Airline 9013A Heater Circuit

[bmccowan]

I recently opened up a Danelectro built Airline 9013A. Its very similar to the Silvertone 1472 and 1482 - inputs differ, as does the heater circuit.
I could not find a fully readable 9013A schematic - and it seems many have looked. So I went through the amp and modified one I had for the 1482. The original blurry one and my redraw are attached.
Question - what is up with that heater circuit? An artificial center tap that uses the pilot lamp from one side to ground, and a 2.2 ohm resister to ground on the other side. No other Dano seems to have this circuit. And it seems like a decidedly bad idea. I plan to redo the center tap with a pair of resistors in the 50-100 ohm range and run the pair to the pilot light. Any issue? And why did Dannyboy do this? so that Monty Wards could beat the Sears price by 50 cents?
Also, the two channels are identical - so I'll be juicing one with a bypass cap and maybe other stuff.
If no errors are found in my redrawn schematic, I'll post it in that section. 

[Platefire]

I didn't notice anything on your new schematic other than a disconnected wire.

My question on the 9013A is did all of them have the lower voltages like the 1472 or did a one point get upgraded to the highervoltages/transformer same as the 1482?

[AlNewman]

I did an amp with a 6x5 rectifier, not sure how similar they are to the 6x4, but I know the 6x5 was fairly unreliable, where they would develop shorts from plate to cathode.  They used lamps as fuses in certain parts of the circuit (sometimes 2 lamps off the plates) to protect the transformer.  Perhaps this is some version of that.

[bmccowan]

I didn't notice anything on your new schematic other than a disconnected wire.
My question on the 9013A is did all of them have the lower voltages like the 1472 or did a one point get upgraded to the higher voltages/transformer same as the 1482?

Thanks - I see the break, and I see a ground I missed - will correct
I will record some voltages when I power it back up. PT is unmarked.

AlNewman - I agree that a lamp or a small wattage resistor can act as a fuse in that location. But I think Dano used the 6X4 in all the amps in that series and only this Airline uses the lamp in that fashion. 

[bmccowan]

I didn't notice anything on your new schematic other than a disconnected wire.
My question on the 9013A is did all of them have the lower voltages like the 1472 or did a one point get upgraded to the higher voltages/transformer same as the 1482?

Thanks - I see the break, and I see a ground I missed - will correct
I will record some voltages when I power it back up. PT is unmarked.

Platefire - I checked the voltage on the Airline. They are virtually the same as those on the 1472 schematic. 270-270 AC; 287 DC node 1 B+. Well below those on the 1482, as you know. I think that is the lowest I've encountered on a P-P 6V6 amp. Gibsons and Valcos are lower than Fender. but are above 300 in my experience. Good tone on this amp though.

[Platefire]

Thanks for checking. I did a study years ago on the differences between a 1472 and a 1482. I've never played over a 1472 or a9013A. Never seen one in person, only in pictures. Attached is my document I created on the differences.

[bmccowan]

Thanks Plate - I saved that as a Word document and added notes on the Airline.
I think I will change the odd heater wiring to a more standard artificial CT arrangement, test all the Sangamo caps for leakage and values. My experience with Sangamos is not good. And add a cathode bypass cap to one of the channels. So far, I am liking the preamp - the power amp is standard fare cathode bias PP. When I get it gussied up I may try 6K6s in it, given the sub 300 voltage. I bet its a good preamp to use with 6AQ5s and/or 6BM8s - someone must have tried that.

[Platefire]

Thanks for your additions. Good info to know for those interested. When folks come up with the same questions we did, and start a search, maybe they just might find this