ext. fp3 heater..read archives still unsure

[Nutube]

Sorry folks I know this topic has been worked over I did look at the archives but notice that stock means od3 for the center (shunt?). ExtendedFP3 this unit has 3 x 12au7. I bought this unit from a friend who bought this unit (buildt by bottlehead for the CES show ) a few years back. I bought it as back up; stored never fired up. Now It is in active duty and really sounds very good. more extended in the extreemes without leaving the mids behind.....this makes me wonder how can the BeePre top this! Well.... history has shown me that it probably will given the proven record of Team bottlehead.  I may just be in line for this upgrade.....
Meanwhile I am anxious to taste the 6sn7 on the ext fp3
i need to order a manual..........................
I  want to use 6sn7 by plugging in adapters (9 pin to octal) for the left and right channel leaving the middle  12au7 as is.

question
given the center tube is 12au7 - to be left untouched
what value resistors do I need for each of the 6sn7 position
btw where is this resistor located I read it is before the caps....It is in play right now,  I will power down tonight to look under the hood.
all your inputs will be appreciated

 

[debk]

See this post

http://www.bottlehead.com/smf/index.php/topic,787.0.html

I did the same thing with my EX FP 3.  Conversion sockets for the 6sn7 and left the regulator tube (center tube) a 12au7

I used a 0.15ohm resistor.

I don't have the manual in front of me to tell you the location of the resistor to change

Deb

 

[saildoctor]

The heaters are all connected and fed by one filter supply - it's on the terminal strip in the back of the chassis by the RCA jacks.  The resistor is a square shaped wirewound 5w.  The extended upgrade has the builder install a second resistor across the stock one to lower the resistance - you might find two there in parallel unless the builder replaced the original with the lower value they purchased separately.

 

[debk]

i removed both and replaced it with a 0.15 ohm

Deb

 

[Nutube]

deb and kerry
It looks like i already have 0.15 ohm hope pic came through
tony

 

[Nutube]

deb and kerry
in my photos is that the resistor we are talking anout? if so and if i am measuring it to be  0.15ohm the i am good to go with plugging in my 6sn7 by way of adaptors correct?
thanksfor input

 

[saildoctor]

Huh that's a little strange.  If it had been using 3 x 12au7's the resistance of the heater should be ~0.41ohms.  If it is only 0.15 then the voltage to the 12au7's would be way off.  Is there a decimal place before the 15 - it's not clear in the picture?  And there are no others going across the same terminal holes?  A multimeter checking resistance might be good piece of mind.  If it really is 0.15ohms then I think you are good to go.

 

[Grainger49]

Kerry,

The 0.15 ohm resistor is in series with the heaters and the smoothing capacitor.  It is a minor voltage adjustment for the circuit to deliver just enough voltage without stressing the heaters due to high voltage.

 

[Nutube]

kerry and grainger
yes I was careful to look at the brown resistor and it did have
0.15 on it. ( POINT 15 ohm) I will check when I power down to see if there is another resistor i parallel to it later tonight.
Meanwhile,  even with a mis match brand of 6sn7 pair not to mention specs...I am getting a very nice overal sound.
I pulled a very strong matched Siemens & Halske CHROME  plates out and put these 6sn7 in and the sound stage is a tad narrower the chrome plates tend to do that i.e detailed hence contributes I feel to  a wider perception of sound stage width.
Overall the usual air around instruments and palpability  and bass resolution seem to go with these 6sn7.
I will be receiving 3 matched pairs tomorrow... one of which is the tung sol black round plates, other is kenrad vt231 and a sylvania vt231 all strong and matched.
also tommorow or the day after the slagle course/fine volume control should be in....but I have ordered a elma selector switch.

would need to ask for help regarding switch and switch transplant. All I know is that each slagle comes with 3 wires.
I would need help in figuring out what wires not to remove.  I will try to post a hand drawn schematic of the wires from the rail to the selector and switches

 

[Paul Joppa]

The best check is to measure the DC heater voltage, ideally between 6.0 and 6.3 volts. The Foreplay does not stress the tubes, so a slightly low heater is no problem, but above 6.6 you are probably running the tubes hotter than ideal for the longest life.

 

[Nutube]

hey PJ
I will do actual measurements once I get the manual from the Queen.
This 6sn7 is captivating... I have been listening all day long these past several days  getting up for medication ( the scottish  malted kind non prescribtion) and meals only. By the time evening gets around I doze off and forgot to measure.
While the 6sn7  is a change in sonic character from the 12au7....it is not,  in my system huge...rather the better 6sn7 seemed more balanced throughout the frequencies ; tad more detailed and airy  relaxed?  "sophisticated"?. I know you folks know it but in case some newbies hungry of all kinds of input before commiting to the investment of 6sn7 might enjoy my 2 bit evaluation.
Linda Ronstadt, ella,  Julie London  sounds more palpable.....but so does La bohme tracks and Bonnie Raid. So glad I have these flexibilities within FP3. ..will be trying the 12bh7.
As you know my electrical knowledge is limited at best. ....but something tells me the beepree is gonna be goood....why..your circuit and  bigger bottle in pre amp is always good...... ;D ;D