input resistor in liverpool

[harris51]

Somebody suggested I use a 33k resistor in place of the 15k on the shielded input wire, any thoughts on the tonal difference? or gain difference?

[Reeltarded]

You mean as a grid suppressor, right at the tube?

33 vs 15 makes no difference to a dog. 220k starts sounding like something to a people.

[leadfootdriver]

I have a 10k on my Express. Transparent.

[gtrcollectr]

33k here....cant hear it.

[geetarpicker]

My original early 90s Liverpool didn't have an input resistor. Worth a try if it doesn't need it there you go. That said I added one later on the 2nd stage via instruction from Ken as I wanted to darken it up a tad.

[Mark]

Glenn that resistor would have to have been a large value.

On a Marshall a 470K sounds quite dark if it doesn't have it's 500pF bypass cap.

What value did you end up going for.

[Reeltarded]

Bypass? Wrong resistors! We are talking about the ones that are 68k and on the board in Marshall land. The same as the 1.5k/5.6k 'swampers' on the output tubes, just moved to the grid terminals of the actual preamp sockets.

I have a bunch of amps with none, and some amps with values as high as 220k. You start picking up Radio Tokyo without them in some rigs.

1st stage purely for RF, and others for RF and suppression of highs, for you (220k) or your dog (33k)

[redshark]

When people say input resistor here, at least I understand is about V1b(pin7) which is coming from the amp's input jack. Glen refers to V1a(pin2), I think the letter said it was a 820ohm resistor that we see also on the "reject" express pictures and maybe in "Ingrid" too.

[Mark]

Bypass? Wrong resistors! We are talking about the ones that are 68k and on the board in Marshall land.

Not quite, the subject is in thread below.

Worth a try if it doesn't need it there you go. That said I added one later on the 2nd stage via instruction from Ken as I wanted to darken it up a tad.

[Super_Reverb]

Aiken amps has an explanation of grid stoppers:

http://www.aikenamps.com/InputRes.htm

And also an easy way to calculate a value that will be transparent for your design.

http://www.aikenamps.com/MillerCapacitance.html

This series resistor is working against the grid-plate capacitance (multiplied up due to Miller effect). Based on a typical grid-anode capacitance of 1.7pF and stage gain of 60 and neglecting minor effects, series resistor needed for a -3dB at 15kHz is f=1/(2*3.14*15K*1.7p*60) ~ 100K Ohms. If you add in some grid-anode stray cap as Aiken example, it changes things.

There are a couple of schools of thought - some like them as small as possible and some like them as large as possible as long as doesn't strip too much high end.

Based on a treble e string @ 12th fret ~659Hz, you'd be able to hear the 22nd harmonic before, the V1 grid stopper affected the timbre of your axe.

rob

[husky]

I definitely hear a difference between none, 15K and 33K. At least I think I can None sounds more strident, edgy and is more quiet when shutting down the guitar volume or not plugging in but susceptible to picking up RF depending on the grounding scheme. The capacitance of the tubes can be all over the place as well it seems. I think you would have to be able to figure out the actual passive pickup impedance curve to further diagnose it. Easier to plug in what sounds and feels good to you but I would say at least 10K for RF

[Reeltarded]

I definitely hear a difference between none, 15K and 33K. At least I think I can

lol me too, but it's not like a direct detection, more of a feeling thing. There seems to be a hhhhhhhhh range above the ssssssssss that counts for something.