The Jimmy Page Sundragon (Supro) Amp- Help!

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

Post by colossal »

For what it's worth, the output transformer appears to be a custom wound 8ohm Classictone with part number 40-17694 and the PT is Classictone 40-17695.
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geoff 1965
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Re: The Jimmy Page Sundragon (Supro) Amp- Help!

Post by geoff 1965 »

002.JPG
this is my 6V6 project,hammond 1750PA and the valvepower PT i removed from my lite2 HT 312-0-312 loaded which i've diode rectified with a 22R sag. so potentially it's in the ballpark for this sundragon, i'm watching this thread and people's ideas like a hawk!
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Re: The Jimmy Page Sundragon (Supro) Amp- Help!

Post by colossal »

Looks great so far! 8)
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fernieite
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Re: The Jimmy Page Sundragon (Supro) Amp- Help!

Post by fernieite »

I don't know if it'll help, but if any of you know LeonC on the Gear Page and other forums, he really knows the old Supros and may have some suggestions. Terry Dobbs as well.
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Janalex
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Re: The Jimmy Page Sundragon (Supro) Amp- Help!

Post by Janalex »

Hi all,

Just joined this forum after finding this interesting thread while researching the Sundragon. I too love the LZ 1 tone and upon seeing the rock and roll hall of fame amp did some research on the old Supros and purchased a 1615T from the late 50s. This amp has an identical circuit compared to the Coronado only it outputs into a single 15” speaker. As expected I quickly learned that it did not have nearly enough distortion to approximate the Page tone although it’s lovely edge of breakup tone and tremolo made it to a few of my recordings. When the sundragon came out I came to all the same conclusions as listed in the first post. I was never going to recone an Oxford with a pulsonic in this lifetime and believing Colbys test results with the Jensen alnico compared to 40 other speakers, I installed a baffle adapter and a modern jensen carefully removing the original p15p. Still sounds great but as expected not the zeppelin tone.

I proceeded to contact Mitch who I met on one occasion to see if I could get more info out of him but unfortunately I couldn’t learn anything new that would help us only that there are some vague minor differences in the circuit.

The first place to start would be to change my output transformer to the Coronado output transformer which I believe measures in the 2 ohm range. This impedance mismatch from 8 to 2 will surely decrease output and increase distortion. The sundragon reaches its full output level almost immediately and then just gets more distorted and bassy as dialed further up and I attribute this in large part to the mismatch. The best I could recommend with regards to the circuit changes is to wait and for hope for some more info from an owner after the release of the second run of the amps but without the correct transformers it’s a nonstarter.

I have already reached out to classic tones who happen to be the original manufacturers of the supro transformers but they tell me these part numbers are proprietary. Maybe someone else will have better luck.

If I could be if any further assistance in this quest let me know how I can help. I will continue to share any info I gain and hope we can all figure this out collectively.

Jan

Janeubig@gmail.com
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geoff 1965
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Re: The Jimmy Page Sundragon (Supro) Amp- Help!

Post by geoff 1965 »

Sundragon STD manual V1.pdf
suprised to see 6L6GC's "30W max PD" in this! i thought with 8 watts clean before breakup and 20W full on they would have used 6L6GB's "23W max PD". what dissipation do you think he's biased them to?
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Re: The Jimmy Page Sundragon (Supro) Amp- Help!

Post by kingamps »

I just made a few measurements of a Sundragon's GE 6L6GC output tubes, wondering whether they were oddly biased for very little headroom. At the tube sockets, with the 6L6GCs in place, I measured:

* Cathode resistor (the 6l6GCs share a common cathode resistor): 252 ohms
* Pin 3 to ground (B+ at the 6L6GC plates): 385Vdc in Standby, 388Vdc with amp On.
* Cathode current (one 6L6GC): 52.8ma in Standby, 48.7ma with amp On.
* Calculated cathode bias (6L6GC cathodes to ground, amp On): 24.5Vdc
* Calculated cathode-to-plate voltage, amp On: 363Vdc
* Calculated plate dissipation, amp On: 17.7W per tube

The Standby switch shorts together the outputs from the phase inverter plates, so the output tubes are always drawing current - my Gretsch 6154 (built by Valco) does the same thing. Since the 6L6GC plate voltage and current draw are slightly larger with the amp off Standby, I'm guessing something minor is happening to the 6L6 operating points with their grids connected together and floating from ground in Standby.

The answer to my original question is the tubes are cathode biased to run cool (70% of max dissipation). Normally, cathode biased tubes in a guitar amp are running at close to max plate dissipation and often more, while the "biasing rule of thumb" says they should run at 90%. Regardless, this Sundragon's 6L6GCs are running at a cool 70%. It explains why the Sundragon does not compress like a tweed Deluxe when pushed and suggests the Sundragon's distortion is in the preamp.
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geoff 1965
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Re: The Jimmy Page Sundragon (Supro) Amp- Help!

Post by geoff 1965 »

are the couplers from the phase to power tubes mis-matched like the supro? also the notes on the supro schematic say some did'nt have a bias capacitor on the power tubes,is there one on the sundragon?
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Re: The Jimmy Page Sundragon (Supro) Amp- Help!

Post by ellis2699 »

Holy smokes!! I've been away from the forum taking care of some life stuff and I'm very happy to come back and see so many of you contributing to this thread!

Lots of great new information since I last checked, especially the goodies from Kingamps- thanks for the bias and voltage information! I think that 'cool bias' and standby switch setup are good clues- my Silvertone 1484 has a standby switch like that (which I replaced with a 1M pot for a poor man's master volume), but I can get surprisingly decent LZ1 tones out of that amp (blasphemy?) which also has a 'cold' ~75% bias on the 6L6s, but different bias circuitry. I'm also wondering if there's a 25uf cathode bypass cap in parallel to the cathode resistor on the Sundragon amps (like on later Supro 1690Ts).

Your comment on the preamp crunch also had me looking around at the schematic for clues, but maybe the biggest clue was in the Sundragon user manual (thanks Geoff 1965!) which has an interesting note under the Tone Control section that states...

"The Tone Control is quite effective. Turning it up (clockwise) adds high frequencies and because it is so effective, it also adds gain for more overdrive."

Why would a passive tone control ADD high frequencies instead of attenuate low and mid frequencies? And why would it ADD gain instead of just sort of recovering it? Mitch would certainly know this, and I'm sure he wouldn't allow that to be printed if it was a mistake.

And here's the best clue from the user manual just below the Tone Control section...

"Note: Because Sundragon has 2 inputs per channel that are voiced differently, the inputs are “open”. The result is that when nothing is plugged into the amp, you will hear background noise when you turn up either Volume control. While this is not the case on some amplifiers, this is normal for Sundragon."

What?! The inputs aren't "open" on the 1690T schematic. According to the schematic there are two switched input jacks in circuit with the two non-switching jacks, which wouldn't cause noise when you turn up the amp with nothing plugged in. Why would Sundragon do this on purpose? Could this suggest that the inputs are wired up in a weird way, maybe to use both sections of the V1 12AX7 in parallel without an external cable jumper? I know you can jumper two channels with or without switching jacks, but I think there's something funny going on here. And from what I understand, the Sundragon amp still has tremolo, so they didn't steal the tremolo section of V2 to add gain.

Also, welcome back ZP! And welcome to the forum, Janalex! Your comment about the OT to speaker mismatch is a good one, and I think has a lot to do with the lo-fi (but thick and juicy!) tone. 2 ohms into a single 8 ohm speaker is not efficient at all but it doesn't mean it can't be fun!

Thanks all, and I can't wait to hear about what you make of these new 'clues'! If we keep this up, we'll all have faithful clones of the faithful clone of Jimmy's Supro... which will sound nothing like Jimmy's Supro. Ha!
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geoff 1965
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Re: The Jimmy Page Sundragon (Supro) Amp- Help!

Post by geoff 1965 »

Check out the reviews of the Supro 1695T as well,it’s supro’s take of the page amp except using 6973 output tubes.they have a parallel link between the channels which lets you use both volume controls for the extra gain.
the tone might be similar to the 18W lite2 which interacts the volume & tone pot and the tone has an effect on volume rather than the normal type tone wiper to ground configuration.
another point regarding gain is look at the 1690T schematic notes on the V2b variant with 220K & 2K2 “very aggressive”
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Re: The Jimmy Page Sundragon (Supro) Amp- Help!

Post by crgfrench »

colossal wrote:
Mon 03/16/20 1:51 pm
For what it's worth, the output transformer appears to be a custom wound 8ohm Classictone with part number 40-17694 and the PT is Classictone 40-17695.
It's a shame only the specs for the 40-180xx series seem to be publicly available. Any idea where to find the datasheet for those?
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Re: The Jimmy Page Sundragon (Supro) Amp- Help!

Post by lovestone »

kingamps wrote:
Sun 01/17/21 6:40 pm
I just made a few measurements of a Sundragon's GE 6L6GC output tubes, wondering whether they were oddly biased for very little headroom. At the tube sockets, with the 6L6GCs in place, I measured:

* Cathode resistor (the 6l6GCs share a common cathode resistor): 252 ohms
* Pin 3 to ground (B+ at the 6L6GC plates): 385Vdc in Standby, 388Vdc with amp On.
* Cathode current (one 6L6GC): 52.8ma in Standby, 48.7ma with amp On.
* Calculated cathode bias (6L6GC cathodes to ground, amp On): 24.5Vdc
* Calculated cathode-to-plate voltage, amp On: 363Vdc
* Calculated plate dissipation, amp On: 17.7W per tube

The Standby switch shorts together the outputs from the phase inverter plates, so the output tubes are always drawing current - my Gretsch 6154 (built by Valco) does the same thing. Since the 6L6GC plate voltage and current draw are slightly larger with the amp off Standby, I'm guessing something minor is happening to the 6L6 operating points with their grids connected together and floating from ground in Standby.

The answer to my original question is the tubes are cathode biased to run cool (70% of max dissipation). Normally, cathode biased tubes in a guitar amp are running at close to max plate dissipation and often more, while the "biasing rule of thumb" says they should run at 90%. Regardless, this Sundragon's 6L6GCs are running at a cool 70%. It explains why the Sundragon does not compress like a tweed Deluxe when pushed and suggests the Sundragon's distortion is in the preamp.
Any chance of a few images of the inside of the chassis?
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Re: The Jimmy Page Sundragon (Supro) Amp- Help!

Post by TriodeLuvr »

kingamps wrote:
Sun 01/17/21 6:40 pm
I'm guessing something minor is happening to the 6L6 operating points with their grids connected together and floating from ground in Standby.
The grids of power tubes should never be allowed to float. Are you sure that's really how it's wired? I would expect bias current to be all over the place in Standby if that's the case.

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

Post by Eulipian »

FWIW, Supro 1690t schematic from Hoffman Forum with notes re similarities to 1615, specifically noting the under powered OT.
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