This amp squelches the signal right at the input jack. How are you supposed to fix it if you cant follow a signal ? Amp will pass signall if i attenuate signal gen to 0 db all the way then you an hear a faint signal. Even at 10db it wont pass signal. Amp comes up fine now . but just wont pass signal. If anyone has any ideas please let me know.
Could be either a short to ground, or an open circuit, on the input jack.
There's a shorting switch that the plug opens up when it's fully inserted,
are you using the right size plug?
Go past the input jack to see if the REST of the amp passes signal.
Are you saying you plug a test signal into the jack and it is not present right on the jack pins? If so, the jack is suspect for not making contact.
Is signal actually reaching the first tube grid? The first tube plate? In other words is it really right at the jack or is it at the first tube? In which case we look for plate and cathode voltages on that tube.
Look at the layout. The input jacks - have you tried both of them? - feed their signal to the rear edge of the board and through a ribbon to the preamp tube board. A broken trace, solder joint, connection, etc anywhere along that path silences the amp.
I don't think signal level matters much in a go/no-go setting. We have NO signal passing, not low or distorted signal. SO I just plug my CD player into the amp and let VanHalen or someone wail. A good strong signal, how far does it go?
Plug the guitar into the FX return, does the power amp part at least work?
Are the preamp tube heaters all LIT?
If Q7 shorts, then the preamp output is grounded off, making the whole preamp seem dead.
Are you saying you plug a test signal into the jack and it is not present right on the jack pins? If so, the jack is suspect for not making contact.
Is signal actually reaching the first tube grid? The first tube plate? In other words is it really right at the jack or is it at the first tube? In which case we look for plate and cathode voltages on that tube.
Look at the layout. The input jacks - have you tried both of them? - feed their signal to the rear edge of the board and through a ribbon to the preamp tube board. A broken trace, solder joint, connection, etc anywhere along that path silences the amp.
I don't think signal level matters much in a go/no-go setting. We have NO signal passing, not low or distorted signal. SO I just plug my CD player into the amp and let VanHalen or someone wail. A good strong signal, how far does it go?
Plug the guitar into the FX return, does the power amp part at least work?
Are the preamp tube heaters all LIT?
If Q7 shorts, then the preamp output is grounded off, making the whole preamp seem dead.
Amp hums so i replaced power supply caps to no avail. 330uf 350 volt 2 each ,also replaced 100 uf caps at 300 volt 2 each. Amp still hums. My buddy in crime plugged a 1/4 " plug with no input into the secondary input. Inconjunction with the 1/4" on the main input with a signal .Now you can hear the signal along with a hum. But still cant find problem. Thanks for all your help.
I think i will pull all of the valves and see if the amp still hums . As i should solve the humming issue before i start to see it wont pass signal. It may be that both problems are interrelated.But probably not. Ive already replaced the power supply caps to no avail. There are a couple of 500volt caps that may be the culprit. Dunno.
I have a Fluke Networks Pro 3000 probe for locating audio. And that hum is coming from the main transformer . you can also hear the hum quite a bit on the three wire connecter that has three orange wires J84 85 and 86. Also the two red wire connector J72 and 79. Im wondering if it can be the Mica caps on the power strip , they are rated at .01DVL, there are two of them . Also there is a Thermal resistor TR1 70240200. Could these cpmponets be causing the hum ? Or do i have a bad transformer ? Which seems implausible, the amp comes up without fail. Just hums.
Mica caps hardly ever go bad. I have a pair from 1961 working fine at 400 v.
Electrolytic caps are doomed to a feeble old age, especially on any Peavey over a decade old.
Thermal resistors tend to slow the turn on surge to not cold shock the tube cathodes. If the heaters light up thermal resistor likely not bad. See if it is in series with the primary of the power transformer, typical.
Enzo seems to have left the building. I don't have the schematic on this, but Peavey's tend to build up hum from bad connections on any punchdown block connectors. Removing & replacing the wires can clear the oxide off. Also, the PowerSupply circuits hum on most of the Peavey equipment I own (bought at bargain rates) where I haven't replaced the electrolytic caps yet.
Electrolytic caps are doomed to a feeble old age, especially on any Peavey over a decade old.
Thermal resistors tend to slow the turn on surge to not cold shock the tube cathodes. If the heaters light up thermal resistor likely not bad. See if it is in series with the primary of the power transformer, typical.
Enzo seems to have left the building. I don't have the schematic on this, but Peavey's tend to build up hum from bad connections on any punchdown block connectors. Removing & replacing the wires can clear the oxide off. Also, the PowerSupply circuits hum on most of the Peavey equipment I own (bought at bargain rates) where I haven't replaced the electrolytic caps yet.
Soulman25, you seem to be getting bogged down in this and loosing your way.
If a secondary power supply component has failed, it is usual that the mains power fuse will blow as diodes and capacitors can go short.
Supplying figures from your Ohms tester is a bit meaningless as the readings will var from meter to meter.
I presume you have a schematic for the correct version of 5150, there are four, all slightly different.
All valves in and in standby, if there is hum, it must be mechanical from the transformer. If it is, this is not uncommon and when on stage, not noticeable.
If there is no hum until out of standby, (Screen grids powered up), then check the bias balance and look for a leaky 6l6.
If removing the phase splitter the hum stops, is it mains hum or twice the frequency? Twice the frequency can be bias or main smoothing.
If the black loudspeaker wire from the output transformer has not got a good connection to chassis, the NFB loop will be wrong and that will cause issues including hum, whining or even low output.
Keep a clear head, BE VERY CAREFUL as lethal voltages are within! use a mains isolation transformer and work methodically from the output to the input.
If a secondary power supply component has failed, it is usual that the mains power fuse will blow as diodes and capacitors can go short.
Supplying figures from your Ohms tester is a bit meaningless as the readings will var from meter to meter.
I presume you have a schematic for the correct version of 5150, there are four, all slightly different.
All valves in and in standby, if there is hum, it must be mechanical from the transformer. If it is, this is not uncommon and when on stage, not noticeable.
If there is no hum until out of standby, (Screen grids powered up), then check the bias balance and look for a leaky 6l6.
If removing the phase splitter the hum stops, is it mains hum or twice the frequency? Twice the frequency can be bias or main smoothing.
If the black loudspeaker wire from the output transformer has not got a good connection to chassis, the NFB loop will be wrong and that will cause issues including hum, whining or even low output.
Keep a clear head, BE VERY CAREFUL as lethal voltages are within! use a mains isolation transformer and work methodically from the output to the input.
If Q7 has 174 ohms when the amp is powered that means one of two things. It means either the part if not being turned off by a gate voltage - and you then look for a gate voltage. Or - more likely - the JFET is bad.
Try removing Q7 and see if the amp wakes up.
You can measure resistance while the circuit is hot ONLY AT THIS SPOT, because there is no other voltage on that part.
Try removing Q7 and see if the amp wakes up.
You can measure resistance while the circuit is hot ONLY AT THIS SPOT, because there is no other voltage on that part.
Indiana Jo , Jon Snell and Enzo . Thank all of you guys for your input. My name is Tim , Amp tech at Heartland music in OKC. OK. Enzo , replaceing Q7 is one of the first things i did. But i will pull out Q7 totally out of circuit to see if amp comes up. Jon Snell i checked all the tubes with my tube tester. I also think this amp is grid biased . which to me means the only way to change the bias is to change out the bias resistors.Do you by chance know what the bias voltage is ? I will also remove the phase inverter valve/tube to see if hum is still there. I will also check the black speaker wire for good connection. But that hum seems to come straight from Xformer.
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