this switch...

[trem]

.....am i reading this schem right.?
Does the power switch flip-flop the Hot/Neutral from one side of the X-Cap to the other for some reason.?
Page #3
Thank You

http://el34world.com/charts/Schemati...ss_with_pa.pdf

[Randall]

Yes, it looks as though it reverses polarity for ground noise. But what is an X-cap?

[Enzo]

The center off toggle switch can be flipped either direction for ON. It reverses the polarity to the transformer primary, and in so doing also swaps which side of the mains is coupled to chassis. It is done mainly for hum reduction. This rarely makes any difference unless the ground prong is removed from the power plug though.

The switch itself came with metal straps crossing between the contacts, no need to wire it that way.

I can't recall at the moment what DVL means next to them on the print, but the caps are rated for this service.

[Leo_Gnardo]

Does the power switch flip-flop the Hot/Neutral from one side of the X-Cap to the other for some reason.?

As Randall & Enzo noted ^^^, yes. On occasion I've seen one of these where the switch contacts must have gotten stuck, AC line shorted within the switch, subsequent arc blows a hole thru one side of the switch body, looks like a little bomb went off. For this reason, I don't much like 'em.

[trem]

This amp has some real bad noise issues. I know very little about tubes, and almost nothing about SS.
But for starts:
1. Are those caps charging and discharging, through the amp, when i flip the switch.? It pops Very Loudly every time it is moved.
Thanks

[Jazz P Bass]

Yes, it looks as though it reverses polarity for ground noise. But what is an X-cap?

http://www.kemet.com/Lists/Filestore...aRFIandSMD.pdf

[Enzo]

This amp has some real bad noise issues. I know very little about tubes, and almost nothing about SS.
But for starts:
1. Are those caps charging and discharging, through the amp, when i flip the switch.? It pops Very Loudly every time it is moved.

Lots of amps pop when the power is switched on and off. Sometimes it is the circuitry charging up. Sometimes it is just the sparking inside the switch getting amplified. Try leaving the switch on, and just unplugging the amp. Does it still pop that way?

Any switch in any application can fail. On the whole, I find those power toggles to be among the most reliable parts in the amps. The few I have had to replace were mostly ones physically broken off or badly bent.

Film caps in AC circuits don't have much room to get charged up. In fact, caps across switches help SMOOTH out sparks.


"Noise issues" is really not specific. The last thing I worry about is turn off pops, so does the amp have other issues?

[trem]

Hey Enzo -
Yeah, i have heard SB Switches pop, but never the power switch and never this loud.
The other "noise".....can i set my DMM to Hz and put it across the speaker terminals to see what it up.?
If i had to guess, i would say 12o Hz, on both channels, and it is effected by Both Pre and Post pots on both channels.
Could be a bad ground somewhere i guess.
The boards and parts look OK.....That is, no burned (that i can see) resistors or diodes, and no bulging caps.
Trying to figure out how to pull the faceplate off of these.
The front left side seems like the trim is pinned in the center or something, and i do not want to break it.
Anyway, right now, the biggest issue is (120 Hz.?) the noise problem.
Thank You

[Enzo]

So it hums?

Unplug the cable to the preamp, does that stop the hum? I bet it does as your volume controls worked the hum.

Faceplate? The front panel comes out the front. ther are two or three screws through the top and bottom into the panel frame. If it sticks to the tolex, just slip something into the gap, a spatula, a credit card, a small screwdriver. You have a MArk 3, I think that is newer than the ones witha couple screws on each end of the front, like a rack mount.

If you mean getting the preamp board off the panel, just pull the knobs, pull the nuts on jacks and pots. It should be intuitive.

[trem]

Hey Enzo -
Yeah, i was thinking it is probably in The Pre. I was wanting to be able to Get At/See the Pre PCB. There are two face-plates and each one has a big, plastic "trim ring" screwed to it. The left side i could not get off.....but after reading your post they can probably stay on and just get pulled with the plate after i get that free.
I will start with that. Yes, there is a Molex Jumper i can pull to see if that isolates the hum or not. I will start there.
Thanks for the guidance.

[trem]

Oh Boy.....I did not turn the amp off when i replaced the Preamp Molex and the whole amp went silent. Do not know if that is a coincidence or if a broke something.
The fuses are fine, nothing got hot or black/brown.
Anyway, i removed Q2 and Q12 so i could measure them... and then knocked them off the table, and lost track of which went where.
They have different part numbers than the schem. But, Q2 is a NPN, right.? And Q12 is the PNP.....just so i get them back in the right place.
Then i can start to check the basic B+ type voltages.
Thank You

[rjb]

Oh Boy.....I did not turn the amp off when i replaced the Preamp Molex and the whole amp went silent...

Anyway, i removed Q2 and Q12 so i could measure them... and then knocked them off the table, and lost track of which went where.

Time to take a break, methinks.
Maybe a walk around the park....

[trem]

Time to take a break, methinks.
Maybe a walk around the park....

Just one of those days.
Getting these two trans back in so i can start checking volts to the schem.
This is the second PV in a row (the other was a 6505+) where the schems vary a bit.
Time to shoot an email to PV and get a clean copy at least.

[Enzo]

What is wrong with the copy you posted? Looks clean to me.

Here is a file:
Guitar Amplifier Schematics and more

Scroll down to Peavey Bass MK III.

A number of people call their 6505+ combo a "6505+". So what was wrong with your 6505+ drawing?

If we have hum from the preamp, why are we pulling pre-driver transistors from the power amp?

Your preamp hums, are both power rails free of ripple? Do any of the op amps have DC on their output pins?

[trem]

Hey Enzo -
Somebody has been in this amp at some point.
Q8-Q7-Q1 and Q12-Q2 were all either removed or replaced, unless they were all just re-flowed for some reason. I was just curious and lifted a couple of parts to see if they tested good.
Then, when i pulled the Molex that is the for -15 and +15 for the preamp, the hum stopped. The amp kept working, but there was no hum. With the amp still on, i reconnected the 15 Volt supply and that blew the mains fuse. The schem and amp say it is 8 Amps, there was a 7.5 Amp fuse in the amp.
The closest i have is 7 Amps. I installed that, put the amp on a 100 watt light bulb limiter, and R58 at Q12 (collector.?) burned up.
The light bulb is still lit bright, i assume there is still a Short/Problem.

With a tube amp, i am a lot more familiar with the circuits, and can pull different parts of the power supply, or pull all the tubes and then start back in with the rectifier and see what happens. SS is a big, new mystery to me.

I have a 47 Ohm resistor to replace the one i burned up, but i do not know what is causing or did cause that to fry.
What can i check at this point to locate this short.?
Thank You
also, on the layout, there is R58 R55 R54 and C18 180pF.
On the amp, C18 looks very much like a lime green resistor. Hard to say what colors...maybe Red Gray Red Silver Silver. It measures about 6k Ohms. Is that a capacitor.? The Ohm value comes up kind of slow, like a cap charging.