Military projector amp - last edited 9/26/22 - layout help needed

[yello]

It appears that something is drawing excess current when the power tubes are plugged in, hence a short in that part of the circuit. This should be detectable
Another hypothesis is the power transformer secondary windings. It's possible there is a flaw in one of those windings. It might stay stabil until a certain amount of current is being drawn. This could be the winding itself or some bad connection perhaps. This is a long shot though.. but we need to consider all possibilities...how do we test this? Disconnecting the secondary windings and running them through a variable resistor to ground reference? Watch out! This is advanced tech stuff... You say you have other similar amps.. you could try another power transformer from one of those working amps. You don't have to remove them, just disconnect secondary wiring and jumper from one amp to the other. don't forget to connect both chassis grounds...
Firts rule out the heater winding by disconnecting the HT wiring from the power transformer and test if the amp stays on with all tubes in. If there's a bias tap you'll have to disconnect that too. That will narrow it down to the HT

Did you try posting this at the Ampgarage? There are some smart oldtimers over there that will feast on problems like these

I can post the issue at the ampgarage - I haven't done that yet.

On testing another PT - I'm not sure I understand how I incorporate the PT secondary wires from another amp. Disconnect the PT connections at points 3, 4, and 5 on my problem amp PT (see pic below), then jumper from those three points to the same points on the other amp's PT? and jumper the chassis together to ground them? Then only my new amp gets plugged in and turned on, the other amp is just sitting there letting a portion of its PT to be used even though it is otherwise not plugged in or functioning?

Here is a photo of the PT - not sure it means anything but there is some separation near terminals 1, 6, 7 and 8, at least visible cracking in the black epoxy coating there, where the neutral comes in and heaters/CT are:

[Bieworm]

It appears that something is drawing excess current when the power tubes are plugged in, hence a short in that part of the circuit. This should be detectable
Another hypothesis is the power transformer secondary windings. It's possible there is a flaw in one of those windings. It might stay stabil until a certain amount of current is being drawn. This could be the winding itself or some bad connection perhaps. This is a long shot though.. but we need to consider all possibilities...how do we test this? Disconnecting the secondary windings and running them through a variable resistor to ground reference? Watch out! This is advanced tech stuff... You say you have other similar amps.. you could try another power transformer from one of those working amps. You don't have to remove them, just disconnect secondary wiring and jumper from one amp to the other. don't forget to connect both chassis grounds...
Firts rule out the heater winding by disconnecting the HT wiring from the power transformer and test if the amp stays on with all tubes in. If there's a bias tap you'll have to disconnect that too. That will narrow it down to the HT

Did you try posting this at the Ampgarage? There are some smart oldtimers over there that will feast on problems like these

I can post the issue at the ampgarage - I haven't done that yet.

On testing another PT - I'm not sure I understand how I incorporate the PT secondary wires from another amp. Disconnect the PT connections at points 3, 4, and 5 on my problem amp PT (see pic below), then jumper from those three points to the same points on the other amp's PT? and jumper the chassis together to ground them? Then only my new amp gets plugged in and turned on, the other amp is just sitting there letting a portion of its PT to be used even though it is otherwise not plugged in or functioning?

Here is a photo of the PT - not sure it means anything but there is some separation near terminals 1, 6, 7 and 8, at least visible cracking in the black epoxy coating there, where the neutral comes in and heaters/CT are:

No.. to test your maybe faulty transformer you have to disengage it and use the transformer you are sure us a good one, so the one from the other amp has to deliver the power to the amp you're working on at the moment. This is very tricky, be aware.
Disconnect your secondaries from the current amp. Attach longer pieces of wire to the disconnected wires. Mark/code them with paper tape so you know which is which. Don't forget to ground both chassis to each other.
The long wires are to be soldered to the good transformer. Heatshrink or tape off the connections between the wires so they can never touch each other.
Then power on the other amp...this will juice up your broken amp.
Use your lightbulb on that one too...

[yello]

No.. to test your maybe faulty transformer you have to disengage it and use the transformer you are sure us a good one, so the one from the other amp has to deliver the power to the amp you're working on at the moment. This is very tricky, be aware.
Disconnect your secondaries from the current amp. Attach longer pieces of wire to the disconnected wires. Mark/code them with paper tape so you know which is which. Don't forget to ground both chassis to each other.
The long wires are to be soldered to the good transformer. Heatshrink or tape off the connections between the wires so they can never touch each other.
Then power on the other amp...this will juice up your broken amp.
Use your lightbulb on that one too...

I see, that makes sense. I do have another of these amps with the same circuit and PT, but it is in non-modded/as-found condition, it is not a working amp.

Seems to me that I would therefore need to remove the PT from the other amp, and swap it into this amp? That wouldn't take too long as it is easy to access, and fairly straightforward. Are there any other tests I should try with this current amp before swapping the PT, like measurements I should be taking of it either off or on? I don't want to replace the PT if it is unnecessary, and its a wild card given it is untested, but if it is the next logical step, I'll tackle it.

And it seems like the Ampgarage has a more extensive fuse blowing testing procedure than I was using, are these good next steps?

https://ampgarage.com/forum/viewtopic.php?f=6&t=32210

I also found this detailed article about blowing fuses:

http://www.geofex.com/ampdbug/fuseblow.htm

[Bieworm]

It's hard to judge from a distance. I just gave it as a possible cause, pretty unlikely though.
In front of the amp I'd be probing and disconnecting until I found stuff that changes things..

[yello]

It's hard to judge from a distance. I just gave it as a possible cause, pretty unlikely though.
In front of the amp I'd be probing and disconnecting until I found stuff that changes things..

I just need more experience and knowledge to know what to probe and disconnect!

[Bieworm]

It's hard to judge from a distance. I just gave it as a possible cause, pretty unlikely though.
In front of the amp I'd be probing and disconnecting until I found stuff that changes things..

I just need more experience and knowledge to know what to probe and disconnect!

Ah.. you're ambitious enough to get there.. keep on going!!!

[yello]

It's hard to judge from a distance. I just gave it as a possible cause, pretty unlikely though.
In front of the amp I'd be probing and disconnecting until I found stuff that changes things..

I just need more experience and knowledge to know what to probe and disconnect!

Ah.. you're ambitious enough to get there.. keep on going!!!

Thanks, I'm determined! And even though this has been weeks of frustration, I am certainly learning my way around circuits and troubleshooting, so its a good education.

Here is my Amp Garage thread if you want to check out the ideas I'm getting on troubleshooting the issue:

https://ampgarage.com/forum/viewtopic.p ... 18#p439518

[Bieworm]

I just need more experience and knowledge to know what to probe and disconnect!

Ah.. you're ambitious enough to get there.. keep on going!!!

Thanks, I'm determined! And even though this has been weeks of frustration, I am certainly learning my way around circuits and troubleshooting, so its a good education.

Here is my Amp Garage thread if you want to check out the ideas I'm getting on troubleshooting the issue:

https://ampgarage.com/forum/viewtopic.p ... 18#p439518

You'll solve this eventually. I was struggling on a new build myself for a week or 2. I knew it was something stupid.. but couldn't find it. Today I finally found the mistake(s) and all is well now.. at the right moment ! I have planned 2 new builds, starting later on this week. A 20W plexi and a high powered 6G3 with reverb. I haven't decided which one I will build first.

[yello]

You'll solve this eventually. I was struggling on a new build myself for a week or 2. I knew it was something stupid.. but couldn't find it. Today I finally found the mistake(s) and all is well now.. at the right moment ! I have planned 2 new builds, starting later on this week. A 20W plexi and a high powered 6G3 with reverb. I haven't decided which one I will build first.

Yeah, I wanna finish this one up as I have several fun amps to build! I have a cool 18 watt waiting, as well as a Princeton kit I got from a friend, and a RobRob 1 watt Deluxe, and....

[JMPGuitars]

Thanks, I'm determined! And even though this has been weeks of frustration, I am certainly learning my way around circuits and troubleshooting, so its a good education.

You certainly learn a lot less if everything works out perfectly every time.

Question: If you suspect your funky filter cap tube sockets, how would you go about testing that theory?

[yello]

Question: If you suspect your funky filter cap tube sockets, how would you go about testing that theory?

Not sure. I have already tried to put in a different filter cap trio (swapped the two identical pairs of cap trios). I could try another pair I just made. But that doesn't get at the socket. I could replace the socket with another identical original socket I have, or put in a brand new one (I might have one on hand). It's only a couple wires and this socket is fairly easy to access.

I wouldn't know how to test it in place, though the thread I posted over ay ampgarage might be leading me down that path with their suggestions. Worth checking out for anyone interested in how they are approaching the problem for me.

[yello]

Over at the ampgarge I'm getting a suggestion to:

"If you want to know how much current is being drawn and you have some clip leads then wire up your voltmeter set for low amps in line with either side of the on/ off switch as might be the easiest place to open up the primary side of the power transformer."

I don't fully understand - am I inserting my meter between the power cord, and the primary input of the PT? To measure if power from the wall is correct? Or is it between the PT primary and something else?

The context is I was removing the wire from plate of each tube going to the OT, and removing the wire from the 6x4 to the OT Center, and looking to measure current.

I asked them to clarify but haven't gotten a response, figured someone here might be able to help.

The thread is here:

https://ampgarage.com/forum/viewtopic.php?f=6&t=35337

[Bieworm]

Over at the ampgarge I'm getting a suggestion to:

"If you want to know how much current is being drawn and you have some clip leads then wire up your voltmeter set for low amps in line with either side of the on/ off switch as might be the easiest place to open up the primary side of the power transformer."

I don't fully understand - am I inserting my meter between the power cord, and the primary input of the PT? To measure if power from the wall is correct? Or is it between the PT primary and something else?

The context is I was removing the wire from plate of each tube going to the OT, and removing the wire from the 6x4 to the OT Center, and looking to measure current.

I asked them to clarify but haven't gotten a response, figured someone here might be able to help.

The thread is here:

https://ampgarage.com/forum/viewtopic.php?f=6&t=35337

I read that too.. I'm not educated enough to know where Stevem is going with this. He'll respond though. People might be occupied with other stuff sometimes.. or sometimes I'm under the impression they get bored and don't show interest any longer.
Maybe try the DIYaudio site. Lots of tech nerd types over there.. or try EL34WORLD.COM, although it's lots of the same people from the ampgarage , and they get bored even sooner when they suspect you are of less knowledge, sadly..
Would love to be of any help and visit Seattle once more.. but it's a 10h flight for me
Seattle stole my heart.. especially the piano guy at Pike Street!!!

[Bieworm]

I think those are really cool projects you have though...

[yello]

I read that too.. I'm not educated enough to know where Stevem is going with this. He'll respond though. People might be occupied with other stuff sometimes.. or sometimes I'm under the impression they get bored and don't show interest any longer.
Maybe try the DIYaudio site. Lots of tech nerd types over there.. or try EL34WORLD.COM, although it's lots of the same people from the ampgarage , and they get bored even sooner when they suspect you are of less knowledge, sadly..
Would love to be of any help and visit Seattle once more.. but it's a 10h flight for me
Seattle stole my heart.. especially the piano guy at Pike Street!!!

Yes, hopefully I will get the advice I need as I really want to sort this out! These amps sound great when working. I just don't know enough yet to troubleshoot myself, so rely on learning from others when they respond. I appreciate you taking the time to keep providing tips and insight, I'm willing to try anything!

Seattle is fun - its definitely changed the last 5-10 years, but there are still highlights.

[JMPGuitars]

Yes, hopefully I will get the advice I need as I really want to sort this out! These amps sound great when working. I just don't know enough yet to troubleshoot myself, so rely on learning from others when they respond. I appreciate you taking the time to keep providing tips and insight, I'm willing to try anything!

The problem only occurred after you changed things, correct? Logically, look at the things you've changed. I think the next thing on the list, in the area you isolated the issue to, is the caps/the socket(s) they're using.

[yello]

The problem only occurred after you changed things, correct? Logically, look at the things you've changed. I think the next thing on the list, in the area you isolated the issue to, is the caps/the socket(s) they're using.

Essentially, yes. The amp was stock and unplayed in decades. I added IEC, new filter caps, and changed one microphonic cap out and two resistors. Plugged it in and played it, seemed to work but had strange crackling. I posted video here of crackling sound. Then after cleaning tube sockets the fuse blew and I noticed the broken resistor.

Given it is old, hard to say if I caused something, or if it was something ready to fail and its a coincidence. If I understand my light bulb limiter test results, the problem is in the power section, which to your point leaves filter cap socket areas. The only things I did there was spray deoxit in those sockets, and put in new filter caps. Filter caps have been tested, no shorts, proper values. I swapped the caps between sockets and no different result.

I think I will change the filter cap socket that holds caps C216 A/B/C, as 214 feeds other parts of the amp not power section. I also made a new filter cap trio to install as a test. Once I eliminate those things, if the problem is still there, I will post results. Not sure what the heck to try after that, unless I need to be testing the PT or OT.

[yello]

I think the next thing on the list, in the area you isolated the issue to, is the caps/the socket(s) they're using.

I unscrewed the cap socket to inspect it, and it looks pristine. I don't see anything about it showing arcing, or a crack, or something to touch/short. Makes me hesitant to replace it, as I replaced the tube sockets thinking they might be the problem, but they were pristine and it didn't fix it.

I suppose I'll try new filter caps in this old socket, then decide about socket, but do you all think i should bother replacing this?

[yello]

Quick update - I tried 6 new filter caps for C214 and C216, in existing sockets (considering I see no discernible issue) and I get the same result. With rectifiers in, amp runs fine. Once I insert a power tube, my limiter glows brightly signaling a short.

I'm running out of things it could be - PT? OT?

[JMPGuitars]

I'm running out of things it could be - PT? OT?

https://www.youtube.com/watch?v=WiH-l5wRGBA

Maybe drink less wine though.