The Jimmy Page Sundragon (Supro) Amp- Help!

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ellis2699
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The Jimmy Page Sundragon (Supro) Amp- Help!

Post by ellis2699 »

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).

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

Post by colossal »

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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geoff 1965
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Re: The Jimmy Page Sundragon (Supro) Amp- Help!

Post by geoff 1965 »

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

Post by crgfrench »

I would get on "The JTM Club" Facebook forum and ask Mitch Colby that question directly.
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ellis2699
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Re: The Jimmy Page Sundragon (Supro) Amp- Help!

Post by ellis2699 »

Thanks colossal, geoff 1965, and crgfrench!!!

I've been been pouring through my notes and all of the Mitch Colby articles and reviews that I can find, and I'm no closer to any conclusions than I was a month ago, but I did find one little gem that may hold some secrets...

Mitch gave an interview where he discussed matching the 'drifted' values of the original resistors, after the previous cloning efforts didn't produce the results he was expecting. He seemed quite comfortable and confident while talking about this, which leads me to believe he found something significant here.

We all know the old carbon comp resistors drift higher (usually) over time, and it seems that the more the amp is used, the higher the drift goes. It's pretty safe to say that Jimmy's amp got a lot of use in the ten years (gone) between '59 and '68-'69. I've also noticed that not all of them drift at the same rates, and some don't seem to drift at all (the original 100k plate resistors on my well-used Silvertone 1484 were still within 1%, but the R1 resistors on the input jacks were 40% over!).

I'm thinking that my build needs to include a break-out feature for (at least) the 'influential' resistors in the circuit- maybe a an under-value resistor in series with a low-value pot, or even a 3-way switch with, for example, a 100k, 110k, and 120k resistor setup. Does anyone have any experience with something like this? I've always thought that someone would have done something like this already with an amp clone build, but I've never seen it. I think I would be cool to see how much the drifted values affect the tone in real time. Plus, it may even get me CLOSER to Page's LZ1 tone than the Sundragon amp, as I'm sure the values have continued to drift in the 50 years between the recording session and Mitch's evaluation. Or maybe Mitch has figured that into his amp also? Hmmm...
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Re: The Jimmy Page Sundragon (Supro) Amp- Help!

Post by JMPGuitars »

What you're chasing is certainly interesting in theory. The issue is, as you said, things don't drift consistently. It's next to impossible to guess what went where, and what they decided to change (or not). The variance in resistor value across an amp can change many aspects of the circuit's behavior significantly. If you keep hunting, you might find the correct values. Or you could experiment for yourself and decide on a sound you personally appreciate.
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geoff 1965
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Re: The Jimmy Page Sundragon (Supro) Amp- Help!

Post by geoff 1965 »

i agree with Josh regarding guessing the amount of drift with the composites it would be next to impossible! plus the fact that allen bradley's are not very good for tolerances i've bought new ones that are nearly 20% out of spec. but there are amps that use a variable resistance switch like your idea,Matamp for one and check out the bass shape switch on this blackstar.
Blackstar-Artisan-30.GIF
a point of interest is if Pages amp was a 59 note the stock schematic says the volume pots were swapped to audio taper in 60/61.
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Re: The Jimmy Page Sundragon (Supro) Amp- Help!

Post by Brianmac »

That large a drop in wattage is likely a drop in B+ voltage IMO. There are a number of ways to do that: high wattage resistor on the PT center tap or in the B+ path at the filter caps; zener diode; VVR; or a different PT with lower voltage but enough amperage. Dropping the voltage significantly definitely changes the grind characteristics. My choice would be to install a VVR and experiment to see where I got the tone I liked.
But, I have to say that I am skeptical about all the information about this amp. After seeing and reading JP interviewed many times and stating that it was an amp in the studio that he plugged into and liked, and that he couldn't recall the particulars. Funny how royalties jog the memory.
To my ears, agree its a 6L6 amp, as I have two 6973 Valcos and built another, and none have that tone - but they have a good tone.
Anyways - what you are trying to do is fun - so I encourage you to soldier (or ramble) on.
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Re: The Jimmy Page Sundragon (Supro) Amp- Help!

Post by zaphod_phil »

Welcome back Ellis2699! Hi-ya I too have been away for some considerable time, having had brain surgery for a pretty nasty tumor. Anyway, it's great to be back on the board that showed me the way to awesome amp tone!

As I have an 18wattish bias (sorry for the pun), if I was building a Supro Thunderbolt type amp, I would do so with 6V6 power tubes instead of 6L6, and an 18W OT,with a rebias to lower the dissipation. 6V6s can handle the voltages with no problem.
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Re: The Jimmy Page Sundragon (Supro) Amp- Help!

Post by geoff 1965 »

welcome back ZP! it's good to see someone who has put so much into the forum back.
i think this thread is intriguing and i've just seen how much he sold those 50 limited editions for! $12,500 each! come off it!
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Re: The Jimmy Page Sundragon (Supro) Amp- Help!

Post by geoff 1965 »

Brianmac,
with the 6973 valco's you have and the one you built which have good tone but not the same as the page amp,what value bypass cap do you have on the power tubes? the 1690T schematic shows 25uf but also say's some earlier amps had no cap.
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Re: The Jimmy Page Sundragon (Supro) Amp- Help!

Post by zaphod_phil »

colossal wrote:
Mon 01/13/20 12:59 pm
The Supros are rather odd ducks with their quirky topologies as compared with the usual rehash of Fender, Marshall, Vox stuff.
But if those amps were good for Jimmy Page, they must be alright! :) I tend to think their paraphase PI plays an important part in producing that thick, warm tone.
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Re: The Jimmy Page Sundragon (Supro) Amp- Help!

Post by geoff 1965 »

can you explain a bit more about that phase inverter ZP? imbalance of coupling caps and grid leaks but no grid resistors into the power tubes?
i'm getting obsessed with all the differences on that original schematic.
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Re: The Jimmy Page Sundragon (Supro) Amp- Help!

Post by zaphod_phil »

Where is this schematic, you're referring to? Paraphase PIs can be crudely simple, or else quite complex. I find it challenging to get my head around the latter kind. I like the fact that paraphase PIs generally have poor balance, which helps create warm even-order harmonics. :)
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Re: The Jimmy Page Sundragon (Supro) Amp- Help!

Post by geoff 1965 »

the schematic is early in the thread ZP, the supro 1690T.

download/file.php?id=11869
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