around here? HELP:
around here? HELP:
PC Win7-64-16G i7-2600/Cubase 5-6-7 32 bit/Tascam US1800/KRK G2-8/Event TR8/SS Trigger Plat Deluxe/Lava Lamp/Big mean dog
I am trying to resurrect an old preamp and have very limited knowledge and unable to obtain a schematic.
I am NOT the guru, but do you have access to any test equipment - multi-meter or volt ohm meter for example?
Also, what is the preamp? And what is the problem - no power, no signal, distortion???
Hopefully someone like ecc83 will wander by and pick this up...
But the more descriptive information you provide, the better.
"Bad speakers in a bad room could be likened to painting in a dark room with coloured glasses on. It really is guesswork." Steenie
I hope this helps.
It is a teisco stereo preamp. Two channel, one clean, one with tremolo and reverb, both with bass, mid and high. I have a clean signal coming through both channels. No reverb or tremolo on channel two though. I have meters, scope, AF generator. I can see the signal on the plate and grid for the input to the reverb tank, I can see the signal at the input of the tank, I see a very weak and distorted signal coming out of the tank, it may not be a signal at all, but just eddy currents or gremlins maybe, I am new to all of this. I can see no signal at all at the output of the reverb tube, either on the plate or the grid. All plates etc. appear to have good DC voltage on them. There is zero DC on the grids I think. The input side of the rever tank also goes to a footswitch, the footswitch I think routes the clean signal back to the output? The output from the tank goes to the deapth control for the reverb, which then gets passed through some resistors and caps that are tied in somehow through the volume and tone controls? It goes to a rail and I am not sure how it gets passed to the out put grid of the tube? I am not sure the tank is any good. It is hard wired, three section it appears, the input comes into the right section and jumped to the other two sections then going to the footswitch. The output section on the tank has three outputs tied together that then goes to the depth control. I have tried the verb with the footswitch on and off. All three inputs and all three outputs also have individual grounds.
As for the tremolo circuit, I can see a signal, a strong one, but I don't know what it is supposed to look like on the scope? When I turn the depth pot I can see a change but not really with the speed control. Both plates for the tube are hooked up to one side of a small transformer. The other side of the transformer has two resistors wired to it which then goes to the output for channel two. I am not sure how the tremolo circuit is supposed to work yet.
There are five tubes total, it was given to me with five 12ax7s in it. Four out of the five tubes are using both sections, one tube is only using half the tube. I am pretty sure I have identified the four tubes that use both sections as channel one and two preamp, one tube for trem, one for verb.
That leaves the tube using only one half that I am not sure of what its purpose is? I can see a change in amplitude on the trem tube and the unidentified tube when turning the volume knob on channel two. I have a bunch of 12AX7s and have tried multiple tubes.
Last edited by dragonworks; 11-28-2012 at 17:44.
a power amp and get output from either 'channel'? With the tone and volume controls working? So far, so good.
That's about all I got. Without a schematic, it is tricky. But you can do it. Go slow, and divide and conquer.
As I stated, the reverb tank is hard wired, no rca plugs. The signal to the input of the tank, as far as I can tell, does not go through a transformer, but through a resistor cap network to get there. On the other side of the tank I have either no signal or a very weak one.
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