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Discussion in 'Amps and Cabs [BG]' started by greengoblin, Nov 9, 2018.
As far as I know, they didn't have the cover initially. Same with the chassis back bottom plate.
I'll second this. I have two '69 SVT's and neither has either.
I'll third it. Mine doesn't have the cover and it used to not have the back plate till Fliptops did a run of replicas and I bought one thinking it belonged there
The chassis on mine is unpainted, but I don't think it is aluminum since it's rusty. Pot's date it to 69. I think I found some parts manufactured in 68 as well, so I was under the impression it was a fairly early one.
The Power PC cover appears to be aluminum. I guess no surprise for an after market part. I think the amp looks a little better with the cover, but it probably doesn't provide any real benefit since I don't think it actually seals out the dust.
Yeah I should call it the silver chassis not aluminum.....
Mine was rusty when I got it and completely gutted it to clean it well.
It's a little frustrating that one of the earmarks of an early SVT is the missing back plate.
Can't say it's ever been an issue for me.
To those who have the unpainted chassis with the TDR (or without), what are your serial numbers on the chassis itself? Just curious.
Made it about 90% of the way through the preamp boards this weekend. Found someone changed to a 12ax7 circuit so I switched that back to stock values. Changed out the electrolytics and any resistors that were out of spec. Left in all of the Tropical Fish caps. Deoxit the pots. switches, sockets and rockers as well as used it to clean the boards. Looked over all remaining solder joints that I did not touch as well. Have one resistor on order that I thought I had, but did not so that is the last item to replace as it tested low on the resistance totem pole. Once I get that replaced I will start the reassembly back in the faceplate/preamp enclosure. The tube sockets all look to be in good shape with the shields intact (no shield on the 7 pin), but if need be I have new belton replacements. Need to find something thinner than what I currently use to retension the sockets as the space in these are tight. The switches are not stock on the preamp so they will be swapped out for the correct and matching switches. After this process is done and reassembled I will start on the power section.
Also ordered the PEC boards from OshPark and will see how I like them. Think I mis-ordered so I may have extras lol. It's really cool that the PEC boards in mine are hand labeled in pencil marking "SVT #1" and "SVT #2", I love finding stuff like this in old amps. They will be tucked away for safe keeping.
Have NOS or test as new vintage tubes for the preamp and power section. A variety of RCA, Mullard, GE and a Telefunken will be part of a tube rolling process in the future. Will probably leave the 6550 set-up and decide which way to go with those. Maybe Sovteks or Tung Sols as NOS Tung Sols or GE's are way too expensive. That is still a long way off.
Regarding the power section cover, I picked one up from Fliptops. It feels to be a slightly thinner gauge than the plate for the preamp and power plates for my V4b. However I could be wrong on the feel. Most pics I see of early models dont have them, but for $15ish we'll see if it goes in.
Serial numbers on the chassis? Long gone.
I don't believe the 6C4 ever had a shield in my amp. No shields on any of the tubes in my 87 Skunk, and its the quietest SVT I have ever played.
The Power PC cover in my amp is mounted with 5 screws...which is correct. Whoever made the plate drilled 6 holes.
What do you plan to do about the screen voltage so the 6550s will make good power; is there already a mod built into the amp? 265W at 5% THD is a common bench test for an amp designed to run 6550s, with a PT putting out ~350V at Node E. Power will likely be much lower with only 220V at Node E.
Note that with the PEC replacement boards the components can be mounted on either side. It depends on if you need pin 1 on the left or right side. Mounting details are in the TB prtaflex wiki.
One socket did not have a tube shield. I use a push-on one in that position though, a Cinch 5020B.
Retensioning can be tricky when space is limited. A wide bore needle, the kind doctors use, can serve.
Honestly, I have not looked at the power section schematics yet or really the power section of the head. I placed it under my bench once pulled and it has been patiently waiting on attention. Was just going by what you had mentioned regarding that it looked like it had been swapped to 6550's. Will cross that bridge when the time comes and do some research before hand.
My "parts" SVT is boxed-up and in storage. My other one has only this tag and IIRC, hand written in marker on the chassis, "Model: SVT"
Not much of an update as I dont have pics, but I have most of the preamp back together with the OshPark PEC boards in place. It is coming along slow, but nicely and I am in no hurry. Decided to mount them to the opposite side of the circuit board since space was an issue on the original side. These are large than the original boards that were replaced.
The bass pot on channel one was not soldered to the board. Instead it had separate wires running to for off-board mounting. With the PEC boards on the other side, it allowed me to remount it to the board.
May have the preamp all back together tonight if I get time. Have to run new switches for power and standby (they had oddballs in place) then reattach the main harness.
Does anyone happen to have the Molex pin part #'s or dimensions? Purchased a new fan from Fliptops and they sent a new wire/connector.
Working through the connector wires to see what goes where and mine is a little diff than the schematic, but I am reading some may be... #3 and #7 show for F, but my 3 is empty (although mine looks to be in #8.. blueish wire) and #7 is yellow which looks correct.
After this I have the switches to go and the preamp will be done...
The umbilical was wired a couple of different ways. My 70 power amp schematic (Rev C) shows pin 3 was NC and the heaters were wired between pins 7 and 8. My 6550 schematic ( Rev D dated 75 I believe) shows the heaters are wired between pins 7 and 3.
If you are careful you can extract pins from the connector and reuse them.
Those pin assignments were moved around. The ‘71 is the only one that I’ve kept a record of.
Pulled the two fan connectors and was able to pry the two prongs that held the wire jacket in place, but the soldered end is pretty tight and wasnt able to pry thme up yet..
Thank you Beans, this forum is such a great wealth of information! Going to have to look at the power amp side as well to see how they correspond with the preamp side for connector alignment before anything gets powered up on the preamp. Was referencing the connector of a linden, nj schematic and a few pins were off and this confirms it as well. While these types of projects are fun to bring back something like this to a working state, sometimes you want to start pulling your hair figuring out what they did and why they did it.. lol
Not everything was well thought through, it was good enough and done to a budget.
It would have been better, in terms of noise, to have two bundles coming from the preamp chassis.
It is good to run the shielded cable outside but strapped to the bundle of other wires. This keeps the preamp signal wire more away from twisted pairs carrying AC.
Since your amp was originally setup to run 6146s, Rev C is probably the right schematic, especially if node H has already already been built into the amp, which I believe you mentioned earlier. Here's the power amp side...I haven't seen the Rev C preamp schematic, but it should be fairly easy to deduce the circuit connections.
The Rev B preamp doesn't quite match up with the Rev C power amp. The pilot light is connected to pin 3 in the Rev B preamp. There may be other differences as well.