peavey tnt 130

[pontiacpete]

yes, that's what happened

mm .. I thought I had check those resistors and they weren't opened but I will test them again,,, and test the zeners.

i'll be back.

[pontiacpete]

Today I pulled one of the zeners and tested it on a power supply and found that it was the culprit, so I changed them both out. Sure enough, Enzo, you were right, the whole amp fell into place and is up and running.
Thank you very much, I learned alot with this one.
And thanks to all who contributed with their suggestions.

Regards,
pete

[Lee_ranaldo]

Enzo does it again!

Glad u got ur amp working

Rock on!

[pontiacpete]

Lee, I'm sure people ask you this alot, but I have to do it myself; are you the same Lee Ranaldo from Sonic Youth?

[Lee_ranaldo]

haha no..... i wish! i just use that nickname to play some homage!.

[pontiacpete]

Cool.. .. they use to rehearse a block away in the 80's. Great band.

Anyway,, thanks for the tips on diagnosing the amp.

[RichardJ]

Peavey TNT 130 Bass Amp

I picked one up (at 80 odd pounds difficult I know!) yesterday, and it plays but has a bad hum, like yours. I suspect that it may be a bad connection as it does not happen until something is plugged in. First question - how do you get the head out of the cabinet in the first place? Also, does anybody have a Service manual of any kind please?

[Jazz P Bass]

Peavey TNT130 Schematic.

Service Manual?
Schematics are all that is available.
Here it is.
There are four screws on the top of the amp that secure the chassis.
The speaker connector on the circuit board must be removed to get the chassis all the way out.

[RichardJ]

Peavey TNT130

I'm sorry I figured that this thread was probably defunct by now so I exchanged a few emails with pontiacpete direct.
If I disconnect the cable from between the 2 boards there is no hum and if I disconnect just the signal (white ) cable again the hum disappears. So is it just the cable or something wrong with the grounding in the preamp board

[Jazz P Bass]

If I disconnect the cable from between the 2 boards there is no hum and if I disconnect just the signal (white ) cable again the hum disappears. So is it just the cable or something wrong with the grounding in the preamp board

Did you check (on that same preamp connector) the +15V & -15V power supplies?
Measure the voltage with the connector off & then with it on.
There should be no change.
The signal pin being disconnected to eliminate the hum does not have to mean a faulty ground.
The cable itself can be checked with an ohmeter for continuity.

[RichardJ]

There is a drop of about 1/2 v on the -15V when the cable is connected
If I put a signal into the power amp (without the cable connected) I get no hum, but if I take the output from the preamp and feed that into another amp, the hum returns

[Jazz P Bass]

So the problem is in the preamp.
Do ANY of the controls affect the hum?
I am not too familiar with this amp.
Are the IC's in sockets?

[RichardJ]

None of the controls affect the hum other than to muffle it slightly using the high filter and the gain control.
The ics are in sockets and appear to be well seated.
When I power off, there is a loud pop but only when the preamp is connected

[Jazz P Bass]

Can you measure the Vac ripple on the +15V & -15V supplies that go to the preamp.
With & without the connector hooked up.
That .5Vdc drop is weird.
If there is no ripple check the ic output pins for unwanted Vdc.
Pin 1 & pin 7.

[RichardJ]

The exact readings are
No Load +15.66v, -15.04v
On Load +15.66v, -14.38v

However, there appears to be 67v AC across the + and - pins. I do not have a scope so that is measured only with a DMM which I am sure is not accurate for this kind of measurement. Also it only shows up with the meter connected in one direction