Danelectro 8424 Guitar Amp

[CJ]

had this Museum piece sitting on the balcony,  boss said that  rick Esterin of little charlie and the Nightcats used this in the studio when laying down harmonica tracks so we had to take a look,

Made by Montgomery Ward, Model # 25JDR8424  Standard Model, no schematics online.

 

[CJ]

3 Ohm speaker, 12 inch with a small magnet,

markings:

285241

Pat # 2517727

5734   

"Rufew" printed on cone,

 

[CJ]

Freed pwr xfmr,  gapped output even though we have two 6V6GT's doing the push-pull routine, 

all inputs are the same, 68K to grid,  needs a hard to find 1950's knob,

 

[CJ]

chassis, dry electrolytics, amp sounds good with the bad caps, while testing, the first cap got real bad and the amp turned into an octave pedal all by itself,

Ham Radio tone cap, had to go online to decipher the value, 

funky cathode resistors, and a small 2.2k feeding the screens and the rest of the amp,

grid leak resistor, 15 M, was not soldered to the tube socket, got thru test at the factory, probably caused hassles down the line which is why it ended up on the shelf,  fixed after about 60 years,

 

[CJ]

input section, guitar signal goes straight into the tone and volume controls before the grid leak 6SJ7,

2.2 Meg plate resistor on V1 means about 36 volts on the plate,

second tube has screen and supressor tied to plate,

 

[CJ]

pin 1 of 6V6 used as star ground for a few wires, coupling caps have no brand name on them,

check the funky dual 470 ohm cathode resistors!  ever seen those before,

 

[CJ]

output is a 52:1 since we have a 3 ohm speak, comes out to 8.2K : 3 ohms,  #21 sec wire,  Pri-Sec,

75 EI core butt stacked like old Triad 108 from the Tweed DeLuxe,  so only 39 Henries, saves the speaker,

don't know the brand, maybe Freed,

 

[CJ]

schematic,  weird tone controls, big plate resistor on the first gain stage, check the screen on the second tube, 10 volts, tapped off the V3 cathode,  ant AC feedback? no, gets swamped by the .1 cap, 

metal 6SJ7 preamp tubes, RCA, smoked glass 6V6GT output tubes, also RCA.

6X4 rectifier,

plate voltage jumped to 286 after good cap bridged across the 16/450 ,

one end of heater voltage grounded, but the amp is still quiet, so lots of hum cancel from smart designers and good layout,

 

[CJ]

output transformer only flat to 5K, from the high turns ratio,  phase shifted pretty bad at only 10K but that's where you get the funk,

probably the worst transformer we have tested as far as response, but for guitar it sounds just fine,

first two shots are sq wave, then sine wave,

 

[mjrippe]

Hey CJ, nice work as always!  I have that volume knob.  PM me your address.

 

[fazer]

Thanks for post on this piece of history.

You seem to separate what's right from wrong and what's wrong from right.

 

[Dyoungblood]

I have the same amp, I made a solid pine cabinet for it and have it pushing a 1965 Jensen 12' 16 ohm speaker. It sounds amazing but the tone controls are lacking. I was wondering if you knew what I would have to do reroute them after the first stage of preamp. I was also wondering about using one of the input jacks to maybe ad a presence control.
I would add that I am complete novice on tube amps, Im mainly a wood worker who can solder very well.

 

[CJ]

i do not know the phasing on the output transformer, so if you put a presence control on there it might feed back. here is the tone section transplanted onto the other side of the first amp.