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

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) 

.

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.

Heater current aside, the 5687 is a drastically different tube, with half the gain of a 6922 and designed to run at much higher current.  I can't imagine it would be a suitable drop-in for a 6922.  There's no way to calculate how it would operate in your preamp without knowing the circuit involved.