6SJ7 Pentode 18 watt Lite...Formerly the ABSOLUTE Minimum

StarGeezers · Post by **StarGeezers** » Sun 10/19/08 9:46 am

Ok, I'm "screwed"... all I have is a pair of 22uf.50 v, pair 1000uf 25V,4700uf 16v (too low).. Checked all my junk...Nada...Rat Shack doesn't have em' ...They do have a 220uf @35V...???Hope they're open on Sun.

StarGeezers · Post by **StarGeezers** » Sun 10/19/08 11:27 am

RS open on Sun. from 12-6...
posted pics at sewatt , no use taking up webspace twice...see all the pics here... http://www.sewatt.com/node/17435?page=33

Post by **zaphod_phil** » Sun 10/19/08 11:37 am

25V caps should also work OK. Your cathode voltage is typically going to be around 11 to 12V at idle.

BTW I doubt that hosting pictures of a PP amp on SEwatt.com is a real good idea. Maybe you could move them to PPwatt.com.... just a thought FWIW....

StarGeezers · Post by **StarGeezers** » Sun 10/19/08 12:16 pm

ZP, talked to the Grand Pooh Bah over there and after kickin' me around a bit, then forgave me,save decapited'.... ....cause' I was bringing the Beer...

RS has a 220uf 35V for 1.39 + gas

... Calling first to see if one is in stock ...otherwise They have a 100uf and a 47uf ...I could parallel those and get even closer...

Phil, Please excuse any minor indiscretions as purely unintentional...I'm just a builder, making some amps to gig with...my theory is "dreadful"

..working on it though...

bigbeck · Post by **bigbeck** » Sun 10/19/08 12:30 pm

StarGeezers wrote:Calling first to see if one is in stock ...

You really think someone will know what a cap is? Expect a reply such as "this is not a clothing store!" "Maybe you should try Dick's Sporting Goods!"

StarGeezers · Post by **StarGeezers** » Sun 10/19/08 2:41 pm

Dick, left to get a pizza

... I went there, got the parts ,and a few extras, naturally...Home , soldered em' in , installed a 2A SB fuse and then realized I hadn''t wired up the speaker side of the OT...DUH!!!

Which brings us to the final question ... got the recommended 125E, but what Z do we want and do I have to run a separate ground to the star or will the chassis /jack ground work ??? Two questions ...

So many choices???

bigbeck · Post by **bigbeck** » Sun 10/19/08 3:17 pm

I'm running mine with a 6.6K Deluxe OT. People that have an 18watt ot run them at 8K. Flip a coin

It's easy enough to change.

Everything should go back to the star.

kyoungsteadt · Post by **kyoungsteadt** » Sun 10/19/08 4:28 pm

Geezer, 8k.

StarGeezers · Post by **StarGeezers** » Mon 10/20/08 6:10 am

Thanks guys , I could only guess, and I guessed wrong !!! On the right track now !!!

StarGeezers · Post by **StarGeezers** » Mon 10/20/08 7:51 am

Just reading about 6V6 plate Vs... using that Edcor PT, I can expect somewhere around 400+ Vs out the PT/SSrecto...I picked up my B+1(A) from behind the 200R first resistor for less Vs... The Huss drawing shows coming off in front of the R, but at 305V(El84s shown in drawing,different PT)..Should I go for the higher Vs in front with the 6V6s??? What about that 100R screen stopper?? Used to using 1Ks there..Is that value right?? Just checking the details before we fire it up...hopefully some time today...

Post by **zaphod_phil** » Mon 10/20/08 3:05 pm

I forgot that the Minimalist schematic is older than the Lite IIb. I would recommend using resistor values from the Lite IIb's power supply and power amp section as a good starting point for your 6V6 version. It runs the screen grids at lower voltage and more protection.

kyoungsteadt · Post by **kyoungsteadt** » Mon 10/20/08 5:03 pm

Phil,

Did you move to Canada?

Post by **zaphod_phil** » Mon 10/20/08 5:26 pm

Yes, all 18W of me.

I'm a Cannuck anyway, so it was just a return home for me...

StarGeezers · Post by **StarGeezers** » Mon 10/20/08 5:40 pm

I'm moving to La La land...

Here's what I have as far as PS values ,added an extra stage of filtering ... red is what I'm looking for ... changes to be made...??? Not a theory guy, just a builder...Totally FN confused...Grrrrr!!! I need another Beer...

StarGeezers · Post by **StarGeezers** » Tue 10/21/08 9:39 am

Fired up the amp ...no smoke , but a moderate amount of hum..and something's extremely microphonic'... just touching the chassis makes a hollow chalky' sound ...just like tapping on a mic... On long enough to check the PS Vs...
B+ 356 from SS recto
B+1 338 to OT
B+2 322 to screens
B+3 281 to PI
B+4 268 to 6SJ7
Tried tapping , but it makes noise everywhere...Grrrr!!!!
Changing taps to the correct positions...

StarGeezers · Post by **StarGeezers** » Tue 10/21/08 11:25 am

Changed 6SJ7, 12AX7, still hums/ extremely microphonic(can't be that)... grounded input jack to Star.. Nada!! Never had something weird like this happen before...

Don't have a clue what to do ??? Any ideas ??? Stumped !!!!

kyoungsteadt · Post by **kyoungsteadt** » Tue 10/21/08 12:33 pm

Geezer,

I saw the pics you have a lot going on in there. I was afraid this might happen and it might hard to troubleshoot the point-to-point stuff. Check every single connection make sure the tube sockets are wired correctly.

bigbeck · Post by **bigbeck** » Tue 10/21/08 1:05 pm

Looks difficult to trace anything

Ditch that 200R dropping resistor after the diodes and the world will be as one!

Mine was also very microphonic too, but it went away.

Don't remember how. Could have been when I changed the value of a resistor or cap on the 6sj7 or changed B+. Maybe dirty pins on the tube? Or a bad solder joint on the 6sj7.

StarGeezers · Post by **StarGeezers** » Tue 10/21/08 5:11 pm

KY, tight yes, but I can get to everything...I'm so used to true P2P that it's easy...sorta'
Big, made all the changes you suggested(elsewhere?) Strange , one 6V6 CG is 16V , the other is 70V... everything else checks out , the hum gets louder with the Volume increase (knob) , the Tweed works , now I'm getting a static sound with the hum ,and some minor squealing (new).. WTF???(Whats this Foolishness)

kyoungsteadt · Post by **kyoungsteadt** » Tue 10/21/08 5:17 pm

SG,

Amp building at its best. Bop those ferrets one by one.

Check for cold solder joints. Make sure your grounding is correct. etc. You know the drill.

Edit: SG, if your input jack is grounded to the chassis you don't need the wire going to the star ground lug. Or use an insulated jack if you want to use the star ground.

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6SJ7 Pentode 18 watt Lite...Formerly the ABSOLUTE Minimum