Hi,
B+ =300VDC
Set cathode bias resistors to 680R.
Tubes will work under the conditions they're being forced to work under for as long as it's within their limits.
To have them work optimally you'll always need to do some work for them first.
Cheers,
EDIT: Aborting the Tai-Kwondo circuit....Too easy.
B+ =300VDC
Set cathode bias resistors to 680R.
Tubes will work under the conditions they're being forced to work under for as long as it's within their limits.
To have them work optimally you'll always need to do some work for them first.
Cheers,
EDIT: Aborting the Tai-Kwondo circuit....Too easy.
i tried12bh7s in the second position and they seemed to work fine. B+ @ 260 and 430r at cathode. if i remember right that produced approx. 7 ma. i also tried them in first position but had trouble with microphonics. a higher stopper value may have helped. they sounded pretty good though. i had popped them in just to see how they'd do, but didn't do any experimenting as i was focusing on the 12au7 into 5687 at that time. maybe soon i'll try the 12bh7s again as i have a small box of them.
selfwilly said:
Interesting, I have the 12BH7 in my first position and 5687 in my second. Both tubes have 330R in the cathodes at 260VDC B+. I think the 12BH7 are flowing around 11ma and 5687 are about 13ma. Not sure if these are too much but right now the sound is a little thin on the bottom end. There is not enough grunt in the mid and lower bass. The mids and highs are sweet but not quite enough depth. I need to play around a bit or even try a different first tube if I can't get this combination to work. Will keep playing...
my impressions of the 12bh7s in first position were based on a very short audition that was compromised by the microphonic issue i had with them. i seem to remember them being very bright as well, but clean. the measurement for current i gave was for tube in second position. the B+ was a approximation from my iffy memory. i have a aikido set now with 470r in first and 330r in second position. i'll take some readings tonight with the 12bh7 and see what i come up with.
Hi Andy, B+ was at @ 210. i tried many settings between 200 to 225. all worked ok. I used 470r on first tube and 330 on second tube. I applied 40-50v to the filament tranny center tap. mine is a two chassis preamp. power supply on seperate chassis.
ONE NOTE: this may pertain to you it may not, i have found that all the variations i tried had way too much gain for my amps. exaggerating any noise or hiss issues that there may be. also could barely use aikido volume pot with out it becoming too LOUD
. i had to install 100k attenuators on my amps and back them off. voila' hiss is gone or minimized, and i can actually turn up my aikido volume control to 11 oclock befor it gets to loud! i use 99db horns.
charlie
ONE NOTE: this may pertain to you it may not, i have found that all the variations i tried had way too much gain for my amps. exaggerating any noise or hiss issues that there may be. also could barely use aikido volume pot with out it becoming too LOUD
. i had to install 100k attenuators on my amps and back them off. voila' hiss is gone or minimized, and i can actually turn up my aikido volume control to 11 oclock befor it gets to loud! i use 99db horns.
charlie
selfwilly said:
Hi Charlie,
thanks for the reply.
I had already thought about attenuating the power amp but wasn't sure it was a good idea.
Maybe a step-down signal transformer might do the trick (lowering at the same time output impedance).
The only problem is that I have no clue about which trasformer could be employed.... suggestions? (not costing a arm and a leg)
Cheers
Andrea
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