Avalon vt-737sp

[TheseGoToEleven]

The meter sits below zero. When I press it in it pins to the right. Definitely no signal on meter and when running into my console nothing. I stated before that the vu adjustment is pushed down alittle from the work they did on it. They replaced some pots and put regular pots. They put some black stuff to protect board. It’s just something I have to fix later on or might order 2 to do while I troubleshoot

Sounds like the VU meter needs calibrating, because with the meter switch pushed in and the compressor button out, the UV meter should show zero. But at least you can say now that mic signal passes all the way through the first two tubes and reaches the output knob.

Next, you might want to try the line input instead of mic input. Set gain and output to 12 o'clock, send in +4dBu and see what you get at T11, T12, and 65. This will see if the line input amp passes signal. If successful, check the line out XLR for signal and see what you get. Hopefully you will see +4dBu there as well.

 

[Jdm5149]

Yeah. In case of meter. I need to replace the pot to let vu adjustment sit correctly to adjust from front panel. K will do at end of week. U guys have been great.

 

[TheseGoToEleven]

Here is an initial set of notes I made about Vt-737sp solder points and relays. This is not even remotely complete but hopefully it can help someone get started with troubleshooting.

 

[Jdm5149]

Wow. Thanks. Really appreciate it

 

[pucho812]

Here is an initial set of notes I made about Vt-737sp solder points and relays. This is not even remotely complete but hopefully it can help someone get started with troubleshooting.

That is very nice.
We should combine notes and make a trouble shooting guide.

I had a 737 on the bench not to long ago where everything worked except 2 mid bands on the eq. they were low level. ended up that there was an issue between the bost/cut pot and pins connecting to the eq card. ended up having to make a jumper but once I did, everything was per normal.

 

[TheseGoToEleven]

I had a 737 on the bench not to long ago where everything worked except 2 mid bands on the eq. they were low level. ended up that there was an issue between the bost/cut pot and pins connecting to the eq card. ended up having to make a jumper but once I did, everything was per normal.

Wow, that's so random! With all the kit on that card, and most of that for the mids, you'd think the problem was somewhere in there, not the interconnects. Well done.

That is very nice.
We should combine notes and make a trouble shooting guide.

Thanks. That's a great idea. Anything you want to add, send it to me and I can combine it with this. Or add these notes to what you already have, and I'll try to send you more.

I'm going to try to grab a 737 and add more audio tracing and relay descriptions to these notes. It's hard to get too far without a unit on hand. Photos can only do so much since a lot of traces aren't easily visible. Being able to define the signal paths in terms of solder points makes troubleshooting so much easier.

 

[Jdm5149]

Not with unit today but just wanted to know about the heater voltage. After warm up it gets up to 6.42v. Is that a problem.

 

[pucho812]

Not with unit today but just wanted to know about the heater voltage. After warm up it gets up to 6.42v. Is that a problem.

I doubt it. Higher heater voltage usually means shorter tube life. Is it consistent at 6.42?

 

[Jdm5149]

Yes. It gets to that and stays. Happy I got it to stay but curious about it.

 

[pucho812]

Yes. It gets to that and stays. Happy I got it to stay but curious about it.

should be o.k. I assume that is with load but never assume.
is that tubes installed?

 

[Jdm5149]

Yes. All tubes. Bought brand new.

 

[pucho812]

Yes. All tubes. Bought brand new.

Ok that’s not that big of an increase your ok

 

[Jdm5149]

 

[amplexus]

I’ve got a pair that I love. Have serviced them now, one came to me that wasnt passing mic signal. Line and Inst. were fine. Traced it to the input transformer that had a bad secondary.

It may or may not have been mentioned but the input trafo is just a rebadged Lundhal LL1538XL.

Also, not incidentally, a Urei B11178B will work in place of the OG trafo with almost no notable change in gain structure.

Following thread with interest re: circuit tracing tho. I don’t have the time to do it myself but if someone was willing to take on a full trace I might be willing to send one of my pair to accomplish the task during some downtime.

 

[Jdm5149]

Hope I don’t get anyone arrested by the tech police

 

[Jdm5149]

Once I get this going maybe a new thread. Altec 446c. Want to mod mine like EMI

 

[pucho812]

I’ve got a pair that I love. Have serviced them now, one came to me that wasnt passing mic signal. Line and Inst. were fine. Traced it to the input transformer that had a bad secondary.

It may or may not have been mentioned but the input trafo is just a rebadged Lundhal LL1538XL.

Also, not incidentally, a Urei B11178B will work in place of the OG trafo with almost no notable change in gain structure.

Following thread with interest re: circuit tracing tho. I don’t have the time to do it myself but if someone was willing to take on a full trace I might be willing to send one of my pair to accomplish the task during some downtime.

actually the input transformer is not a rebadged 1538XL although they are similar and both made my Lundahl. they both do the 1:5 and have the same pinout. I forget what the differences are exactly.

 

[TheseGoToEleven]

Not sure, but I thought the input transformer might be this one? Ratio of 1:4.5 with a 600 ohm static secondary resistance. It's difficult to reach the secondary pins to measure anything without moving the tube card, which means desoldering a handful of wires. Edit: I think this is the right dimensions and row spacing too.

EDIT: Nope, this isn't the correct one despite the Avalon name being on the data sheet. Wrong size, wrong spacing, wrong static resistances.

 

[pucho812]

Not sure, but I thought the input transformer might be this one? Ratio of 1:4.5 with a 600 ohm static secondary resistance. It's difficult to reach the secondary pins to measure anything without moving the tube card, which means desoldering a handful of wires. I think this is the right dimensions and row spacing too.

Interesting. Never seen that doc before

 

[TheseGoToEleven]

Interesting. Never seen that doc before

I couldn't remember where I saw it either, but just found it again on Lundahl's website here.