pre amp tube switching question

[shreder75]

ok, here's one for you...I was talkin' to someone awhile ago and they suggest a certian type of groove tube to put into my pre amp section of my b-52...not to replace all of them, but just to replace on of the existing pre amp tubes with a groove tube in the V5 position....from what I understand, the phase inverter spot is V1 and sits right next to the last power tube...so I guess I just count over till I hit the fifth position?

anywho, there's more...next to the five pre amp tubes there's an additional two 12ax7 that have metal cylinders around them...are those 'extra' tubes or are they the tubes for the reverb and the fx loop?

thanks!

 

[aleclee]

Re: pre amp tube switching question

I dunno if the person you were talking to was doing this but the convention regardging V1, V2, etc. is that V1 is the first tube in your signal chain, not the leftmost or rightmost tube in the chassis. Fortunately, builders generally arrange the tubes in the order in which they appear in the signal chain so according to the convention I describe, V1 is normally the preamp tube closest to the input jack. Typically, V1 is the tube that has the greatest impact on your tone.

I'd be very surprised if those were "extra" tubes. Reverb and FX loop are a good guess.

Have fun with your tube swap. It's a pretty fun way to tweak the tone of an amp.

 

[Scott_F]

Re: pre amp tube switching question

I know nothing abotu a B-52, but you really ought to get a layout sheet or a schematic so you'll know what you're changing. Alec is right though, find V1 and play there first.

On most amps I've messed with, in fact, all amps I've messed with, V1 is the tube furthest away from the power tubes. The phase inverter has always been the tube closest to the power tubes.

What are you trying to do to the tone of this amp? Answer that and we'll all probably chime in on tube replacement suggestions. Also, what power tubes is this amp running, what is the speaker config?

 

[Curly]

Re: pre amp tube switching question

I'm guessing that he was telling you to use a "matched" phase inverter, which would be the slot next to the power tubes.

Some feel (Myles @ guitar amp blueprinting is one) that a matched PI in certain circuits will smooth out your tone, and help any "dead spots" in the harmonics

V1 is the first preamp tube, the one furthest away from the power tubes. That position has the most overall affect on the preamp tone and gain.

 

[aleclee]

Re: pre amp tube switching question

This thread probably has more than you ever wanted to know about balanced phase inverters.

Hogy is the guy who builds Komet amps, splatt is David Torn (a grammy-winning guitar player) and Roccaforte Amps is Doug R., the guy you builds (you guessed it) Roccaforte Amps. There are also a couple of very knowledgeable amp techs posting on that thread.