Unusual tubes to drive a JAN 829B

[larc99]

Now rather than make my first tube amp easy and use someone elses schematic I want to make my life more difficult and design my own. What I want to design is a Single-ended 829B amp by tying the two grids together into one grid and the two anodes into one anode. Making one beam tetrode out of dual.
I have a few questions though.

With the 829B set up like this would Ultra-Linear be an option?
I'd like to drive it with an equally strange looking tube like an acorn or one of those tubes that look like they have horns. I don't know very many tubes off the top of my head so what are some suggestions for odd looking but not ridiculously expensive tubes that I could drive this with?
What are the advantages/disadvantages of parafeed (i was thinking of using it in the design)? I read a few articles and post where people hate it and others where they love it.

[pmillett]

You can do UL with a parallel connected 829B. There is an internal cap between screen and cathode but it doesn't seem to have any effect at audio. Safest to keep the plate voltage under 300 or so, though many (myself included) have gone as high as 400V without problems.

Dual-plate-cap tubes that come to mind are the RK34/2C34/DET20 dual triode, and the 2C22/7193 single triode (basically 1/2 6SN7 with P and G on caps). Also RK60/1641 rectifier, more or less 5R4 with two plate caps.

Pete

[larc99]

thanks for the reply.
I think I'm gonna go with the 2c22 for the driving tube. Also thanks for the suggestion on plate voltage.

I have another question though can parafeed and ultralinear be used together?

[korneluk]

Originally posted by larc99
I have another question though can parafeed and ultralinear be used together?

That would require two caps. I have never seen such circuit.

-- josé k.

[larc99]

thats why i'm asking as I've never seen it do either so it makes me think that it won't work but it couldn't hurt to ask. If I had enough time, money, and more than just a multimeter to work with I would just test and see for myself but...i don't.

Also why would it need two caps?

[korneluk]

Originally posted by larc99
Also why would it need two caps?

Parafeed (parallel feed) connection requires a DC blocking cap between the tube and the transformer. In single-end topology, there is only one connection from the plate to the transformer, thus one cap.

In single-ended ultra-linear topology, the plate and the grid of the tube conect to the transformer; thus, what you're proposing would be a "single-ended, ultra-linear, parafeed topology" with two caps, one at the plate and one at the UL connection.

Here is a link to a SE parafeed 829B amp:

http://829b.com/829B_1.aspx

To connect it as a UL parafeed, remove R9, and place another cap between the grid the the UL tap of the transformer.



I hope this helps,

-- josé k.

[Yvesm]

Originally posted by korneluk

. . .
To connect it as a UL parafeed, remove R9, and place another cap between the grid the the UL tap of the transformer.

... and add an "appropriate" resistor from screen to B+.

Yves.

[larc99]

Think I'm just gonna stick to ultralinear until I get a better understanding of tubes...though I'm noting this down for use in a future project. Gonna draw up an extremely rough schematic some time tonight for guys to take a look at.

Thanks for the help thus far!

[CarlyBoy]

You could go with a couple of 6D22S half-wave rectifiers.

[larc99]

Well heres the ultra-rough-probably-screwed-something-up schematic. Yes I know there are no values on anything but I want to know if I set the schematic up properly and I'd like to know what would be suggested as the value of the output transformer. I'm looking for a Hammond one as they seem to be the most bang for the buck.

Also TinyCad doesn't have a dual beam tetrode available for schematics so I used two single beam tetrodes.