6AU6 replacement

[pancaQe]

Hi,
I'm in a pickle. I'm in the middle of building a 6V6 push pull mono amp with one 12AU7 and two 6AU6. I just realized I don't have any 7BK tube sockets but have some 9A sockets. So I'm trying to find a sharp cut off pentode in a 9 pin socket with the same characteristics as a 6AU6. Any help would be appreciated. Here's the schematic I'm working off.

http://www.freeinfosociety.com/elect...ew.php?id=2394

 

[kevinkr]

Should not be hard to get the required sockets in about the same time frame as any alternative to the 6AU6A which you probably also do not have on hand. Changing to a different type of tube may require some additional tweaking.

 

[pancaQe]

thanks for your quick response kevinkr. I have hundreds of tubes, lots of time and no money to put into this project. So if I can get a couple of possibilities the chances are good I already have the tubes.

 

[TheGimp]

What topology are you using it in?

What plate current?

 

[pancaQe]

B+ is 460v (unloaded)
what do you mean by topography? You'll have to forgive me this only the second tube amp I've built so I'm a little green.
thanks

 

[TV7]

EF86? they're cheap for good NOS and can be found in many leak circuits..... triode all the way for me.

 

[Wavebourn]

The complete analog is 6SJ7, but it has octal socket. In 9 pin bulb most probably 5879 is the closest one.

 

[vinylkid58]

B+ is 460v (unloaded)
what do you mean by topography? You'll have to forgive me this only the second tube amp I've built so I'm a little green.
thanks

Did you copy the power supply from the schematic you posted? That poor little 5Y3.

jeff

 

[morinix]

Tube Lore says it is based on 6SH7, another octal tube.

 

[pancaQe]

vinylkid 58: Yes I did, I've pretty much copied that schematic exactly. It looked simple and I thought it might be fun to give it a try. What do you think would be a better choice. Actually if there are any improvements that wouldn't be too far off the original, I'd be willing to try it. It's all just an experiment to me. wavebourne, morinix thanks for your suggestions I take a look at them. thanks

 

[DF96]

9-pin RF pentodes were never very popular in the US, although common over here. You could try EF80/6BX6 with some resistor changes. That may have more gain, so other adjustments might be needed too.

 

[SY]

Although the title says "RCA," I seriously doubt the provenance. The "designer" has made some... ummmm... creative choices. I'd suspect a Chinese origin.

 

[TonyTecson]

no SY, i saw that from a webpage many years ago by an english speaking guy....it does not use global negative feedback, the pentodes are run at less than 1ma current and i suspect that the gain is rather very high......

 

[SY]

But ultimate origin? Not RCA, I think. The input stage is a poor version of the Williamson (there must be almost 0.3mA going though the cathodyne!), the feedback arrangement is relatively ineffective, and RCA engineers were smart enough to understand feedback from the OPT secondary.

RCA's actual pentode driver amp was quite an excellent and innovative design.

 

[DF96]

It is RCA. It appears in RC-19 receiving tube manual: circuit 19-11 on page 361. It is described as "High-Fidelity Audio Amplifier, Class AB1, Output 10 Watts". The verson linked to is slightly redrawn, but clearly the same circuit. No GNFB. Same component values. My guess is that RCA published it in different places, not clear with they would redraw it as printing plates were expensive.

 

[pancaQe]

Can anyone suggest a simple, quality 6V6 push pull amp design/schematic. At this point it looks like I'm gonna have to back track anyway. I'm looking at schematics using 6SN7. Any suggestions?

 

[SY]

Well, Dave, you've thoroughly disillusioned me!

 

[DF96]

I must admit I was surprised, but I guess even RCA employed some designers who were not as good as others. Or maybe it was a Friday afternoon design?

 

[Joe Roberts]

That is a Japanese-drawn circuit. I think it came from Asano's famous book of the 1970s in which he give circuits and photos for dozen of tube amps that he built. Ultimately he built over 100 amps.

DF96 is correct in that it is the late 50s RCA tube manual suggested design.

Many of those tube manual designs strike me as a bit odd looking at them with modern eyes!

 

[DF96]

My guess is that it is a low-power version of an originally higher power amp, where the extra driver stage might have a purpose. There is a 35W circuit, with some similarities, on the next page of the RCA manual. A 100-200W PA amplifier somewhere might be the original?