OTL amplifier

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Re: OTL amplifier

Postby azazello » Sat May 26, 2012 7:40 am

Tubeamp wrote:Hello,

I have build lately this OTL amplifier, any improvement suggestions?

Image

Please, post schematic of power supply and heating!
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Postby Tubeamp » Sat May 26, 2012 8:31 am

Hi Azazello...Hope you are doing well!

Ok...I will post the psu schematic in the next couple days!
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Postby Tubeamp » Sun May 27, 2012 9:31 am

Here is the OTL amplifier's power supply schematic .

Image
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Postby azazello » Fri Aug 03, 2012 10:12 am

Thanks Tubeamp!
Here is my OTL, idea is from Your schematic 6080 /I used 6AS7GA/, fase splitter of Rusian guru A.Manakov and my decision for preampl. PCC88-Tesla.
https://picasaweb.google.com/1095707775 ... 0833103202
Here is bellow schematic of fase splitter with very good and exact adjusting with R7:
http://sergeev21.narod.ru/manakov.htm
You can select: Двухтактнъй усилитель на 6П3С, ЕЛ34.
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Re: OTL amplifier

Postby psonderman » Tue Oct 13, 2015 5:56 pm

Hi, Is the speaker load going to be 16 ohms or more? I have all of the components, but would have to make up the speakers to match the output of the amplifier.
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Re: OTL amplifier

Postby Tubeamp » Thu Oct 15, 2015 2:40 am

psonderman wrote:Hi, Is the speaker load going to be 16 ohms or more? I have all of the components, but would have to make up the speakers to match the output of the amplifier.


Hi.....According to the measurements I took on my amplifier I got the following results,

Rload=16 Ohms resistive, Pout = 16W @ 1kHz

10Hz 38Vpp
45Hz 40Vpp
200Hz 43Vpp
1kHz 45Vpp
2kHz 45Vpp
10kHz 45Vpp
20kHz 45Vpp
30kHz 44Vpp
60kHz 31Vpp

Rload=32 Ohms resistive, Pout = 25W @ 1kHz

10Hz 66Vpp
45Hz 70Vpp
200Hz 76Vpp
1kHz 80Vpp
2kHz 80Vpp
10kHz 80Vpp
20kHz 80Vpp
30kHz 78Vpp
60kHz 55Vpp
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Re: OTL amplifier

Postby Geek » Thu Oct 15, 2015 5:35 am

I'd also add a variable resistor on the anodes of the phase splitter for AC balancing - critical for good THD in a circlotron.

Cheers!
-= Gregg =-
Fine wine comes in glass bottles, not plastic sacks. Therefore the finer electrons are also found in glass bottles.
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Re: OTL amplifier

Postby Tubeamp » Thu Oct 15, 2015 10:40 am

Geek wrote:I'd also add a variable resistor on the anodes of the phase splitter for AC balancing - critical for good THD in a circlotron.

Cheers!


I agree....it's a good practice to include the AC balance pot !
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Re: OTL amplifier

Postby psonderman » Sun Nov 22, 2015 10:44 am

HI, What would the AC balance of the anodes look like in schematic form? I've seen balance in the cathode circuits of some OTL amps. Thanks, Phil
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Re: OTL amplifier

Postby Tubeamp » Mon Nov 23, 2015 3:51 pm

psonderman wrote:HI, What would the AC balance of the anodes look like in schematic form? I've seen balance in the cathode circuits of some OTL amps. Thanks, Phil


You just add a potentiometer at the triodes anode feed point. You have to disconnect the +HT line and the 2 100K resistors. You connect the +HT line at the wiper of the potentiometer and the 2 100K resistors at the free ends of the pot, one to each end. Adjustment is easy to do. Apply a sinewave to the input and monitor the outputs of the LTP with an oscilloscope . If there is an unbalance between the 2 outputs you adjust the potentiometer till both are exactly equal.
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Re: OTL amplifier

Postby Geek » Mon Nov 23, 2015 5:33 pm

If you want to go all "Goldburg", you can go to an autobalancer:
http://www.dogstar.dantimax.dk/tubestuf/driver02.htm

A hybrid version of this is in my DynaMutt.
-= Gregg =-
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Re: OTL amplifier

Postby psonderman » Sun Dec 13, 2015 2:46 pm

Hi, Thank you for the balance pot information. One more question please? What would be the current rating of the transformer be for the two 150 volt supplies?
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Re: OTL amplifier

Postby psonderman » Sun Dec 20, 2015 3:49 pm

HI, So, if the voltage p-p @ 1khz (16 ohms), is 45 volts. Then, 45 x .707 for RMS volts = approx. 32. I=E/R (I know this is a DC approximation), 32 volts/16 ohms = approx. 2 amps. Is this the kind of current required at 150 volts, for each 150 volt supply? Or, does this mean that I need one amp. of current for each 150 volt supply, given that the amplifier requires two 150 volt supplies? Thank you. Phil
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Re: OTL amplifier

Postby Tubeamp » Wed Dec 23, 2015 3:50 am

For 16W into 16 Ohms the voltage should be 16Vrms . According to the power formula P=V^2 / R we have 16W = 16^2 / 16 . The p-p voltage it is converted into rms value by diving it by 2.8 , so 45Vp-p would be 16Vrms and not 32 . The current into 16 Ohms should be P=I^2 x R or I=sqrt (P/R) thus we have I=sqrt(16W / 16 ohms) = 1A which I think is rather high for 2 or 3 tubes (6080 ) . Better to use a 32 Ohms speaker, the amplifier will deliver 80Vp-p or 28Vrms at 0.85A and the output power will increased to 25W .
In my amplifier I have used a 200VA power transformer per channel.
I suggest to read this article by Turner Audio, has a lot of information regarding OTL amplifiers.
The link is :
Code: Select all
http://www.turneraudio.com.au/OTL-amps-pros-cons.html
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Re: OTL amplifier

Postby psonderman » Wed Dec 23, 2015 10:44 am

Hi, Thank you for the information and the link. The transformers I have are 250VA, so I'll go with those, and your recommended 32 ohm speaker arrangement, for my first attempt at a OTL amplifier. Phil
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