.
Yes, the 6AN8A can be used in place of the 6AN8
Here's the data from the ones I could find with the data labels on them. This is percent THD at 50 watts at 1 KHz.
I think the one labeled CBS and the ?brand is made by GE but I can't be sure.
Motorola GE RCA Sylvania CBS ? brand
0.15% 0.075% 0.053% 0.047% 0.097% 0.062%
0.057% 0.096% 0.066% 0.105%
0.9% 0.081% 0.065%
dead 0.088% 0.058%
1.56%
6.9%
WOULD YOU SEND ME THOSE WEEY 6AN8 I WANT TO TRY EXPAREMENTS WITH THEM