Avalon vt-737sp

[Jdm5149]

Haha. 200$ is becoming 2000 fast. I do like the sound of it so it’s worth it. Plus im learning more. Also if another comes along cheap I can get another. The attack and release pots have 3 pins and are the same pot so I am gonna solder them like those in the pics.

 

[kags]

I had a friend who bought a 737 second-hand in non-working condition for $700, thinking he could put new tubes in and flip for a profit. After I replaced the tubes, light bulbs, molex connector, regulator, and caps, he paid me around $300 for parts and another $350 for labor. Around LA, you're lucky to sell a used 737 for $1500 because most people know used units may soon need work. Maybe he made a couple hundred on the flip.

He would have a nice unit for the money if he wanted to keep it for himself, but if anything else was wrong (pots, meter, switches, etc...) it would have been a loss for sure.

In this case, it's a great but costly learning experience and you'll hopefully wind up with a unit that you use and love. I love 737s on bass (Inst input) and for voiceover work, plus they do look great in the rack to clients.

I hope yours turns out great in the end...

 

[Jdm5149]

Thanks. No flipping here. Does sound good on bass. Would love 2 of them for singer / acoustic setup. I’m really addicted to finding great equipment at great deals. I parted together a tc electronics m5000 for like a total of 300$. I love it. I’ve gotten re201 space echos for 200$ a pc. Just missing fuses. Got a eatly 5150 script signature head for 200$ also that wasn’t working. Opened it up and noticed connection was corroded. Cleaned it and it booted right up. When I got this I thought it was also something easy but like u said, in the end I think it’s also gonna be a great add on for my studio.

 

[pucho812]

Haha. 200$ is becoming 2000 fast. I do like the sound of it so it’s worth it. Plus im learning more. Also if another comes along cheap I can get another. The attack and release pots have 3 pins and are the same pot so I am gonna solder them like those in the pics.

Pots wire as a voltage divider or as a variable resistor.
Check carefully, not all pots in a 737 utilize all 3 pins/6pins(dual)

 

[pucho812]

What is the latest here?

 

[Jdm5149]

Haha. Figured I give everyone a break. Have to mail back pot to audio rehab. They sent wrong pot. Need the bass eq pot. So as soon as they get the return they will send correct pot. Going to Indiana for a wedding so rest of week I will be away. I found two washers to fit over the attack and release pots since last tech/owner drilled out openings to fit those larger pots. The gain pot is also not original but new one should fit ok. Just have to know the wiring. Sent note back with return asking for some guidance. It’s 6 pin like one that’s in there now. Don’t know if I can just swap out wires. They also said they could get me a meter but gonna put off on that yet. Might try to reverse wires to meter to test. Thanks for all the help so far. It’s gonna be a great add on to my studio. Especially for vocals. I recently got a tlm103 and a akg414 that needs work. It gonna pair up nicely. Someone is selling another 737 and he’s down to 1000$ from 1300$. Says needs maintenance. A pair would be great lol

 

[pucho812]

Sounds good

 

[TheseGoToEleven]

I wonder, does anyone have a photo of the top side of the tube card? I have a unit on hand but don't want to desolder a bunch of wires if I don't have to.

 

[pucho812]

I wonder, does anyone have a photo of the top side of the tube card? I have a unit on hand but don't want to desolder a bunch of wires if I don't have to.

I have a spare tube card. It has failed film caps. I haven't tested it further to figure out what else is not working with it. Let me grab that for you in the morning. Is there a specific area of the board that you need?

 

[TheseGoToEleven]

I have a spare tube card. It has failed film caps. I haven't tested it further to figure out what else is not working with it. Let me grab that for you in the morning. Is there a specific area of the board that you need?

An overall shot of the top side of the board with the component labels would be great. It’s really hard to view since it’s hidden under the motherboard. For example, I want to know the names of the two relays on there. I assume the relay near tube V1 is labeled K1, and the other one is labeled K2, but it would be nice to have a photo to match.

 

[pucho812]

Yes they are k1 and k2
K1 is to the right of solder pads 8 and 9

K2 is by pads 13,14 and 15.

 

[Jdm5149]

Hey there guys. Been busy loading my stuff into storage to make room to work in house. I finally have all the right pots that need to be replaced but putting off til I have time to do so. Thanks again for all the help so far and have a great Memorial Day Weekend !!

 

[Jdm5149]

Update! Well been busy loading my gear into storage while I work on my house. I did order new meter and knobs and pretty much have it all put together. Only thing is now the meter pegs hard right instead of left when meter switch depressed. I even swapped the two wires and it still pegs hard right. When pressed I can zero it out and adjust compression. Weird. K any idea welcome. Would love to finally finish this piece

 

[Jdm5149]

This is what was marked on circuit board by prior tech I guess

 

[pucho812]

Meter pegging usually indicates the driver ic is not getting its bipolar supply that it is single ended. So one of the ic chips is not getting +/-15 -18vdc. I forget which vdc it’s aupposed to be. There are 78xx and 79xx regulators on the main pcb for thst action. The meter is op07 ic drives the meter. I believe it’s under the I/o card which is to the left of the psu in the back corner.

 

[Jdm5149]

Thanks a lot. Will check over the weekend. Pretty much all that’s left I hope new meter looks real nice.

 

[deveng]

.......calling whisperer........

I also have a 737sp on my bench. Just started to investigate. Opened up and found a bunch of burned parts on the small pcb 5600-7372. I've contacted AudioRehab and they provided the part values. A couple of requests for "partial blocks" of the schematics seems to be a no go. First step for me will be to remove burned parts, clean and inspect the PCB. If traces are burned open I'll see if I can repair. There are no replacement boards available currently so repair is my only option at the moment.


I'd like to know what this board's general functions are??

 

[pucho812]

.......calling whisperer........

I also have a 737sp on my bench. Just started to investigate. Opened up and found a bunch of burned parts on the small pcb 5600-7372. I've contacted AudioRehab and they provided the part values. A couple of requests for "partial blocks" of the schematics seems to be a no go. First step for me will be to remove burned parts, clean and inspect the PCB. If traces are burned open I'll see if I can repair. There are no replacement boards available currently so repair is my only option at the moment.


I'd like to know what this board's general functions are?? View attachment 134270

That’s the I/O board.
Replace the resistors.
If resistors are burning or have burned out. Recap the units and confirm transistors are ok.
I usually replace those vishay caps with Panasonics.

 

[a soBer Newt]

Q9-12 are all part of the same gain block so I would check to see if any of them are shorted.

 

[deveng]

Q9-12 are all part of the same gain block so I would check to see if any of them are shorted.

That’s the I/O board.
Replace the resistors.
If resistors are burning or have burned out. Recap the units and confirm transistors are ok.
I usually replace those vishay caps with Panasonics.

Thanks for the info. That was my plan and to repair any damaged traces. Since the unit is more than 10 years old a recap was also on the list.