Trainwreck Songbird 30

[M Fowler]

All voltages are good. I wondering if Edcor screwed me again in wire color verses hookup diagram. Might have to disconnect OT and measure it out.

[johnnyreece]

So when you say 1/2 power, you mean, like sound-wise? I thought you meant the voltages were 1/2. Whoops! Yeah, might be time to get some measurements from your OT.

[M Fowler]

Sound wise not much push. I've been messing with this amp since last January. Shoved it off to the side and continued with other projects. Measured, traced, tube rolled and nothing changes.

[johnnyreece]

Yeah, I checked the diagram at Edcor's site...looks like you've got it right (assuming the white/blue and white/brown aren't connected, I think). Nothing's jumping right out at me at the moment.

[kwijabo]

have you tried changing the larger coupling cap in the preamp to a higher value? i see its 0.022uF, up'ing it to 0.1uF may bring in more signal to fill it out.

also, that 330k resistor in the preamp - the higher that is the more you're cutting the signal. what about a 220k?

[Littlewyan]

Have you tried all 3 impedance settings?

[kwijabo]

actually i think its where the NFB hits the phase inverter. look at what you have compared to the real gutshots. the 39k should NOT go to the 0.047uF cap. it goes to the 4.7k resistor, which then goes to the 0.047uF cap.

[Littlewyan]

Yeah it looks like you need to swap the NFB and Ground wire around.

[M Fowler]

I actually already tried that and didn't change anything. I swapped that around and even disconnected the NFB at one time that's why that area looks all burnt.

[johnnyreece]

Looks like more than a wire swap is necessary. Got a resistor going to the cap when it looks like the 4.7k should be between the resistor and the cap. Hard to tell...

[Littlewyan]

I think thats right the 39K connects to the .0047uf Cap. Look at other amps and you'll see the tail resistor connects to the cap.

[johnnyreece]

Yeah, that's why I didn't think anything of it at first glance. I was hoping it was something that easy...

[kwijabo]

I think thats right the 39K connects to the .0047uf Cap. Look at other amps and you'll see the tail resistor connects to the cap.

it doesn't look like thats what it does in the SW30. take a look at one of the SW30 pics and you'll see you the 39k doesn't connect to the 0.047uF.

[M Fowler]

Not the problem area and besides like I said I've played around with that area as my first thought. I do need to move that tail resistor back to correct position though.

[Littlewyan]

Looks like you might have to measure that OT Mark. I would say mismatch the impedance to see if there is a difference, but could be bad news if its already mismatched.