Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: TerryD on December 31, 2015, 08:32:44 am

Title: Do I have in "essence" 1 meg already?
Post by: TerryD on December 31, 2015, 08:32:44 am

Thanks for all your help with this Fender 100 PA head.  It's starting to all come together.  The champ layout and schematic moved things forward in the schematic reading .

Three more questions.

With regards to changing one channels tonestack to BF Twin.  The volume control on the PA 100 is 250 K.  The difficulty is that, this is the pot with the extender bar thing soldered to it.  That would not be easy to get off and reconnect.  I did think about just making that the bass pot.  All the stuff would just be a little lower that goes on that extender thing.

BUT  (question 1) The 250 K volume control, on the PA 100 right now, is followed by a 270k resister AND then another 270k resister on it's way to V5 and then to PI.  Isn't that in effect a 1meg resister v5 is looking at??  Therefore, am I good to go and putting the 1 meg with those two resisters would have been like 1600k?

Also would the sound be the same?  Do I get the same sonic result w three resister for the 1 meg vs. the 1meg pot?

Second question:  I put a guitar cord from channel 3 to channel 4, with my guitar plugged into channel three. Each channel has only 1/2 a 12AX7.  I like the effect of the little more grit.  What is the best way to connect the two halves of that tube before the signal moves on to V5?  Then I will have stock channel, twin bf channel and the 3&4 chained.

Third and final question:  I'm knocking out one input jack on a channel.  Does the two 68ks from the two input jacks effectually come down to 33k per resister or does the amp not see them in parallel?  Should my resister set up (which I'm installing)  from a single input to V1= one 68k resister with 1 meg to ground or one 33k resister with 1meg to ground?


http://www.prowessamplifiers.com/schematics/fender/pa100.html (http://www.prowessamplifiers.com/schematics/fender/pa100.html)

Title: Re: Do I have in "essence" 1 meg already?
Post by: Willabe on December 31, 2015, 12:17:16 pm

Look in here, scroll down to hi-lo input jacks;

http://sluckeyamps.com/misc/Amp_Scrapbook.pdf (http://sluckeyamps.com/misc/Amp_Scrapbook.pdf)