The Coppertone Saga Continues...

[Gerry Rzeppa]

Forgive me, guys, but I was forced by circumstances beyond my control to use microscopic valves in this one. I did, however, manage to include seven very large "tubes"!

[lord preset]

Yep, those are indeed big tubes.

[xtian]

Jeez Christo, we've got ourselves a poet. Or a jester Seuss. That was a spank dandy missive, Gerry.

Where's the auction?

[Gerry Rzeppa]

Jeez Christo, we've got ourselves a poet. Or a jester Seuss. That was a spank dandy missive, Gerry. Where's the auction?

Thanks for the encouragement, xtian. The auction, together with more (and better) pictures of the finished Model T ("T" for "tubes"), is here:

http://www.ebay.com/itm/171379737587

We're very curious to see what happens with it.

In the meantime, I'm wondering where to go from here...

Technical question that might affect the answer but will definitely reveal my inexperience in all things tubular: I've noticed a couple of things studying various tube schematics: (1) the power supplies always step-down the voltage with resistors to feed the various stages; and (2) different kinds of tubes are typically used for the pre-amp and power-amp stages. Now (elaborately ornate Coppertone amps notwithstanding) I'm a minimalist at heart and was wondering: would it be possible to configure an amp using just a single voltage throughout, with the same kind of tubes throughout? The AA764, for example, with everything at 360 volts and a couple of 6V6s in the pre-amp stages instead of the 12AX7s? Perhaps even configure a 6V6 as a rectifier as well?

[Leo_Gnardo]

I've noticed a couple of things studying various tube schematics: (1) the power supplies always step-down the voltage with resistors to feed the various stages; and (2) different kinds of tubes are typically used for the pre-amp and power-amp stages. Now (elaborately ornate Coppertone amps notwithstanding) I'm a minimalist at heart and was wondering: would it be possible to configure an amp using just a single voltage throughout, with the same kind of tubes throughout? The AA764, for example, with everything at 360 volts and a couple of 6V6s in the pre-amp stages instead of the 12AX7s? Perhaps even configure a 6V6 as a rectifier as well?

If there wasn't some RC "decoupling" between the amp stages in the power supply, then the PS would become a feedback route. No telling what kind of howling, shrieking and rumbling would ensue. I "suppose" you could build several parallel power supplies, each one serving a different stage but that doesn't feed the simplification idea very well does it.

As for all the same tubes, power tubes don't have much voltage gain, a tenth at best what pre tubes do. You'd have to string up a couple extra 6V6 or whatever. Not a simplification move. At the power amp end, there is some hope though. There's a very interesting amp invented by a fellow on Maui who goes by the screen name of Poindexter on Audio Asylum. He uses a pair of 6AQ5 as the front end of an amp with a pair of 6V6 outputs. Seeing as the 6AQ5 is a "miniaturized" 6V6, I suppose one could build that amp with all 6AQ5 or all 6V6. You'll have to search the AA website - the schematic is there somewhere. I hope Poinz is OK - havent' seen him post AA for a year or two. His regular job is building custom yachts. Could be he's concentrating on that.

[xtian]

There are plenty of folks who went before you, following the route of simplification (and, really, lowering costs as much as possible). There are some neat push-pull designs using only three glass packages (twin-triode for preamp, combination triode-pentode for PI/power), but you can't reduce parts counts enough to make any improvements in costs for the power supply. You CAN spend way less on capacitors by buying radial instead of axial, and of course, buying in bulk (or having the whole damn thing mass produced in Asia). And the least expensive parts are always salvage, used, or lucky finds.

If you want to continue your hobby, I'd just advise patience--don't be in such a hurry to sell at auction. Set a fixed price and let the listing serve as advertisement. Build yourself some nice web pages that collect your work. I was thinking how the execs of Silicon Valley, for example, would love to have your work in their corner offices to sit next to their 50s Gretsch white penguins.

Just rambling.

[Gerry Rzeppa]

If there wasn't some RC "decoupling" between the amp stages in the power supply, then the PS would become a feedback route. No telling what kind of howling, shrieking and rumbling would ensue... As for all the same tubes, power tubes don't have much voltage gain, a tenth at best what pre tubes do...

Thanks, Leo. Very helpful info.

There's a very interesting amp invented by a fellow on Maui who goes by the screen name of Poindexter on Audio Asylum. He uses a pair of 6AQ5 as the front end of an amp with a pair of 6V6 outputs. Seeing as the 6AQ5 is a "miniaturized" 6V6, I suppose one could build that amp with all 6AQ5 or all 6V6. You'll have to search the AA website - the schematic is there somewhere.

Found some interesting posts on the subject, but the schematic was elusive. Thanks anyway. Every little bit helps.

[Gerry Rzeppa]

There are plenty of folks who went before you, following the route of simplification (and, really, lowering costs as much as possible).

Indeed. That's why I went with the Leo's tried-and-true 5c1 on the previous Coppertone. No sense re-inventing the wheel. But it's not just low-cost I'm interested in -- it's conceptual simplicity; something that can be explained to a first-time kit builder.

There are some neat push-pull designs using only three glass packages (twin-triode for preamp, combination triode-pentode for PI/power)...

Combo tubes may lower the part count, but they don't give me the conceptual simplicity that I'm looking for; they essentially cram two stages into one package and that's the opposite of what I want.

...but you can't reduce parts counts enough to make any improvements in costs for the power supply. You CAN spend way less on capacitors by buying radial instead of axial...

I have to admit I like the idea of radial caps, including those multiple-cap "cans", though that's the opposite of what I said about tubes just above!

...and of course, buying in bulk...

We will be buying in bulk eventually...

(or having the whole damn thing mass produced in Asia)...

...but I'm not real big on long-distance relationships.

And the least expensive parts are always salvage, used, or lucky finds.

That won't do for this project; the thing has to be repeatable, mass-producible.

If you want to continue your hobby, I'd just advise patience--don't be in such a hurry to sell at auction. Set a fixed price and let the listing serve as advertisement. Build yourself some nice web pages that collect your work. I was thinking how the execs of Silicon Valley, for example, would love to have your work in their corner offices to sit next to their 50s Gretsch white penguins.

Yes, I could see a very-high-priced Coppertone (with more care in the craftsmanship) sitting next to a Gretsch White Penguin in some rich guy's office; but that's not the audience I'm aiming at. I'm thinking of thousands of not-so-rich kids and other first-time amp builders creating something from an inexpensive kit that's not only useful but beautiful and unique as well; I'd like to put the extraordinary within the reach of those who think they're destined to be nothing more than ordinary.

So there is a method in my eBay madness: I need to see for myself what is (a) easy to understand, (b) easy to construct, (c) easy on the eye, (d) easy on the ears, and (e) what "pops" in the "street market". And thus I'm investing my R&D budget in wild and crazy ideas and ten-day auctions with $1 starting bids. Product development and market research combined.

Once I've found a suitable partner for this endeavor, and we manage to design, construct, and sell a suitable prototype, we'll take it all to KickStarter and get some capital for those volume purchases mentioned above. In the meantime, here are some photos of previous Coppertone prototypes in "no-solder, screwdriver and glue" kit form for us all to dream about...