Modded TCM1150 APEX460 disaster

A

amzavareei

New member
I did all kinds of mods on this. And like the tool I am, I didn't test after every mod. Just went and did them all at once. So now I don't know what's wrong with it! I turned it on, let it warm up, and no signal! Opened it up, and the tube was warm like it's supposed to be. I changed the tube, same thing. Changed again... And again... turned it on once without a tube, realized it, and switched it back off. Now no tube warming. I tested the tube with a multimeter, and the three pins that are suppposed to be getting voltage are. Continuity on the board is fine, and I checked all the connections to match the schematics. Oh, and the pattern control voltage is working fine too.

Changes I've made:
Changed 2 diodes on PSU to 56v zeners, to lower voltage to tube to about 106
Replaced a couple PSU caps to elnas (the ones going to the transistor)
Replace a couple signal caps to ansar and black gates
removed the LPF caps going to the tranny
replaced the transformer with a Cinemag C2480
changed the tube to a Mullard 12AT7 / CV4024
got a studio projects litz cable
that's basically it.

Anyone have any suggestions on helping me figure out this problem? Thanks!
 
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I know some people frown upon posting the same stuff on other MB's, but if the smart guys here like MSHilarious can't help, you might want to check on Gearslutz and Studio Forums-- I decided to get my TCM1100 modded by Dave Thomas based on threads there and there's a lot of technical discussion of the mods for these mics on those boards and posts by people who were able to successfully mod these mics themselves-- someone might be able to help you on those boards too.
 
...hopefully Flatpicker (Tim) or Philgood will come along shortly and shed some light on the problem...I opt to let those guys call the shots as to the mods I've considered along the way... ;)
 
I had the same thing happen to one that I did. It turns out that a wire to the tube socket had come off due to a bad solder joint. Look carefully for open ends of wire, then check the socket for a soldering point with no wire.

Check the areas that you soldered the caps to the motherboard. make sure there are no shorts.

Did you check the polarity on the Black Gate cap? It should only go one way. Same with the zener diodes. There should be a polarity mark.

Try it with the original cable.

Let us know what happens after you check it.
 
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It was an N series Black Gate, so supposedly non-polar. Anyway the long end was put where the positive was on old cap. Diodes go the same way. I am reading the proper voltage going to the tube. Yeah, I tried both cables. I haven't really checked the socket. I'm going to go over the whole thing again momentarily.
 
Well, if you're reading proper voltage at the plate and filament there's only two things it could be. Capsule or transformer. Did you use the center tap on the transformer?
 
I just looked all over it. The transformer seemed to be fine. I got like 1k on one side and 50 on the other.

The new transformer and the old transformer both have 4 leads. No center cap. Is there something wrong with that?

If there's something wrong with either the capsule or the transformer, would that cause the tube to not warm?
 
OK,

In most cases the answer is so easy that it makes you slap your forehead, saying: "It is so stupid!!!!" But getting to that stage might be somewhat painful and take some time.
I don't have the schematics in front of me, so will speak from memory.

First, I have no idea why would you want to lower the plate voltage, but it is unrelated issue.

Power up the damn thing with no tube inside.
Check voltages on the tube socket. The pins 4 and 5 are connected, so you should read around 6-7V between either 4 or 5 and 9, to make sure the heater supply reaches there.

Either pin 1 or 6 should show 112V.

Nothing at any other pin.

Then turn the thing off, wait a few minutes and insert tube.
Turn the sucker on. If it still does not glow and you read good voltage for the heater, the tube is way south.
Change it for a good tube and let's assume it glows fine. I don't remember which side is which, so you should read either something like around 50V on pin 1 and 112 on pin 6, or vs. versa. Respectively, the pins 3 and 8 should show something around 2V and let's say 60V, or vs. versa.

Either, pin 2 or 7 should read a plate voltage (i.e. if you read 50V on pin 1 from previous test, then it should appear on pin 7. If you previously read it on pin 6, the it should be on grid of another half, i.e. pin 2).

If you got confused, just read the voltages on each pin, post it here, and we can go from there.
 
amzavareei said:
I just looked all over it. The transformer seemed to be fine. I got like 1k on one side and 50 on the other.

The new transformer and the old transformer both have 4 leads. No center cap. Is there something wrong with that?

If there's something wrong with either the capsule or the transformer, would that cause the tube to not warm?
Click to expand...

No, there's nothing wrong. In fact if there was one I would tell you not to use it.

Also, check the back of the boards to make sure you didn't disconnect any wires by accident.

I sent you a PM. Check your inbox.
 
PhilGood said:
You are referring to R8?

Any suggestions for changing it?
Click to expand...

No... unless you change the transformer ratio (i.e. different transformer if you want to keep the CF stage). I think, I mentioned in another thread about getting rid of CF stage, at all (then you can keep the existing transformer and can relam it). As it is, it just does not make any sense.
 
Marik said:
No... unless you change the transformer ratio (i.e. different transformer if you want to keep the CF stage). I think, I mentioned in another thread about getting rid of CF stage, at all (then you can keep the existing transformer and can relam it). As it is, it just does not make any sense.
Click to expand...

Yeah. I've been wanting to do that, but can never seem to find the thread. Gus had also posted some instructions on doing it, but I wasn't really able to follow his instructions. A before and after schematic would help it make sense.
 
Marik, I'll try what you suggested later this evening. But I've tried 3 different tubes that I know to be good tubes. So what if it's the capsule? It's not wrinkled, and all the leads are going to the right places. Could the soldering gun have burned anything out through the wires? I'll post some voltages tonight.

Ironically, in the search for loose wires, the only ones I've found were ones I loosed searching for loose wires.

So I'm going to mic shootout at Avatar Studios today. Some companies are coming in to show off their mics, and maybe donate some. Maybe Neumann will be handing out KM184s like so many lollipops of yesterdays evening. I should be so lucky to get one!

One of the engineers there has modded the apex 460, and is actually having them manufactured per his design. It's called the Avatar U76. Clever, huh? I'm not sure what he's done exactly, but I should learn a little tonight. He did put some sort of pot on the PSU I believe. Maybe also to lower the plate voltage. Here's some info on that at Studio Forums
 
amzavareei said:
Marik, I'll try what you suggested later this evening. But I've tried 3 different tubes that I know to be good tubes. So what if it's the capsule? It's not wrinkled, and all the leads are going to the right places. Could the soldering gun have burned anything out through the wires? I'll post some voltages tonight.

Ironically, in the search for loose wires, the only ones I've found were ones I loosed searching for loose wires.

So I'm going to mic shootout at Avatar Studios today. Some companies are coming in to show off their mics, and maybe donate some. Maybe Neumann will be handing out KM184s like so many lollipops of yesterdays evening. I should be so lucky to get one!

One of the engineers there has modded the apex 460, and is actually having them manufactured per his design. It's called the Avatar U76. Clever, huh? I'm not sure what he's done exactly, but I should learn a little tonight. He did put some sort of pot on the PSU I believe. Maybe also to lower the plate voltage. Here's some info on that at Studio Forums
Click to expand...

Are you referring to the "Advanced Audio U67" being made by Dave Thomas, or something else? I've read that thread which led me to send my old, unused Nady TCM 1100 to Dave for the full treatment. I missed the reference to the "Avatar"
 
No, this is different. Avatar Studios is one of the few major studios left in New York. My roommate's working on the new Dream Theater at the moment. They have a three month lock-out. The rough mixes without the vox and quiet keys is really great. They are insane. But it's only gonna go from great to worse.
 
amzavareei said:
No, this is different. Avatar Studios is one of the few major studios left in New York. My roommate's working on the new Dream Theater at the moment. They have a three month lock-out. The rough mixes without the vox and quiet keys is really great. They are insane. But it's only gonna go from great to worse.
Click to expand...

That's awesome-- I have a Berklee buddy who's a huge Dream Theater fan. It sounds like the mods are ultimately going to be very similar though as the basic mod only involves a few cap changes and the tube swap. Will your friend do the capsule and transformer mods too? I might want more of these depending on how my uber-Nady turns out :D
 
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