Peavey 6505+ DC Heater question

[Helmholtz]

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.

[Enzo]

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.

[Steelwitch]

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 there’s something about how those windings work that I don’t understand..

[Steelwitch]

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

[Enzo]

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.

[Steelwitch]

I see what you mean. The 6505+ I’m 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

[Enzo]

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.

[The Dude]

......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.

[Enzo]

Yes, troubleshooting procedure doesn't change, just model-specific details need to be dealt with.

[Steelwitch]

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 didn’t 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.

[Enzo]

Yes, they are substantially different.

[HaroldBrooks]

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.

[Jon Snell]

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?

[Enzo]

It is his AC heaters going out.

[Jon Snell]

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.