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simple 6080/6as7 ppp/circlotron project

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With the 6080 cathodes connected to halfway points of the voltage doublers and the plates connected to the full voltage doubler, there is DC current thru the T? xfmrs (unbalanced load on the voltage doublers). The xfmrs are going to get hot.

Biasing of the 6080's appears to be auto-bias by R11 and R18.
 
circlotron

I noticed the bias voltage as half of the doubler voltage with the return through R2 and also the supply of the splitter tubes both crossing through the output transformer and tough in opposite direction innbalance can easily occur especially with three 6080 in parallel and this would defy the whole purpose of the circlotron which is not suppose to pass DC through the load This was the reason I asked for the bias adjustement .

monyse
 
With R16 at 100K and R12 at 360K, it looks like auto-biasing by R11 will be around 2/3 control and ground reference thru R2 around 1/3 control (which as you say, goes thru 1/2 the V multiplier.). So line voltage will affect biasing for sure. I could see where some control like this could be useful to keep the 6080's regulated versus line voltage, but this seems like too much effect.

The floating supply connections to R3 and R17 may be intended as bootstrapped (CCS like a'la McIntosh) ) loads for the 6AU6's, but the amount here seems excessive. Probably positive feedback.
 
circlotron

Hello Singh

Does it make a difference with the adjustment?
I see you also changed the splitter tube . Is 6AR11 linear enough for the task ? Also did you measure the output RMS voltage of the splitter for max power and total distortion of the amp?
Sorry for so many questions ; I am just curious because I played a lot with 6080/6AS7 tubes.

Thanks

Mony
 
Hello Monyse,
I've made some measurement to the amp.
Input 1.1v at 1kilo Hz.
outputs at primary of opt.Xfmr.96vRMS. & 7.1V at secondary on 4 ohms resistor load.The output Xfmr.is 600:4. That is 15W on Pri.12.5W on 4 Ohms some loss on Xfmr.Pic.attached.I couldn't tell what's the THD.I ain't got a distrotion meter
RE:The adj. is very diff.enough to blow the 6080.
RE:6ar11 It's only two 12by7 in one.I do not know it's linear enough.I used this because High Gm and looks good on my amp.also save space.A citation II used 12by7.
Rgds!
Singh
 

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smoking-amp said:
With the 6080 cathodes connected to halfway points of the voltage doublers and the plates connected to the full voltage doubler, there is DC current thru the T? xfmrs (unbalanced load on the voltage doublers). The xfmrs are going to get hot.

Biasing of the 6080's appears to be auto-bias by R11 and R18.
Hi to all,
This is how I bias the 6080 in my project. Attacted Schematic.
Thanks to all !
Singh
 

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  • 6080bias.pdf
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smoking-amp said:
The biasing looks fine, but the tube current still appears to be only going thru half of the voltage multiplier still. DC current thru the xfmr will make for a hot running xfmr.
Hi,
the biasing current is less then 1mA.you saw there are to Xfms in my schmo.but actually is two windings in one, they'll cancell like any pp does.My amp runs with no hot tranformer after hours.It will keep running cool!
Rgds!
Singh
 
"you saw there are two Xfms in my schmo.but actually is two windings in one, they'll cancell like any pp does"

OH, OK. Wasn't obvious from the schematic.
I would check the capacitance between the windings though if they are on the same xfmr. I prefer to use two xfmrs for Circlotron mode, each with split bobbins, to mimimize common mode capacitance.
 
smoking-amp said:
"you saw there are two Xfms in my schmo.but actually is two windings in one, they'll cancell like any pp does"

OH, OK. Wasn't obvious from the schematic.
I would check the capacitance between the windings though if they are on the same xfmr. I prefer to use two xfmrs for Circlotron mode, each with split bobbins, to mimimize common mode capacitance.
Yeah,It is better to use fullwave rectifier 1 for B+ other for Biasing.It will be no more Simple......
Rgds!
Singh
 
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