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Old 24th February 2010, 08:30 AM   #1
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Default 300b tube life

Hi
I was after advice on the following dilema(s).
I am happy to build a pse 300b amps as I have all the iron et al. Given the price of 300b's nowadays and given some reading on the topic I was wondering what tube life one could reasonabley expect from a 300b operating within its parameters.
The second question pertains to wether the heaters are dc or ac for the 300b's. Given there is no centre tap will dc ruin the tube? I figure hum can be conquered with ac supply
Thirdly: is it fact or fiction that current production 300bs dont have a centre tapped heater like the we 300b. If this is the case then wouldnt different voltage potentials manifest along the cathode? what does this do to biasing if anything?
Lastly and this is the curly one.. with so many variants nowadays which ones have the sound, quality of build and longevity?
OR do I build pse 6550 (triode mode) given the interchangeability of the OPT's?. I admidt I really like the sound of my little chinese 300b amp but If I have to retube it too often at 1500 dollars a quad, then i will forgo it.
If Jim McShane or other tube dealers read this, then please feel free to give your thoughts on the matter(s)

Many thanks for any replies
Nick
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Old 24th February 2010, 06:03 PM   #2
kevinkr is offline kevinkr  United States
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This is all very anecdotal, but perhaps you'll find it somewhat helpful.

I've been using the same two matched sets of JJ 300B for nearly 10yrs and they have not deteriorated significantly in measurable or audible ways. (I rotate the sets periodically and estimate > 5000hrs combined on both pairs so far with no problems. Conditions 400Vp, 75 - 80mA, fixed bias, CC filament heating.) Not sure whether or not the current JJ is as good, but I believe mine are not all that different from current production types. I have not checked lately.

I have not had good experiences with Valve Arts, Shuguang, or Svetlana (SPB) 300Bs in the past, but I have no recent experience. The newer Shuguang by all accounts are OK, but longevity is an unknown.

A lot of my friends are using various incarnations of the TJ300B or the EML 300B and like them a lot - again not sure of the durability.

$1500 seems like a lot for a matched Quad, mine cost somewhat less than a third of this, and you could probably do as well for about half your quoted amount if you shop around.

My production SE amps were all fitted originally with WE300B and the PP amps mostly with Valve Arts or Svetlana. None of these gave a particularly good long term account of themselves. The few sets of JJ tubes installed have not been a problem.

In any event any replacement 300Bs you purchase should have been subjected to a thorough burn-in and test/match by the vendor.

Jim McShane should be able to provide you with good guidance on what to buy, as I've indicated the comments I have made are entirely anecdotal, but show that some 300B tubes can be very reliable over long hours of use.

Vintage WE300B or STC4300B often had service lives in excess of 10K hours..

I should have also mentioned that the JJ 300B version I have are amongst the best sounding I have used and that includes some exotics not listed here. (No longer available)
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Last edited by kevinkr; 24th February 2010 at 06:06 PM.
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Old 24th February 2010, 08:38 PM   #3
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I have a pair of JJ 300Bs, in constant use for over ten years, thousands of hours. The getter is beginning to thin out a little on one, but they still sound good. Run at 350V 60-70mA, where I like them best.

Worth searching archives here and on AA, as the JJ of 2003 or so was reported by some folks to be lower quality. I haven't seen the latest JJ, but the old one really looked & felt like a quality article.

I have experienced filament breakage on Sovtek 300Bs from a while ago, and hear that EH and Svetlana and others have also suffered that weakness, at least in the past.

One way to help protect the filament is to use constant current heating. You then avoid the Cold surge that can really shock the filament. The bonus is a massive uplift in all-round sound quality compared to ac or dc (voltage reg).

New DHT heater
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Old 24th February 2010, 10:39 PM   #4
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Thankyou to both of you. Kevin the sophia electric 300b's are about 1200 for a quad and the kr's evn more exe. The cooking versions are cheaper. I wonder what the new jj's are like wrt to quality as the tnt review (thoerstens review) stated the quality was a bit iffy.
Rod do you sell a version of your cc heater board?
Thanks again
Nick
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Old 24th February 2010, 11:18 PM   #5
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Nick, I don't have one ready now, but I have had some requests... maybe I should look at laying it out.
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Old 24th February 2010, 11:28 PM   #6
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Default Let me know

Hi Rod
It seems you might have some homework to do
I will read up on the thread to familiarise myself with the design
Let me know a time frame when possible
Thanks
Nick
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Old 3rd December 2012, 05:11 PM   #7
cotdt is offline cotdt  United States
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I still use a 45 tube that has been used for 70 years (older than me). Now I run it at 320V 38mA and it delivers much more power than before.

300B should last longer than 45, because they are bigger and better constructed.
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