Need help identifying these components

[JMMP]

I'm working on an amp I have no information on, a TNT Circuits Softwatt 50. No schematic exists that I can find. Came to me with a fried screen resistor, so I replaced both (1k 5w) along with the el34's, my guess is a tube shorted taking out the resistor. In going thru the amp it seems to be prone to oscillation, with the cover off the bottom I can't get within two feet of it without it squealing. Trying to find my way around the pcb, there are at least a dozen tiny components about the size of small signal diodes, brown with a single black stripe around them. They read 0 ohms. Anyone know what these are and what their purpose is? Any information on this amp above and beyond that it was designed/built by a couple of guys in Florida who closed up shop? Thanks in advance.

[The Dude]

Do they look like this?



If so, it's a 0 ohm resistor. Mostly used to jump connections over traces. They are also used often when boards are stuffed by machine. Many machines can't stuff a plain wire jumper. They need a "body" to grab.

[JMMP]

Do they look like this?

[ATTACH=CONFIG]46093[/ATTACH]

If so, it's a 0 ohm resistor. Mostly used to jump connections over traces. They are also used often when boards are stuffed by machine. Many machines can't stuff a plain wire jumper. They need a "body" to grab.

Yes, just a bit rounder. There are also wire jumpers on the board, must be stuffed by hand. Wonder if putting a small cap, say 100p across the PI plates would tame the oscillation, thoughts?

[alexradium]

Pics?

[JMMP]

Pics?

Several in this pic, and this youtube echos what The Dude said.

https://www.youtube.com/watch?v=rzH59zK-3UQ

[J M Fahey]

I think what alexradium asked is whole amp pics, both outside, inside, PCB both full and closeups, tube and transformer side, wiring, etc. , to try to guess what you have there and maybe offer some suggestions on how to curb your oscillations.

Happy you endow us with such high divination powers, but

it was designed/built by a couple of guys in Florida who closed up shop?

does not really help much

That said, most nobody really designs from the ground up, by any means, most boutique/custom amps out there are basically some Fender/Marshall/Soldano with some twists and tweaks ... if that much ..... some are plain "photocopies".

What you show of the PCBs strongly hints at homemade ones, and hand assembled.
Zero ohm resistors can be used anyway and to some look neater than a plain bare wire jumper, and they cost next to nothing, so .... why not?

And welcome to the Forum.

[drewl]

Yes, it's a zero ohm resistor.

I've used them in things because we have thousands lying around at work.

[JMMP]

I think what alexradium asked is whole amp pics, both outside, inside, PCB both full and closeups, tube and transformer side, wiring, etc. , to try to guess what you have there and maybe offer some suggestions on how to curb your oscillations.

Happy you endow us with such high divination powers, but does not really help much

That said, most nobody really designs from the ground up, by any means, most boutique/custom amps out there are basically some Fender/Marshall/Soldano with some twists and tweaks ... if that much ..... some are plain "photocopies".

What you show of the PCBs strongly hints at homemade ones, and hand assembled.
Zero ohm resistors can be used anyway and to some look neater than a plain bare wire jumper, and they cost next to nothing, so .... why not?

And welcome to the Forum.

Thanks all, here are a couple of pics. The controls are clearly labeled, hard to read the font.

[J M Fahey]

Well, the weird font is hard to read, even if it were sharp and well illuminated, and the backwards illumination makes it worse.

Main light source (as the window in the background) must be on your side, and illuminating the subject from its front, not its back.

In any case, the translucid PCBs mean itīs relatively straightforwrd to "lift" and draw the schematic.

Looks roughly like some JCM800 cousin ... which is also known for being unstable and hard to tame.

Not sure because I canīt even read front panel labels, go figure.

I suggest you download and print, preferrably on a double sheet for visibility and comfort , a JCM800 schematic and compare it with what you have there.

I guess large chunks at least will be very similar, saving you tracing time.

Then we can suggest something, but just for starters, I donīt like that unshielded and exposed input jack just across the (I suppose) are speaker out jacks.

At least introduce some shielding between them, a grounded piece of metal, or a piece of aluminum paper , that alone should improve the situation.

In general itīs better to shield than to kill a lot of highs to kill oscillations because that makes all sound dull.

[J M Fahey]

Well, the weird font is hard to read, even if it were sharp and well illuminated, and the backwards illumination makes it worse.

Main light source (as the window in the background) must be on your side, and illuminating the subject from its front, not its back.

In any case, the translucid PCBs mean itīs relatively straightforwrd to "lift" and draw the schematic.

Looks roughly like some JCM800 cousin ... which is also known for being unstable and hard to tame.

Not sure because I canīt even read front panel labels, go figure.

I suggest you download and print, preferrably on a double sheet for visibility and comfort , a JCM800 schematic and compare it with what you have there.

I guess large chunks at least will be very similar, saving you tracing time.

Then we can suggest something, but just for starters, I donīt like that unshielded and exposed input jack just across the (I suppose) are speaker out jacks.

At least introduce some shielding between them, a grounded piece of metal, or a piece of aluminum paper , that alone should improve the situation.

In general itīs better to shield than to kill a lot of highs to kill oscillations because that makes all sound dull.

[nickb]

I see the big signal wires to the output transformer are on the bottom left and that is right next to the sensitive input stage. These need isolating from each other. Try twisting the wires to the input jack tightly or use screened cable. Similarly twist the three wire from the PCB to the output transformer. If that doesn't do it add a metal screen from the chassis up as high as you can go next to the PCB just below the input stage