Hi John K:
My 8" speaker is a Jensen Syntox ceramic, not alnico, Concert Series (click pic to see speaker codes).
[IMG:800:614]http://i142.photobucket.com/albums/r106/capnjuan/jensen8in.jpg[/img]
It came out of a Gibson Maestro GA1RT; it wasn't stock. It sounds fine but not as fine as the Celestion G8L that's in that amp now. More on the amp that it's sitting on in this post below. Yours for shipping au Canada if you choose.
Power Supply: Matsickma is right about the power supply; it needs to be rebuilt from the ground up; caps / power resistor / bias diode and cap if present; any cost savings by just picking at it will be foregone down the road when an original part fails. This is particularly true of the power supply caps; old units either short out or leak acid...either condition can toast everything - whatever you have, they have to go.
Loose 12AX7:
Do not yank it out. Bathe it in electronic contact cleaner - not WD40 which leaves a gunky residue - and gently wiggle it back and forth to break the 'weld' caused by corrosion between at least one pin and its corresponding pin socket. If you mess up and leave one of the pins in the socket, it's a 2-hour bench task to disconnect and drill out the old socket, install a new one, and re-wire it. Depending on rates, that move could cost you $100 by itself.
Plate resistors: The pre-amp tubes operate on high voltage at the plates. The constant exposure to HV over the years will cause the plate resistors to drift in value, sound crappy, and pose a risk to reliability. Each 12AX7 has 2 plate resistors; wired to pins 1 and 6 below:
[IMG:168:168]http://i142.photobucket.com/albums/r106/capnjuan/12AX7schmatic.jpg[/img]
For sound and service reasons, these have to be replaced. The Guild T1 RVT uses metal film resistors everywhere including plates; they are arguably quieter than carbon composition. If you want spunk (Fender, Gibson), use carbon compositions, if you want clean, use metal films.
Multi-section caps: If your amp has at least one smooth aluminum cylinder 1 1/2 to 3 inches high in the general area of the power transformer, then your amp uses the old-style Sprague/Mallory multi-section caps; one section for the outuput plates, others for screens, pre-amp sections as so on.
If you replace these, you'll have to make a decision about whether you want to honor the original design or overcome some of it's commercially-induced limitations. Multi-section caps were a convenience to mfrs; several caps in one package, save space, save time installing and wiring.
Ted Weber makes and sells replacements (scroll to bottom):
https://taweber.powweb.com/store/capord.htm
Unfortunately, the problem with multi-section caps is that capacitance and voltage handling are directly proportional to the physical space consumed by the package; if you want at least one 40uf section (for the output plates), then you are normally limited to two other sections; you can get 4 sections in one package but the largest section might only be 20uf.
There are some new and some NOS multi-sections. NOS means it's been sitting around for some time full of an electrolytic paste similar to what's in a battery. You might want to ask yourself if you'd buy a 40-year old battery.
In addition to smoothing DC ripple, the PS caps provide a resevoir of energy when called upon by both signal amplitude and pitch; if you want more bass and punch in the output, then you'll have to have more capacitance in the power supply than called for in the original design.
Since your amp, thanks to the seller, won't exactly qualify as a 'Mint' or collectible, you'll have to ask yourself whether the objective of your build-back will be to have an original-as-possible copy of the amp or one that is reliable and robust. There is something of an analogy between amps and rehabbing older cars; am I trying to have a faithful copy of something or do I want the amp's circuit to perform at its maximum?
Unless you give the amp back to the seller, you will be the owner of a FrankenGuild anyway. The Jensen speaker in the pic is sitting on an early 1960s Gibson GA18. I re-built its power supply including increased capacitance, NOS one and two watt carbon composition resistors everywhere I could fit them in and NOS carbon comp resistors every place else, new pots, OFHC speaker feeds, fresh lineup of JJs, and a new 10" Weber alnico.
Unlike your amp, mine came in a solid, very fine tweed cabinet. Nevertheless I wanted to give the amp's circuit a chance to perform as well as its design would allow and if that meant wandering away from design intent (principally in power supply capacitance) so be it.
It now does what it was designed to do absolutely beautifully; rock-a-billy, country, vintage R&R, and blues. I don't care if it's not perfectly stock or whether it 'beats' a Fender Princeton; all I care about is how it sounds, whether it's reliable, and if it works to its best ability.
I have no comments on your switching schemes other than to say that you may need to resolve other issues first; are you keeping it? do you want it authentic or enhanced? and, when stabilized, does it generate enough quality signal to justify the effort/cost of additional switching.
Good luck,
JH
