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Any Ideas

jaymanaa

jaymanaa

RIP 1961-2018
I was just sitting down here in the shop thinking about what to do for a project, and these arrived.:yes: I wasn't really looking for OPTs when I found them, but they went awfully cheap, so I figured I'd take a chance. They are Tomiko 5k PP with KT66 as the suggested tube. From the looks of them I'm guessing somewhere around 30 watts maybe. I'd like to try a "different" tube, maybe something intended for TV. I dunno, just thought I'd ask here for ideas. So, whatcha think?:scratch2:
 
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A pair of 6BG6's would be nice or push pull parallel 6KY8A's would be nice ,use the pentode sections in PPP and two of the triodes as drivers and two triodes as the front end . A 6LR8 and some others in this family of tube would work .

I realy like the Antek toroid ouputs i have , buy a toriod power transformer and make a very compact amp .

Mark
 
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d00d... jayman... time for a screen drive (G2 drive) "enhanced triode mode" amp!

Those toroids don't like DC offset (one tube with higher bias than the other)- they saturate quickly... screen-drive amps have almost NO bias current in the first place (for example, the Berning EA230 only uses about 3ma of bias current!), so it's almost impossible to cause saturation. Even with 100% imbalance, that's only 3ma differential!

Ever wanted to make a Berning clone or something similar? You got the right iron! 6JM6/6JN6/6JB6 or anything similar, in G2 drive PP...
 
Looks like I have plenty of those sweeps to play with. The only copies of the Berning schematic I can find are very hard to read though.
 
I made some triode curves for 6AV5. Run at about 300V, 50mA per tube, and you'd make nearly 16 watts output. 6JM6, 6JN6, and nearly a horde of other sweep tubes are very similar to the 6AV5 (so this could apply to them as well). Can still do triode (and with cheap tubes) :yes:
 

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bricktop said:
I made some triode curves for 6AV5. Run at about 300V, 50mA per tube, and you'd make nearly 16 watts output. 6JM6, 6JN6, and nearly a horde of other sweep tubes are very similar to the 6AV5 (so this could apply to them as well). Can still do triode (and with cheap tubes) :yes:
Click to expand...

Hmm, looks like I may end up with more voltage than that. I need to do some digging I guess. I'd like to do this as stereo on one chassis and save the 6B4Gs for big mono-blocks (just thinking out loud here). I think I have a crap load of 6AV5s, are any of them better? I seem to remember George (tubelab) saying something about two different types of plate structures with one type being bullet proof and the other down right wimpy.:scratch2:
 
jaymanaa said:
Looks like I have plenty of those sweeps to play with. The only copies of the Berning schematic I can find are very hard to read though.
Click to expand...

Is this the one you have, or is it any better? My eyes aren't anything to write home about, and I can make out what's going on. If you got any questions, feel free to ask... I think I got it sussed out.

attachment.php


Note that he uses a 6.5K output transformer... from what I've been reading from George (Tubelab) and others, the 6JN6/6BJ6 should actually be able to make more power into a 5K loading. Given that it's "quasi-triode", it has pretty low plate impedance, and can handle some pretty serious loading...

One thing I might think about doing differently than Berning- he's using plate-to-cathode feedback from the OPT plate to the diff amp cathode. Might it be better to use Micah's plate-to-plate feedback... i.e, going from the plate of the OPT to the plate of the diff amp?

Another thought- 12DW7 for the input tube? High gain first stage, low gain phase splitter? Or, if you did a stereo amp on one chassis, a 12AX7 for both channels gain, then a 12AU7 or 12BH7 as the concertina for both channels? A little more gain there might allow a little more plate-to-plate feedback...

And a last thought- might putting in a switch, so that you can parallel the output tube cathodes (putting the two 33 ohm resistor in parallel, and connecting the cathodes in the process) reduce distortion a bit? I remember reading somewhere how an unbypassed common cathode resistor on output tubes could act to reduce distortion. And since the resistors are already there (for bias current sense), it'd be easy to try jumping the two cathodes together. Shouldn't change the bias anyway (it's fixed bias- you just set it, then close the jumper/switch)...

Regards,
Gordon.
 
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It's a Williamson circuit (sorta...) - there are gain stages after the phase inverter, so it doesn't have to swing much voltage. Since the first two stages are DC coupled, you will have some adjustments to make if you use different tubes. If you have an extra 6.3V winding, bias it positive and run the cathode followers on it (minimize heater-cathode voltage). 6CG7, 12BH7, 6GU7 could be used here too.

I've been thinking about this circuit with 6AV5s - I also have some 6FW5s which are an uprated 6AV5 (18W plate).
 
It is pretty much like a Heathkit W6 with a screen-drive output stage, isn't it?

It'll need more gain than a W6 (since the 6JN6/6JB6 in screen-drive has very little gain)... hence the 12AT7 first stage... but otherwise, it's very similar...

The nice thing, is that neither gain stage needs to "source" much load... the cathodyne has very high input impedance, as does the cathode follower driver stage. So, even high-plate-impedance tubes such as 12AX7 and such can work in both positions, if more gain is desired. I'd be tempted to use something like 12AX7 or a pentode (think Dynaco circuit- just graft the pentode gain/triode cathodyne onto the diff amp, driver and output stage) for the first stage, and a 12AT7 or such for the diff amp...
 
I need someone to splain this to me in simple terms. How does this circuit insure that the current on each side of the OPT primary (CT) will be the same? That's what I need to be mindful of right? Sorry, but this is getting really close to over my head.:scratch2:
 
I was looking at some Acrosound data and noticed they actually give a spec for allowable primary imbalance of like 10%. I'm assuming that a torid is much, much lower than that.
 
Bias is determined/adjusted by the DC voltage on the screens of the output tubes. Potentiometers P1 and P2 control the screen voltages of each output tube.
 
bricktop said:
Bias is determined/adjusted by the DC voltage on the screens of the output tubes. Potentiometers P1 and P2 control the screen voltages of each output tube.
Click to expand...

So, any circuit with adjustable bias would allow me to keep the current balanced in the OPT primary? I was thinking there was more to it.:scratch2:
 
GordonW said:
Is this the one you have, or is it any better? My eyes aren't anything to write home about, and I can make out what's going on. If you got any questions, feel free to ask... I think I got it sussed out.

attachment.php


Note that he uses a 6.5K output transformer... from what I've been reading from George (Tubelab) and others, the 6JN6/6BJ6 should actually be able to make more power into a 5K loading. Given that it's "quasi-triode", it has pretty low plate impedance, and can handle some pretty serious loading...

One thing I might think about doing differently than Berning- he's using plate-to-cathode feedback from the OPT plate to the diff amp cathode. Might it be better to use Micah's plate-to-plate feedback... i.e, going from the plate of the OPT to the plate of the diff amp?

Another thought- 12DW7 for the input tube? High gain first stage, low gain phase splitter? Or, if you did a stereo amp on one chassis, a 12AX7 for both channels gain, then a 12AU7 or 12BH7 as the concertina for both channels? A little more gain there might allow a little more plate-to-plate feedback...

And a last thought- might putting in a switch, so that you can parallel the output tube cathodes (putting the two 33 ohm resistor in parallel, and connecting the cathodes in the process) reduce distortion a bit? I remember reading somewhere how an unbypassed common cathode resistor on output tubes could act to reduce distortion. And since the resistors are already there (for bias current sense), it'd be easy to try jumping the two cathodes together. Shouldn't change the bias anyway (it's fixed bias- you just set it, then close the jumper/switch)...

Regards,
Gordon.
Click to expand...

What is that first resistor right on the input, 8.2K maybe? I'm just re-drawing the whole thing on graph paper. Oh, and what's the deal with that goofy looking diode in the fil. string?
 
BTW, I got a few bits together and cut a hole. Gotta start somewhere I guess.:yes:
 
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