Getting rid off the brittle high end in BF Princeton Reverb???

[Bruce / Mission Amps]

Without re-reading the whole thread.... have you tried a simple cross-cut filter at the output of the phase inverter driver caps?
I would think a 1/2 watt 250K trim pot and a .0022uf to .0047uF cap would be adjustable enough to roll off the 3k5Hz sizzle and more!

[HTH]

If its using a typical Fender tonestack with a 100k slope resistor and 250pF treble cap, try changing the slope resistor to 47k to shave out the high mids and shift the mids down towards the lower mids, this should fatten the sound and roll off some high-mids/treble.

Also, a simple treble roll-off after the tonestack would help here to dump some highs to ground without changing the overall tone of the amp too much. The way Mesa do this works a treat... from treble pot wiper >>> 22k resistor into a 3300pF cap into a 25k pot to ground. The signal from the treble pot wiper to the next stage remains as it is right now.

[kleuck]

Not really, because the input (a tube's grid) is not an inductive and reactive load, first, and second, because harps mics are designed with a high output impedance, to match what a guitar amp "needs" (impedance and level wize)
All the tricks wih the Tonestack won't work either, because it's not (most of the times) a bandpass issue, but an impedance issue, trust me or not, i don't care, but i assure you that you cannot in anyway nail the effect of a zobel with any tonestack variation in the world.
It's pretty obvious : if someone cannot get rid of the harshness with its tonestack - guitar amps TS can always cut highs by a BIG amount- the issue is NOT TS related.

[Chuck H]

All the tricks wih the Tonestack won't work either, because it's not (most of the times) a bandpass issue, but an impedance issue, trust me or not, i don't care, but i assure you that you cannot in anyway nail the effect of a zobel with any tonestack variation in the world.

How is the impedance at an amps input affected by a shunt filter on the PT primary???

[kleuck]

How is the impedance at an amps input affected by a shunt filter on the PT primary???

It can't obviously, hum, did i say that ?

[dai h.]

and second, because harps mics are designed with a high output impedance, to match what a guitar amp "needs" (impedance and level wize)

I looked at a couple of Shure mic (that were listed on a harp oriented site) datasheets, and indeed the intended load seems pretty high (up to around 1M IIRC), so the input loading (lack of damping) might not be an issue.

[tubeswell]

A 5751 can be a good V1 tube for a harp amp because its a bit 'darker' than a 12AX7. A quick and easy sub. JM2CW

[HTH]

Not really, because the input (a tube's grid) is not an inductive and reactive load, first, and second, because harps mics are designed with a high output impedance, to match what a guitar amp "needs" (impedance and level wize)
All the tricks wih the Tonestack won't work either, because it's not (most of the times) a bandpass issue, but an impedance issue, trust me or not, i don't care, but i assure you that you cannot in anyway nail the effect of a zobel with any tonestack variation in the world.
It's pretty obvious : if someone cannot get rid of the harshness with its tonestack - guitar amps TS can always cut highs by a BIG amount- the issue is NOT TS related.

nor did I say you could - I just offered an alternative to try.

the treble rolloff after the tonestack will get rid of any treble harshness with ease.

[kleuck]

If you are thinking of a cap between the anodes of the pi, or a high-cut between the to grids of the power tubes, not always, if the harshness is impedance related, these tricks won't do anything good, or more precisely, won't do anything good before killing all the amp's liveliness.

[R ski]

My preferred method of taming down a brittle amp is locating the feedback resistor that connects to the output tranny to the splitter, start with 500 PF across that component and add more capacitance to tame down those highs

[Steve A.]

Without re-reading the whole thread.... have you tried a simple cross-cut filter at the output of the phase inverter driver caps?
I would think a 1/2 watt 250K trim pot and a .0022uf to .0047uF cap would be adjustable enough to roll off the 3k5Hz sizzle and more!

Yes- a variation on the Vox AC30 Cut control comes in very handy trimming the excess highs. I hadn't thought of using a trim pot- I'd just get my drill out and add another pot... which I would set just once and leave it there.

As for 8 inch speakers, if you want some bass response get an Eminence Beta 8 driver (rated at 225 watts!). I think it is intended for PA or bass cabs but I put in my li'l Kustom Tube 12 and I used it many times playing gigs in small bars. (I put the original speaker back in for playing lap steel, since the Beta 8 wasn't whiny enough... ♪♫♪☺☼°

Steve