On each tube, the pins are keyed (meaning there is a space between pin 1 and 7 or pin 1 and 9, or in the case of OCTAL TUBES there is a key pin in the middle that only goes in one way. If the markings of the tubes are wore off, and you are missing the markings on the chassis, take a sharpie, and pull each tube (one at a time) and write the tube type on the side). DO THIS WITH THE TUBE COLD! (You wouldn't believe how many people do this with the tube hot and wonder why they got burned!)
Also mark on the tube the position it goes in( v1, V14, etc.). This way you put the tube back in the same socket. very important on the RF/IF tubes (tuner tubes)).
True the EL37 is "A" Euro version of the 6l6. However there are many versions 6l6. The one thing you are going to be looking at is plate dissipation in TRIODE connection of the tube in "PUSH-PULL at whatever plate voltage you have have on the gear.
For example your plate voltage is 450V. Maximum plate dissipation of the EL37 is 25Watts. You want a tube that will dissipate 25watts or more. So you are limited to those 6L6's that dissipate 25 or more watts. So Older 6l6GC, 6l6WGB, 7581a should be ok.
The guy you need to talk to is Jim McShane. His tubes are tested to hell and gone, can match to the nTH degree and is super knowledgeable. He'll get you in a tube that WILL work (no Saleman BS), are matched(not just factory matched for "looks", but matched for Emissions, GM, and damn near everything else that a tube can be tested for, under REAL OPERATING VOLTAGES!), teach you about the stuff you need to know a hell of a lot better than I can about tubes, and won't charge you an arm and a leg. Matter of fact I go to him with questions, and buy my tubes from him. (Very Satified customer). Ask around on AK about him. Bet he gets a better than 99.9999999999999999999999999999999999% rating.
Before you go buying tubes that might be wasted on a unit that possibly doesn't work, lets test the ones you have. They may be perfectly fine. I have some 6l6WGB's that can be used for testing (somewhere around here, let me check my stock, meager as it is). And if the one EL-37 is just loose in the base, I can reset it in the base. But let's get the tubes tested 1st. Until you do that, you don't really know what you have. Testing them before anything else gives you a good baseline, and eliminates them as a or part of the problem. If nothing else the original outputs can be used for testing if they match for sub-type.
Larry
