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Old 26th June 2013, 08:59 PM   #1
kevinr is offline kevinr  United States
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Join Date: Jun 2009
Default need tube upgrade advice please sir

Hello;
I am the happy owner of a Nuera 7 watt class A tube amp and it works well and sounds good with my full range speakers .
I bought it new from Parts Express and it came with the stock brown base tubes which are Chinese, as is the amplifier.
I recently changed the stock Chinese preamp tubes out in my little dot mark 2headphone amp for some NOS Mullard 8100 from England and it sounds fatter and not as tinny as the stock ones. Much improved .
Anyway , I'm wondering if anyone can recommend good affordable tubes to upgrade the 5AR4 , 6SN7 and EL34 tubes in my Nuera SET amp ?
I thought about getting some new JJ tubes for the 34 and 5AR4 tubes but have read online ( so it must be true ! ) that their quality control has really taken a turn for the worse lately . My class AB was tubed with JJ 12AX and AT tubes about seven years ago and they seemed a good compromise, well rounded and rich sounding, made well but not the last word in air.
EH makes the 6SN7 and I've read some good things about them online, but my past experience with EH and Sovtek 12AX7 and AT7 tubes in my guitar amp and class AB amp were poor.
I had a quartet of Winged C Svetlana tubes in my Class AB amp but two of them took a dump after about six months.
Has anyone done any tube rolling of the EL34, 6SN7 and 5AR4 tubes recently that they can share their thoughts on ? I guess one alternative is to look for NOS but that can be a crap shoot and/or expensive
thanks
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Old 27th June 2013, 01:25 AM   #2
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Yes, all of JJ's Octal production is highly suspect.

The Sovtek 5AR4 is the best of the current crop, but it is not without shortcomings. The attached SS diode tweak ensures that the Russian tube operates reliably. Use UF4007s instead of the 1N4007s shown in the graphic, as UFnnnn parts generate FAR less switching noise than their 1Nnnnn counterparts. The vacuum rectifier blocks "sand" diode noise from entering the B+ rail, but less crud, from the very beginning, is (IMO/IME) better.

The EH 6SN7 is OK and its "stable mate", the "reissue" TungSol is good. The way to get nice NOS at something resembling a rational price is by fabricating adapters from Loctal sockets and Octal plugs and installing 7N7s. The Loctal base 7N7 is electrically "identical" to the Octal base 6SN7. Ignore branding on Loctal tubes, as they were all made by Sylvania at a time when Sylvania's production quality was 2nd to none. Another adapter possibility is the Octal based 6F8G. Here, a top cap must be dealt with.

If you can source a set of SED (=C=) EL34s from a reliable source, that variant is a possibility. New Sensor has 2 "reissue" EL34 family tubes that are good: GEC labeled KT77s and Mullard labeled EL34s. I almost forgot the EH 6CA7, which may be the best value available.
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Last edited by Eli Duttman; 27th June 2013 at 01:30 AM. Reason: added 6CA7 remark
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Old 27th June 2013, 02:17 AM   #3
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I have a few pairs of RFT EL34s for sale. PM if interested.
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Old 26th November 2013, 12:00 PM   #4
kevinr is offline kevinr  United States
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I was lucky to recently pick up a quartet of clean tested Raytheon 6SN7's a few miles from home for $16 and one RCA EL34 and one Sylvania EL34 for $8.
Also sniped a clean tested General electric 5AR4 on feebay for $30.
Now my Sovtek AR4 and Tung Sol El34's are spares and my amp sounds better
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