Anyone use a 5687 with adapter in place of a 6922/6DJ8/7308/6N23P?

How many of 5687 tubes is used in the equipment. Just one?

You could increase the AH rating of the battery. 

The 5687 draws over twice the heater amps as the 6922 tube.

Did you read the part where it says the glass envelope of the 5687 runs hot. Care must be taken.

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The preamp uses two 6922, one per channel, albeit only one triode per double triode is used.  It's quite remarkable to me that this, what I think is the only audio gain structure of it's kind, generates 16 dB of gain.

Regarding Ah; I've gone to LiFePO4 batteries which upped the Ah from "factory" (read: Gary Dodd's shop) 20 (lead acid) to 24.  The 4 batteries are housed in the preamp chassis, so I think going any higher in Ah would require an external arrangement...at least with current technology, though this technology is advancing rapidly.

The heat, oh yeah, I remember that from amps they used to play in.

I'm disinclined to risk a difficult to find and repair piece of gear without some evidence of previous successful traversals of this trail.  I was hoping someone here would have experience with this particular modification.

I'll stick with experimenting with adaptered versions of the 5670/396a/2C51 family of tubes for which there's an abundance of documented successful traversal.

Thank you for your engagement with my question jea48.

Well I’m wrong again...means I’m learning :)

Can get to 36Ah with onboard batteries:

https://www.ebay.com/itm/335892876560?_trkparms=amclksrc%3DITM%26aid%3D1110013%26algo%3DHOMESPLICE.SIMRXI%26ao%3D1%26asc%3D20201210111452%26meid%3D195dc9e5742a482faf71ed2b9ec5d9c1%26pid%3D101196%26rk%3D1%26rkt%3D12%26sd%3D395846265325%26itm%3D335892876560%26pmt%3D1%26noa%3D0%26pg%3D2332490%26algv%3DSimRXIVIWithAspectRecallAndDiversity&_trksid=p2332490.c101196.m2219&itmprp=cksum%3A335892876560195dc9e5742a482faf71ed2b9ec5d9c1%7Cenc%3AAQAKAAABAOqMkuSAG6ItrRvsdD9sfIOitRvq9S3zkbLwWuQv0VbI6jNBMxuv2D6ql7XdjmAaGt3Ud0drfGP00JE5DWAC%252BxApCW1Ue5GJNG%252BWapf53z0co3ivpjaG0O%252BdAfILHF231AkW7MmKTPuWejC%252BcocjjEHCwp%252F8QgQDYaZz37O9yIdLEoH360%252FqK4m98TOIEfsVP83D36mP%252F1OqFL3bI62KMZFKPV12X%252Fl%252F%252B8SH%252B0SSelS%252FRUZ5P%252FBEqEk1OBuoF8APPwl%252F3sNXp58VVSlo4sk5oTgob5oplAXXdbz5CrJy0Hrqn0omGM%252FU0fTjgVFY5kDPVDiTKuVJxgV2MxP2lWibOZk%253D%7Campid%3APL_CLK%7Cclp%3A2332490&itmmeta=01K4BP7S5THXYM45GKRYBANW11

I’m unclear if adding these would have any effect on the likelihood of success of the contemplated stunt...thinking the circuit controls how much voltage gets to the tubes, not the voltage of the power supply...essentially I’m thinking that the circuit functions as a voltage valve that doesn’t care how much amperage is in the tank as long as it’s enough pass the valve’s design flow.  If correct, I think I’d need to alter the circuit (voltage valve) to pass more voltage to properly excite the 5687,  

I remain happily confused, always indicative of awareness of ignorance...much better than unawareness of ignorance.

Others’ insights welcome.

Gary Dodd’s preamp? You might want to try and speak to someone, tech support if possible, before trying the 5687 tubes in the preamp. 

thinking the circuit controls how much voltage gets to the tubes, not the voltage of the power supply...essentially I’m thinking that the circuit functions as a voltage valve that doesn’t care how much amperage is in the tank as long as it’s enough pass the valve’s design flow. 

 Heater 6.3Vdc voltage should be constant. It should not vary. It may even be regulated. How is the 6.3VDC created? Any idea of the circuit? Voltage divider? If a voltage regulator is used to maintain a constant 6.3 DC voltage, will it handle over twice the current of the two 6922 heaters? The preamp was designed for two 6922 tube heaters. 0.3 amps each tube heater.

Current should pretty much be constant through the heater filament of each tube. Maybe a slight inrush current on a cold start up but settle down to normal quickly. 

Ohms Law is at play. I = E / R

I (current) = E (voltage) / R (Resistance of heater filament) 

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This punk's not feeling lucky 😊.  I'll stick with 6DJ8 and variants and adaptered 5670 and variants.  

Thanks for your input jea48; it helped me make a sane decision.