The Jimmy Page Sundragon (Supro) Amp- Help!

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The Jimmy Page Sundragon (Supro) Amp- Help!

Postby ellis2699 » Mon 01/13/20 4:01 am

I'm back on the 18watt boards after being away for a decade or so, and I'm glad to see the site is as busy as ever! I've built a half-dozen amps since my first build in 2005 (Graydon's GDS 18 Watt Tremolo kit), but I'm still obsessed with trying to build an accurate replica of Jimmy Page's mysterious, mystical, mythical Supro amp.

I've researched the hell out of this amp, weeding through countless 'facts', made-up stories, and falsehoods, and had reluctantly concluded that it was probably a late-'50s Supro Coronado with a replacement (radio/hifi?) 12" speaker. I knew it was NOT a Thunderbolt, Dual-Tone, Model 24, Trojan, Super, or any 6973-based amp.

It turns out I wasn't too far off (except for the speaker). The new Sundragon amp seems to nail the LZ1 and pre-Led Zeppelin tone, and it was reverse-engineered from Jimmy's actual Supro, which Jimmy has confirmed was THE amp on those early recordings. Here are the specs that the amp's engineer (Mitch Colby) somewhat reluctantly revealed during interviews at the 2019 NAMM Show, and later discussed in Guitar Player Magazine-

- 1959 Supro Coronado
- One 12" Oxford Speaker w/ PulseSonic cone
- American 6L6 tubes
- British ECC83/12AX7 tubes
- Original Transformers
- Repairs (mods?) by a 'creative' amp tech that used what he had laying around to "make it work".
- The repairs/mods changed the output from "about 20 watts to 8 watts clean". THIS IS WHERE I NEED YOUR HELP!

What kinds of repairs would have been required after an amp falls out of a van? I get that the speakers and tubes were replaced, and maybe a few pots, but what kind of repair/mod would cause the output of a pair of 6L6 tubes to put out 4 'clean' watts each?

I'm guessing they measured the clean 8 watts at the speakers during their output test, so that doesn't rule out a possible impedance mismatch between the original 8 ohm OT and an improvised (maybe 4 or 16 ohm, but likely an 8 ohm) speaker, but could 8 ohms into 4 ohms, or 8 ohms into 16 ohms cause a 60% cut to the output?

Or maybe some internal components were damaged when the amp fell, but I don't know- those old Supros were very well-built, and I can't see a resistor or capacitor being damaged from a physical blow to the cabinet from a drop, other than the large-ish 250 ohm, 7 watt cathode bias resistor. If the 1960 amp tech substituted a larger value here, would that lower the output by 60%?

I'd love to hear what you guys think! I can't afford the $3875 to buy the real Sundragon amp, and I really doubt Mitch Colby would agree to send me a schematic (and I wouldn't dare ask).

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Re: The Jimmy Page Sundragon (Supro) Amp- Help!

Postby colossal » Mon 01/13/20 12:59 pm

Nice work on all the diligence. Would you be able to post a schematic that is "close enough" as a baseline to get some discussion going? There are some ways to reduce the output significantly to fit those numbers. As far as the falling-off-the-back-of-the-van story, I agree, the amp was probably fine and the cabinet took the majority of the abuse. Im sure it trashed the baffle board so it was a good time to put a 12" speaker in. As far as the mod "to make it work" and some of the language around the amp seems to be obfuscation. The Supros are rather odd ducks with their quirky topologies as compared with the usual rehash of Fender, Marshall, Vox stuff.
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Re: The Jimmy Page Sundragon (Supro) Amp- Help!

Postby geoff 1965 » Mon 01/13/20 1:05 pm

here's the "stock" schematic
Supro 1690T.pdf
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Re: The Jimmy Page Sundragon (Supro) Amp- Help!

Postby crgfrench » Mon 01/13/20 7:37 pm

I would get on "The JTM Club" Facebook forum and ask Mitch Colby that question directly.
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