Just picked up a Peavey Super Festival VTA-400 amp, 200W into 2 ohms from 4x 6550. There was a larger version made, the VTA-800, with 8x 6550 
and the two amps were built on the same chassis.
From the schematic, it appears that both amps share the same power supply. Is there any reason I shouldn't stick another output transformer and power amp in there? 4 more 6550s would get me 400W easily, if I go that way. I figure I can run into two cabinets, or tie the output transformer secondaries together as in the oldest 100W Marshalls.
Here's the real question: If I decided to put another power amp in there, why not put in a different type of output tube? I was thinking keep the 6550's for 200W of mostly clean power, and then a 120W-ish side running a little dirty. Are there any tubes out there that can take 615V on the plates without melting down? I have 350, 300, and 285V available in the power supply for the screens. I was thinking I could run big-bottle 6CA7s if they'd take the screen voltage. I can always drop it, if I need to.
Some kind soul put a master on this thing years ago, so I'll just copy that and put a second master feeding the second output channel. Preamp is 3x 12AX7, then a 6AN8 for the PI. The PI is on the same PCB as the power amp, looks like you just drop another board and transformer in there for the VTA-800 version.
Ideas / suggestions?
and the two amps were built on the same chassis.From the schematic, it appears that both amps share the same power supply. Is there any reason I shouldn't stick another output transformer and power amp in there? 4 more 6550s would get me 400W easily, if I go that way. I figure I can run into two cabinets, or tie the output transformer secondaries together as in the oldest 100W Marshalls.
Here's the real question: If I decided to put another power amp in there, why not put in a different type of output tube? I was thinking keep the 6550's for 200W of mostly clean power, and then a 120W-ish side running a little dirty. Are there any tubes out there that can take 615V on the plates without melting down? I have 350, 300, and 285V available in the power supply for the screens. I was thinking I could run big-bottle 6CA7s if they'd take the screen voltage. I can always drop it, if I need to.
Some kind soul put a master on this thing years ago, so I'll just copy that and put a second master feeding the second output channel. Preamp is 3x 12AX7, then a 6AN8 for the PI. The PI is on the same PCB as the power amp, looks like you just drop another board and transformer in there for the VTA-800 version.
Ideas / suggestions?
Hi Pharaohamps
If you can post your schematic that would be a lot of help. I have seen instances, and understand why, a manufacturer would use the same parts in two different models of product. But the power transformer is a large part of the cost of the amp, so I queston if that part would be the same. If you could post pictures of the insides of both models that would also help. If there is extra capacity in the power transformer it should be possible to do something with it. I have built a guitar amp where two output sections shared a comon power supply, so it can be done.
Ill watch for more info, and perhaps do a little poking myself.
Bob
If you can post your schematic that would be a lot of help. I have seen instances, and understand why, a manufacturer would use the same parts in two different models of product. But the power transformer is a large part of the cost of the amp, so I queston if that part would be the same. If you could post pictures of the insides of both models that would also help. If there is extra capacity in the power transformer it should be possible to do something with it. I have built a guitar amp where two output sections shared a comon power supply, so it can be done.
Ill watch for more info, and perhaps do a little poking myself.
Bob
Schematic:
http://www.pharaohamps.com/temp/schem/vta400.pdf
I don't have pics of the VTA-800, but I can take some pics of my 400 this week hopefully.
http://www.pharaohamps.com/temp/schem/vta400.pdf
I don't have pics of the VTA-800, but I can take some pics of my 400 this week hopefully.
Well
I found a picture of the 400 outside view-----and
http://www.peavey.com/support/technotes/hartley/chapter_1.pdf
This is a great article by the man himself.
Yea the schematic says that "VTA 800 has 2 power amplifiers"
but is the trans big enough? Also I think you better plan on a seperate PI section for the other tube set.
I found a picture of the 400 outside view-----and
http://www.peavey.com/support/technotes/hartley/chapter_1.pdf
This is a great article by the man himself.
Yea the schematic says that "VTA 800 has 2 power amplifiers"
but is the trans big enough? Also I think you better plan on a seperate PI section for the other tube set.
Attachments
Pic of the back of the amp:
The PT looks pretty beefy...
An externally hosted image should be here but it was not working when we last tested it.
The PT looks pretty beefy...
OK
So you plan implies that the power transformer is about twice as big as is needed for the existing tubes. Is there any information such as manufacturer name and part number on the trans? We need to know what it can do. It is concievable that Peavey used the same transformer on both models because they crunched the cost numbers and why buy two different parts when they could just stock one part for both amps? This is kind of a long shot, but if it is true then it should be possible to ad another power section. Also you would need room for the extra tubes ect. Not too encoraging, but if we can find out the info on the power capacity of the trans somebody on this forum can probally do the math and say if it is possible.
So you plan implies that the power transformer is about twice as big as is needed for the existing tubes. Is there any information such as manufacturer name and part number on the trans? We need to know what it can do. It is concievable that Peavey used the same transformer on both models because they crunched the cost numbers and why buy two different parts when they could just stock one part for both amps? This is kind of a long shot, but if it is true then it should be possible to ad another power section. Also you would need room for the extra tubes ect. Not too encoraging, but if we can find out the info on the power capacity of the trans somebody on this forum can probally do the math and say if it is possible.
I took the amp apart tonight, and it looks as though the 800 uses a different chassis. The chassis in the 400 contains only the power tubes and PI, and then that connects to the preamp board which is mounted on the back of the faceplate. The 800 probably uses the same cabinet with a bigger chassis in the bottom, and probably a bigger PT. I ran it pretty much cranked for a couple of hours tonight and the PT was warm but nothing to write home about. It's probably sized about right for an amp of this wattage. I'm thinking that the 800 may or may not have a different PT - the schematic doesn't specify at all. The 800 has four output jacks, and you have to use at least two cabinets to get full output from it, so that would suggest two OT's in that model. To be honest, the 400 is as loud as I'd ever need in a bass amp. It's also razor-sharp in the treble department, and has clarity that has to be heard to be believed - probably compensating for the horrible-sounding folded-horn 18 cabs that these amps came with from the factory. The preamp is dirt-simple to work on, so I can always mod it for more bass if I want, but I think I'll leave it alone. It's pretty awesome as-is.
I'm planning on running it into my SVT cabinet, and then pairing that up with a Peavey Classic Series 120 power amp + tube preamp into a Peavey 4x12 bass cabinet (the tall ported model from the late '70s / early '80s.) Run the Super Festival clean and the Classic 120 a little bit dirty... Should be tasty.
I'm planning on running it into my SVT cabinet, and then pairing that up with a Peavey Classic Series 120 power amp + tube preamp into a Peavey 4x12 bass cabinet (the tall ported model from the late '70s / early '80s.) Run the Super Festival clean and the Classic 120 a little bit dirty... Should be tasty.
Ok I was just about to suggest some kind of external power section with its own cabinet. The schematic indicates something called "overdrive outputs" but I don't see those on your picture. That point could be used to get a signal over to the external power unit allowing you to use the same controls on the preamp. It sounds like you have some pieces to play with. Have fun.
bob
bob
Hi,
Have a look here:
http://www.peavey.com/assets/literature/manuals/vta400_800.pdf
The overdrive outputs can be linked to the other channel (low inpu) for quite some overdrive.
Nice feature..
But the 800 bust be very heavy.
Allthough the VT Classic from Ampeg is heavy to.
Tarzan
Have a look here:
http://www.peavey.com/assets/literature/manuals/vta400_800.pdf
The overdrive outputs can be linked to the other channel (low inpu) for quite some overdrive.
Nice feature..
But the 800 bust be very heavy.
Allthough the VT Classic from Ampeg is heavy to.
Tarzan
Geek is right - this amp is perfect as-is. I replaced the output tubes and am mating it up to a Peavey speaker cabinet of similar vintage with some nice, efficient speakers. Since it's only 200W, I don't have to worry about putting in super heavy-duty drivers like I would if I were running 600-800W of solid-state through it.
Thanks for all the advice, guys - I appreciate it.
Thanks for all the advice, guys - I appreciate it.
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