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Thread: Peavey 6505+ DC Heater question

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    Peavey 6505+ DC Heater question

    I have a Peavey 6505+ up on the bench with intermittent AC heater supply due to a bad connection in the spade connector. My plan is to replace the spade connectors with turrets for a better connection. I have read that the rectifier for the DC heater supply (in4003 at 1A) is way under spec for the current rating and fail often. Iím looking to replace them with a 3-5A diode that will fit onto the board. Any suggestions?

    I have had a few people recommend using a 10A bridge rectifier mounted to the chassis between the PT and circuit board, but my customer would prefer to keep the cost down so Iím looking for other options. Thanks!!

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    The rectifier gets hot and fails, a set of 3A 1n540*, (* meaning any of the range), mounted off the board so there is at least an air space between the diodes and the pcb. I usually form a spring shape with the leads, that helps to dissipate the heat.
    Replace the spades with whatever you think but I would recommend, replacing the tags and soldering the wires to them. Something else that is less likely to fail in the future.)

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    Quote Originally Posted by Jon Snell View Post
    The rectifier gets hot and fails, a set of 3A 1n540*, (* meaning any of the range), mounted off the board so there is at least an air space between the diodes and the pcb. I usually form a spring shape with the leads, that helps to dissipate the heat.
    Replace the spades with whatever you think but I would recommend, replacing the tags and soldering the wires to them. Something else that is less likely to fail in the future.)
    Can you clarify what you mean by replacing the tags? Do you mean soldering directly to the connector?

    I really like the spring shape idea. Do you have any pics? Interested to know how you get a tight coil on the component leg

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    Member Jon Snell's Avatar
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    Yes, remove the connector on the wire end and solder directly to the tag. I have never had them burn out though.
    I get a component and wrap the leg around a small phillips screwdriver blade.
    I then adjust the turns to the required shape to fit the pcb holes or tag strip.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Lifetime Member Enzo's Avatar
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    The 6vAC heater connectors are under spec and burn up. SOlder the wires directly.

    I never encountered rectifier failure, the load on each supply is just 150ma for tube heaters. Add a few milliamps for the couple relays.

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    Cool, Iím still trying to figure out if turrets will be the best way, since thereís two pads for each terminal I may drill out one of them on each transformer side and route the wires through Marshall style for strain relief and solder directly through to the pad. Maybe itís not needed. I donít love the idea of soldering directly to the terminals though!

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    Just ordered some in5408ís for the DC heater supply. I havenít gotten one where the rectifier burnt up but there are plenty of threads with issues like that, so Iím just gonna go ahead and do it, itís less time for me to do it while itís here than to come back later when itís smoked

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    I have had four in for repair with destroyed diodes and bad contacts on the spade connectors but many more that didn't fail. I replaced the diodes and connectors anyway as I was in there replacing the swollen capacitors, belt and braces.
    Mounting them away from the board also helps and you will never see that amplifier in again for the same fault.
    A 1N4002 is fine but the 1N540* series is more reliable.

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    With 1N400x diodes in power applications always use the glass-passivated (GP) types. These have much better long time reliability/lower failure rates (FIT values) than the cheaper standard versions.

    In one of my former products (a kind of SMPS) the calculated mean time to failure (MTTF) could be increased by a factor 10 using GP type 1N4007 rectifiers.

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    Last edited by Helmholtz; 04-04-2020 at 05:50 PM.
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    Member Jon Snell's Avatar
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    Nothing wrong with soldering to the terminals, as long as the pad on the pcboard has not been damaged.
    It is the poor crimping on the connector that is the problem so new connectors will fix it as well, if you have a professional crimp tool that has a force of a couple of tons that is.

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    I just had a 6505+ 112 combo on the bench with a bad DC heater circuit... it was a shot rectifier diode...1N4002 diodes I think....I replaced them with 1N4004 diodes and I clipped off the spade space connectors and hard soldered them to the board....no worries now...

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    Quote Originally Posted by Jon Snell View Post
    Nothing wrong with soldering to the terminals, as long as the pad on the pcboard has not been damaged.
    It is the poor crimping on the connector that is the problem so new connectors will fix it as well, if you have a professional crimp tool that has a force of a couple of tons that is.
    I donít have a crimp tool but I should! The stuff I have crimped I did with rounded needle nose pliers strategically. Iíd probably be more confident that I can crimp something better than peavey if I had a better tool 🤔

    Anyway, still waiting on these diodes since itís the end times, Iím glad I could even get them. Good to know the DC heater rectifier is a persistent issue and that IN5408 was the right way to go. I was tempted to find a 10A diode but thereís probably no way to fit them on the board. Would have to be a bridge rectifier mounted to the chassis between the transformer and circuit board.

    Peavey had the right idea with their Classic 212 models, those things never smoke all on their own. PTP output section and everything. Really nice stuff.

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    If you don't have a crimp tool, it also works to flow solder into the crimp connector around the wire. I'll often do that, even after crimping, for a little insurance.

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    After handwiring everything in, and replacing the DCH rectifier with IN5408, to my amazement: the AC heater supply is still intermittent. Iím reading 3.5v on one lead, 0v on the other. When it does come on, I can see 7v on the winding that is supplying voltage and 0 on the other. A bit confused by this. I guess the PT is faulty? Whatís a way to know for sure? Reading .4ohms between the leads of the AC heater, and the rest of the circuit looks normal. Not getting AC voltage of any kind to either output tubes or the PI, which probably means no current

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    Quote Originally Posted by Helmholtz View Post
    With 1N400x diodes in power applications always use the glass-passivated (GP) types. These have much better long time reliability/lower failure rates (FIT values) than the cheaper standard versions.

    In one of my former products (a kind of SMPS) the calculated mean time to failure (MTTF) could be increased by a factor 10 using GP type 1N4007 rectifiers.
    Hi Helmoltz,

    Can you explain to me the difference between glass-passivated (GP) types and any other 1N4007 diodes ? How do I spot the differences when someone is selling them over the internet ?

    I didn't realize there was any difference, but I want to be on the lookout for the "Better" type next time I purchase them.

    Thanks for the help.

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    Can you explain to me the difference between glass-passivated (GP) types and any other 1N4007 diodes ? How do I spot the differences when someone is selling them over the internet ?
    Only buy from a reputable distributor.They typically specify glass-passivated types and provide the datasheet e.g.:
    https://www2.mouser.com/ProductDetai...roP3EzTqv8Nw==
    https://www2.mouser.com/datasheet/2/...gp-1768051.pdf

    Often the letters GP are silk screened on the plastic case.

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    Lifetime Member Enzo's Avatar
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    Well the rectifiers would have no effect on the AC heater supply.

    WHERE are you measuring that voltage? Measure it right on the wires from the transformer. Not on the tube sockets or the circuit board, right on the wires themselves. Transformers do fail, but VERY rarely. Far more likely the 10A fuse HOLDER has gone intermittent.

    Also you need to read voltage from one wire to the other. NOT from each wire to ground.

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    It may have been a bad connection in the circuit board internally. I disconnected the leads and wired them directly to the tube socket pins and it has worked perfectly without fail. The problem has ONLY been in the AC heater supply. Probably was this problem to begin with but can you elaborate a little more about why to test like that? Maybe thereís something about how those windings work that I donít understand..

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    Quote Originally Posted by Enzo View Post
    Well the rectifiers would have no effect on the AC heater supply.

    WHERE are you measuring that voltage? Measure it right on the wires from the transformer. Not on the tube sockets or the circuit board, right on the wires themselves. Transformers do fail, but VERY rarely. Far more likely the 10A fuse HOLDER has gone intermittent.

    Also you need to read voltage from one wire to the other. NOT from each wire to ground.
    I was testing them on the pads that the leads were soldered to. I got a different result after disconnecting them

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    Lifetime Member Enzo's Avatar
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    Not sure where I left you, but unlike most amps, there is no ground reference to the heaters, like a center tap. Thus measurements to ground from each wire are meaningless. As to why I specify the wires, when we measure at the tubes, we have not only the transformer, but also the fuse and holder plus all the interconnecting wires. The ribbon from main board to the power board is notorious for burning connector pins.

    You were suspicious of your transformer, so by measuring directly on the transformer wires, we eliminate all those other potential problem areas. If the voltage is still iffy when measured direct, then teh tranny is suspect. If the voltage at the wires is OK and stable, then the other stuff must be the problem.

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    I see what you mean. The 6505+ Iím working on is one of the newer models. No molex no fuse on the AC heater line and there is a reference to ground with 2 100R to ground at the end of the heater line.

    https://www.thetubestore.com/lib/the...-Schematic.pdf

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    Lifetime Member Enzo's Avatar
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    Ah. Well your first post said you had a 6505+. The schematic you just posted is for a 6505+ 112. They are not the same amp.

    So which do you have, the 6505+ head or the 6505+ 112 combo. Then we can all be on the same page.

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    Quote Originally Posted by Enzo View Post
    ......You were suspicious of your transformer, so by measuring directly on the transformer wires, we eliminate all those other potential problem areas. If the voltage is still iffy when measured direct, then teh tranny is suspect. If the voltage at the wires is OK and stable, then the other stuff must be the problem.
    Regardless of head or combo, ^^^^^ this is still good advice and reason to check right at the transformer wires.

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    Lifetime Member Enzo's Avatar
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    Yes, troubleshooting procedure doesn't change, just model-specific details need to be dealt with.

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    Quote Originally Posted by Enzo View Post
    Ah. Well your first post said you had a 6505+. The schematic you just posted is for a 6505+ 112. They are not the same amp.

    So which do you have, the 6505+ head or the 6505+ 112 combo. Then we can all be on the same page.
    Sorry Enzo! I have a Peavey 6505+ 112, I didnít realize they were different or else I would have specified. That is very good advice, the amp is working perfectly after wiring the leads directly to the tube pins.

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    Yes, they are substantially different.

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    Quote Originally Posted by Helmholtz View Post
    Only buy from a reputable distributor.They typically specify glass-passivated types and provide the datasheet e.g.:
    https://www2.mouser.com/ProductDetai...roP3EzTqv8Nw==
    https://www2.mouser.com/datasheet/2/...gp-1768051.pdf

    Often the letters GP are silk screened on the plastic case.
    Good, I bought the last batch from Mouser ! Thanks.

    Sorry Steelwitch, this ended up being a short hijack of the post, I am out.

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    Measure the 32volts AC for the heater wiring from the transformer and follow it up to your bridge rectifier. If it is there when your heaters go out, it is not the transformer. Revert to DC and measure the DC from the bridge rectifier, follow it through to the valve bases.
    R47 and R49 can get dry joints on them and they feed the heaters for.
    I am assuming you mean the FIL 12AX7 heaters and don't forget they get their heaters from the +-24volt supply!

    Or do you mean the Power Valve heaters?

    Yes the 6505plus it totally different.
    Check the AC supply on your bridge rectifier in fault condition, assuming you mean when faulty V1 - V4 go out.
    Check R82 0.68 5W for dry joints and follow the DC path to the valve holders pins 4/5 and 9.
    Where is the break?

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    Last edited by Jon Snell; 04-14-2020 at 09:12 AM. Reason: Wrong information given out.
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    Lifetime Member Enzo's Avatar
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    It is his AC heaters going out.

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    Member Jon Snell's Avatar
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    Measure the 32volts AC for the heater wiring from the transformer and follow it up to your bridge rectifier. If it is there when your heaters go out, it is not the transformer. Revert to DC and measure the DC from the bridge rectifier, follow it through to the valve bases.
    R47 and R49 can get dry joints on them and they feed the heaters for.
    I am assuming you mean the FIL 12AX7 heaters and don't forget they get their heaters from the +-24volt supply!

    Or do you mean the Power Valve heaters?

    Now I have found out that it is the 6505+ 112 Let's try again.
    Assuming you mean the 12AX7 valves, V1 - V4.
    Under fault conditions measure the 6.3v AC supply on the transformer wires, trace the voltage to the bridge rectifier. If all good, check for DC out of your bridge rectifier and through R82 a 0.68 Ohm resistor. Follow the voltage from the negative end of C83 up to pin9 of the valves V1 - V4.
    If OK check the positive side of C83 to pins 4&5 of the valves.
    Finally check across pins 4&5 and 9 of each valve.
    From that method it will be obvious where your fault is.

    If A/C heaters, (output valves etc) there will be a dry joint.

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    Last edited by Jon Snell; 04-14-2020 at 11:18 AM. Reason: More info supplied and more info given.
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    The A/C heaters are the main output valves!
    Why change the bridge rectifier?
    It will be a bad connection.
    I give up.

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    Quote Originally Posted by Jon Snell View Post
    The A/C heaters are the main output valves!
    Why change the bridge rectifier?
    It will be a bad connection.
    I give up.
    As far as I can tell, the amp was fixed in post #18. The rest was academic. The bridge issue was ruled out earlier.
    If you don't have the 'linear mode' selected for thread viewing, it can really mess up the order of the posts. Upper right area at top of page, button labelled 'display'. Set for 'linear' and you will see the posts in chronological order.

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