The PPIMV (Post-PI-Master-Volume) thread.

chopperferrari · Post by **chopperferrari** » Mon Jul 15, 2013 9:07 am

Hi Guys,

Do i need to re-bias after fitting the PPIMV? if so do i do it with the master fully open or o 0?

Thanks!
Ben

novosibir · Post by **novosibir** » Tue Jul 16, 2013 7:25 am

Re-bias is not required, but
Control is good, confidence is better. [Lenin]
or
Trust, but verify. [Ronald Reagan]

Larry

cebix · Post by **cebix** » Thu Jul 18, 2013 4:27 pm

toner wrote:cebix,
I doubt the PPIMV pot has anything to do with the squeal although it may have been damaged as you mentioned. Did the amp squeal at similar volume and presence settings before the PPIMV?

The fact that the presence pot affects the squeal may indicate that some wires need to be moved around. Try moving the NFB wires around and keep them as far away from other wires as possible, especially the wire from the presence pot to the board. Keep it away from the OT wires and tone control wires.

Since it doesn't squeal with the guitar volume down it may just be the guitar pickups feeding back. ?

Well since then I fixed the issue... kind of. What I didn't realise is that I would stand in front of the amp while turning the MV knob in the back... standing with the pickup directly facing the input jacks... so as I passed a certain point it would start squealing not because of some internal failure but just because I was very close to the input jacks and from what I know standing right there will cause squealing no matter what. So yeah still enjoying the LarMar but have to keep it above 50% so it won't fizz. The best mod that could be done to this amp. Thanks again Larry.

novosibir · Post by **novosibir** » Thu Jul 18, 2013 5:06 pm

cebix wrote:Thanks again Larry.

Nice to see so many guys being happy with my PPIMV

Larry

coldengray · Post by **coldengray** » Thu Jul 18, 2013 6:08 pm

Originally I had a Marshall style knob on my LarMar MV in the back...I quickly realized it is a lot better to have a chicken head knob so you can feel where it is set!

malig · Post by **malig** » Sat Jul 20, 2013 11:27 am

Larry,
In my 1959 with the PPIMV it seems that I have a bit more noise when the PI saturate (but it seems that it was my amp who was noisy). So I rewired everything (heather and power section), and I replaced the plate resistor with metal film, it helped very little.

If I replace the resistors in the bias section (47K,15k,27K) with Metal Film, will it help ?

Thank you again for your PPIMV

novosibir · Post by **novosibir** » Mon Jul 22, 2013 6:14 am

malig wrote:If I replace the resistors in the bias section (47K,15k,27K) with Metal Film, will it help ?

No, nothing.
Noise usually arises in front of the circuit around V1 & V2
Check your lead dress & grounding, swap preamp tubes.

Larry

malig · Post by **malig** » Mon Jul 22, 2013 3:11 pm

OK, now I feel ashamed, I rewired the poweramp and the heathers... I was ready to fire the solder Iron again to check the preamp and change the ppimv pots .... BUT IT WAS ONLY A BAD PREAMP TUBE !!!!!!

But I wasn't noticing the noise because I didnt push the preamp before (it was too loud without master....

Thank you Larry and sorry for this

I'm an idiot lol

novosibir · Post by **novosibir** » Mon Jul 22, 2013 3:28 pm

No, you're not an idiot. You just have learned a bit more.
And you've had the balls, to admit your mistake publicly.
That's cool. Many can't do this

Larry

malig · Post by **malig** » Mon Jul 22, 2013 4:57 pm

I really appreciate your guidance, and the time you put in for us !!!

When I will get a decent salary I will buy everyone of your amps (not only to thank you, but because they're the best !!!
Until then take care

bill bokey · Post by **bill bokey** » Fri Oct 18, 2013 5:41 am

Sorry if it's already been discussed but I didn't read the 100+ pages.

Is it possible to replace the 220k resistors on the board with the 2m2 instead of soldering them on the pot ?

novosibir · Post by **novosibir** » Fri Oct 18, 2013 8:44 am

No

Larry

syscokid · Post by **syscokid** » Sat Oct 19, 2013 10:14 pm

bill bokey wrote:Sorry if it's already been discussed but I didn't read the 100+ pages.

Is it possible to replace the 220k resistors on the board with the 2m2 instead of soldering them on the pot ?

The recommended pot is 250k of resistance. To bring the Grid/Leak Bias resistors to a value of 220K for EL34's, you must install the 2.2M R's parallel to the 250K pot to achieve the desired results.

For 6550's, you would want Grid R's value to be about 150K. Therefore, using a pair of 470K's parallel with the 250K pot, would give a value of 160K...close enough!

Bob · Post by **Bob** » Sat Oct 19, 2013 10:49 pm

syscokid - would you want a different value for 6L6Gs?

bill bokey · Post by **bill bokey** » Wed Oct 23, 2013 8:16 am

Thanks guys.

A friend of mine has an amp (modded 1959RI) that needs fixing and it has a 500K pot and two 470k resistors on the board. SO I just wondered if it was possible to place the 2m2 in place of the usual 220k (and 470k on this particular amp).

I'll go with the usual 250k pot + 2m2 resistors.

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