Intermittent problem with NOS 2A3 RCA blackplate tubes

[LonestarBlues]

I need some diagnostic help. Fedex delivered the 1947 pair of RCA blackplates from Tube World this afternoon. Used Fedex Air. I pulled the Sovteks and put the RCA's in the Moondogs. Turned on the system and let it warm up 15 minutes. I was playing the tuner and the right channel started making some popping noise and the music cut out for several seconds and then came back. I continued to let it play for a while and the right channel made a few more intermittent popping noises but the music did not cut out like before. I shut the system down, let it cool down and switched the

RCA tubes around to see if the tube was the culprit & would do the same thing in the left channel. It has been playing for over an hour and so far it is ok. I don't know what to think. I have not experienced this problem with the Sovteks. Do I have a bad or possibly damaged RCA tube? The packing was not that good in my opinion. A large Fedex box 18-1/2" long x 12-1/2" wide x 3-1/4" tall. The tube boxes were wrapped up in newspaper & were in the center of the box with crumpled up newspaper on both sides. When I bought a pair of RCA 5692 tubes from Welborne, the tube boxes were wrapped in bubblewrap and placed in a box full with foam peanuts. The box had multiple fragile stickers on it. Thanks for any help.

Regards, Mike

[Cut-Throat]

If your moondogs have the fancy Yamamoto sockets, you may just have a loose pin. If the RCA tubes have slimmer pins they may not be making contact all the time. Try tightening the pins with a very small screwdriver and see if this fixes it.

If you don't have the Yamamoto sockets, then I give up!

[D-MAN]

generally, as I cannot inspect the thing and even then, I can only guess, so here's my guesses:

1) if the tube is shock damaged to the point that it fails, it usually fails for good like a lightbulb. it would not fix itself. That is not to say that it is not damaged, we are only making some estimations here...

2) intermittant failure is probably from another source, such as a connection or even a single pin with a less than effective electrical contact. I would go there first.

3) capacitors would be my next guess as tolerances change due to age ; this can cause an intermittant discharge for who knows what reason and the tube loses bias, and signal goes bye-bye. it then comes back when the cap recharges.

4) tubes can be finicky as we all know, so who knows?!

Good luck!

DM

[LonestarBlues]

Yes, my Moondogs have the Yamamoto sockets. I have not experienced any more problems so far since I switched the tubes around. I will have to look at the tube sockets this weekend and tighten the pins. Hopefully that is my problem. The ceramic sockets on my Llano amp have the G.I. Joe kung fu death grip on the tubes. It takes some effort to change the tubes out unlike the Moondogs. Thanks for the help.

Regards, Mike

[jazman]

Lonestar,

Poor tube pin connection within the socket is the most likely problem, based on your description. Enjoy those RCAs. They require some break in time to sound their best. The Sovteks have more upper extension, but lack the midrange body of the RCAs.

Klipsch out.

[Daddy Dee]

Hopefully you won't hear that again.

[T2K]

Dang! I was going to say the same thing Ryan did, he just beat me to it by an hour-and-a-half.

Keith

[mobile homeless]

I am really leaning towards the PIN CONTACT problem mentioned above. This is a VERY common problem with 2A3 amps with certain sockets including the Yamamotos. In fact, I have run into this problem from mail from others with the little WRight Sound 2A3 amps being culprits on quite a few occasions.

One of the problems stems from certain sockets which allow you to insert the tube in the incorrect position. Thus, the larger pin on the 2A3 will be inserted in the wrong hole and ENLARGE and widden the contacts. Then when the tube is reinserted, the smaller pin does not get the right grip. This is a common problem with those that tube roll a lot. Actually, the STOCK sockets taht Welborne uses are much better in this one parameter. I have received quite a few Wright Sound owner mail that report of this. Our very own Wolfram suffered as well. They do not share the same sockets as the Moondogs usually.

Still, see if you can find the offending socket and make sure the contacts are gripping tightly.

kh

ps- The shipping from Brendan is a bit disappointing.

[mobile homeless]

An addition to the above points below.

A closeup shot of the offending WRIGHT SOUND 3.5 4-pin socket. You can see how the clamp contacts can get distorted and loose their ability to contage effectively. The Wright WILL allow you to insert the 2A3 WRONG sadly enough. I remember a few years ago, someone blew one of their monos when trying to run it this way. See the post/mention in the SET Asylum.

kh

[leok]

I've experienced similar problems with the fancy sockets in my modified Moondogs. Since I ofted swap tubes the problem occurs now & then. I clean the sockets and tube pins with Caig DeoxIt and very gently push-in the sides of the socket terminals to make them a bit tighter.

My RCA has more narrow pins than the TJ Mesh (actually there's solder on the outside of the TJ pins, which increases their diameter.

Various 6SN7s have also acted up.

Finally, nobody to blame but myself: I had one or two cold solder joints.

Leo

[dubai2000]

Kelly is right - in my Wrights a whole tube clip was missing! Once a new socket was installed - no more problem! So hopefully you'll have a similarly 'light' problem.

Wolfram