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Tube Substitution Question
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03-15-2017, 05:22 AM
Hi all you Ampeg folks. My first post here and newby to Ampeg amps. Have an M-12 Mercury on the way and the previous owner is supplying a couple of adaptors for the 6SL7 tube sockets that enable the use of 12AX7 types. No experience with these 6SL7 tubes on my part. Is this safe or would there have to be changes made inside the amp to allow safe operation?
 (03-15-2017, 05:22 AM)journeyman Wrote: Hi all you Ampeg folks. My first post here and newby to Ampeg amps. Have an M-12 Mercury on the way and the previous owner is supplying a couple of adaptors for the 6SL7 tube sockets that enable the use of 12AX7 types. No experience with these 6SL7 tubes on my part. Is this safe or would there have to be changes made inside the amp to allow safe operation? Honestly, there is no reason to change. finding NOS 6SL7s isn't too hard, or expensive. Alternately New sensor remakes them under the Tung Sol brand. and they are pretty good. the adaptors might be nice to keep on hand just in case you need a tube in a pinch and don't have any spare 6SL7s but for the most part it they are not hard to find, and they can be ordered online and delivered in a matter of days.
03-15-2017, 08:49 AM
No real plans to make the change; just curious and wouldn't mind hearing the difference. Looking forward to receiving the amp. I also just got a 1967 (I think that's the year) Reverberocket 2. Very pleased with it overall, although the reverb might need some attention as the footswitch doesn't turn it off and it is very trebly; oscillates easily too. In a way it is part of the charm of the amp, but it seems just a tad not quite right.
I am a fan of the reverberocket II. It's a great amp. The reverb should deffinitely not sound like how you describe it.
It should be lush and deep. Although I have always found the ampeg reverb circuit to be a bit noisy. Regarding the 6SL7s, I would be interested to hear your thoughts on the differences with the 12AX7/adaptors.
03-22-2017, 04:31 AM
The M-12 Mercury is here and out of curiosity used the adaptors to try a pair of 12AX7s in place of the original octal 6SL7s. The sound was what one would expect; slightly more gain; a tad more agressive with more top end; slightly earlier breakup; not quite as warm. No big deal but good to have as an option. The difference is subtle. I like the warmth of the 6SL7s.
The amp has some noise issues and from what I have been able to find on line, the hum is caused by some grounding issuss. The solution coulc be a simple matter of uncoupling the ground by moving a couple of wires. When I get the time in a month or so I'll get it to my tech and give a report after that. In the meantime, here is a link a thread in another forum that addresses the issue, post #21 in particular: http://www.tdpri.com/threads/1960-ampeg-...905/page-2
03-22-2017, 12:43 PM
Journeyman,
That is an interesting solution. typically one only sees a single grounding point for star grounding, rather than 2. I wonder why they did it that way. interesting to hear the differences in the 12ax7 and 6SL7. I am not surprised of course. I think the 6SL7 is an amazing tube. The 6SN7 is also amazing, one of my favorites. -Steve
03-23-2017, 02:54 AM
(03-22-2017, 12:43 PM)Hangman Wrote: Journeyman, Is the 6SN7 a drop in sub for the 6SL7? If so, I assume they have different amounts of gain. How are they different?
03-24-2017, 10:46 PM
the 6SN7 is a medium mu dual triode. I think the amplification factor is 20. The 6SL7 is a high mu dual triode and the amplification factor is 70.
they are pin for pin compatible, but I don't think it would make sense to swap a 6sn7 in for a 6SL7. you'd lose a lot of gain |
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