Epiphone Galaxy 25 Guitar Amp

[CJ]

we need to tear down a tube amp,

see here>

 

[CJ]

this is the back>

 

[CJ]

what the chassis looks like>

 

[CJ]

nice sounding amp,  ext spk cab was used, plugged got pulled while running, this makes the OPT unhappy,

 

[CJ]

here is a link to this and other Epiphone amps - pdf style...

http://www.blueguitar.org/new/schem/electar/

looks like a fender with EL84 pwr tubes,

here is a voltage chart with the bad OPT, only had 150 mv on 8 ohm sec,

maybe mod inverter, make R18 = 1.2 K and R17 = 47K like VOX,

some say too much pwr supply filtering, can't vouch for that,

individual bias pots a plus,

green is AC volts

 

[sahib]

nice sounding amp,  ext spk cab was used, plugged got pulled while running, this makes the OPT unhappy,

Spark plug ?

 

[CJ]

exactly like a spark plug only different, 

 

[CJ]

this thing is done, wound a new OPT, Princeton Reverb type only on a 75 EI instead of 625 EI, 1/8" thicker tongue,

fired it up, runs but rice krispie sounds, ripped it apart again, installed 100K 2 w in place of 100K 1/2 watt, no more cereal, replaced phase inverter with 12AT7 as 12AX7 showed hi freq osc at certain freqs,
problem went away, replaced 75K inverter plate resistor with 82 K, rebiased pwr tubes and it sounds great,

original output was a real mess of wires, hope the pwr trans will be ok,