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1969 SVT restoration project

So that means that all 6 need to be matched about equally in power to run at its most efficient, or do you set up pairs of AB to push/pull and only have to worry about matching two at a time?

BTW, Psycho, I'm inclined to agree with you about the speakers. I will get them reconed identical to the originals.
 
No. The two trios need to be matched to each other more than they need to match their "opposite" counterpart. With two matched trios that bias differently, the SVT's bias controls can be set to different levels for each side and it will still amplify evenly. IOW, you don't need three pairs, you need two trios.
 
So that means that all 6 need to be matched about equally in power to run at its most efficient, or do you set up pairs of AB to push/pull and only have to worry about matching two at a time?

BTW, Psycho, I'm inclined to agree with you about the speakers. I will get them reconed identical to the originals.


It's not actually pairs, but "sides". Think of it as a car engiine. A V-4 will run 2 pistons "up" and 2 "down" at any given moment, a v6 will run 3 and 3 (the svt is a v3). The svt will let you match 2 different sets or three tubes using pot, so basically you'll need two individually matched trios.
 
Hey, I appreciate you all bearing with my Tube 101 questions. I want to get all the tubes in order before I take it to Birddog. Got a pretty good local tube shop that deals in NOS, so I shouldn't have much of a problem getting them if I need them.

OK, so just bear with me here and make sure I have all this right:

PREAMP:
Three 12DW7, one 6C4, one 12AX7

POWER:
12DW7 for phase inverter
Two 12BH7 for drivers
Six 6146B for power

Psycho, the one tube I can't find is this relay tube you speak of. I assume it goes in the far left empty socket behind the power transformer, correct? What kind of tube is it? I can't find it on the schematic.
 
Psycho, the one tube I can't find is this relay tube you speak of. I assume it goes in the far left empty socket behind the power transformer, correct? What kind of tube is it? I can't find it on the schematic.

It was made by Amperite (who are still in business making similar products BTW); I don't know the model offhand, but IRCC, it's really expensive. It's not essential or even desirable. That tube is a timer relay that doesn't allow the amp to come out of standby until after a certain amount of time has passed in warmup. Your amp has already been modded to not need it; that socket isn't empty, it has a shorting plug in it, and you have a standby switch.
 
I can shed a bit of light onto the recovering of your rig. I recovered my old '71-72' SVT/810 rig a couple of years ago. First of all, to do it right, you will need to invest quite a bit of time. To recover both the head and cab, I invested about 20 total hours! I called Ampeg (pre-Loud) and a tech walked me through the process.

1. Order the tolex. Ampeg will sell you the modern, rough tolex that is used on today's Ampegs. Fliptops can usually get you the similar tolex to the older Ampegs, like your's. Both of these companies will be able to tell you how much to order. However, they cannot pre-cut the tolex for you. It will come in bulk, rolled-up form.

2. Order a good adhesive. I like to use a water-based contact cement. You'll want to use a strong adhesive that won't wrinkle or melt the tolex. I would suggest ordering no more than 1/4 gallon.

3. Disassemble the amp and cab. By this, I only mean taking the chassis, front/back panels, corners, etc. off of the head and the grill, speakers, jack, etc. off of the cab. The desired result is having the bear wooden boxes by themselves.

4. Strip off the old tolex and adhesive. However, make a diagram of how the old tolex was cut. You will use the patterns for the re-tolexing. The tolex should come off with little effort. The old adhesive will be the fun part. Get a fair amount of adhesive remover from a hardware store. You'll also need some tarp plastic and putty knives. In small sections, apply coats of the remover to the bare adhesive. Cover the area with tarp and allow it to do its magic for, at least, an hour. Remove the tarp and start scraping with a putty knife. It is very important to get all of the adhesive off. Repeat this process for the rest of the rig.

5. Once you have the head and cab boxes adhesive-free, now it's time for some sanding. I recommend a hand-held belt sander and a supply of hand-sanding paper for corners. I chose to start with a medium-grit and worked to a fine-grit. Use a tack cloth to get ALL sawdust off when you are done.

6. And now for the actual re-tolexing. First, make sure the wood is completely dust-free and very smooth. Using a wood filler maybe necessary if you have blemishes in the wood. Second, start measuring and cutting the new pieces of tolex. Make the pieces slightly larger than the old stuff; you will cut off the excess as it is attached to the cab. After all tolex pieces are cut, start applying your contact cement to the wood AND the back of a new tolex section. The adhesive needs to be applied evenly and not too heavily. They will need to lightly dry or "flash off" before you apply the new tolex to the wood. Now apply the new tolex piece to the wood carefully. A water-based contact cement will allow you to easily wipe away excess and mistake amounts before it dries. Let the piece dry to the wood for awhile. You need to make sure every piece is dried and firmly in-place before adding another piece. Keep repeating this step for the rest of the sections. For a perfect fit, use a very sharp utility knife to cut the sections' excess tolex off, while applying.

7. Allow the boxes to completely dry before putting everything back together.

Now, this is just a very simplified version of what I did. If you intend of doing the recovering yourself, I do seriously suggest researching this more and/or consulting professionals.

Here's a pic of the head when I got done with it...
 

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I'm starting to consider just stripping the cab and letting a pro recover it. First, I didn't have a pattern to go by when I did it before because it was all ruined. Second, I tend to butcher things I haven't done before and end up taking them to a pro anyway. I think I could do it, but maybe it would be worth a couple hundred not to have to. But your info is very helpful.

Man Psycho, you weren't kidding when you said those tube relays are expensive...$144! But I really can't see not doing it when my whole idea was returning this to original spec at whatever it costs. I'll forget about the $144 eventually, but I'll never forget that empty socket mocking me ;)
 
OK, as I promised, the process starts in earnest today. Here's my agenda:

Take the tubes and go to Skycraft Surplus and test them.

Go to the tube store and buy the tubes that need replacing (BTW, it's really weird how old SVT's use these uncommon tubes and newer ones use traditional tubes like 6550's and 12ax7's, yet they don't sound that much different at all).

Take the head with tubes installed to Birddog Bobby.

Go get my 8-10" cab out of storage, take pics of it as it sits now, then take the speakers out and start stripping the old vinyl.

Prepare an order for parts at Fliptops.net and/or Vintage Amp Restorations.

Then I will call my bank and get my line of credit extended to pay for it all ;)

I predict that I'll get as far as picking up the cab before I pass out. Didn't sleep well last night, and now it's time to get to work on it. Fortunately, I have no gigs until New Year's Eve, so I should be able to get a lot of stuff accomplished with it this week. Stay tuned because the big stuff starts now!

BTW, I was looking at Ebay where they have 3 Blue Lines for sale (one has already ended), and I noticed that none of them had a tube relay, nor did they even have a socket for one. So mine must be a super super early one. Wish I could find a serial number. It must have fallen off with the rear coverplate.
 
-single tube (12w I think), the one closest to the front of the amp, is the phase splitter(or inverter, call it what you will) .

The preamp tubes , well, if i remember correctly most are used by channel 1

Now, about the power tubes, you should see about getting them all replaced to 655o', instead of finding a replacement for the original tube. The tubes in your amp are hard to find (if you even find them), and were replaced by 6550's for reliability on the later svts. You could do this conversion yourself actually. Basically the tech was right about you needing to rewire the whole output section, but it's relatively simple operation if you can understand what you are doing.

If you wan to play out, i'd put 6550s in there because the original output section is not very reliable. Also, do remember that putting 6550s is competely reversible, so if you ever want to sell the amp with original specs, you could rewire it yet again.

The phase inverter if I remember correctly is also a 12DW7, and channel 2 uses the only 12AX7 in the amp.

6146B's (and 6146W's which are interchangeable with them) are transmitter final tubes and used by many hams, I use 6146A's in mine. You can find pairs on ebay for about 30 bucks, they are as easy to get as 6550's on ebay nowadays. Ampeg switched to 6550's because guitarists used to also use them and overdrive them which heated up the plates and destroyed the tube. I don't know of many bass players who do that. They actually have 5 more watts of plate dissipation than a 6550 and the 6146 amps are rated at 330 WRMS. There was a good article about the various 69-79 SVT's in Vacuum Tube Valley magazine which is out of print now I think.

Here is a good deal on a matched sextet of NOS GE's which I'd snap up if I had that amp.

item # 350009063172 ebay.
 
Got as far as getting the cab out of storage. Didn't take the head into Birddog quite yet. I think I may see about rewiring the last power tube socket myself before I take it to him. Doesn't look like much...just pulling the plate wire off the socket and attaching a cap, then checking that it's still wired the same as the other sockets. I think I could do that. I got a cap today that will work until I can find an original. Hopefully the first tech didn't take the original wire off. Eh, I doubt he was that ambitious to put a new wire on ;)

So finally, here are some pics of the cab. It looks crappy now, but I must say that for someone who never did a recover before, my worksmanship isn't horrible. I've seen worse. But I would really like a pattern to cut the new tolex and I need to study some more pics of original cabs to see how it's attached and trimmed. So you guys with original 69 cabs, go take some detailed pics for me, and take the amp corners off, too!

About the speakers...4 of them are recones and will obviously have to be reconed again to match the old cones. But as much as all 8 cones need to be replaced, I can't help but think about future collectability with the remaining original cones. But really, does anyone really want 40 year old cones that have been rained on, shined on, heated on, snowed on, smoked on, snorted on, peed on, and "Inna-Gadda-Da-Vida"'ed on? I personally would rather have recones. They still work, but I can hear sag in them, and I'd much rather have new cones in the original baskets even if I was a collector. Since 4 of them have already been done, I doubt I'll hurt its "collector's value" by reconing the rest. So I guess recones all around it is.

So Psycho, about that tube store trip...:hyper:

I have to put in a plug for this fantastic tube store in Orlando called www.vacuumtubesinc.com . The guy has nothing but NOS out the wazoo! Plus he tests tubes for free and gives you tons of info about your tubes while you wait, and he gives you a 30 day warranty. One thing he told me was I said how I had thought that one SVT sounded much like any other regardless of what the tubes were or when they were made. He told me that the 12DW7 preamp tubes are actually a 12AX7 and a 12AU7 built together, and that a lot of times in amps, they wire the tubes in so only one side works, and my tubes showed evidence of wear on one side but not the other. And that's why I didn't hear much of a difference when they went to 12ax7's and t7's.

Psycho, I know you warned me not to buy tubes yet, but it was a good thing I went down there and had them tested. Every single one of my power tubes were completely shot. Not one of them could be saved, so I would have had to buy them anyway. He ended up going through thirty NOS GE 6146B's to match two sets of three for me and only charged $2 extra per tube. All the rest of the tubes were good except for one 12DW7. He tried to get me to get the 6146W's because they were mil spec and the highest quality out there (and a couple of my power tubes were W's and even one plain 6146), but alas, he said something like they were only made to mil spec from the 70's and later, and since they didn't exist in 1969 and that's the whole deal of this restoration, I opted for the B's at $3 more a pop. I'm glad that I didn't have to replace any other tubes except the one 12DW7, because it turns out they were all Mullards, and NOS Mullards ain't exactly cheap.

I have to say that I've dealt with tube store owners before, and they're usually very no nonsense "get what you need and get out and quit wasting my time" types, especially with musicians. But this guy just went on and on about the different types of tubes and their specs and knew everything off the top of his head. And he seemed like he actually enjoyed having someone to talk to for a change. The guy really eats, sleeps and breathes tubes. And he's got an amazing vintage tube collection. Some are bigger than bowling pins! So just on the basis of his CS alone, I give Jim and www.vacuumtubesinc.com a big thumbs up and recommend them highly for your NOS needs.

So now the next step is to put all the tubes in and see where we stand. In the meantime, here are some pics of the cab...btw, before you ask, the logo looks newer because it was painted white with Testor's paint. It's long since lost any enamel it used to have. But it's original, so anyone who buys it when I retire will just have to deal with it, or if there's a place anyone knows about that could do a re-enamel that would last, I would do that as well.

But enough of my yakkin'...I've got tubes to install! Here's the pics:
 

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Welp, I put in 5 of the new power tubes plus the 6550, and I put in all the rest of the tubes except I was one 12DW7 short (forgot I broke one taking it out and didn't get a replacement) so I subbed a 12AX7A for this short test, and...

For the first time in 10 years, I got sound! Unfortunately, that sound was only a thump from turning the standby on. Otherwise I got nuthin'. The tubes all lit up at least, though. So it is my considered opinion that this amp is still broken ;)

That's all for tonight.
 
Not to belabor the point, but you shouldn't be attempting to power up your amp AT ALL. There are several things in an SVT that could be on edge and a hard-start (non variac) could cause serious catastrophic failure. I also think it's funny you're so dead set on having to have that Amperite relay, yet you're willing to sub 12AX7's or 12AT7's for the 12DW7's. The 12DW7 is essential for the amp to work properly. The relay is not. What I said before stands, if you value the amp and to a lesser extent, your life, don't try to repair or diagnose it yourself in ANY capacity.