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Thought that a 6SL7 / 6SL7 driver board might sound pretty good so I thru one together. I always like the sound of the Mapletree board so I used the 6SL7 long tail of that design with the 6SL7 of what I think is the "IKE" anyway it sound real nice. I do however have questions on the voltages of the 6SL7 input stage that maybe someone here might be willing to answer for me.

The borrowed front end (6SL7) uses a 100K plate resistor and calls for a 215VDC feeding that resistor with 146VDC actually on the plate. I have 221VDC feeding the plate resistor with 124VDC actually on the plate. I have 1.04VDC across the 1K resistor which would be a little over 1mA Am I correct? If so am I in the ballpark for the 6SL7 operation or am I driving it too hard?

It looks like your VA stage 6SL7 is drawing about 1 mA plate current, (indicated by the cathode voltage, so that would equate to about 100V across the 100K plate resistor.

You are OK for 6SL7 operation, but if you want higher (140V) plate voltage, which means less plate current, try about 1.3K for the cathode resistor, that should get you pretty close.

The IKE board is designed for either 12AX7 or 6SL7 VA stage, and the values of the plate and cathode resistors are more appropriate for the 12AX7, the 6SL7 has a somewhat different gain, gm and rp.

Tubes are not "precision" devices, if your actual voltage measurements are within 10% of those whown in the IKE documentation, that is perfectly good.

HTH

/ed B

Thanks for your reply. This is probably a stupid question but I have 124volts on the grid of the 6SL7 long tail with about 212 on the plate and 129volts across the cathode resistor. Does this sound ok also?

I'm not real familiar with the Mapletree design, but I suspect it is a pretty standard VA stage direct coupled into the LTPI, much as with the Eiclone (IKE) design.

6SL7 data sheet: http://frank.pocnet.net/sheets/127/6/6SL7GT.pdf

The grid voltage on the LTP is determined by the VA plate voltage, and the values will change if you change the driver's 1K cathode resistor to 1.3K. Doing this will change all the measurements around the 6SL7 LTP.
Your persent voltages appear to be fairly normal, what value is the long tail resistor?

/ed B

Tha cathode resistor for the long tail is 54.9K

129V across 54.9K indicates about 2.3 mA total for both halves of the LTPI, which is a good value for this tube (max plate current per section 2.3 mA, max PD 1 watt) .

/ed B

I guess I am wondering about the heater to cathode voltage. I forgot how that all ties in.

Changed the plate resistor on the input tube to 200K and it increased the gain and drive capabilities. After listening to it a few hours I am well pleased with it. It is extremely clear and clean sounding and it has very good punch and low end. It is surprising that I could achieve enough drive without having to use a pentode.

Now you get to roll 6SL7s. I have a 6SL7 SRPP on 300Bs and got turned onto RCA VT229s from WWII, and nothing else makes the soundstage up like they do. Of course everything sounds different on different amps and the short bottle brown base Syls with the Chrome Domes are really good but I really found the tall tubes with the larger plates to sound best. Older the better too. Maybe they got to use chemicals on the tubes that are known to cause cancer, or the women had better hands, there is something about the octal dual triodes from 43/44 that make people close their eyes and smile. Buy used, strong testing, broke in tubes. They cost less, they probably won't change their readings very fast and you know how they are after being used. I used to scrounge things for pulls and in most situations like a used, tests like new better than a NOS, why should we test it, it's new, or new tubes that change when they break in. They might sound better broken in but not read the same or last like you want. Pulls tested on good machines by people who do it for a living typically never disappoint, cost less so you can get more flavors.
This has probably been gone over and it is just an opinion. The VT-229 is shared by many and the RCA VT-229 by even more. I wouldn't go much over a hundred for a good pair with all 4 sides testing 85% or better, the the market does speak.
Thatch