You might find that pin 6 is not used.
Have a look at the JJ for instance http://www.hebertech.com/datasheet/jj/el34.html
The Mullard http://www.hebertech.com/datasheet/mullard/el34.html notice pin 6 is denoted as NC (not connected)
Again with the Telefunken http://www.hebertech.com/datasheet/telefunken/el34.html
Also, for the 12AX7 replacement have you considered the JAN-GE 5751 http://thetubestore.com/jange5751.html although the Preferred Series 7025 looks very good also.
Have a look at the JJ for instance http://www.hebertech.com/datasheet/jj/el34.html
The Mullard http://www.hebertech.com/datasheet/mullard/el34.html notice pin 6 is denoted as NC (not connected)
Again with the Telefunken http://www.hebertech.com/datasheet/telefunken/el34.html
Also, for the 12AX7 replacement have you considered the JAN-GE 5751 http://thetubestore.com/jange5751.html although the Preferred Series 7025 looks very good also.
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Edit: While my amp was still a Yaqin I replaced the .1uf coupling caps with Mundorf silver & oils, and replaced the resistors in the signal path with Kawame's, this was after Triode strapping the EL34's and severing the GNF line, all this made marked improvements to my ears. Although reducing the output power.
Severing the GNF would really up the output impedance and demo the OPT's damping factor. Didn't doing this trash the bottom end?
After triode strapping the EL34's it was done as all it did was add distortion throughout.Severing the GNF would really up the output impedance and demo the OPT's damping factor. Didn't doing this trash the bottom end?
The bottom end was better, as overall the the amount of distortion was less, and it also gave the sense of greater gain.
Edit: I'm using the same transformers now with a new (better circuit), Triode strapped with only local feedback, and I have a better sound than I ever have.
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The triode (if we ignore Nelson's new devices) are the most linear amplifing devices made by man, so one can get away with no GNF.
dave
The 10L doesn't use triodes though, it uses power pentodes which have MUCH higher plate resistance than triodes. Higher plate resistance = higher output impedance, which if not rectified via GNF, = poor damping factor which = boomy, mushy bass...or so I thought.
A 510r 3w resistor is a good value, 270r 2w minimum for strapping. A lot of folk use something like a 100r 1w, but that's not safe as far as I have been taught.
Remove the UL connection and insulate well and tie back in a safe position, sever GNF. I just snipped out the cap & resistor in the GNF line of each channel that live on the pre board.
Remove the UL connection and insulate well and tie back in a safe position, sever GNF. I just snipped out the cap & resistor in the GNF line of each channel that live on the pre board.
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How does the plate resistance of a triode strapped El34 compare to a true triode like the 300B? What sort of damping factor can you maintain with the NF removed? Sorry for the newb q's, I have a 20L and they're somewhat similar. I'm just starting to learn a bit about tube circuits.
The Yaqin MC-20L is switchable between UL and Triode mode, as you know, whether the switching also switches out the GNF I have no idea, but in such a mode the GNF is not needed, and without it reduces distortion considerably.
Sorry but I'm not sure on the damping factor differences, and haven't the time to look into it, all I know is the MC-10L when triode strapped sounded much cleaner once the GNF was removed.
Sorry but I'm not sure on the damping factor differences, and haven't the time to look into it, all I know is the MC-10L when triode strapped sounded much cleaner once the GNF was removed.
I actually never use it in triode mode, ultralinear seems to have a little fuller midrange. Playing around with the GNF sounds interesting, though I am concerned about any impact on the bottom end. This amp is already a bit on the bright side and I'd hate to lose any bass.
I actually never use it in triode mode, ultralinear seems to have a little fuller midrange.
Which is better is very speaker dependent
dave
I wouldn't sever the GFB on that amp unless you fix it in Triode, but you could reduce it, the GNF on the MC-10L was high.
And from what Dave has said about those speakers they are a load , so best to run it as you are in UL. An I see what Dave means, with the curve where the port takes over....
And from what Dave has said about those speakers they are a load , so best to run it as you are in UL. An I see what Dave means, with the curve where the port takes over....
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Did a little more digging about the damping factor of triode strapped El34's and I found an article by Menno Van Der Veen where he listed a comparison of various circuit types using El34's w/o GNF. In ultralinear, the circuit had a DF of 0.315. In triode mode it had a DF of 0.948 (both are w/o GNF). Does a DF of just under one mean the bass will be sloppy? Well, I found another article that compared the bass note decay time between various DF values. The difference in decay between DF>2000 and DF=1 is about 0.03 seconds. 3/100's of a second! I don't think that is even audible...at least not by me. So this has gotten me more interested in removing the GNF from the triode mode on my amp. I think I'll investigate adding a switch to turn off GNF for triode mode.
There were some old amps that had adjustable DF...do you think they did this by varying the GNF? Could one add a pot in place of the resistor to make GNF adjustable?
There were some old amps that had adjustable DF...do you think they did this by varying the GNF? Could one add a pot in place of the resistor to make GNF adjustable?
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