Tele~Star Amplifier

[Arn C.]

I have this old Tele-Star amplifier  someone gave me.  It has a tone control vollume control , 1/4" phono input and 2- 1/4" instrument inputs.  It has three tubes  :  50EH6 (or 8 or 3 for the last #), 35W4 , and 2AU6.  I am guessing about 5 watts or so output power.

Does anyone have a schematic for this,  I swapped out all the caps and resistors, because it was a bit noisy, not real bad tho.  and I also put on a 3 prong cord for the power.   Now all I get is a major hum and can barely hear any guitar.

Thanks if you can help!
Arn C.

[theehman]

I'll bet it doesn't have a power transformer.  Those tubes (preamp should be 12AU6, not 2AU6 and the output tube is probably 50EH6) are typical in AC/DC amps which usually don't have a power transformer to isolate the circuit from the line voltage.  Is there 2 transformers on/in the chassis or just 1?

[petemoore]

and I also put on a 3 prong cord for the power.
 Schematic always helps, but I'd take a second look or whatever to see that the 3 prong adaptation is truly safe, and whether this is what is causing the hum.
 IIUC you need another 1:1 transformer at the AC input to safely wire the 3rd lug.

[theehman]

and I also put on a 3 prong cord for the power.
  Schematic always helps, but I'd take a second look or whatever to see that the 3 prong adaptation is truly safe, and whether this is what is causing the hum.
  IIUC you need another 1:1 transformer at the AC input to safely wire the 3rd lug.

You could try disconnecting the green ground wire and see if the hum clears up.

[Arn C.]

Thanks for the replies!

Well, unless that first # was erased it is a 2au6, the 50EH6 looks right.

Anyhow, Yes only 1 transformer-output.

So maybe I best put back the old 2 prong chord and see if that works first, then if that doesn't work still, then I will have to figure out if I made a mistake or not on subbing in the new parts. 

Thanks again!
Arn C.

Update:  I cut off the ground wire and taped it up and I will try it out tonight!

[theehman]

Well, unless that first # was erased it is a 2au6, the 50EH6 looks right.

117v - (12v (12AU6) + 35v (35W4) + 50v (50EH6)) = 20v/.150mA (filament current) means there's probably a large 130 ohm or so resistor in the filament line to drop the remaining voltage.  All the filament voltages and the voltage dropped by the resistor should equal the line voltage, which in this case is 117v.  I just finished drawing out a schematic for a Decca DMI-61 which is very similar, tube-wise, to what you've got.

Let us know what happens now that the ground is disconnected.

[petemoore]

Don't really wanna run anything to it without the safety ground, because that can cause permanent damage to humans and other equipment.
  Know that this is like plugging your guitar ground into one of the slots in an AC plug.