RE: JJ 300B Quality and Reliability?

Posted by tube wrangler (M) on September 2, 2008 at 20:56:03

In Reply to: RE: JJ 300B Quality and Reliability? posted by mikeyb on September 2, 2008 at 20:22:44:

Directly- Heated- Triode shorts are extremely rare unless the tube is run at higher than sensible currents and voltages, UNLESS there is shipping damage.

Usually, elements are displaced in DHTs by damage done in shipping-- dropping boxes and rough handling of them by carriers. The tubes are packed well, and will almost never be broken, but internal elements will be somewhat displaced-- close to shorting.

For this reason, I buy tubes by one of two ways: (1) In person, using high-magnification equipment to see anything that is displaced-- even slightly. (2) Buying in bulk. If I need say--- 4 power tubes, then I will buy 12 or so, negotiating for a quantity pricing. I expect 4 of these to be good and usable. I DO NOT expect the other 8 to have survived shipping in very good shape. This simply DOES NOT HAPPEN with todays shippers/carriers. Your tubes WILL receive rough handling, and some WILL be internally damaged.

This is NOT brand-sensitive. What we see is "good batches" and "bad batches" from ALL manufacturers. People get good ones and rave about that brand. All that means is THAT box wasn't dropped.

Of course, some brands have better construction. Among modern-produced DHT types, I have found JJ 300B and 2A3 superior to all other current DHT production in being rugged. The "keep" rate on these is about 60%-- which is FAR better than average-- average is about 20-25%.

Smaller tubes with closer-spacing of supporting elements can stand more shipping abuse. Indirectly-heated tubes are MUCH more rugged about being dropped, as their build is tighter.

Is this a reason to avoid JJ DHTs? Certainly NOT. Buy enough of them to assure some good ones, and delight in their performance, and extremely long-life if run right. Right is about 2/3 of rated plate voltages and currents.

---Dennis---

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Follow Ups Full Thread

Topic - JJ 300B Quality and Reliability? - MikeT 16:25:45 09/02/08 (26)

RE: JJ 300B Quality and Reliability? - slownlo 08:34:41 09/03/08 (0)

Toast after 1yr medium use - RioTubes 21:58:15 09/02/08 (17)

No free lunch !!! - drlowmu 05:51:02 09/03/08 (16)

RE: No free lunch !!! - RioTubes 09:46:09 09/03/08 (1)

I can't trouble shoot with you on line...... - drlowmu 10:34:37 09/03/08 (0)

Dr. - please review the schematic more closely. - Michael V 08:03:07 09/03/08 (3)

RE: Dr. - please review the schematic more closely. - drlowmu 08:24:59 09/03/08 (2)

RE: Dr. - please review the schematic more closely. - JimL 08:54:55 09/03/08 (1)

RE: Dr. - please review the schematic more closely. - drlowmu 09:16:16 09/03/08 (0)

Schematic of Properly Designed Amp - MikeT 07:37:33 09/03/08 (2)

I have one.... - slownlo 09:28:32 09/03/08 (0)

RE: Schematic of Properly Designed Amp - drlowmu 07:43:39 09/03/08 (0)

RE: No free lunch !!! - Alpha Al 06:07:13 09/03/08 (6)

RE: No free lunch !!! - drlowmu 06:32:06 09/03/08 (5)

You know, when this circuit was published..... - JimL 09:02:22 09/03/08 (4)

RE: You know, when this circuit was published..... - Michael Koster 14:39:20 09/05/08 (0)

Shawshank Redemption....(nt) - slownlo 12:42:45 09/03/08 (2)

Sorry, I've never seen that movie, so don't get the reference. NT. - JimL 15:42:56 09/04/08 (1)

RE: Sorry, I've never seen that movie, so don't get the reference. NT. - drlowmu 13:05:03 09/05/08 (0)

RE: JJ 300B Quality and Reliability? - mikeyb 20:22:44 09/02/08 (6)

RE: JJ 300B Quality and Reliability? - tube wrangler 20:56:03 09/02/08 (0)

RE: JJ 300B Quality and Reliability? - drlowmu 20:35:15 09/02/08 (4)

RE: JJ 300B Quality and Reliability? - mikeyb 05:40:37 09/03/08 (3)

RE: JJ 300B Quality and Reliability? - tube wrangler 13:09:31 09/03/08 (2)

RE: JJ 300B Quality and Reliability? - mikeyb 19:37:21 09/03/08 (1)

RE: JJ 300B Quality and Reliability? - tube wrangler 22:44:42 09/03/08 (0)

Follow Ups

RE: JJ 300B Quality and Reliability? - tube wrangler 20:56:03 09/02/08 (0)

RE: JJ 300B Quality and Reliability?

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