help valuing parts from 1971 Fender Twin Reverb.

[mikepukmel]

With the full B+ on those wires that would be definitely the wrong way to go about it. I use a DPDT toggle, and steal the hole where the "ground" switch is to mount it.

The handful of schematics I found on a quick search, e.g.:
http://mhuss.com/SmallBox/1987.gif

used the same resistor prop. soldered to the pin on pin4, so either the plate, or B+ (2) would go through the resistor to the screen grid. But this is a "marshal" like schematic. they used a 1K 1W. For the twin case, is it 'close enough for folk music' to have either side go through the same 4701W? (I think I have a bunch of 470 2W on hand) Or should the resistor on pin4 be different for the two cases, i.e. 470 for screen grid to B+ something else for screen grid to plate?

[mikepukmel]

Well, yes, exactly that.
Only you drill a hole in the back panel and add a switch to do the wire swapping thingie.

Leave the dangling wires, 2 prong mains plug, death cap and original swelling caps to those who want to "keep collector value" .... whatever that means

This one's a junker so I'm not worried about collector value. It will never be a museum piece. (There's a pre-cbs version of this amp, a "real" original blackface for sale in our area, asking 3800, has been for sale forever, and ever, and ever and ever ...)

[mikepukmel]

Ohh, important question: is the reason that the guy used a 5W on pin4

http://mhuss.com/SmallBox/1987.gif

because its switchable, and on one switch position where the screen grid goes to the plate, more current flows through than if it only went to B+ (2)?

[Justin Thomas]

While I don't think Twin Reverbs are as low in value as many may think (just takes the right buyer in the right spot at the right time), $3800 for a 63/64 TR is a bit heinous. Maybe a white Twin or a Tweed Twin, but not a BF.

Justin

[Enzo]

Amps are worth whatever someone will pay for them, no more, no less. If I ask $10,000 for something and a guy ponies up the 10k, then it is worth $10k.

[The Dude]

Ok. Call me silly, but the idea seems a bit counterproductive. I'm not trying to be a critical a$$, but this:

We want to make a low wattage, lighter, smaller amp so we start with large/heavy iron from a 100W amp and bang the wattage down via triode configuration or other methods? Again, I'm not trying to be argumentative, but transformers are some of the heaviest parts of the amp. It would seem a better idea to just use smaller transformers if the goal is as stated.

[J M Fahey]

True, just that it looks like today´s menu is "beater but repairable" Twin hardware and apparently it won´t be moved much if at all.
In that case $150/200 for a set of iron, chassis, cabinet and speaker looks interesting.
Almost forgot: killer reverb.

Only problem is it´s too loud.

Personally I hate triode-pentode switches because they knock perceived power very little and they kill bite and punch very much but being an experimental amp there´s many other options, from the variable +V thingie which can tame large amps down to whisper levels to some tasty PPIMV (which shine in "clean" amps such as Fender) to .... gulp!!! ..... some kind of attenuator.

Many fine ways to keep owner-tweaker happily busy ... which I guess is some of the justification behind it

[mikepukmel]

Ok. Call me silly, but the idea seems a bit counterproductive. I'm not trying to be a critical a$$, but this:

We want to make a low wattage, lighter, smaller amp so we start with large/heavy iron from a 100W amp and bang the wattage down via triode configuration or other methods? Again, I'm not trying to be argumentative, but transformers are some of the heaviest parts of the amp. It would seem a better idea to just use smaller transformers if the goal is as stated.

Well, for some, but for me: I don't care about the weight, or the size, a tank is fine. I only need a way to switch to lower power, but if I cant do that, I have a set of those big aircraft mechanic hearing protectors.

[mikepukmel]

True, just that it looks like today´s menu is "beater but repairable" Twin hardware and apparently it won´t be moved much if at all.
In that case $150/200 for a set of iron, chassis, cabinet and speaker looks interesting.
Almost forgot: killer reverb.

Only problem is it´s too loud.

Personally I hate triode-pentode switches because they knock perceived power very little and they kill bite and punch very much but being an experimental amp there´s many other options, from the variable +V thingie which can tame large amps down to whisper levels to some tasty PPIMV (which shine in "clean" amps such as Fender) to .... gulp!!! ..... some kind of attenuator.

Many fine ways to keep owner-tweaker happily busy ... which I guess is some of the justification behind it

Thanks, Ive never run a tube amp with pentode/triode switching. Well, Ive talked to a few people about attenuators and most folks hate them. But not completely against one.

[Justin Thomas]

Only problem is it´s too loud... many other options...

Pansies... (Not you, Juan! The "guys in charge")
My two cents: make the amp work as designed. I've got a variety of amps, from 15 to 100W, I live in a connected house on main street in a "city," and I live with 14 other people in the house. I somehow am able to find a way to get my big ones up about 5 or 6 or sometimes 10...

I'd pull two power tubes and disconnect a speaker (and only "maybe" on the speaker) and leave it at that. Eventually, you'll get to a bigger room and you'll want an amp that can push air. And if your options really ARE "lower power or hearing protectors," just let the Twin be a GLORIOUS Twin and wear hearing protection. All my opinion, of course...

Justin

[Enzo]

I think you are not looking for lower power, I think you are looking for lower volume. They are not the same thing.

[g1]

Ohh, important question: is the reason that the guy used a 5W on pin4

http://mhuss.com/SmallBox/1987.gif

because its switchable, and on one switch position where the screen grid goes to the plate, more current flows through than if it only went to B+ (2)?

1K5W is pretty much the standard Marshall screen resistor, the amp in the example is based on a Marshall.

[The Dude]

Well, for some, but for me: I don't care about the weight, or the size, a tank is fine. I only need a way to switch to lower power, but if I cant do that, I have a set of those big aircraft mechanic hearing protectors.

Oh, sorry. I got the impression from reading your post #6 that you wanted something smaller and lighter. At any rate, I wasn't trying to be all uppity. I just (apparently) misunderstood the intent of the build.

[mikepukmel]

Oh, sorry. I got the impression from reading your post #6 that you wanted something smaller and lighter. At any rate, I wasn't trying to be all uppity. I just (apparently) misunderstood the intent of the build.

I didn't take it that way. You guys are awesome.

I got some more photos of one of the twin reverb's for sale, and its way too nice to tear up. Im going to put in an offer, and just fix whatever small stuff needs and leave it stock. I don't have the heart to tear it up.

[Leo_Gnardo]

its way too nice to tear up. Im going to put in an offer, and just fix whatever small stuff needs and leave it stock. I don't have the heart to tear it up.

Stock or try a couple of the "stealth" mods that don't change its appearance but do make it more versatile: change norm channel's tone stack, send both chan's to reverb & vibrato. And try the triode mod. Juan's not much a fan of it I know, but I have a number of customers who like it just fine. It's cheap and fast enough to do, then at least you'll know what it does and judge for yourself.