Testing a 300A on a B&K

maxro · 29th May 2011, 01:50 AM

Greetings,

A while back I got a mixed box of tubes at the local auction house. I figured there were enough gems (four Mullard xf2 EL34, anyone) amongst the TV and series-string radio jobs to offer a bid. It was not until I got it home that I realised that a box labeled as 811A actually contained a Northern Electric 300A.

Having recently been lent a B&K 707 tester, I looked for a means of testing the 300A and came across this method. I made the UX4 to octal adapter and tried it out in the non-Dyna-Jet section of the 707, which happens to take the same settings as the 606, used in the pdf instructions. The emission test result was 92% (good from 66-120%), no shorts and no grid current.

So, my question is regarding the veracity of the testing method in the link. Can I trust the results? Obviously the tube isn't a dud, but is the sensitivity setting for a 6L6 really close enough? Oh, and I am correct in thinking that a 300A and 300B are identical, save the bayonette pin orientation, no?

ps. The EL34s all test "good" 73-86% mutual conductance.

danFrank · 29th May 2011, 02:27 AM

Yes the 300A and 300B are the same electrically. Check your tube tester's instructions and see if there is tester data for the 6B4G tube. It is the same tube as a 6A3 but in an octal socket.
The only part I would question on the "testing 300B as a 6L6" link you provided is that the 300A/B will take more grid bias than the 6L6 to get a correct reading. If your tester has data for the 6B4G, the 300B data will be similar to this tube but change the filament voltage to 5 volts for the 300A/B.
Have you checked the prices on Ebay for the 300A? They go for insane money; even more than the 300B. If that is the only one you have, You may want to sell it and take that money and buy lots of any other tube you may be interested in.
Daniel

maxro · 04:29 AM

Quote:

Originally Posted by danFrank

Have you checked the prices on Ebay for the 300A? They go for insane money; even more than the 300B. If that is the only one you have, You may want to sell it and take that money and buy lots of any other tube you may be interested in.

Ebay was the plan. $3K each is what the last couple I watched went for.

Thanks for the 6B4G tip. I have settings for the 6B4, which I assume is the same. I will test and report back.

Edit: Tested at 88% when set for 6B4.

29th May 2011, 01:50 AM	#1
maxro diyAudio Member Join Date: Dec 2004 Location: Survey says: Least happiest city in Canada	Testing a 300A on a B&K Greetings, A while back I got a mixed box of tubes at the local auction house. I figured there were enough gems (four Mullard xf2 EL34, anyone) amongst the TV and series-string radio jobs to offer a bid. It was not until I got it home that I realised that a box labeled as 811A actually contained a Northern Electric 300A. Having recently been lent a B&K 707 tester, I looked for a means of testing the 300A and came across this method. I made the UX4 to octal adapter and tried it out in the non-Dyna-Jet section of the 707, which happens to take the same settings as the 606, used in the pdf instructions. The emission test result was 92% (good from 66-120%), no shorts and no grid current. So, my question is regarding the veracity of the testing method in the link. Can I trust the results? Obviously the tube isn't a dud, but is the sensitivity setting for a 6L6 really close enough? Oh, and I am correct in thinking that a 300A and 300B are identical, save the bayonette pin orientation, no? ps. The EL34s all test "good" 73-86% mutual conductance. __________________ "Part of the reason a poot into a toilet bowl sounds the way it does is because of phase shift." -Andrew Eckhardt

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29th May 2011, 02:27 AM	#2
danFrank diyAudio Member Join Date: May 2005 Location: California	Yes the 300A and 300B are the same electrically. Check your tube tester's instructions and see if there is tester data for the 6B4G tube. It is the same tube as a 6A3 but in an octal socket. The only part I would question on the "testing 300B as a 6L6" link you provided is that the 300A/B will take more grid bias than the 6L6 to get a correct reading. If your tester has data for the 6B4G, the 300B data will be similar to this tube but change the filament voltage to 5 volts for the 300A/B. Have you checked the prices on Ebay for the 300A? They go for insane money; even more than the 300B. If that is the only one you have, You may want to sell it and take that money and buy lots of any other tube you may be interested in. Daniel

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