'73 Ampeg SVT pre-amp

OTGMB · #1 01-17-2011, 07:15 PM

Hello all,
I am new to the forum and the proud new owner of an original '73 SVT power amp. I need other parts (empty head cab, hardware, and the PRE-AMP section) to restore this. I have looked on Evilbay for the last few weeks and found nothing but a "new" empty SVT head cab. Does anyone know where to find vintage parts for this? I really would at least like to find a empty circuit board for the pre-amp so the layout is correct. I have the schematic and have the know how to build one. I'm so excited, I can't stand it, but realize it may be next to forever until I can complete the beast with the correct parts.
Thanks for any helpful info. Mucho appreciated.

Jonyak · #2 01-17-2011, 07:22 PM

www.fliptops.net

OTGMB · #3 01-17-2011, 07:26 PM

Yea, I had already tried fliptops. Forgot to mention that. No circuit boards.

Jonyak · #4 01-17-2011, 07:28 PM

ahh sorry.

OTGMB · #5 01-18-2011, 12:19 AM

Thanks anyways. Any other ideas?

JimmyM · #6 01-18-2011, 01:44 AM

just the usual ebay craigslist stuff. i think patience will be required on this one.

beans-on-toast · #7 01-18-2011, 06:14 AM

There is a copy of a service manual that a TB'er posted here. The board layouts are included. The schematics are a bit fuzzy but they are available elsewhere.

For scale, the main pre-amp circuit board measures about 9 11/16" X 3 7/16". The two tone PC boards measure 4" X 1 1/8".

beans-on-toast · #8 01-18-2011, 06:25 AM

Here is a pic of the boards:

OTGMB · #9 01-18-2011, 10:43 AM

Helpful. Thanks Beans-on-Toast

fu22ba55 · #10 01-18-2011, 11:25 AM

I'm not an amp builder by any stretch of the imagination... but how hard would it be to re-build the circuit on some turret board? Do you need the PCB if you alread have the schematic?

I'd take turret board over PCB any day, but again... I have no idea what a PITA it would be. Maybe the circuit is too complex for turret board.

If you find a builder willing to do it, count me in for a turret-board version of the SVT pre. (Cheaper to build two than one, no?)

Spencer! · #11 01-18-2011, 11:28 AM

Quote:

Originally Posted by fu22ba55

I'd take turret board over PCB any day, but again... I have no idea what a PITA it would be.

A colossal PITA, especially considering you wouldn't hear a difference.

fu22ba55 · #12 01-18-2011, 12:20 PM

Quote:

Originally Posted by Spencer!

A colossal PITA, especially considering you wouldn't hear a difference.

Rats.

Would it be any easier if you eliminated all the ultra high & low rockers and just left the 1-2-3 mid EQ selector?

(It's my understanding that the only advantage to turret is durability and ease of diagnosis... but maybe if he doesn't need all the rocker switches, would be feasible? I'm only asking because I'm kicking the idea around of having a tech build me a custom SVT, and he's a turret-board guy.)

OTGMB · #13 01-19-2011, 02:00 AM

That might be my only option. I've looked over the schematic for a while and I don't think it is too awful bad. It is doable. I'm concerned about the layout. That is where the turret board could be a problem. If I used the PCB, the layout is mostly done for me. Trying to stay true to the original is all. I'm going to give it some time to see what might pop up. My patience could run out before too long and I will do the turret board then. I would be doing it myself so if you want one, I would be buying double of all the parts is all. I'm not sure what to charge for time. I'm not the fastest nor the builds are the prettiest. I have only built stuff for myself in the past. Only bad thing is, obviously, we won't know what it sounds like until one is finished. Let me know if you want in on it. I'm going to try and hold out for a couple months before I start that venture.

okabass · #14 01-19-2011, 05:57 AM

You can relatively easy make a PCB.
Take a 1:1 photocopy of the PCB pic in the service manual. Put then transparent paper on it and draw the layout (the darker the better). Then buy a photo sensitive PCB, and go with the instructions.
I bet you'll most likely can find somebody in your area who is willing to make it for you.
In my knowledge there'll no problems making it using turret or eyeletboard (as I did).
http://www.okabass.suntuubi.com/data...inen%20176.jpg

Or here's a little simplified SVT-type pre using a mini turretboard.
http://www.okabass.suntuubi.com/data...e%20valmis.jpg

http://www.ele.tut.fi/~telok/MakePCBs/
http://www.electricstuff.co.uk/pcbs.html
http://www.qsl.net/k5lxp/projects/PCBFab/PCBFab.html

beans-on-toast · #15 01-19-2011, 06:58 AM

If you want to make a circuit board, one option to consider is to use the services of a fabrication plant. Here are some good places to deal with: 4pcb, expresspcb, batchPCB. Okabass has a reference to a couple of them in his last link. When you consider the start-up cost of making a PC yourself, these places are worth considering. I've both made my own boards and used PCB fabrication companies. The latter wins out when you want a professional looking board.

Building the SVT on a turret board has a lot of advantages. You can easily tweak the circuit (this is an iterative process and hard to do with a PCB) and make it quieter (twist those heater lines!).

The Baxandall (James) related components can be built on the tone pots as shown here. The tapped 800 milliHenry inductor is the only atypical part in the amp. You might be able to buy the part from Loud as they use it in the SVT-VR. You can get one custom built Sowter or if you want to learn how to do it, build one yourself 1, 2. The most cost effective approach is to use three off the shelf inductors.

OTGMB · #16 01-19-2011, 03:31 PM

Thanks for the info. How does your board sound? Happen to have the layout for that? I'm starting to lean towards the turret/eyelet board. Seems more practical.

OTGMB · #17 01-19-2011, 03:36 PM

Thanks so much. Very helpful. Leaning towards a turret/ eyelet board now. More practical and yes, easier to go tweak it later. I'll have to try Loud for the 800 milliHenry inductor. I was just on the phone with them the other day. I've never heard of Sowter before. Good to know.
Thanks again.

okcrum · #18 01-19-2011, 03:39 PM

I dunno. I'd probably wait for a junker SVT with blown power and/or output transformers. It would be cheap, and you'd get everything you need at once.

beans-on-toast · #19 01-19-2011, 04:04 PM

Quote:

Originally Posted by okcrum

I'd probably wait for a junker SVT with blown power and/or output transformers. It would be cheap, and you'd get everything you need at once.

Yes, that's the way to go if you can find one. Building one from scratch can get expensive.

A lot of amps and instruments were damaged in the Nashville floods last year. A TB connection there or even calling some shops in the area might lead to finding what you're looking for.

OTGMB · #20 01-25-2011, 02:09 AM

I thought I would share. She just came in today. Believe it or not, this is after the first stage of clean up. With the exception of a few parts (3 plate resistors at least,) I think she's mostly stock. I've got my work cut out for me. Power amp only, no tubes, no enclosure, no pre-amp, etc. I bought a "SVT survival kit" and a pair of coupling caps for parts that came in last week. Ordered a Driver tube cover plate today from Fliptops. Thanks all for the info already given. Any more thoughts or suggestions are encouraged and appreciated. I realize its pretty rough and only half of the glory here, but I am freaking out..... never owned a vintage SVT before.

http://s129.photobucket.com/albums/p...view=slideshow