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Peavey Blazer revival questions

Started by Tim Escobedo, April 10, 2022, 12:54:40 AM

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Tim Escobedo

I've recently picked up a couple Peavey Blazer amps, from different sources and eras. Amp #1 appears to be a late 90s "Made in USA" version, amp #2 is a "Designed in USA" made in China red stripe version I'm guessing is about 15 years old. Both have some issues.

Amp #1 curiously has a two prong plug that's original, wired directly into the power transformer. The closest schematic I can find seems to indicate a grounded plug, but who knows. I've tried contacting Peavey for the proper schem, but they've never replied. Should I consider replacing the power cord with a properly grounded three prong plug? Secondly, the recovery coil of the reverb tank seems to have gone open. Anyone know the specs for a replacement reverb tank? I have one that's 600 Ohm in and out coils, but I don't know what's optimal.

Amp #2 has an intermittent distorting problem in the audio chain somewhere. Sometimes happens upon powering up, sometimes happens after the amp has been on for a while. It's characterized by a thinner, slightly buzzy tone, more easily noticed on the clean channel, but also happens in overdrive (though a little harder to notice in high gain). I suspect a bad connection somewhere or perhaps a bad solder joint. When it happens, it is always remedied by a good solid whack on the cabinet. However, it's been impossible to reproduce pushing on the PCB with a chopstick at various points while powered up. All the joints have been physically inspected under magnification and look OK. And I'm 99% sure it's before the power amp, as I've been able plug an audio source into the CD/Tape input when it happens, which isn't affected. I have a suspicion it might be the Modern/Vintage EQ switch (which the older Amp #1 lacks), since it is almost, sort of, reproduced when I really fiddle with the switch and kind of balance it in the in-between position. However, it isn't quite the same sound, just similar. Contact cleaner on the switch hasn't seemed to help. Any other leads as to what I could be missing?

Interestingly, the reverb tanks on both amps had become unmoored, as the adhesive foam holding them down disintegrated into fluff. The tank of Amp #1 was wedged between the circuitboard and the chassis, shorting something out, leading the previous owner to think it was not functional. But works fine other than the busted reverb coil. The reverb tank of Amp #2 was flopping around loose inside.

Enzo

#1  Y'know, I wouldn't bother sticking a three wire power cord on it.  You describe the original Blazer  It has op amps in the preamp.   If I recall, this had the little open frame reverb guts.  Just the small spring assembly, no pan around it.  It would be the equivalent of an EB type pan though.

#2  The whack test tells you it is a connection.  Use your wiles to isolate the sensitive area.  It may not be solder.  A poor contact in the headphones jack , the ones that are speaker cutouts.  And there are the channels switches, could have dirty contacts.

Tassieviking

Eliott from ESP has a good article on "Care and Feeding of Spring Reverb Tanks",
https://sound-au.com/articles/reverb.htm
At the bottom of the page he has a list of part numbering of reverb tanks, Table 4.
In the table he lists the bobbin colour that match the impedance for that coil.
So if you have say a red bobbin its a F type coil with an impedance of 1475 Ohm.
I don't know if this is always the case, especially with older tanks but it might help.
There are no stupid questions.
There are only stupid mistakes.

g1

Quote from: Enzo on April 10, 2022, 02:22:52 AMIf I recall, this had the little open frame reverb guts.  Just the small spring assembly, no pan around it.  It would be the equivalent of an EB type pan though.
The closest thing for those little mini tanks seems to be the accutronics AMC2EF3, which are cheap but no one seems to have stock right now.  https://www.amplifiedparts.com/products/reverb-tank-accutronics-amc2ef3-long-decay-2-spring

It does seem that 600ohm input is right, so I would suggest Tim try the 600/600 tank he has if there is room for it.  Worst case it will be a bit weak at output end.

Tim Escobedo

Thanks for the schematics and the ideas.

I might give the reverb tank I have try. It's a more normal sized one, not like the little 4 inch assembly they house inside the chassis, so of it works, I'll have to mount it probably on the floor of the cabinet. Both amps seem to have plenty of recovery gain in the reverb circuit, too much, really, in my opinion, with the stock spring unit. So the 600/600 ohm tank might be fine.

That stock foam reverb mount is a regrettable choice, and that they both had failed completely is a heads up for anyone who might come across one of these little amps, of things to watch out for. The one that was loose, but functional, was remounted by cutting some of that open cell eggshell-cut cushioning foam that came from a test equipment case. I cut a cavity for the reverb assembly in a piece of foam, whole whole thing large enough to get securely wedged in the closed chassis, where the unit is suspended within the foam. Seems to work quite well.

I think I'll leave that two prong power cord alone. It isn't causing a problem, leave well enough alone.

Tassieviking

I would not be using the reverb tank you have, I think it should be a 8FB or 8EB tank, you have a working tank so measure the DC resistance of that one and work it out from there.
If you use a tank that has an input that is too low you could burn out the Op-Amp.

I personally would replace the 2 wire mains cord with a 3 wire earthed one.
You could get electrocuted if the mains transformer shorts out if there is no earth wire going to it. But that is just my feelings on the subject.
There are no stupid questions.
There are only stupid mistakes.

Enzo

It is like an electrical appliance in your home.  If double insulated, no need for earth.   Just my opinion.

g1

Quote from: Tassieviking on April 11, 2022, 05:26:52 AMI would not be using the reverb tank you have, I think it should be a 8FB or 8EB tank, you have a working tank so measure the DC resistance of that one and work it out from there.
If you use a tank that has an input that is too low you could burn out the Op-Amp.
He said his tank is 600 ohm at both ends, so 'E' input impedance, same as the Peavey.

Loudthud

Quote from: Enzo on April 11, 2022, 12:54:41 PMIt is like an electrical appliance in your home.  If double insulated, no need for earth.   Just my opinion.
All you need is a double insulated guitar and you're set. Without the safety ground, you can get hum and mild shocks when you touch microphones or other guitar players :(

joecool85

Quote from: Loudthud on April 12, 2022, 07:05:24 AM
Quote from: Enzo on April 11, 2022, 12:54:41 PMIt is like an electrical appliance in your home.  If double insulated, no need for earth.   Just my opinion.
All you need is a double insulated guitar and you're set. Without the safety ground, you can get hum and mild shocks when you touch microphones or other guitar players :(

I always fully ground my amps.  No reason not to, and plenty of reasons for it.
Life is what you make it.
Still rockin' the Dean Markley K-20X
thatraymond.com

Tassieviking

Quote from: Enzo on April 11, 2022, 12:54:41 PMIf double insulated, no need for earth.   Just my opinion.

I don't think I have ever seen a guitar amplifier that is in a plastic box, with plastic pot shafts and knobs.
I think any older amplifier, especially  from the last century, should be earthed if at all possible.
When an appliance is directly connected to your body (strings), there is a potential of electrocution.
Even if the appliance in question (amp) is correctly manufactured we don't know who has modified it, or used the correctly rated parts in any repairs made to it.
Not all power transformers have the right insulation between the primary windings and the secondary windings, when a transformer malfunctions it can short the mains voltage to the low voltage rails and then you end up doing a weird little dance if you are on the other end.
Thankfully it only hurts until you pass out.
I could rave on about the "handy man" installed power outlets I have come across in the last 45 years working as an electrician, how I have seen someone use a wire coat hanger as cable to connect a second power point beside the first one, or thin speaker wire,etc.
I must have found dozens of power outlets where the neutral and earth wires have been swapped, or active and neutral swapped.

Anyway, if it has a metal chassis then I earth it, if any metal you can touch is connected to the circuit (like guitars, microphones etc) then earth it.

If I was a performing artist I would carry a small power point tester with me, and I would most likely have an earth leakage protecting plug on the lead to my amp, and any other equipment that plugged into a power outlet.
At least in Australia you can get plugs that will protect against electrocution that you can fit on the end of a power lead.
There are no stupid questions.
There are only stupid mistakes.

Enzo

If you want to earth it, then earth it.  Peavey made any number of models in the modern era with the two wire power plug, and met whatever electrical approvals they are asked to.  What those are I cannot say.  That was all I was thinking.

g1

Play safe and don't count on anything.  If you are holding strings and going to be touching a mic, or another player, do a shock test first (with something other than self).  Same if you play barefoot or standing in water. ::)

It takes multiple failures at the same time or catastrophic single failure to put you at risk of serious harm.  Otherwise, like loudthud said, it's just really annoying (like the static zap I get everytime I open a cooler door at the grocery store).

Outlet polarity checkers will not show you a 'bootleg ground' so they are not failsafe.
With double insulated equipment, 3rd prong ground is not required to go direct to chassis so you can't necessarily count on that either.
The double insulation is deemed safe and if they are not, I guess the lawsuits are being settled out of court. ;)
Know the risks and act accordingly.

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Tassieviking

Ops...sorry if I raved on a bit too much in my last post about earthing.
I hope I didn't offend Enzo or anyone else here.
I guess I am a bit sensitive about safety when it comes to electricity.
I have had to revive work mates after getting zapped, not a nice thing.
There are no stupid questions.
There are only stupid mistakes.

g1

It's a very legitimate concern and I don't think you can over-state it.
If you really want to be fail-safe, isolate your string ground (isolation transformer at amp input) or go wireless.