Is there such an amp?

[tribi9]

I want to build a different amp on a Vibrochamp chassis.

Is there an amp that meets the following:

2 X octal tubes

2 X 9 pin tube

Diode rectified and clean sounding.

I have a 330 - 0 330 PT and I also have a push pull OT with an 8K primary with multi secondary output.

Cheers and thanks for ay input.

[Sonny ReVerb]

I'd probably recommend a Princeton variant. You could easily sub diodes for the tube rectifier. You might have to mess with the B+ a bit to get it where you want it.

http://www.schematicheaven.com/fenderam ... _schem.pdf

http://www.schematicheaven.com/fenderam ... _schem.pdf

Or, if you could add a third 12AX7, a 6V6 Plexi!

http://mhuss.com/Plexi6V6/index.html

[Phil_S]

4 tubes...330-0-330...lots of choices. SS will give you b+ of about 450vdc. That is enough to power a couple of 6L6 or EL34 but 8K primary is probably wrong for those. As high as the B+ is going to be, I'm not sure what I'd choose for a primary tube. You don't say how many mA you've got available, or how many watts your OT is rated for. Have you got a particular sound in mind?

Actually, here's something that will work well with what you've got:
http://home.comcast.net/~psymonds/6SN7amp.htm
Use 12AX7's or 5751's instead of the 6SL7's. You don't want to run the 6SN7's over 450V, so you'll be taking it close to the edge, but I think it will work. If I recall, mine was done with a 340-0-340. You may want to increase the dropping resistors in the B+ supply ladder to reduce preamp voltage a bit, too. Keep the concertina PI. Triode outputs don't like to be pushed too hard.

[tribi9]

The princeton sounds tempting but would that be clean enough?

I want to build something maybe Traynor/Fender flavored but any good clean sounding amp will do.

What would be the proper OT primary impedance for say a 2x6L6 or a 2 X EL34?

Also Phil, I want to go with 2 octal and 2 nine pin as I don't want to enlarge the holes, also Im not sure what the mA is on the OT. How do I go about finding out?

[Phil_S]

What is the primary DCR on the PT? The lower the better. That will suggest a VA rating. I have a chart somewhere...post what you find out.

For the OT, it's a guess based on core size. I'm not much good for that. Do you know what tubes it was running before? That would be your best sign.

For that schematic I posted the link for...use 12AX7's instead of 6SL7's and you're good to go with 2 noval and 2 octal. Or is it the position of the holes that you want to use noval power tubes? That's more of a problem with the design I showed you. You can sub 12AU7 for 6SN7 nicely, but those small tubes won't stand up to B+ at 450. The spec says 12AU7 max voltage is 330.

The problem I'm seeing is that you need power tubes that will work well at ~450V into an 8K OT. This probably fits for a pair of JJ 6V6 (so I've heard, not tried) and a pair of 6SN7 (four triode sections). You've got an odd combination of iron there.

[Firestorm]

Since your OT has multiple secondaries, you're not limited to the 8K primary: put an 8-ohm speaker on the 16-ohm tap and you've got a 4K primary. Reasonable territory for 6L6 or EL34. The biggest issue is the current rating of the PT's 6.3V winding. That more than anything will dictate what kind of tubes you can use.

[tribi9]

The PT is an old vintage PT I got. The only thing I know about it, is the wires

Green 6.3, (I would like to think that it is rated at 3A but I don't know for sure.)

Red Secondary 340 - 0 - 340 (I double checked with a meter)

Blue 6.3 (Second 6.3 V tap)

Yellow 5.1

The OT, I got no clue on it save for the fact that it has an 8k primary.

Phil, I'd like to try something slightly different than an AA763 tho' and maybe with a neater layout just because Im a n00b and easy to follow diagrams are my friend.

[tribi9]

I already drilled some extra holes for the standoffs. Pic of what I'm working with...

[IMG:800:600]http://i114.photobucket.com/albums/n271 ... C02460.jpg[/img]

[tribi9]

I'd probably recommend a Princeton variant. You could easily sub diodes for the tube rectifier. You might have to mess with the B+ a bit to get it where you want it.

http://www.schematicheaven.com/fenderam ... _schem.pdf

Actually I have decided to do the AA964 as it matches the faceplate I already have in the amp plus I have a few NOS 6V6"s I've found around.

I'm going to google for info on how to to do the diode rect instead of the tube or if anybody here has a diagram they would want to share it'd be appreciated.... Remember this is only my second amp so I'm still learning...

[dave g]

Actually I have decided to do the AA964

Good choice! My favorite 6V6 Fender

I would suggest changing the .1uF couplers in the PI to .02uF, though.

[Phil_S]

Now that I see what you've got, I might be tempted to use a pair of 6L6 in cathode bias, doing what Firestorm suggested to make the OT function at 4K primary. I see you've decided...well...whatever.

To build a solid state rectifier is simple. Just follow the attached. You can use either a full wave bridge or the simple full wave. I usually hang this on a single terminal strip by making the thing "flat" instead of square...same connections, just squished <tech term>.

[tribi9]

Now that I see what you've got, I might be tempted to use a pair of 6L6 in cathode bias, doing what Firestorm suggested to make the OT function at 4K primary. I see you've decided...well...whatever.

To build a solid state rectifier is simple. Just follow the attached. You can use either a full wave bridge or the simple full wave. I usually hang this on a single terminal strip by making the thing "flat" instead of square...same connections, just squished <tech term>.

Tell me more and thanks for the link. Is there a schematic/layout on the 6L6 beast you're talking about?

[Cliff Schecht]

It's usually as easy as beefing up the cathode bias resistor to 10W and throwing in 6L6's with those old Fender amps, you'll notice that the cathode resistor is 250 Ohms in most all of them. The only difference is 6V6 amps get a 5W unit and 6L6's get a 10W one. Of course check the bias after you do this but you should easily be able to run the 6L6's no problem. I did the same thing recently on a 5C3 build and it worked out great from the first chord.

[Phil_S]

Now that I see what you've got, I might be tempted to use a pair of 6L6 in cathode bias, doing what Firestorm suggested to make the OT function at 4K primary. I see you've decided...well...whatever.

To build a solid state rectifier is simple. Just follow the attached. You can use either a full wave bridge or the simple full wave. I usually hang this on a single terminal strip by making the thing "flat" instead of square...same connections, just squished <tech term>.

Tell me more and thanks for the link. Is there a schematic/layout on the 6L6 beast you're talking about?

Nah, real amp builders don't need no stinking schematics
Seriously, what Cilff said. Any 6V6 circuit with a beefier cathode resistor. I might be inclined to go higher than 250 ohm, but probably not higher than 470 or 500 ohm. You'll need to experiment with it. I'd look for about 25W output.

[Cliff Schecht]

Yeah the 250 Ohms comes from using a 5R4 rectifier with a 330-0-330V transformer. You'll need to adjust the bias depending on your HV, if it's higher than you'll need to make the value a bit larger to compensate. The value is also dependent on the transformer you are using. In other words, the lower the impedance and higher your HV line, the larger that cathode resistor will need to be.