WHy is that a hack?  That woud be exactly what we would do after a gain stage in a guitar amp to control the amount of signal.  In fact we usually put them on the panel and label them.

D2 and unity inverter U1B with D1 form a full wave rectifier that turns the signal into a DC voltage lightly filtered by C5 as an average signal level indicator.  That voltage in turn runs the FET.  All the FET does is ground off the incoming signal through C2, at least to the extent that it is turned on.  SO you want the FET to turn on earlier - at a lower signal level.  This is not my forte, but looking at it, it seems to me you could massage the value ratio between R4 and R6 to set the operating point of the FET.

Just putzing around with it may have cured its ills.  Speakers cut out because insert jacks and FX return jacks have intermittant cutout contacts - the very resistances we are checking.  But also some extension speaker jacks have cutouts.  And of course back to parts having cracked solder.

The first thing to check is the jacks.  And this will relate to the channel jumping and level shifting as well.

Look at all the jacks inside the amp.  Note how when a plug is inserted, it lifts the little metal contacts up.  Note further than there is an additional contact underneath each upper contact, and the lifted contact normally touches the lower contact when there is no plug inserted.   The upper moving contact and hte lower stationary contact act like a switch.  When no plug is inserted, the "switch" is closed.  If this contact gets electrically dirty, the switch doesn;t close reliably.  This causes varioous problems.

Use your meter set for ohms, and measure resistance between the upper and lower contacts when no plug is inserted.  it should measure less than 1/2 an ohm - 0.5 ohm or less.  if it measures higher, the contacts need cleaning or the jack needs replacing.  If the resistance is low, like 1 or 2 ohms, the circuit will work, but that higher resistance is a sign that the contacts are not pristine, and at some later time that 2 ohms will blossom into 2000.

I usually make these readings from the underside, since the next step is to check the solder under there anyway.  I want to avooid presing down on the moving contact, since that affects the contact resistance.  Probing the solder side avoids this.

Check the solder under each jack, and also under each control along the panel.  Also, there are several large rectangular cement power resistors, check the solder under those.

Please, wean yourself from NTE.   No reason to cross a 2SD613 to NTE, MCM sells real 2SD613 for $1.11 each.  But the 100v 6A transistor is also pretty much the same thing as a TIP41C.  Mouser sells TIP 41C for 40 cents each  The TIP41C has a higher power dissipation that the D613 too.

Yes, check your mains wiring.  make sure hot and neutral are wired correctly and that the third prong goes to chassis and neither of the other two prongs go there.

More likely a bad filter cap or just broken solder to one.

To expand a little bit, "acoustic amplifiers" are really small PA systems.  They are mostly there to amplify a full range signal faithfully.  A guitar amp in contrast is part of the instrument and is intended to color the sound.

A good experiment is to plug your electric guitar into a hone stereo system, or even into a mixer channel input on your band's PA system.  Listen to how it sounds through those full range speakers with tweeters.  it generally sounds thin and tinny.

In short, we don;t put tweeters on guitar amps because nothig we want to hear would come out of them.

Amen, a 250kC30 pot is a 250kC30 pot, regardless of what circuit they stick it in.

fender using up old stock is a quaint notion.  They made and are making endless thousands of Frontman series amps, all using the same parts.  Like most all OEM parts, they order them custom, so if they want 250kC30 pots they call Alps or whoever and order them.   They didn;t turn up in that amp because they were surplus.

The real question to me would be whether you plan to use multiple cabs.

If you use one cab, it can pretty much be whatever you want.  But if you have a 4 ohm cab, it gets difficult to add another.  If you start with 8 ohm speakers, you can add another 8 ohm cab and stil have a 4 ohm load for the amp.  or start with 16, add a 16 for 8.

In fairness, to many of us, the transtube versions of the Peavey amps sound a lot better than the op amp versions.   They don't claim any tubes in there.  The circuits are based upon darlington pairs of transistors for the most part, and they are wired in a fashion to emulate a tube circuit.   No, they don;t sound like tubes.  But they don;t sound like op amps either.

B&D Enterprises says they have the TA7200 in stock for $5.95.  Says it is a Toshiba.

I have always had success buying parts from them, the Sanken power semis I have ordered have always been real, no fakes.


www.bdent.com

Whenever looking for a part, often just googling the part number yields interesting results.  In this case the B&D source, as well as a discussion of subbing the thing., and data sheets.

Some people refer to vacuum tube stuff as "hollow state."

SOlid state basically refers to non-tube stuff.  SOlid state includes transistors as well as integrated circuits.

In a vacuum tube, electrons leave a cathode, and fly through empty space - the vacuum - until they reach the plate of the tube.  In transistors, the electrons flow through solid matter the whole time.

The distinction between transistors and integrated circuits is largely one of semantics, since integrated circuits are really made up of many transistors all in one part.

You will sometimes see an amp or circuit referred to as "hybrid."  That means the circuit includes both tube and transistor circuits.

Power block?  Try these.

The warranty doesn;t care if the amp was a gift.  If the family member has the sales receipt, then your warranty is accessible.  ANY authorized Fender repair center can handle the process, but indeed the original dealer can exchange it.  In this model Fender would want to replace your unit rather than repair it anyway.

Watch out with those assumptions.  he said the problem occurs in the A channel.  Unless he also says the other channel works fine, I can't assume that it does.  A lot of guys only use one channel all the time and will simply report the one used without ever checking the other.  I don;t know that that is the case here, but believe me, I hear it all the time.

"Uh, my lead channel cuts out."  "does the clean channel cut out too?"  "I don't know, I never use it, dude."

Problems are not always bad parts.  The connections between them can cause trouble too.  Electrically dirty switch or relay contacts, cracked solder joints, broken traces, and jack contacts all routinely cause trouble.

To me the large clue is that he can crank the amp up to 9 or 10 and it will pop back into play.  This is the classic description of dirty shunt contacts in an effects loop return jack, and if not that, any of a number of other contact issues.  The increase in signal level is enough to overcome the resistive contact and the circuit comes alive.  That doesn't sound like a bad semiconductor to me.

And be wary of "multiple cap failures."  If the problem still occurs after that cap change, chances are the amp was never really repaired in the first place.  They went inside, changed out a cap, the amp woke up at that time, they assumed the correlation meant causality, and closed it up.  Then a little later the same unrepaired problem resurfaces, and they noodle around some more and solder another cap, etc.

Of course, whatever it is, we'd like to hear the results.