Ampeg V4 filter supply rebuild, and some misc circuit questions

[liddokun]

I have an early 70s Ampeg V4 amp that I am working on. 

It is the Rev E. schematic, attached. 

Electrolytics will all be replaced with fresh ones.  I'm opting to ditch the multi-can caps and use smaller discrete caps, including slightly increasing the filtering values.  I combed through multiple forums and found a post where Pete (DummyLoad) detailed some changes he made with his filtering.  The schematic is also attached.  Apart from the slightly higher capacitance values overall, can someone help me understand the slight differences between the filtering as implemented stock, and the way Pete has laid it out?  Can I increase preamp filtering caps to 68uf with no real issues? 

My additional question pertains to input grid stoppers and shunt caps.  Schematic has inputs going through a 1k resistor with a 50pf shunt cap (c1/r1, c4/r7, though an asterisk states this will not appear on all circuits.  It does not appear on mine, do I gain anything from adding this? 

Lastly, in searching for the answers for the above question, I came across a post from someone suggesting to place a 10k resistor in series with c6 as well as c3 because: 
"they have both a pot and a switch on output, so in some position of a switch and a pot anode is connected to ground through a cap and low resistance of a pot, so current flowing through ground creates a voltage drop on HF enough to cause oscillation".   Something I should consider? 

Thanks in advance!  Have worked on a bunch of Marshall, Fender, and Vox flavoured circuits up until now, I know the Ampeg stuff has its quirks. 

[Willabe]

I think 1 of the diodes in Pete's mods drawing of the FWB is oriented wrong? 

[liddokun]

I think 1 of the diodes in Pete's mods drawing of the FWB is oriented wrong?

Right, didn't catch that. D1 looks to be flipped. 

Was too focused on the filter caps to notice!

[PRR]

> preamp filtering caps to 68uf with no real issues?

Why? 40(39)uFd is ample. And ALL the hum in these amps is from the heater traces on the PCBs. No the humdinger is not a complete fix. However if you PLAY IT LOUD nobody can hear the hum.

> 50pf shunt cap

Anti-radio. Does no harm and may save the gig if you ever play a truckstop or near an AM tower.

> current flowing through ground creates a voltage drop on HF enough to cause oscillation".

Ignorant malarky.

[liddokun]

Great, this is super helpful.

I was going to go with 68uf for preamp filtering just because local supplier was backordered on 40uf, but now that I'll be ordering from Mouser guess I'll go with the regular value. 

[PRR]

> 50pf shunt cap
Anti-radio. Does no harm and may save the gig if you ever play a truckstop or near an AM tower.

Here's a Traynor service-note for an equivalent part, found to be "necessary" after the drawing was drawn and some amps were in the field. Yes it is transistor but a JFET is not so different from your tube and responds similarly.

[DummyLoad]

I think 1 of the diodes in Pete's mods drawing of the FWB is oriented wrong?

Yeah dum dum here has D2 reverse biased. Nice,! Magic smoke ensues with that plan!

My apologies for the error, and noob one at that! Shame!

--Pete

EDIT: attached corrected mods schema.

[sluckey]

Now D1 and D2 are backwards.   

[DummyLoad]

Now D1 and D2 are backwards.   

Ugh! I've drawn that 100's of time! Note to old self: Don't work on stuff after midnight.