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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colossal
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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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kingamps
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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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