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Old 9th October 2010, 10:37 PM   #1
Brit01 is offline Brit01  United Kingdom
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Default First OTL breadboarded



First OTL amp (circlotron concept) breadboarded and sweet music coming out albeit only with 2 x 6080's on 1 channel.
Driver topology a little different to most.

But with only 1-4mV DC.
You can see the voltmeter on the 2000m setting.

Still trying out different designs of CCS on the LTP but so far so good.

Now it's time to build up the tube bank of 6080's and buy some bigger transformers.

Also would like to incorporate some kind of speaker protection.
Maybe relays?
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Old 9th October 2010, 10:38 PM   #2
Brit01 is offline Brit01  United Kingdom
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Old 9th October 2010, 11:15 PM   #3
Brit01 is offline Brit01  United Kingdom
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One question about the DC offset.

If I keep the grid bias below -29 volts the dc if low (1-10mV).

If I begin the increase the grid bias to then the dc on the output increases!

I thought the DC balance was due to the balance of the signals from the splitter/LTP.

Also without a 8 ohm dummy load the DC offset is higher. (100mV or more). When I switch on the dummy load or speaker if falls.
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Old 10th October 2010, 07:46 AM   #4
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Hello Brit01,
It does look sort of fun, However I would stand outside the door when you turn that thing on. There is a certain fear factor. DC offset make me think transformer.
Keep on truckin brother.
DT
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Old 10th October 2010, 08:43 AM   #5
banat is offline banat  Serbia
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Quote:
Originally Posted by Brit01 View Post
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Hello Brit 01

Cool electronic `Jungle`on Your experiment breadboard,hey but Your Circlotron Amp WORK! from first `hit` and thats good

Not sure what kind the driver stage You use there,Tube or SS, but usually DC offset drift come from this driver stage

Keep continue your work,but take care beacose chance to made mistake or circuit short is bigger in that `Jungle`

All the best Man
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Old 10th October 2010, 02:11 PM   #6
Brit01 is offline Brit01  United Kingdom
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The DC offset wonders a little but only in the 2-15mV range which is no problem. (my SS has 12-15mV)


Whenever I tried setting the grid bias on each rail equally this is when I got more DC offset.

I could reduce the DC to zero but with each grid bias set to within about 5 volts of each other (in any range, low or high).

I check out and saw that one of the floating supplies voltage is slightly different to the other (maybe explaining the grid bias differences).

I have a small pentode sink on the LTP. I will fiddle with this and also try a SS sink (but had problems finding any negative voltage regulators here. They only have low voltage ones).

Could I use a sink comprised of transistors, maybe DN2540, or 3904's on the LTP?

I've only had experience of cascode DN2540 as sources on anodes but never sinks.

Could a cascode DN2540 be used as a sink to ground on the cathode?
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Old 10th October 2010, 02:16 PM   #7
SY is offline SY  United States
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Originally Posted by Brit01 View Post
Could a cascode DN2540 be used as a sink to ground on the cathode?
Only if you want superb balance and overall performance with a simple, inexpensive circuit.
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And while they may not be as strong as apes, don't lock eyes with 'em, don't do it. Puts 'em on edge. They might go into berzerker mode; come at you like a whirling dervish, all fists and elbows.
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Old 10th October 2010, 05:06 PM   #8
Brit01 is offline Brit01  United Kingdom
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Quote:
Only if you want superb balance and overall performance with a simple, inexpensive circuit.
How would this be implemented as the tail resistor sink in an LTP?



I've only used them as plate sources.
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Old 10th October 2010, 07:21 PM   #9
Brit01 is offline Brit01  United Kingdom
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I will try something like this using DN2540 as a sink:

http://www.triodeguy.com/Triodeguy%2...0AMP%20SCH.pdf
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Old 10th October 2010, 08:55 PM   #10
Brit01 is offline Brit01  United Kingdom
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DN32540 implemented! Works fine. DC hovers between 0-20mV, back and forth a little.

I have fets as source followers, I have a difference in current through these with 5K on the source.

Is it possible to use Current sinks on a mosfet as source follower?

Instead of a neg. voltage through a resistor on the source output, could I use a cascode DN2540 to ground on the FET?

Last edited by Brit01; 10th October 2010 at 09:07 PM.
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