What preamp tube dominates the tone chain?

[Leo_Gnardo]

What are Jet City Retrovalves? Solid state tube replacements? Well give it a try & let us know what ya think. Late 70's Mesa sent out some of their amp with Fetrons - the SS tube replacement of the time in a metal cylinder riding a 9-pin plug-in header.

So where does the power go when you drop ~200V to 12-24V? Would these things glow red like a toaster?

When Mesa was equipping their (I guess) MkII with Fetrons, there was a toggle switch on the bottom of the chassis that selected the voltage supply they would run on. If I recall at all @ 240V for tubes and @ 180V for Fetrons, not all that much of a difference - and that's the voltage at the "high" end of the plate resistors. I guess they used FET's specified for hi voltage use or crammed even more resistors inside the Fetron tube. The Fetrons did not noticeably heat up.

Glow red like a toaster? Heck you can get those Estonian flash memory tubes and glow any color you want like kids' cereal, Razzberry Red, Goofy Grape, Orange Orange, Mutant Chinchilla Blue, Seasick Green, Jaundice Yellow. Now if we could only put those memory chips to good use, playing incredible licks while the "musician" just poses... that'd be for me!

[EtherealWidow]

It's a cool idea, kind of, but they can't do DC coupling as cool as tubes can

[M Fowler]

These little tubes replacements look cheesy and I really wasn't interested in trying them. Miles yes I am a lazy bastard indeed.

[rp]

Without heat.. it has a little power resistor and a tiny current demand

But ss runs on 12-24V, how do they get that from a plate voltage of 150-300V? Or do they just block that and run if off the heater? But then how do they pass signal btwn the stages?

[vibratoking]

I have no idea what the design is, but I doubt they're dropping voltage without heat. Physics applies. My guess is they run cooler cause they don't have a heater.

FETs are available that can handle high voltage.

[rp]

I guess they used FET's specified for hi voltage use or crammed even more resistors inside the Fetron tube. The Fetrons did not noticeably heat up.

Ok that makes more sense. I can see designing for them like Mesa did. I'm not sure what those jet city things really are, must you just use then in a JC dedicated amp or can you stick them in any amp? Looks like the latter.

BTW all this begs the question, with a little patience you can get a really nice SS amp like a Roland Cube or the Smaller Jazz Chorus or a zillion others like Vox etc off Craigslist for like $50-$100. Why try and turn your tube amp into a SS amp? I know, I'm a party pooper.

[Firestorm]

I have no idea what the design is, but I doubt they're dropping voltage without heat. Physics applies. My guess is they run cooler cause they don't have a heater.

FETs are available that can handle high voltage.

That's gotta be it. If they dropped voltage, it would likely mess up the signal swing and they want them to be drop-in replacements. I wonder if the LEDs (I assume) are run off the heater supply. Ideally you'd want some kind of network in there in case the heaters were wired in series (there are a few semi-modern amps that do that).

[Reeltarded]

Why try and turn your tube amp into a SS amp? I know, I'm a party pooper.

Shudup

[stephenl]

An LND150 (depletion mosfet) can drop in as a tube replacement quite readily. It sounds good in the first position - very low noise. I used one as a cathodyne PI and it was very well behaved. I wouldn't use it as a gain stage subject to being overdriven though.

[Bob S]

Wow...
On the OP's question the simple answer is a 60's Mullard ECC83 in V1.
Anyone who disagrees can donate their Mullards to me.
Anytime.

[Reeltarded]

I'll take the ones that read low!!

Seriously, if you guys have any that aren't up to your 160% stadards I'll take all the low 100%ers!

[Leo_Gnardo]

An LND150 (depletion mosfet) can drop in as a tube replacement quite readily. It sounds good in the first position - very low noise. I used one as a cathodyne PI and it was very well behaved. I wouldn't use it as a gain stage subject to being overdriven though.

Thanks for this stephenl - very interesting!

Hey, I know where Marlborough is - you got that tiny airport there. Right next to Sudbury. If things go right I'll be visiting cousins in that area for Thanksgiving. Nice area.

[stephenl]

Hey, I know where Marlborough is - you got that tiny airport there. Right next to Sudbury. If things go right I'll be visiting cousins in that area for Thanksgiving. Nice area.

Heh, we live up off of Farm Rd about a mile from the airport. It is tiny, just single engine and small helicopters, I think.

[roberto]

Yes, they are LND150 and just a led for the heaters.
I use LND for CF in clean amps when I need low impedance on the outlet, but mainly for Fx Loops. They are pretty perfect.

European Store Tube Town sells some kits for it:
https://www.tube-town.net/ttstore/produ ... ND150.html

http://new.diyitalia.eu/forum/download/file.php?id=6985

[JazzGuitarGimp]

An LND150 (depletion mosfet) can drop in as a tube replacement quite readily. It sounds good in the first position - very low noise. I used one as a cathodyne PI and it was very well behaved. I wouldn't use it as a gain stage subject to being overdriven though.

Hey Steve,

How much gain can be expected from this circuit? I looked at the LND150 datasheet, but I'm not seeing an indication of gain.

Thanks,
Lou