Got one of these in a trade recently.... it is in pretty bad condition and a candidate for rehab!

I can only make out the letter "A" after Model No. on the chassis. It utilizes a 6X5 glass tube rectifier and 6J5, 6AG7 and a 6SJ7 - all black, metal jacketed.

Plugged it in to a current limiter to see if the tubes would light, etc. The large blue (enameled) resistor in the center of the attached pic started flashing on each end.

Well I removed it and I can't read the value... so a schematic or even an educated guess would be helpful. This resistor comes from pin 8 on 6X5 rectifier and ties into the filter cap can, along with a wire from the OT.

 

 

Update: I put in a 2k2 5 watt resistor and powered it up! I'm getting a bit of crackling thru the speakers, but no sound with an instrument plugged in.

 

My In-Circuit capacitor tester suggests all the caps are OK. At least no shorts, uf values not withstanding....

 

So now it is off to the guessing game.... appreciate any help!

 

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History of Valco

The Valco company has its roots in the National String Instrument Corporation, which was founded in 1927. The company is famous as the first manufacturer of resonator guitars, which were hugely popular in blues and (a bit later) bluegrass music. National merged with the Dobro company, another maker of resonator guitars, around 1932 to form the National Dobro Corporation. The company began producing electric instruments in the 1930s that included electric guitars, lap steels, mandolins and amplifiers. These pre-war electric instruments are fairly rare today, though the lap steels pop up with some regularity. The archtop bodies for the guitars were sourced from Regal and then from Kay, but the electronics were developed and manufactured by National-Dobro. The Supro brand name was introduced in the mid-‘30s for cheaper electric instruments.

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